Materials for nanoelectronics and nanophotonics

Resume : This invited talk presents an overview of the most important experimental and theoretical results on electrically induced spin dynamics in ferromagnetic nanostructures mechanically coupled to ferroelectric substrates. In such multiferroic hybrids, the substrate serves as a piezoelectric transducer converting an electrical input signal into a mechanical stimulus acting on the ferromagnetic overlayer. Under appropriate piezoelectric deformations, the overlayer magnetization loses stability against precessional motion owing to the magnetoelastic coupling between spins and substrate-induced strains. Depending on the input signal and the device design, a strain pulse, bulk elastic wave, or surface acoustic wave is created in the ferromagnetic heterostructure. As a result, the electrically excited magnetic dynamics can have the form of a steady precession, spin reorientation transition, magnetization switching, or a spin wave. This remarkable feature makes ferromagnetic-ferroelectric hybrids promising for the development of advanced spintronic devices with ultralow power consumption. In particular, hybrids comprising magnetic tunnel junctions can be employed as electric-write magnetoresistive nonvolatile memory cells. Furthermore, efficient spin injectors based on dynamically strained ferromagnet/normal metal bilayers could be developed. Other discussed applications include logic elements utilizing elastically generated spin waves and electrostatically tunable microwave devices.

Resume : Metal–oxide semiconductors are widely used to fabricate metal–oxide–semiconductor field effect transistors [1] (FETs), solar cells, and photodiodes [2]. IGZO has drawn more attention from researchers due to its high field-effect mobility, low threshold voltage, transparent and low-temperature deposition. [3] In spite of this, IGZO has been known that the optical bandgap is Eg = 3.2 eV, which indicates that it could not be activated on the condition of UV wave length greater than 400 nm [4]. This problem can be reduced by coupling n-IGZO with p-type material. In this research, p-GeSe/n-IGZO van der Waals heterojunctions were fabricated on a SiO2/Si substrate to study the electrical and electronic properties. GeSe has an indirect bandgap of 1.08 eV in bulk and a direct bandgap of ~1.7 eV in monolayers [5,6]. It has been reported that GeSe has a high photo responsivity along the a3 (perpendicular to the plane) direction. [7] The IGZO (In–Ga–Zn = 1:1:1) layer of 30 nm thickness was deposited on SiO2/Si with 50W power for 1200 Seconds with 3% oxygen at 0.5 Pa in ambient argon. The film was deposited by means of RF Magnetron sputtering. The deposited IGZO was then annealed at 400°C for 1 h to improve the crystal structure and stability of the IGZO. After annealing, few layers of GeSe was exfoliated and transferred on IGZO Hall bar to make a hetro-junction. Au/Ti (50 nm/5 nm) contacts were deposited over GeSe by Ebeam Lithography. References 1) Kurokawa, Y et al. Applications of Crystalline Indium-Gallium-Zinc-Oxide Technology to LSI: Memory, processor, image sensor, and field programmable gate array, Fifth Asia Symposium on Quality Electronic Design (ASQED 2013), 2013, 26-28, pp 66-71. 2) Jariwala, D. et al. Gate-tunable carbon nanotube–MoS heterojunction p-n diode. Proceedings of the National Academy of Sciences, 2013, 110 (45), 18076-18080. 3) Zhang, J. et al., A. Flexible indium–gallium–zinc–oxide Schottky diode Operating Beyond 2.45 GHz. Nature Communications, 2015, 6, 7561. 4) Chen, W. T. et al. High-performance light-erasable memory and real-time ultraviolet detector based on unannealed indium-gallium-zinc-oxide thin-film transistor. IEEE. Elec. Dev. Lett. 2012, 33, 77–79 (2012). 5) Makinistian, L. et al. A. J Phys-Condens Mat 2007, 19, (18). 6) Gomes, L. C. et al.Phys Rev B, 2016, 94, (15). 7) Mukherjee, B. et al. Acs Appl Mater Inter 2013, 5, (19), 9594-9604

Resume : Metal-2 dimension semiconductor Schottky-barrier diodes with forward and reverse I‐V characteristics have been fabricated using asymmetric metal contacts. In this research work, a p-type Germanium selenide (p-GeSe) was fabricated. p-GeSe belongs to the family of IV-VI layered chalcogenide semiconductors with orthorhombic structure (Pnma) [1] and band gap, 1.07 eV [2]. A single unit cell contains eight atoms situated in two adjacent double layers along the z-axis. The atoms in each double layer are bonded to their three nearest neighbors in a zig-zag fashion. The neighboring Ge atoms surrounding the Se atoms. The van der Waals force between the adjacent layers makes the crystal cleavable along its x-y plane [3]. Single crystalline flakes of p-GeSe were mechanically exfoliated by using 3M scotch tab [4] and the Deterministic dry transfer method was used to transfer the good quality of few layers flakes onto the Si/SiO2 [5]. Electrodes were designed in desired geometry over p-GeSe flakes by Electron Beam Lithography. The Schottky-barrier has been made due to the asymmetry of ultra-low Palladium/Gold (Pd/Au) and high resistive Chromium/Gold (Cr/Au) metal contacts. The Schottky diode has performed an explicit rectifying behavior with an on/off ratio of ̴103. References [1] Makinistian L and Albanesi E A 2007 Ab initio calculations of the electronic and optical properties of the germanium selenide J. Phys.: Condens. Matter 19 186211 References [2] Eymard R and Otto A 1977 Optical and electron-energy-loss spectroscopy of GeS, GeSe, SnS, and SnSe single crystals Phys. Rev. B 16 1616 [3] K. S. Novoselov , D. Jiang , F. Schedin , T. J. Booth , V. V. Khotkevich , S. V. Morozov , A. K. Geim , Proc. Natl. Acad. Sci. USA 2005 , 102 , 10451 . [4] Yi, M., & Shen, Z. (2015). A review on mechanical exfoliation for the scalable production of graphene. Journal of Materials Chemistry A, 3(22), 11700–11715. doi:10.1039/c5ta00252d [5] Castellanos-Gomez, A., Buscema, M., Molenaar, R., Singh, V., Janssen, L., van der Zant, H. S. J., & Steele, G. A. (2014). Deterministic transfer of two-dimensional materials by all-dry viscoelastic stamping. 2D Materials, 1(1), 011002. doi:10.1088/2053-1583/1/1/011002

Resume : Active using of display at both indoor and outdoor condition is one of the challenges in display technology. The transflective display which uses backlight at indoor and external light at outdoor is fabricated for this purpose. Nevertheless, the transparent part and mirror part is separated that cannot be control the degree of application of mirror or transparency. Reversible electrodeposited devices have transparent and mirror state which can apply to the transflective devices. It is activated by electrochemical reaction of ions and electrons which make deposition/dissolution of Ag on the working electrode. Hence, it is adjusted the degree of mirror or transparent state. However, bi-stability of deposited Ag thin films is low due to the existence of dissolution agent, 〖Cu〗^ and 〖Br〗^- ions in electrolyte. The 〖Cu〗^ ions help clear dissolution of Ag when bleaching mechanism, however, it is a main reason of erasing process of Ag thin films. Therefore, elimination of 〖Cu〗^ ions from electrolyte can effectively improve the bi-stability of devices. Furthermore, the counter electrode is needed as mediator of electrochemical reaction to prevent reaction of 〖Br〗^- ions which is a self-erasing agent. TiO2 thin films is a candidate for counter electrode which can store and release both electrons and ions when their reduction/oxidation processes. In this study, we fabricated the reversible electrodeposited devices based on the TiO2 mediator which can effectively limit the reaction of self-erasing process. Layered TiO2 thin films were investigated to find suitable charge balance with working electrode. Moreover, the starting redox reaction balance between working and counter electrodes were achieved by pre-deposited Ag thin films.

Resume : We report deterministic conversion of write once read many times (WORM) resistive switching (RS) memory to a volatile and non-volatile RS memory in a simple Ag/CoFe2O4/Pt devices via tuning the compliance current (ICC). The ICC = 10-1 A causes a WORM type resistive switching behavior with a large resistance ratio (~106). The WORM type RS behaviors could be attributed to the formation of a thick and stable conducting filament formed of oxygen vacancies and Ag ions. A simultaneous magnetization and resistive switching confirm the multifunctional behavior of the WORM device and suggests the presence of valance change mechanism of resistive switching. With the controlled application of ICC, the reversible volatile and non-volatile resistive switching can be obtained. For the smaller ICC the device exhibit the volatile RS behavior with atomically sized conducting filament showing the quantum conductance. An intermediate ICC causes the non-volatile bipolar RS behavior in the Ag/CoFe2O4/Pt devices, which could be originated from formation and rupture of filament consisting of Ag ions. The device shows a low resistance state (LRS) and a high resistance state (HRS), which are stable with time and reproducible in RS cycles. Endurance characteristics of the present RS device (> 500 switching cycles) show no noticeable degradation, and the ultimate resistance ratio always remains ~ 103, which ensures reproducibility, reversibility and controllability of the RS features of the present device. The HRS of the device shows semiconducting conduction mechanism, whereas the LRS was found Ohmic in nature. The temperature dependent resistance studies revealed that the electrochemical metallization plays an important role during the switching process in volatile and non-volatile modes of resistive switching of present device. The compliance current controlled resistive switching modes with a large memory window make the present device a potential candidate to pave the path for future resistive switching devices.

Resume : Molecular switches have attracted a great attention in the field of Nanotechnology due to their ability to reversibly switch between several states by means of external stimuli (such as light or electrical current), and thus to display several functions and mixing electronic with optical, magnetic or sensing properties. In order to achieve such multi-functionality, we can introduce molecular switches as building blocks in order to form responsive components and interfaces to be integrated into electronic devices to gain a dynamic control of their properties. In our work, several theoretical approaches and characterization methods were employed to characterize various switchable architectures. In a first stage, Molecular Mechanics and Dynamics (MM/MD) simulations were used to evaluate the different forces driving the self-assembled patterns obtained with a multi-state compound formed by three azobenzene groups, which could be employed as building blocks of responsive host-guest systems or organic frameworks. Ultraviolet Photoemission Spectroscopy (UPS) measurements were then confronted to Density Functional Theory (DFT) calculations to shed light on the change in the electrode surface properties upon adsorption of switchable Self-Assembled Monolayers (SAMs) based on diarylethene (DAE) molecules, which can be exploited to dynamically tune the amount of current injected in devices such as organic field-effect transistors (OFETs) and light-emitting diodes (OLEDs). Finally, the transmission through Donor-Acceptor (D-A) dyad based switchable junctions, where the perchlorotriphenylmethyl (PTM) radical acts as electron acceptor (A), was analyzed with the Non-Equilibrium Green Function method coupled to DFT (NEGF-DFT) calculations in order to develop new functional rectifiers.

Resume : We have use ion irradiation as a tool to tailor the surface of epitaxial graphene (EG) on SiC for sensing application. EG was irradiated with 30 keV and 100 MeV silver (Ag-) ion at fluences range of 5× 1012 - 5× 1014 ions/cm2 and 6.6× 1011 - 2× 1013 ions/cm2, respectively. Structural modifications were studied through Raman and XPS while morphological modifications were investigated using AFM. Raman spectra shows decrease in 2D with increase in fluence for both low and high energy samples. We also observed an initial increase in the intensity of D peak with increase in fluence up to 1× 1013 ions/cm2 and 5× 1013 ions/cm2 fluence in low and high energy samples, respectively; after which, the D peak starts decreasing with increase in fluence. For irradiated samples we systematically investigate structural changes in SiC substrate as well as EG. Raman spectroscopy results shows that at low fluence, point defects are generated and formation of amorphization nuclei and coalescence of amorphous domain occurs at higher fluence. In addition, ion irradiation did not result in structural phase transformation since signature of any other SiC polytype was not observed. We observed carbon nanodots in both irradiated samples. In case of 30 keV silver irradiated sample, we have observed maximum concentration of carbon nanodots at fluence 1× 1013 ions/cm2. In case of high energy irradiated samples, we have observed also wrinkles and folding in the EG, which was not observed in low energy irradiated samples. Further, we have done gas sensing on the samples in ppb and ppm range of NH3 and NO2 gas, preliminary results show an increase in gas sensing and the work is currently in progress. This study opens a new platform for tailoring surface of EG for various sensing applications.

Resume : Redox-based resistive random access memory (ReRAM) has shown low power consumption, fast switching speed and ultra-dense integration capability [1]. However, one time electroforming process, that is required to initiate the switching process, consumes more power than that of switching cycles. The higher power consuming step makes these devices incompatible to low-voltage CMOS technology. Therefore, it is important to have forming-free ReRAM devices. In this talk, we show the impact of ion-implantation process on the forming voltage and other resistive switching properties. The Forming-free ReRAM devices can be obtained by the ion-implantation of different dopants in binary metal-oxide thin-film during the device fabrication process. These forming free devices show very high endurance and retention [2]. Besides their potential as memory, the ReRAM devices in crossbar configuration offer implementation of memory-intensive computing paradigm and adds an extra edge to this technology. With multi-level switching capability, an intrinsic modular arithmetic using a ternary number system will be presented. This opens up the computing space beyond traditional binary values [3]. References [1]. R. Waser, V. Rana, S. Menzel and E. Linn, “Energy-efficient Redox-based Non-Volatile Memory Devices and Logic Circuits,” 3rd Berkeley Symposium on Energy Efficient Electronic Systems, vol., pp. 1-2, 2013. [2]. W. Kim, A. Hardtdegen, C. Rodenbücher, S. Menzel, D. J. Wouters, S. Hoffmann-Eifert, D. Buca, R. Waser and V. Rana, “Forming-Free Metal-Oxide ReRAM by Oxygen Ion Implantation Process,” 2016 IEEE International Electron Devices Meeting (IEDM), San Francisco, USA, December 3-7, 2016, 2016, pp. [3]. W. Kim, A. Chattopadhyay, A. Siemon, E. Linn, R. Waser and V. Rana, “Multistate Memristive Tantalum Oxide Devices for Ternary Arithmetic,” Sci. Rep., vol. 6, pp. 36652, 2016

Resume : Industrial development of chemical solution and vapor routes to inorganic nanomaterials (e.g., sol-gel, MOD, MOCVD…) is strongly dependent on the molecular engineering that involves design of tunable metal-organic precursors having desirable properties. These molecular precursors are usually the starting point of the processes that influence the micro- & nano-structure and, therefore, the nature and the properties of the obtained materials.1-4 The use of well-defined precursors and isolation of molecular intermediates during molecules-to-nanoparticles transformation also allows to establish relationships between precursors and the final material and, therefore, to get some insight in to their transformation. This presentation will address different concepts of the ‘bottom-up’ approach of the synthesis of inorganic nanomaterials with a special emphasis placed on the design of homo or heterometallic (‘single-source’) precursors should have (i) a formulation that matches well with that of the final materials, particularly stoichiometry of metals for multimetallic materials, (ii) appropriate physicochemical properties (solubility, thermal stability, volatility…), (iii) the required chemical functionalities (coordination sphere with an appropriate set of ligands), and (iv) a clean, low temperature conversion into nanomaterials with minimized undesired residues in the end. Different catalytic applications of the obtained nanomaterials will be described. Keywords: molecular precursor, nanomaterials, Sol-Gel, metal-organic decomposition, metal oxide, metal selenide nanoparticles, metal fluoride composites, photocatalysis REFERENCES [1] S. Mishra, S. Daniele, Metal-organic derivatives with fluorinated ligands as precursors for inorganic nanomaterials, Chem. Rev. 2015, 115, 8379-8448. [2] a) S. Mishra, F. Morfin, V. Mendez, P. N. Swamy, J.-L. Rousset, S. Daniele, Nanometric NaYF4 as an unconventional support for Gold catalysts for oxidation reactions, ACS Omega, 2019, 4, 5852−5861; b) Y. Chen, S. Mishra, G. Ledoux, E. Jeanneau, M. Daniel, J. Zhang, S. Daniele, Direct synthesis of hexagonal NaGdF4 nanocrystals from a single-source precursor: Upconverting NaGdF4:Yb3+,Tm3+ and its composites with TiO2 for near-IR-driven photocatalysis. Chem. Asian J., 2014, 9, 2415‒2421. [3] a) S. Gahlot, E. Jeanneau, F. Dappozze, C. Guillard, S. Mishra, Precursor-mediated synthesis of Cu2-xSe nanoparticles and its composites with TiO2 for improved photocatalysis, Dalton Trans. 2018, 47, 8897–8905; b) S. Mishra, D. Du, E. Jeanneau, F. Dappozze, C. Guillard, J. Zhang, S. Daniele, A facile molecular precursor-based synthesis of Ag2Se nanoparticles and its composites with TiO2 for enhanced photocatalytic activity, Chem. Asian J. 2016, 11, 1658-1663. [4] a) S. Mishra, E. Jeanneau, S. Mangematin, H. Chermette, M. Poor Kalhor, G. Bonnefont, G. Fantozzi, S. Le Floch, S. Pailhese, S. Daniele, A convenient and quantitative route to Sn(IV)–M [M = Ti(IV), Nb(V), Ta(V)] heterobimetallic precursors for dense mixed-metal oxide ceramics, Dalton Trans., 2015, 44, 6848–6862; b) S. Mishra, V. Mendez, E. Jeanneau, V. Caps, S. Daniele, A single source precursor route to group 13 homo- and heterometal oxides as highly active supports for gold catalyzed aerobic epoxidation of t-stilbene, Eur. J. Inorg. Chem., 2013, 500‒510.

Resume : Computational design can accelerate the discovery of new materials with tailored properties, but applying this approach to plasmonic nanoparticles with diameters larger than a few nanometers is challenging as atomistic first-principles calculations are not feasible for such systems. To overcome this challenge, we have developed a novel material-specific approach that combines effective mass theory for electrons with a quasistatic description of the localized surface plasmon to identify promising bimetallic core-shell nanoparticles for hot-electron photocatalysis. Specifically, we have calculate hot-carrier generation rates of 100 different core-shell nanoparticles and find that systems with an alkali-metal core and a transition-metal shell exhibit high figures of merit for water splitting and are stable in aqueous environments. Our analysis reveals that the high efficiency of these systems is related to their electronic structure, which features a two-dimensional electron gas in the shell. Our calculations further demonstrate that hot-carrier properties are highly tunable and depend sensitively on core and shell sizes. The design rules resulting from our work can guide experimental progress towards improved solar energy conversion devices.

Resume : Scanning Electron Microscope (SEM) is nowadays basic accessible tool for materials characterization at nanoscale. SEM microscope is usually equipped with Energy Dispersive X-ray Spectroscopy (EDX) system which is used for quantitative chemical analysis. Due to the electron beam interaction with matter the X-ray generation volume is of the order of micrometer, which limits the spatial resolution of EDX. In the presentation the results of quantitative chemical analysis of metallic nanostructures resulted from thermally induced self-assembly of thin Au layer (few monolayers) deposited on various semiconductor surfaces i.e. Ge(001), InSb(001) will be shown. This leads to formation of Au-rich nanostructures with size of ~50nm. For each surface morphology hyperspectral EDX data were collected, where in each pixel full EDX spectrum was recorded. Next by using Machine Learning Blind Source Separation the EDX signal coming from nanostructures was separated from the signal of bulk semiconductor. This allowed for chemical composition quantification of formed nanostructures by EDX ZAF method [1,2]. The presented approach breaks the spatial limit of the EDX method and allows for chemical composition quantification of various nanomaterials by using affordable and accessible SEM/EDX instead of TEM measurements. [1] B.R. Jany et al., Nano Lett., 2017, 17 (11), pp 6520–6525 [2] B.R. Jany et al., Collected SEM EDX data at nanoscale together with analysis program, doi:10.13140/RG.2.2.19558.93763

Resume : The development of new catalysts for oxidation reactions is of central importance for many industrial processes. Plasmonic catalysis involves photoexcitation of templates/chips to drive and enhance oxidation of target molecules. Raman-based sensing of target molecules can also be enhanced by these templates. This provides motivation for the rational design, characterization, and experimental demonstration of effective template nanostructures. In this work, we study a template comprising of silver nanoparticles present on aligned peptide nanotubes, contacted with a microfabricated chip in a dry environment. This template enables efficient plasmonic catalysis activated and controlled by application of an electric field. Raman detection of biomolecules are also dramatically enhanced by the template. We demonstrate that this optoelectrical device enhances photocatalytic conversion for model oxidation reactions exploiting the facile field-activated trans-template charge transfer. We also demonstrate that this same approach can be used to enhance the strength of Raman scattering from low Raman cross-section molecules such as glucose and DNA-based molecules, establishing the potential of our template design for sensitive detection and analytics. Reference Enhanced photocatalysis and biomolecular sensing with field-activated nanotube-nanoparticle templates. Nature communications, in press.

Resume : The efficient functionalization of metal oxide nanostructures with organic dyes is a prerequisite to achieve hybrid materials for dye-sensitized solar cells, sensors or photocatalytic devices.[1] The stability of these materials in the ambient, e.g. in the presence of ubiquitous gaseous water, plays an important role during production and operation. Starting from gas-phase grown TiO2 anatase nanoparticles (~12 nm) we produced thin TiO2 films by inkjet printing. Powders and thin films were functionalized with 2H-Tetraphenylporphyrin (2HTPP) in the gas phase under high vacuum conditions. In the course of these experiments we added gaseous water before or after porphyrin adsorption. The influence of surface hydroxyls on the porphyrin adsorption process and the stability of the hybrid material in aqueous environment was addressed by tracking porphyrin adsorption and consecutive surface reactions by UV/Vis absorp-tion and photoluminescence emission spectroscopy. Significant crystal modification related differences in porphyrin adsorption can be observed for the anatase and ru-tile samples. Furthermore, the surface protonation reactions of adsorbed porphyrin molecules upon formation of 4HTPP2 species was observed, while 2HTPP adsorp-tion on hydroxylated TiO2 surfaces shows no significant change.[2,3] Literature: [1] Ardo, S., Meyer, G.J. Chem. Soc. Rev., 2009, 38, 115 [2] Schneider, J., et al. ACS Appl. Mater. Interfaces 2018, 10, 16836 [3] Schneider, J., et al. in preparation

Resume : We combine droplet epitaxy with low energy electron microscopy imaging techniques to map the surface phase diagram of GaAs(001). The droplet epitaxy phase patterns produced are interpreted using a simple model which links the spatial coordinates of phase boundaries to free energy. It is thereby possible to gain important new information on surface phase stability, based on the observed sequential order of the phases away from the droplet edge. This can be used to improve existing phase diagrams generated by density functional theory calculations. We establish the existence of a (3x6) phase and confirm, that the controversial (6x6) is thermodynamically stable over a narrow range of chemical potential.

Resume : Layered nanowires (NWs), consisted of alternating layers of magnetic and nonmagnetic metals, seems promising for GMR, elements for microelectronics and spintronics. Track membranes (PET films, pores diameter 50-200 nm and density 10 8) were used as templates. Layered NWs Ni/Cu and Co/Cu were obtained using the solutions of corresponding salts and pulsed deposition. TEM measurements were made: thickness and elemental compositions of NWs were determined. It was shown that copper layers consist of pure Cu (Fm3m), while Ni layers (Fm3m) or Co layers (hex.) always include Cu admixture (up to 15-20%). Two fractions of crystallites were found (size 5-10 nm and up to 100 nm). (These data was in accordance with X-rays investigations). Passed-charge control gave better homogeneity of layers that pulse-time control. It was also shown that reduction of layer’s thickness is effective down to 20 nm. For “thinner” layers interfaces between them became irregular and metal distribution between layers became irregular. Another result of reducing the deposition time was formation of “core-stick” structure. Magnetic measurements demonstrate that NWs with thick layers (higher than 100 nm) demonstrate high magnetic anisotropy, while NWs with thin layers (50-100 nm) were isotropic. Magnetic Force microscopy of the single NW were carried out in two geometries – for NW’s top and for horizontal NW. The effect of external magnet (16 mT) on magnetization reversal was demonstrated. The influence of NWs on each other was also shown – only part of NWs could change their magnetization Another approach - “double-bath” method was also used and compared with commonly used “single-bath” technique. Acknowledgements. State Task of FNIC “Crystallography and Photonics” of RAS.

Resume : Inorganic perovskites are key materials for many technologies going from high Tc superconductors, to high-k dielectrics, from piezoelectric to colossal magnetoresistance materials, from ionic conductors to multiferroics. Perovskites are compounds with ABX3 formula where the anion X form together with A a cubic compact packing, thus A is twelve coordinated, while B, occupying the octahedral holes, has a six-coordination. The countless potentialities of perovskites arise from the possibility to dope both the A and B sites giving rise to a great variety of compositions and properties. In this presentation, a simple synthetic strategy based on metal organic chemical vapor deposition (MOCVD) for the fabrication of inorganic perovskite thin films will be presented. Depositions have been realized in a customized hot wall reactor, employing argon as a carrier gas and oxygen as a reactant gas. Multicomponent mixtures consisting of appropriate β-diketonates have been used as precursor sources. Films have been grown on conventional and conducting substrates of 10 mm x 10 mm surface. Some case studies will be reported with particular attention to the ferromagnetic manganites and the piezoelectric/ferroelectric bismuth ferrite. Part of this work is supported by the European Community under the Horizon 2020 Programme in the form of the MSCA-ITN-2016 ENHANCE project, Grant Agreement N.722496.

Resume : On account of their exceptional electronic and optical properties, organometal halide perovskite materials have been extensively explored in the various optoelectronic applications for last few years. Recently, alkylammonium lead halide perovskite nanoparticles also received considerable attention as active materials for LEDs. In the LED applications, alkylammonium lead halide perovskite nanoparticles exhibit superior optical properties such as high color purity with narrow band width, broad color tunability covering entire visible region either by varying halide composition or particle size, and almost unity photoluminescence quantum yield (PLQY). However their practical applications are often hindered by the poor stability of perovskite materials against water and polar solvents. Additionally, patterning technology of perovskite materials is highly demanded for creating the high resolution pixels. As a way of addressing above mentioned problems, perovskite nanoparticle composite films have been fabricated by using size-exclusive mass-flow lithography Perovskite nanoparticle composite films with capability of high-resolution patterning (≥ 2 µm) and excellent resistance to various aqueous and organic solvents have been prepared by in situ photosynthesis of acrylate polymers and formamidinium lead halide (FAPbX3) nanoparticles. Both positive- and negative-tone patterns of FAPbX3 nanoparticles are created by controlling the size-exclusive flow of nanoparticles in polymer networks. The position of nanoparticles is spatially controlled in both lateral and vertical directions. The composite films show high PLQY (up to 44%) and broad color tunability in visible region (λpeak = 465-630 nm).

Resume : It is undoubted that organic-inorganic hybrid perovskites have been representing a scientific breakthrough in the photovoltaic field since 2009 when they were applied to replace photoactive dyes in hybrid solar cells. Further development has been highly boosted by a large and enthusiastic effort of the worldwide scientific community to improve the response to sun light. The current certified maximum efficiency is 23.7%. The exceptionality of this class of materials resides in their soft nature. The long diffusion lengths of the photo-generated carriers, the wide absorption range, the direct and tunable bandgap are mainstays. It is equally true that the low structural stability of the hybrid perovskites, primary MAPbI3, risks to severely retard their wide-range applications in low cost/high yield devices. A large effort is consequently needed to frame the instability sources and degradation mechanisms in relationship with the operation conditions, including temperature, illumination, humidity, contaminants and boundary materials in the final architecture. One of the most used strategies is this perspective is the changing or mixing different cations, (MA+, FA+ and Cs+) to improve the lattice stability. Although the overall scenario is brighter than years ago, reliable and long-lasting solutions to avoid back-reaction of perovskites to the starting organic and inorganic components and indeed to extend cell durability are under spotlight. For the market uptake, moreover, device architectures, to be produced via simple and sequential steps, being free of contaminants and at low environmental impact, are warmly encouraged to catch the interest of investors. A critical analysis of the available data indicates that degradation under ambient conditions is a defect-generation process that is highly localized on surfaces and interfaces, while it is further enhanced above the tetragonal-cubic transition at ∼54 °C. Within this context, we discuss the conservative role of N2 and propose strategies for the emergence of industrially viable hybrid photovoltaics. The paper will thus frame strengths and weaknesses of hybrid perovskites for next-generation photovoltaics in view of their extended use and dissemination in daily life.

Resume : As displays and imaging technologies become more sophisticated, advances in sensor technology that make up the camera also have become indispensable. Recently, as the importance of image sensors used for automatic driving in automobile industry becomes more important, not only the resolution but also the response speed of the sensor has become an issue to be surely improved. In this study, we fabricated quantum dot (QD) based vertical type photodiodes by using ZnO and MoOx as electron and hole transport layers, respectively. Rising and falling times were measured to be τr = 28.8 ± 8.34ns and τf = 40 ± 9.81ns. Comparing with previous results with the transit time of 300 ns, our QD photodiodes show practical potential for applications. Such high-speed operation is due to metal oxide and ligands which make easier to extract carriers at interface between ZnO and QDs and will be presented in more details. This work was supported by Pioneer Research Center Program through the National Research Foundation of Korea funded by the Ministry of Science, ICT & Future Planning (NRF-2013M3C1A3065033) and the Future Resource Program (2E29300) of Korea Institute of Science and Technology (KIST).

Resume : The atomic displacement magnitudes of nearest neighbor atoms around the (001) surface F-center in ABO3 perovskites are considerably larger than the related displacement magnitudes of nearest neighbor atoms around the bulk F-center. In the ABO3 perovskites the electron charge is considerably better localized inside the bulk F-center than in the (001) surface F-center, where the oxygen vacancy charge is more delocalized over the nearest neighbor atoms than in the bulk F-center case. The (001) surface F-center formation energy in the ABO3 perovskites is smaller than the bulk F-center formation energy, which triggers the F-center segregation from the ABO3 perovskite bulk towards its (001) surfaces. In most cases the (001) surface F-center induced defect level in the band gap of ABO3 perovskites is located closer to the (001) surface conduction band bottom than the bulk F-center induced defect level to the bulk conduction band bottom [1-3]. In contrast to ABO3 perovskite bulk and (001) surface F-centers, the CaF2, BaF2 and SrF2 bulk and surface F-center charge is very well localized inside the fluorine vacancy. The atomic relaxation magnitudes around both bulk and surface F-centers in CaF2, BaF2 and SrF2 crystals, as a rule, are considerably smaller than the relevant atomic relaxation magnitudes around bulk and (001) surface F-centers in ABO3 perovskites [4,5]. References: 1. R.I. Eglitis and A.I. Popov, J. Nano-Electron. Phys. 11, 01001 (2019) 2. R.I. Eglitis and S. Piskunov, Comput. Condens. Matter 7, 1-6 (2016) 3. M. Sokolov, R.I. Eglitis, S. Piskunov, Y.F. Zhukovskii, Int. J. Mod. Phys. B 31, 1750251 (2017) 4. H. Shi, R.I. Eglitis, G. Borstel, Phys. Rev. B 72, 045109 (2005) 5. H. Shi, R. Jia, R.I. Eglitis, Solid State Ionics 187, 1-7 (2011)

Resume : Inserting suitable interfacial materials between the photoactive layer and the selective contacts in organic semiconductor (OSC) and perovskite (PeSC) materials based solar cells has become one of the most important strategies to enhance charge extraction and suppress charge recombination in both types of solar cells. Here, we systematically engineer the cathode interfaces of OSCs and PeSCs by using molecular materials such as porphyrins, pyrenes, polyoxometalates and others all bearing functional groups, including carboxyl, amine, isopropyl, phenethyl and tert-butyl-phenethyl groups, and study their electron extracting/surface passivation capability. The main outcome of this study is that the judicious control of the interaction between organic semiconductor/perovskite surface and molecules can realize effective electron extraction through the reduction of the electron extraction barrier and surface passivation both leading to significant device performance.

Resume : Metal halide perovskites, initially emerged as effective materials for solar cells, are currently also attempted to use for other devices such as photodetectors and light emitting diodes, lasers. However, despite many unique advantages perovskites also have some undesirable features which still limit their applications. Performance of both photovoltaic and electroluminescent devices suffers from non-radiative recombination losses related to carrier traps. The trapping influence has been demonstrated to be reduced in perovskite nanocrystals, or in hybrid quasi-two-dimensional (2D) perovskites, due to the spatial carrier confinement. Here, by using ultrafast spectroscopy and transient electroluminescence (EL) techniques, we addressed charge carrier dynamics in 2D perovskite-based LEDs. In particular we demonstrate that 3D domains present in 2D perovskite rapidly trap carriers of one type preventing trap-assisted nonradiative recombination in host 2D material. EL dynamics under device pumping by short electrical pulses, revealed importance of spatial electron and hole distributions within perovskite layer in determining the EL efficiency. Weak overlap of electron and hole distributions diminish radiative carrier recombination rate, and are partly responsible for the efficiency roll-off of perovskite LEDs at high current densities. Strong EL pulse, known as EL overshoot, was observed after voltage switch-off. The overshoot effect suggests an unconventional way to achieve high-pulsed electroluminescence intensity with a low current density, which opens new prospects towards optical gain and implementation of electrically pumped lasers.

Resume : Perovskite has been emerged as an active layer for such devices, due to its low cost, low-temperature solution processing, and outstanding performance. The beneficial characteristics of perovskite is high illumination, highly sensitive response to visible/UV light prevents perovskite use as an active material for X-ray detectors due to the interference with UV/visible light as indirect semiconductor is the typical material for X-ray detector to avoid such noise. In this work, we explore indirect bandgap perovskite, for the first time, that it is not suitable for light absorption in contrast of other perovskites, however, it is ideal for practical perovskite based x-ray as it does not have light interference noise, allowing to detect x-ray only with higher sensitivity than that of commercial ones. We used theoretical studies and several experimental investigations using time-resolved spectroscopy to demonstrate the bandgap structure. Different inorganic perovskites of four CsPbX3 (X = I, Br) nanocrystals are synthesized by novel method. Their XRD measurements imply that the direct bandgap CsPbBr3 cubic phase and the CsPbI3 orthorhombic yellow δ-phase. No other phases are shown, confirming high structural quality. Transmission electron microscopy is used to confirm the structural properties of the materials. The X-ray detector based on the indirect bandgap CsPbI3 perovskite reaches a sensitivity of 83.6 μCGyair-1cm-2 (which is superior compared to commercial x-ray detectors) using a very thin (6.6 μm) active layer, which is essential for device miniaturization. The devices based on indirect bandgap CsPbI3 show very weak performance under visible light compared to the direct bandgap CsPbBr3, eliminating the interference noise.

Resume : Methylammonium lead halide perovskites (CH3NH3PbX3, where X = Cl-, Br-, I-) have attracted attention as prospective materials for optoelectronic devices due to the many advantages such as tunable bandgap, high electron/hole mobilities, and low-cost solution processing. However, solution processed perovskite (PS) holds defect states such as grain boundaries and/or film surface, and the instability of PS films in humidity remains the most important issue to be overcome. Therefore, suppressing these defect states and improving stability are key factors for development of PS-based devices with high-performance and long-term stability. Surface passivation is a general solution for reducing charge traps induced by structural defects and for protecting surface from moisture in air. In this paper, we present the charged carrier transport (CT) phenomenon in surface-passivated PS films by CdSe/ZnS quantum dots with different dot sizes. The CT process between mixed halide PS and CdSe/ZnS core-shell quantum dots (QDs) has been investigated by using photoluminescence (PL) and time-resolved PL. The diameter of QDs used in this studywas varied from 2.7 to 6.5 nm. The QD/PS hybrid structure samples exhibited much stronger PL intensities and longer PL decay times compared with that of pristine PS sample. The enhanced PL intensity and lengthened decay time in QD/PS hybrid structureare attributed to the CT from QDs to PS. As a core diameter of CdSe/ZnS QDs decreases from 6.5 to 2.7 nm, the CT efficiency in QD/PS hybrid structures also varied from 5 % to 56 % due to the enhancement of CT rate caused by the control of energy-level alignment of QDs. These results allow us to understand the fundamental mechanism such as CT process from QDs to PS as a function of size of QDs.

Resume : Ge/Si heterostructures with self-assembled quantum dots (QDs) are considered as one of the possible means for creating silicon-based light-emitting devices. Advantages of these structures are a relative simplicity of their formation and a room-temperature luminescence in the range 1.3?1.6 ?m. However, a significant disadvantage of such light-emitting structures is low efficiency of radiative recombination. This problem can be resolved by embedding GeSi QDs into microresonators, including those based on two-dimensional photonic crystals (PhCs). We consider various approaches to integrating ordered GeSi QD arrays into resonators based on two-dimensional photonic crystals and present the luminescent properties of the structures obtained. We used the Ge/Si structures with QDs grown on the pre-patterned surface. Creation of ordered arrays of QDs solves the problem of amplification of the emission from QDs by precise embedding them into microcavities, based on PhCs, where the quantum dots are located in positions of maximum concentration of the electric field. For structures with PhCs formed on arrays of ordered QDs, an increase in the PL intensity at room temperature in the range 0.9 ÷ 1.2 eV was detected, which is associated with the interaction of the structure radiation with the modes of the PhCs. Parameters of the PhCs are experimentally determined for the interaction of the QDs radiation with the radiation modes of the PhC itself as well as the microcavity created in the PhC.

Resume : Semiconductors with low dimensional feature can display remarkably optical, electrical and magnetic advantages over their bulk counterparts. Within the scope of low dimensions (0D, 1D and 2D), the control of doping, assembly and stability of materials appears more challenging, if possible, which can better serve us to understand some abnormal physical and chemical phenomenon and further explore novel application ways in nanoelectronics and nanophotonics. In this talk, for different application scenarios, popular VA-group 2D elemental semiconductors (mainly phosphorene and antimonene) are employed to demonstrate the possibility of tailoring their functional properties. Similar to graphene, the elements from the VA-group (or pnictogen group) can also form 2D materials. Black phosphorus (BP) has an orthorhombic and layer-dependent direct band structure, which lead to the development of several thinning strategies including micro-mechanical and liquid exfoliation. However, the oxidation of BP can easily happen and is often considered as a synergistic role of oxygen and water. In general, the chemical functionalization is an effective way to overcome such a problem but cannot keep for a long time. Herein, we have first utilized inorganic semiconductor zinc oxide (ZnO) to fabricate type-I and -II heterostructures and compared different stabilization mechanisms. Based on a flexible self-assembly strategy, different 0D/0D and 0D/1D combinations composed by ZnO and BP can be formed and contribute to distinct device performances including photodetection, resistive memory and surface enhanced Raman scattering (SERS). Compared to BP, rhombohedral structured antimony exhibits a stronger interlayer covalent interaction and a significant disadvantage in single and few-layer material synthesis. On the other aspect, its monolayer type (antimonene) has an indirect band structure and has not been experimentally utilized to develop transistor device. So in this talk, we will introduce an electrochemical exfoliation and synchronous doping technique to prepare them. By choice of Na and F doping elements, direct bandgap and magnetic antimonene can be obtained, respectively, shielding light on its potential for optoelectronic and spintronic applications. References: [1] Liang Hu, Yu-Jia Zeng,* et al. Black Phosphorus Quantum Dots with Tunable Memory Properties and Multilevel Resistive Switching Characteristics, Advanced Science 2017, 4, 1600435. [2] Liang Hu, Yu-Jia Zeng,* et al. Phosphorene/ZnO Nano-Heterojunctions for Broadband Photonic Nonvolatile Memory Applications, Advanced Materials 2018, 30, 1801232. [3] Liang Hu, Yu-Jia Zeng,* et al. Charge Transfer Doping Modulated Raman Scattering and Enhanced Stability of Black Phosphorus Quantum Dots on a ZnO Nanorod, Advanced Optical Materials 2018, 6, 1800440. [4] Liang Hu, Yu-Jia Zeng,* et al. Robust Above-Room-Temperature Ferromagnetism in Few-Layer Antimonene Triggered by Nonmagnetic Adatoms, Advanced Functional Materials 2019, 29, 1808746.

Resume : (GeTe)x(Sb2Te3)1-x alloys belong to the class of phase-change materials are among the most promising functional materials for new data storage and data visualization concepts. In (GeTe)x(Sb2Te3)1-x the optical dielectric constant is 70–200% larger for the crystalline than for the amorphous phases. These materials provide evidence for a disorder-driven metal–insulator transition. Furthermore, crystallization in these materials can be extremely rapid and can occur in less than 100 ns. In the present work, we studied the fluctuations of the absorption around the fundamental absorption edge in some (GeTe)x(Sb2Te3)1-x alloys. This study is aimed to reveal the correlation between the structure and optical properties of studied alloys in this range. We studied the absorption edge fluctuations that are linked to the variations of the bandgap, the width of localised electronic states, the Tauc parameter, and average halfwidth of Raman bands in some (GeTe)x(Sb2Te3)1-x alloys.

Resume : Mg, Cu and/or rare-earth elements doped ZnO films were prepared on glass substrates using water based coating solutions. Their efficiency in view of water purification by means of photocatalysis was evaluated on various industrial dyes including methyl violet, brilliant blue, methylene blue, malachite green, brilliant green, phenol red, rhodamine B and crocein scarlet. The solutions were based on either demineralised water or natural seawater. Besides using a UV lamp as an irradiation source, direct solar illumination was also studied as a preliminary test for field applications. Regeneration of the films after several runs was investigated using heat treatments coupled with studies of the thermal decomposition process of the dyes and their degradation products.

Resume : In the last decade, the area of nano-plasmonics has attracted increasing interest for real applications such as directed nano-emitters or high-performance sensors. While traditional fabrication, such as electron beam lithography, provides very high lateral resolution, they are often limited to flat surfaces. To overcome this limitation, additive direct-write methods are ideal candidates, although techniques for reliable sub-100 nm fabrication are only few. Focused electron beam induced deposition (FEBID) is one of the promising technologies, which not only meets the resolution requirements but also allows true 3D nano-printing on almost any material and surface morphology. In a previous study, we used FEBID for fabrication of plasmonically active, freestanding 3D architectures with sub-30 nm branch diameters composed of pure gold. Although gen-erally successful, we found two aspects, which require further research to exploit the full potential of this approach. First, individual branches revealed a certain side wall roughness and slightly conical shapes. Second, the required purification step after ini-tial fabrication affects the antenna morphology even further, which leads to a reduced plasmon resonance performance compared to traditionally fabricated nano-structures. Based on this situation, we here present our latest activities towards highest shape fi-delity of 3D nano-pillars including the material transfer into pure Au nano-antennas for high-performance 3D nano-plasmonics.

Resume : In this work shows the results of producing nanowires based on tobacco mosaic virus (TMV) and gold nanoparticle, which are perspective object for nanotechnology [1]. New method was developed for nanowires preparation based on citrate method synthesis of metal nanoparticles and includes the preparing of the metal source and reductant stock solutions and the gold recovery process through several cycles of mixing solutions, in the presence of the purified and modified TMV. A study of the physicochemical properties and the morphology of the nanowires were carried out by atomic force microscopy and X-ray photoelectron spectroscopy. The hybrid bio-inorganic virally-gold structure was about 50 nm in diameter and 150-400 nanometers in length. Uncoated gold TMV virions were not detected. It was found that the nanowires prefer to cluster ordering. Its interaction with the substrate is characterized by С–N bond, while the bond N-C=O is characterized by binding virions with each other. The electronic Au 4f core levels demonstrate shift towards lower binding energy at nanowires formation. It has been established that the obtained nanowires have optical activity with a maximum at 540 nm. The studies will be perspective to produce nanomaterials based on plant viruses and metal nanoparticles for nanoelectronics. [1]. X.Z.Fan et al. Tobacco mosaic virus: A biological building block for micro/nano/bio systems // J. Vac. Sci. Technol. A 31, 050815 (2013).

Resume : One of the key points in development of thin film-based devices for optical applications is accurate knowledge of the properties of substrates, on top of which the films are deposited. Lanthanum aluminate (LaAlO3 or LAO) is widely used as a substrate enabling epitaxial growth of numerous materials including such important perovskite oxides as ferroelectrics, metal-insulator-transition oxides, magnetoresistive oxides, and others. The optical properties of LAO are not well documented, especially at low temperatures. In this work, the optical properties of a 1 mm thick epitaxially polished (001)LAO substrate (MTI Corp.) were investigated by spectroscopic ellipsometry in the temperature range of 10-300 K. Spectra of the ellipsometric angles ψ and Δ were measured by a J.A.Woollam VUV-WASE ellipsometer. The optical constants were extracted using WASE software. The modeling parameters and the obtained optical constants will be presented. The refraction, extinction, and absorption coefficients will be shown in the spectral range of 0.8-8.8 eV at different temperatures of 10, 50, 100, 150, 200, 250 and 300 K. It is found that the direct bandgap is 6.1 eV at 300 K and monotonically increases to 6.7 eV on cooling to 10 K. This behavior complies with that known in many semiconductors. In contrast to the profound changes of the bandgap, the refraction coefficient from the visible spectral range is remarkably stable with temperature. The high transparency in the broad spectral range and thermal stability of refraction make the LAO substrate attractive for research and potential applications.

Resume : Our objective in this work is focused on the investigation of an adaptive neuro-fuzzy inference system for predicting the ageing of Double Gate (DG) TFET devices. Such trend is expressed by assessing the degradation of some performance criteria due to the presence of interface traps. In this context, the ION to IOFF ratio, the swing factor and small signal parameters are adopted to reveal the ageing phenomenon. The employment of ATLAS 2-D simulator allows the elaboration of the dataset to be used for the training of the neuro-fuzzy system. The obtained simulation outcomes show the good performance of the developed system for predicting the ageing degradation of the considered TFET design. Moreover, the proposed approach can play an important role to investigate TFET-based nanoelectronic circuits including the ageing-related degradation effects.

Resume : Historically, Raman studies have played an important role in optical characterization of carbon allotropes and have also become a powerful tool for understanding the phonons in graphene. Different properties including strains, defects, doping and the force type between graphene-substrate could be deduced from Raman spectra and are strongly investigated theoretically and experimentally. The graphene is obtained by high-quality chemical vapor deposition (CVD) and transferred to the h-BN substrate. We focus our attention on annealing effect at 1040 C on single graphene layer (SGL) and bilayer graphene (BLG) on an h-BN substrate using Raman spectroscopy. The Raman spectroscopy study of BLG heterostructure shows that the two layers of graphene have different orientations. Before annealing, the analysis of the Raman cartography of the graphene bands, G and 2D, shows the presence of angles that depend on the spacing between the two layers of graphene. After annealing, the analysis of Raman spectra reveals the presence of uni-axial stresses induced by h-BN. Since the possibility of controlling the angle formed by the orientations of the two graphene layers, in a rotated graphene bilayer, will make it possible to produce new devices, we were interested in the way in which the angles change of value following the annealing based on the intra-layer and inter-layer processes. This makes it possible to change the structure of the graphene electronic band.

Resume : The purpose of this research is to obtain CdTe nanocrystals by electrochemical deposition in a-SiO2/Si -n track template. A conventional electrolytic cell was used for electrochemical deposition. The voltage on the electrodes was 1.5V, t = 5 min. electrochemical deposition of CdTE was carried out on two different solutions. An X-ray structural analysis showed to form cadmium telluride nanocrystals of the hexagonal phase (wurtzite) together with the amorphous phase. The use of chloride and sulphate electrolytes leads to the formation of the dominant amorphous phase of CdTe over the crystalline hexagonal phase. Subsequent annealing leads to the dominance of CdTe nanocrystals.

Resume : We present here the use of the pulsed laser annealing (PLA) method to improve (or activate) optical properties of nanostructured oxides doped with rare-earth metals. Depending on operating conditions of PLA (e.g. laser wavelength, laser fluence, number of shots, ambient pressure), a material structure changes and subsequently optical properties are affected. In this work, we prepared Eu doped Lu2O3, Y2O3 and ZnO thin films by pulsed laser deposition (PLD). They were deposited on fused silica substrates at room temperature in an oxygen atmosphere at a pressure of 1 and 2 Pa. Optical and structural properties of the films (both as-prepared and laser-annealed) were studied as well as their chemical composition and film morphology. The film morphology was analyzed by atomic force microscopy (AFM) and scanning electron microscopy (SEM), the chemical composition was determined by x-ray photoelectron spectroscopy (XPS) and the structure was characterized using x-ray diffraction (XRD) and by XPS. UV-VIS ellipsometry, spectrophotometry and photoluminescence were used to analyze optical properties.

Resume : First, a thienylene-vinylene-thienylene (TVT) derivative with cyano groups in the 3- and 3'- positions was synthesized as a building block of semiconducting polymers for high mobility organic field effect transistors (OFETs). (E)-1,2-Di-(3-cyanothiophen-2-yl)ethene (2CNTVT) was copolymerized with diketopyrrolopyrrole (DPP) units via Stille coupling reaction to give 2DPP-2CNTVT and 7DPP-2CNTVT. The properties of these two polymers were compared with those of the corresponding polymers without cyano groups in TVT (2DPP-TVT and 7DPP-TVT). The effects of CN groups and branched alkyl position were found to have a significant influence on the optical, electrochemical, morphological, and charge transporting properties of the polymers. The average hole mobilities of OFETs fabricated with 2DPP-TVT and 7DPP-TVT OFETs were 1.63 and 2.2 cm2 V–1 s–1, respectively, and the average electron mobility for both 2DPP-2CNTVT and 7DPP-2CNTVT OFETs was 1.2 cm2 V–1 s–1. Second, semiconducting polymers consisting of TVT derivatives and benzo[1,2-b:4,5-b']dithiophene with conjugated thiophene side chains (BDTT) were designed and synthesized to investigate the effect of fluorine and cyano groups in the 3-position of the thiophene ring in TVT on the photovoltaic properties. The corresponding PBDTT-TVT, PBDTT-FTVT, and PBDTT-CNTVT copolymers containing TVT, di-fluoro TVT (FTVT), and di-cyano TVT (CNTVT), respectively, demonstrated considerable variations in optical, electrochemical, morphological, and charge transporting properties. PBDTT-FTVT showed suitable frontier orbital energy levels, favorable face-on orientation, and a well-mixed and smooth morphology in the blends with 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (ITIC) and [6,6]-phenyl-C71-butyric acid methyl ester (PCBM). In contrast, PBDTT-CNTVT showed unfavorable frontier orbital energy levels and bimodal orientation in the thin film state, which interrupted efficient charge transport in organic photovoltaic devices. The device fabricated using PBDTT-FTVT exhibited the highest power conversion efficiency (PCE) of up to 6.50% with ITIC and a slightly lower PCE of 6.35% with PCBM.

Resume : Our group has reported donor-acceptor type copolymers based on thieno[3,4-c]pyrrole-4,6(5H)-dione (TPD) linked with alkyl substituted-thieno[3,2-b]thiophene as π-bridge for highly efficient organic photovoltaic cells. In this work, we developed and synthesized a bi-TPD as acceptor moiety linked with alkyl substituted-thieno[3,2-b]thiophene as π-bridge to control the optical and electrical properties. Synthesized bi-TPD components with two different side alkyl chains were polymerized with benzodithiophene as donor miety to give PBDT-biTPD(BO) and PBDT-biTPD(HD). Compared to that of a polymer composed of mono-TPD, PBDT-biTPD series displayed red-shifted absorption spectra with deep highest occupied molecular energy level because bi-TPD, which consists of two TPD components and, possess longer conjugation length and stronger electron withdrawing characteristic than mono-TPD with improved solubility. The synthesized polymers were able to offer high device performance when blended with both fullerene derivative (PC71BM) and non-fullerene derivative (IT-4F). From grazing incidence X-ray scattering measurements, both neat polymer and blended films exhibited preferential face-on orientation, which is beneficial for vertical charge transport in the OPVs. Consequently, fullerene based OPV devices displayed power conversion efficiency (PCE, 8.65 and 8.99 %) for PBDT-biTPD(BO):PC71BM and PBDT-biTPD(HD):PC71BM, respectively. Comparison with the fullerene based devices, the device of PBDT-biTPD(HD):IT-4F achieved the best PCE of 9.65 % with a significantly increased short circuit current because IT-4F unit is able to more harvest absorption spectra to 800 nm compared to that of PC71BM. It is demonstrated that bi-TPD component is a promising accepting building moiety for highly efficient OPVs.

Resume : Tin methylammonium iodide (MASnI3) is a p-type semiconductor with excellent optical versus electrical properties. This work introduces a stable process for growing high-purity MASnI3 thin films via thermal evaporation. The growth process was proposed and discussed. The gas sensing properties of the MASnI3 thin film were investigated at room temperature with/without illumination. The film exhibited the highest selectivity toward NO2 (limit of detection: 25 ppb). Furthermore, the highest response of the film (i.e., slightly >40) toward 1000 ppb NO2 was realized after three measurement days. The gas sensing mechanism of the device was discussed and illustrated in a three-dimensional model.

Resume : Our dependence on fossil fuels has increased continuously since the Industrial Revolution. Currently, nearly 80% of the world’s energy comes from coal, oil, and natural gas. However, petrochemical fuels have contributed significantly to global warming because they release large amounts of carbon dioxide when burned to generate energy. This has led to extensive efforts in recent years all over the world to develop alternative energy sources in order to reduce the dependence on oil and coal. These alternative sources include biomass, geothermal and marine sources, and wind and solar energies. Among these, solar energy, a renewable form of energy that can be developed sustainably, shows the greatest promise. At present, the solar cells available can be categorised as follows: those based on (i) crystalline silicon substrates, (ii) thin films, and (iii) compound semiconductors. Despite this variety, the market is currently dominated by silicon-semiconductor-based solar cells, which have a conversion efficiency of approximately 25%. However, these solar cells can be expensive and have long production times. Further, the substrate used poses several limitations. As a result, they are impractical for use in domestic situations or in regions with harsh environments. This has led researchers to study other types of solar cells as alternatives. Dye-sensitised solar cells (DSSCs) have attracted a lot of attention because of the simplicity of their manufacturing process, low manufacturing cost, environmental friendliness, and commercial potential. The successful operation of DSSCs depends on minimising the recombination processes that occur at the injected electron/oxidised dye or electrolyte interface and ensuring efficient electron transport and subsequent electron collection. There have been several studies since 1991 on the use of TiO2 nanoparticles as photoelectrode materials in DSSCs, whose use has led to a conversion efficiency greater than 10%. The main focus has been to increase the surface area and hence the dye-adsorption capability. However, it has proven difficult to increase the efficiency further because of phenomena that occur within the grain boundaries, namely, charge trapping/detrapping events. Furthermore, the long-term stability and carrier mobility of TiO2 are also low. Some researchers have investigated the possibility of using SnO2, ZnO, or other metal oxides for producing semiconductors that can be used as photoelectrode materials, in an attempt to improve the charge-transport characteristics of DSSCs. ZnO has attracted significant attention because its wide bandgap (3.37 eV), which is similar to that of TiO2. Furthermore, its electron mobility, which is approximately 2–3 orders of magnitude higher than that of TiO2. Hence, the use of one-dimensional (1D) ZnO nanostructures (NSs) has great potential to improve the performance of DSSCs. However, the conversion efficiency of DSSCs based on these NSs is less than desirable and their photoelectric conversion efficiency also remains low. It has been reported that this is attributable to the insufficient light adsorption by the photoelectrode owing to its low surface area, and various methods have been proposed for improving the surface adsorption properties and quality of ZnO NSs. These include using the chemical solution method to fabricate the nanostructures, as this method has the advantages of being low cost, easy to control, and suitable for large-scale fabrication. Most studies on the use of ZnO NSs as photoelectrode materials in DSSCs have attempted to evaluate the dye-adsorption capabilities of various types of NSs, and very few have analysed the effects of their optical properties on DSSC performance. In this study, photoelectrodes for use in DSSCs were prepared using two types of ZnO NSs, which were fabricated using the low-temperature chemical solution method. The morphologies and optical properties of the ZnO NSs were evaluated in detail. The 2D ZnO NFs exhibited better dye adsorption properties and a higher haze value than did the 1D ZnO NRs. Simulations were performed using the FDTD method, and the results were found to be consistent with those of actual light-scattering measurements. Moreover, the results of transmittance measurements performed over a range of incidence angles indicated that the attenuation of incident light was not as pronounced in the 2D ZnO NFs, owing to which the DSSCs prepared using them exhibited higher photoelectric conversion efficiency. In addition, their light-scattering ability resulted in improved light trapping during the variable-angle I–V measurements. With the decrease in the cell efficiency with increases in the incident light angle being only 12% for the devices with the 2D ZnO NFs. Thus, DSSCs based on 2D ZnO NFs should be suitable for wide-angle applications.

Resume : Organic molecules enable the fabrication of large-area and flexible electronics with low energy consumption [1]. In organic field-effect transistors (FETs), the characteristics depend heavily on the thickness of the device and the charge transport at the dielectric-organic interface [2]. To improve the devices performance, the optimization of dielectric properties and the orientation of semiconductor molecules are crucial. Herein, we present the method of self-assembled monolayers (SAMs) as functional layers in FETs, which combine dielectric and semi conductive properties in one molecular layer with full control of surface coverage and high reliability in layer formation from solution. The newly designed organic molecules with specific anchor groups and molecular design as a toolbox for p- and n-type self-assembled monolayer field-effect transistors (SAMFETs) are shown [3]. We will demonstrate SAMFET devices based on small molecules as an integration concept, which enable the fabrication of organic complementary FETs as well as the realization of integrated circuits. The CMOS inverter using photolithography process with region selective deposition of p-/n- type SAMs in the channels, successfully operate at a low supply voltage and a high signal gain of 48. These results are expected to contribute greatly to the development of integrated circuits with high-speed operation with SAMFETs. [1] Wang, Sihong, et al. Nature 555 (2018) 83-88. [2] Yokota, Tomoyuki, et al. Nature nanotechnology 13.2 (2018): 139. [3] T. Schmaltz, et al. ACS Nano, 11 (2017) 8747–8757.

Resume : Flexible and Stretchable electrodes are intensively studied because of their attraction along with the development of wearable devices, flexible displays and soft electronics. Conventional electrodes are mainly made of metal oxide or printed metal wires so that they have very low ductility and elastic deformability. To replace such rigid electrode, new materials are intensely studied such as metal nanowires, graphene, metal meshes, carbon nanofiber or conductive polymers. For the advanced electronics applications, the complex of metal nanoparticles and carbon nanotube (CNT) were developed to have both flexibility and conductivity at the same time. And we also employed the 3roll mill and planetary mixer to well dispersed hybrid of chemically modified CNT and Ag paste. Furthermore, the EA gripper including metal-CNT flexible electrode was demonstrated its feasibility and the electrostatic field generation wase verified according to the applied voltage and its mechanical behavior.

Resume : ZnO is a well-known wide band-gap (3.3-3.4 eV) semiconductor suitable for many applications in optoelectronic industry for optical sensors and light emitting diodes (LEDs). In the present work, a white LED structure based on rare earths (RE) doped ZnO materials is considered. A complete preliminary study of the effect of post annealing treatment on the structural and optical properties of Tb-Eu doped ZnO is presented. The doped films (about 150 nm thick) were grown by radiofrequency magnetron sputtering on (100) Si substrates. They were then annealed at various temperatures (up to 1100°C) for 1h under a nitrogen flow. Transmission electron microscopy observations revealed a diffusion process of the REs toward the film/substrate interface for annealing temperatures up to 700°C. For higher temperatures, the annealing treatment led to the appearance of silicate phases (Zn2SiO4 phase) at the bottom of the film. For the extreme temperature values, new phases (RE silicates) appeared giving rise to high PL emissions from Eu suggesting an energy transfer from Tb towards Eu. An attempt to explain the origin and the evolution of the PL emissions is presented. By mixing different colors coming from the RE emissions, a white LED structure has been tempted and the first electroluminescence data on Ce, Tb and Tb-Eu doped ZnO multilayers (about 65 nm thick) annealed at 700°C are reported.

Resume : Alloying of ZnO with CdO leads to the gradual reduction of the bandgap, which results in tuning of luminescence from UV to VIS region. Thus, ZnO/CdO heterostructures can be used of light emitting and laser diode sources operating from UV to green/blue wavelengths. The subject of investigations were ZnO/CdO multilayer that had been fabricated on a (111) Si substrate. The optical properties were analyzed by PL and the structural studies by AFM, SEM, XRD and micro-Raman spectroscopy. The micro-Raman spectra show phonon modes originating from the Si substrate and the ZnO layer. A significant broadening of the A_1^LO ZnO line with comparison to the one observed for pure ZnO layers, can indicate the formation of a ZnCdO alloy. The near resonant Raman measurements exhibit phonon modes characteristic only for the ZnO layer, namely the A_1^LO peak and its two replicas. For both excitation wavelengths the Raman spectra present a significant shift of the A_1^LO ZnO. The shift of the A_1^LO Raman line has been observed in the case of Zn1-xCdxO films. It was assigned to the inhomogeneous micro-strains. We can conclude about the existence of ZnCdO layer in the investigated samples, formed by incorporation of Cd into the crystal lattice of ZnO during the growth of ZnO/CdO multilayers. XRD measurements reveal the structure is polycrystalline with dominant orientation in the (0001) crystallographic direction. For the lower values of 2θ angles XRD signal is coming from ZnCdO and the next one from ZnO, confirming the formation of ZnCdO layer.

Resume : III-nitride ultraviolet (UV) emitters have an expansive application potential for polymer curing, air purification, solid-state lighting, and sterilization. However, high external quantum efficiency and low forward voltage of UV emitters are very challenging due to poor light extraction efficiency and high contact resistance. The prevailing structure for high power emitters is flip chip emitters with Al electrode which has high reflectance in UV range than Ag electrode. However, the Al electrode causes the degradation of electrode due to high contact resistance. Thus, it is essential to develop an electrode for high efficiency UV emitter that has a high reflectance and a stable ohmic contact between metal and p-AlGaN layer. In this study, we demonstrated the ITO nanograins between p-AlGaN layer and Al electrode to solve the ohmic contact problem by lowering the Schottky Barrier Height. We fabricated the various micro-hole arrays of dia. 4, 6, 8, and 10 μm with 25 μm-pitch and 75 nm depth on top of p-AlGaN layer. The 15 nm ITO layer for ITO nanograin was deposited on the patterned p-AlGaN layer. The Al electrode embedded with ITO nanoparticles has the high reflectivity of 77 % at 365 nm and low contact resistance of 7.9 ×10-4 Ω·cm2. Due to the improvement of these properties, the output power of the UV emitter was improved by 72 % compared to the UV emitter with single Al electrode.

Resume : The shingled module method using conductive adhesive (ECA) can be processed at a low temperature of 120 to 180°C, the efficiency is improved by reducing thermodynamic stress on c-Si. In this paper, we fabricated the c-Si cutting cells using green laser and then cell bonding was performed by using ECA for module fabrication. As experiment conditions, curing time was changed from 30 to 120 sec and curing temperature was changed from 130 to 210°C. The number of curing were changed 1-3 times and the efficiency was measured after module fabrication with various conditions. As a result, the bonding between the cutting cells did not proceed smoothly when the curing time was very short. The silver(Ag) particles, which are the main component of ECA, were not formed densely and the connection between the conductive particles was broken. As a result, the highest efficiency of 20.27% was obtained in the condition of the curing time of 60 seconds, and it was judged that a electric current path was formed due to the densely formed surface structure of the Ag particles. It was 20.27% in the primary curing times, 19.67% in the secondary curing times and 19.58% in the tertiary curing times, and showed the highest efficiency in the primary curing times. It was considered that the crack occurred due to the deterioration phenomenon in the conditions after the secondary curing times and the efficiency was gradually lowered. As a result, it was found that the highest efficiency was 20.27% at curing time of 60 seconds, curing temperature of 150°C and primary curing times. The efficiency after module fabrication increased by about 2.67% compared with the conventional cutting cell efficiency.

Resume : Because ZnO basically has n-type property due to oxygen vacancies and interstitial Zn as the point defects, it is difficult to make p-type ZnO (p-ZnO) thin films with high reliability. In addition, the capacity of the acceptor is low and the self-compensation effect is high. Nevertheless, ZnO has attractive advantages such as a large free-exciton binding energy (60 meV), relatively low costs, and direct bandgap (3.37 eV). To realize these applications such as transparent conductive electrodes (TCEs), gas sensor, and ultraviolet LEDs, stable p-ZnO growth is essential. It is necessary to understand that has a crucial effect on the structural and electrical properties for realization of the p-ZnO having excellent features and high reproducibility. The p-ZnO can be made by doping with group-V elements such as nitrogen, phosphorus, arsenic, and antimony. When a group-V element is used as a dopant for ZnO and p-ZnO can be produced because an acceptor level is formed by substitution of a group-V element in the oxygen sites. In this study, we demonstrated to grow group-V element doped ZnO using radio frequency (RF) magnetron sputtering and annealing process for a high quality p-ZnO thin film. A buffer layer was applied to decrease defects as donors. Therefore, we confirmed the electrical and optical properties of the p-ZnO thin film grown by RF sputtering. The ZnO showed the hole concentration of over 1017/cm3 after dopant activation by annealing process.

Resume : Semiconductor nanowires have become very important material for optoelectronic applications. Recently, free-standing semiconductor nanowires have considerable attention in applications involving photovoltaic devices. The efficiencies of solar cells on nanowires have increased and have reached up to about 20 %. High electrical conductivity (∼104 Ω−1 cm−1), electron mobility of 15000 cm2⋅V−1⋅s−1 and high transparency (97.7% transmittance in the visible spectrum) have been recognized in monolayer graphene and predestine it for various applications, including solar cells, flexible electronics, transparent electrodes and energy storage. Here in this work we wanted to integrate graphene and nanowire technologies together. InP nanowires on epitaxial graphene on SiC substrates were grown. The growth was carried out without gold nanoparticle catalyst in a metalorganic vapour phase epitaxy (MOVPE) an AIX 200 reactor. The source gases were TMIn and PH3. The quality of nanowires was studied by means of SEM, PL and Raman Spectroscopy.

Resume : We study the behavior of electrical permittivity and mobility of ferroelectric HfO2 and HfZrO2 grown by atomic layer deposition and, respectively, of graphene/ferroelectric structures. The aim is to gain insight into phenomena at graphene/ferroelectric and ferroelectric/substrate interfaces and to extract useful information for nanoelectronic applications. The capacitance and loss tangent of ferroelectric HfO2 and HfZrO2 layers on Si/SiO2 were measured as a function of temperature and frequency. For each temperature, in heating-cooling cycles between 30 and 300oC, measurements were performed at several frequencies in the 42 Hz-5 MHz range. The heterostructures stabilize starting from the second cycle, but the capacitance and losses depend on the contact types (Au/Cr or Ag) and on the SiO2 thickness. The capacitance decreases steadily as the frequency increases, the frequency dependence of losses being more complex. At high frequencies, the capacitance is minimal at a temperature at which losses are maxima. The mobility was determined from direct Hall Effect measurements at room temperature and below for a graphene/ferroelectric layer configuration. Whether essential in nanoelectronics, mobility estimation is not straightforward. Besides Hall effect, it can be extracted from drain current-drain voltage or transconductance measurements of graphene/ferroelectric field-effect-transistor configurations. A comparison between these mobility values shows that the value extracted from transconductance significantly underestimates this parameter. ACKNOWLEDGMENTS: This work was supported by a grant of Romanian National Authority for Scientific research, CNCS-UEFISCDI, Project PN-III-P4-ID-PCCF-2016-0033.

Resume : The screen printing method is widely used for silicon solar cell electrode formations. However, it has a disadvantage of having high contact resistivity between wafers and electrodes. Laser-doped selective emitters (LDSE) technology can reduce contact resistivity and increases efficiency of solar cells. In this study, the selective emitter was formed to reduce contact resistivity after laser optimization experiment. We used nanosecond green laser and doped c-Si wafers with sheet resistance of 100 Ω/□ for LDSE process. The laser conditions were changed with laser power of 25 ~ 45% (2.5 W ~ 4.5 W) and laser speed of 30 ~ 60 mm/s. As a result of laser power variable experiment, the process was not performed due to low energy density under 25% or less power conditions and the process was changed from 30% or more power conditions. At 40% or more of the power, it was determined that the heat affected zone (HAZ) was gradually occurred, affecting LDSE formation. The HAZ occurs as the laser remains on the wafer for a long time, which reduces the efficiency of the solar cell. At 35% laser power, we obtained about 7 mΩ·cm2 contact resistivity and power was fixed for optimization of the LDSE process. In the laser speed variable experiment, the formation of HAZ was small and low contact resistivity about 4.8 mΩ·cm2 was obtained in the condition of laser speed of 40 mm/s. As a result, we confirmed LDSE formation and low contact resistivity in laser power of 35% and laser speed of 40 mm/s.

Resume : Aluminium Nitride (AlN) nanostructures – nanotubes, nanowires and nanoparticles have been successfully synthesised by using a high temperature, highly non-equilibrium DC arc plasma method and investigated with different methods, including XANES, FTIR, neutron powder diffraction and inelastic neutron scattering [1-3]. Here we report the results of the cathodoluminescence studies of the AlN nanotubes and nanoparticles, which have been measured between 80 K and room temperature (RT) under electron irradition with 10 keV energy. Low-temperature CL spectra of nanostructured AlN have been compared with those of the commercially available AlN powder. The significant difference between emission spectra of the three investigated samples has been established. Commercial AlN has been found to emit a band peaked at 3.47 eV which is commonly ascribed to oxygen impurities. Emission of the AlN nanoparticles is centered around 3.66 eV while CL spectrum of AlN nanotubes show complex character with at least three peaks at 2.2, 3.0 and 3.5 eV in the photon energy range of 1.8 – 3.8 eV. CL intensity of the nanostructured samples has been found to decrease significantly at RT, most probably due to a combination of non-irradiative relaxations at the surface, electron-phonon interactions and the reabsorption of the emitted light. CL of AlN-nanotube/CsI-scintillator composites has been also studied. Energy transfer via luminescence emission from CsI scintillator to AlN nanotube is demonstrated. Luminescence properties AlN nanotube/polymer composites were also studied and compared with those obtained for AlN nanotubes and nanoparticles. References: [1]. Balasubramanian C., et al. Journal of Physics: Condensed Matter 18 (2006): S2095. [2]. Bellucci S., Popov A.I. et al. Radiation Measurements 42 (2007): 708-711. [3]. Bellucci S., Balasubramanian C., Ivanov A., Popov A., Schober H. J. Neutron Research, 14(2006); 287-291.

Resume : The photosensitive pHEMA-TiO2 hybrid material based on organic poly-hydroxyethyl methacrylate (pHEMA) network and titania nanoparticles, are photochrome and photorefractive bulk solids exhibiting a large electrons storage capacity [1, 2]. Their high photonic sensitivity results from an efficient separation of the photoinduced charges at the organic-inorganic interface. These materials open the potential applications of laser-induced polymerization in many fields as optics, electronics, optoelectronics, protective coatings, sensors, etc. In the present communication, we report on the synthesis of pHEMA-TiO2 hybrids by photopolymerization. The polymerization kinetics of pure 2-hydroxyethyl methacrylate (HEMA) and HEMA-TiO2 hybrid solutions under UV irradiation is monitored in situ by Raman spectroscopy. The changes of propagation and termination rate constants along the reaction are determined from the evolution of the rate of polymerization with time. The influence of UV laser intensity and photoinitiator concentration on the reaction kinetics are analyzed. The effects of TiO2 nanoparticles loading on polymerization of HEMA are also discussed. 1. P. Gorbovyi, et al., "Alkoxysilane effect in hybrid material: A comparison of pHEMA-TiO2 and pMAPTMS-TiO2 nanoparticulate hybrids," Mater. Res. Bull., 114, 130-137 (2019). 2. A. Uklein, P. Gorbovyi, M. Traore, L. Museur, and A. Kanaev, "Photo-induced refraction of nanoparticulate organic-inorganic TiO2-pHEMA hybrids," Opt. Mater. Express, 3(5), 533-545 (2013).

Resume : The CdS buffer layer is has a disadvantage of causes environmental pollution. Therefore Cd-free buffer layer such as ZnS, ZnSe, Zn (Se, OH), Zn (O, OH), Sn (S, O) and Zn (O, S) is actively being developed. In this paper, the characteristics of thin films according to various complexing agents in ZnS buffer layer fabrication using solution reuse were analyzed. The ZnS thin films were deposited on the ITO substrate using EDTA, trisodium and HMTA as complexing agents. The experimental conditions varied from 0.0125 ~ 0.2 M of EDTA, 0.0125 ~ 0.1 M of trisodium and 0.0125 ~ 0.1 M of HMTA. Also, the experiment was conducted by reusing the solution up to six times through filtering. As a result, ZnS thin film was uniformly formed at all concentrations of trisodium, but the ratio of Zn ion to S ion was measured to be closest to 1:1 at 0.025 M. After trisodium was fixed at 0.025 M, solution reuse experiment was conducted. It was confirmed that the particles of ZnS thin film were uniformly deposited up to three times. EDTA confirmed the most dense and uniform film at 0.1 M. EDTA was fixed at 0.1 M and solution reuse experiment was conducted. As a result, it was confirmed that pin-holes were formed on the surface after four times of solution reuse. HMTA was uniformly grown up to 0.025 M, but the pinhole was formed on the surface from 0.05 M. HMTA was fixed at 0.025M and solution reuse experiment was conducted. As a result, it was confirmed that the particles were grown small form the experiment of solution reuse three times. However, thin films were deposited without cracks or pinholes up to six times reuse. Finally, all the complexing agents were reused up to 2 ~ 3 times, and it was confirmed that a uniform ZnS thin film was deposited.

Resume : The lightweight sensory device has gained popularity in the application of correlating the effect of environmental climate on health, growth, and photosynthesis process of plants. In this study, we report a leaf-mountable strain sensor for plant growth monitoring with the sandwich configuration of Ecoflex as a biocompatible base material and CNT-Ecoflex composite as a sensing material. The strain transduction was achieved by two different structures monitoring resistance(R) and capacitance(C). With R-type strain sensors, the linearity R2=0.945 has achieved in semi-logarithmic scale with gauge factor(GF) over 50 at strain greater than 50%. Hysteresis and drift due to the nature of CNT network in viscoelastic materal were investigated in R-type. C-type strain sensors were fabricated as in-plane interdigitated electrodes shape and demonstrated the linearity of R2=0.978 in linear scale and the sensitivity(GF) of 0.4 along the lateral strain range from 0% to 100%. Hysteresis and drift performance were greatly improved since the capacitance was purely governed by geometry deformation. The fabricated sensors were integrated with RFID sensor tag device and remote data acquisition of strain signal was successfully measured.

Resume : There is a wide range of barrier requirements for flexible passivation thin films depending on the application. Alternating inorganic and organic layers are proven to be a good technique for developing multilayer passivation films for flexible applications. For instance, commercial application of multilayer passivation thin films in flexible organic light emitting displays require ultra-high barrier properties such as high resistance to water vapor and oxygen and high optical transmittance. However, their broad adoption has been impeded by delays and interruptions introduced by fabrication in multi-deposition chambers. Most of these conventional approaches are not only expensive and complex, but also require long process time and high deposition temperatures. In this presentation, we investigated poly-para-xylylene (parylene) and Aluminium Nitride (AlN) multilayer passivation thin film, fabricated within a single chamber at room temperature. A fast deposition rate was achieved for the thick parylene layer after optimizing the cracking chamber with an internal structure. We obtained the high optical transmittance of 90% and flat surface roughness of 3.16 nm (root mean square) for PEN/parylene/AlN film. The barrier properties were analyzed in terms of water vapor transmission rate using the analysis of electrical resistivity of evaporated metal thin film.

Resume : Nanotechnology requires both characterisation methods, that can look at the nanoscale and monitor processes and a scale that is typically not accessible by optical techniques, and nanofabrication methods, that can modify the local surface structure and chemistry in a well-defined manner. In this contribution, we will show recent advantages in focussed ion beam lithography (FIB) utilizing three different ion beams, namely Helium, Neon and Gallium and particularly their combination. In FIB the surface is modified through sputtering and no mask or resist is required. In contrast to electron beams at similar beam energies, ion beams travel in a much straighter fashion and allow e.g. the fabrication of high-aspect ratio structures. While relatively large structures (100 x 100 µm2) can be fabricated in reasonable time using Gallium ions, Neon and Helium ions allow very precise structuring of individual objects and polishing of structures and surfaces. We could show, that latter aspect is relevant to fabricate smooth and effective plasmonic waveguides and circuit elements.

Resume : Metallic nanoparticles (NPs), sustaining localized surface plasmon resonances, are currently of great interest for enhancing light trapping in thin film solar cells. To be directly applicable in the photovoltaic industry, the NPs fabrication needs to be simple, reliable, low-cost and scalable. As such, self-assembly processes are most commonly used, and Ag is the preferred material, due to its high radiative efficiency and low imaginary permittivity⁠. After exploring the correlation between structural and optical properties of Ag NPs fabricated by solidstate dewetting process on various substrates, we identified the fabrication conditions in which desirable NPs are obtained, but we also evidenced unexpectedly high parasitic absorption, main obstacle for photovoltaics. Thus, we introduced a novel spectroscopic method which enables the quantification of absorption enhancement and parasitic losses and demonstrated that the optical losses in the NPs are insignificant in the wavelength range of interest, while the NPs provides up to 90% useful absorption enhancement, which can be attributed to both the random front surface texture, originated from the conformal growth of the material over the NPs and to the scattering of light by the plasmonic NPs. Our optimized plasmon-enhanced thin film solar cell shows a pronounced broadband enhancement of external quantum efficiency and remarkably high short circuit current density in comparison to those reported in the literature.

Resume : The diode structure consist of ZnO:N grown by MBE on SiC (6H) n-type substrates. The turn-on voltage is at about 3.5 V under forward bias and the reverse breakdown voltage is higher than 5 V. The forward to reverse current ratios are at about 2x10^2. Forward biasing characteristics show four regions, indicating different conduction mechanism at this stages. At low voltage the slope of log(I)-log(V) plot is close to 1 - Ohmic region, at higher voltage the plot obey the relationship characteristic for recombination-tunneling, multistep-tunneling or multi-tunneling capture-emission current and next space charge limited current comes SCLC to play a role. The injection current is dominated by the injected electrons under the forward voltage and the single-carrier current forms because the barrier is higher for the holes than that for the electrons. The diffusion lengths of minority carriers, extracted from the EBIC line scan, are 130 nm for holes in n-SiC and 74 nm for electrons in p-ZnO regions. The maximum of electroluminescence EL is located at ~ 500 nm and initiated at ~-6V; the EL intensity began to increase rapidly together with the electrical current for heterojunction LEDs, indicating that the EL emission is a result of carrier transport through the p–n heterojunction. The electrical parameters was supplemented by XRD and optical analysis. Obtained results demonstrate that a high quality heterojunction between ZnO:N and SiC has been achieved.

Resume : Systems composed of organic molecules grafted on silicon nanowires promise new landscapes towards the design of materials with controlled features and functions. Possible applications span in physics, chemistry, engineering and life science. The organic molecule chosen for this experiment, the diethyl 1-propylphosphonate (DPP), presents the advantage to self-assemble by forming one monolayer onto the Si surface making this hybrid material the ideal platform to be studied by high resolution microscopy techniques. Another characteristics is that upon thermal annealing the molecule decomposes providing phosphorous atoms which diffuse inside Si where they work as dopant sources. For this reason, this approach can be used as an efficient doping method for 3-dimensional Si nano-architectures. We conformally deposit a single DPP layer over silicon nanowires and for the first time observe them by scanning Transmission Electron Microscopy at high resolution. We complement the results with numerical simulations on the molecule/silicon interaction mechanisms.

Resume : Numerous medical studies highlighted that frequent exposure to improper light, such as intensive white light or light consisting of strong blue emission considerably suppresses the secretion of melatonin (MLT) [1-4]. When such lights are rapidly utilized at night, the lack of MLT secretion disturbs the human circadian rhythm including sleep-wake behavior, cell function, and gene expression, jeopardizing human health. Moreover, circadian disruption by light-at-night markedly increases the risk of various types of cancers, including breast-, colorectal-, and prostate- cancers. The reason behind this may be a light source with high color-temperature or short wavelength light that has a remarkably high suppression effect on the secretion of the oncostatic hormone, MLT [1-4]. Amongst all the lighting sources available in the market, candles, and oil lamps are currently the friendliest lighting source to human eyes, physiology, ecosystems, artifacts, environment, and night skies due to their blue light-less emission [5-6]. Unfortunately, these hydrocarbon-burning based lighting measures suffer from several disadvantages such as energy-inefficient, fire hazard, flickering nature, greenhouse gas releasing, and hard to tune or dim. Besides, they also release fine particles of PM2.5, which leads to the risk of lung cancer, the most common type of cancer occurred all over the world [5-6]. In response to the solution for the above-mentioned issues, here, we demonstrate the design and fabrication of electric driven low color temperature candlelight style solid state lighting source based on OLED technology, which is blue hazards free, besides being energy saving and physiologically friendly. The reason why OLED technology is preferred is because of its high degree of freedom in chromaticity design, besides showing plane-light, being soft, glare-free, thin, flexible, transparent, fully dimmable, and printable, etc [7]. Furthermore, all the OLED devices were fabricated by cost-effective solution process and thermally activated delayed fluorescence mechanism enabling exciplex forming co-host systems were used to precise confinement of charge carriers and excitons in the desired recombination zone, which are highly essential to improve device performance. The resulting 1,976 K candlelight OLED can reach a maximum brightness of 47,000 cd/m2, equivalent to 51,900 candlelight in one square meter, and its efficacy is 180 times that of the candle (~0.27±0.03 lm/W) and 3.6 times that of an incandescent bulb (~15 lm/W). Additionally, the designed light source delivers a sensationally pleasant and warm environment and attracts fewer insects after dusk. Its deep-blue light-less nature makes it less hazardous to night skies and artifacts. References: [1] S. M. Pauley, Med. Hypotheses, 2004, 63, 588–596. [2] P. R. Mills, S. C. Tomkins and L. J. Schlangen, J. Circadian Rhythms, 2007, 5, 1–9. [3] R. G. Stevens, G. C. Brainard, D. E. Blask, S. W. Lockley and M. E. Motta, Ca-Cancer J. Clin., 2014, 64(3), 207–218. [4] S. Davis, D. K. Mirick and R. G. Stevens, J. Natl. Cancer Inst., 2001, 93, 1557–1562. [5] J. H. Jou, Y. T. Su, S. H. Liu, Z. K He, S. Sahoo, H. H. Yu, S. Z. Chen, C. W. Wang and J. R. Lee, J. Mater. Chem. C, 2016, 4, 6070 [6] J. H. Jou, H. H. Yu, F. C. Tung, C. H. Chiang, Z. K. He and M. K. Wei, J. Mater. Chem. C, 2017,5, 176-182 [7] J.H. Jou, S. Sahoo, D. K. Dubey, R. A. K. Yadav, S. S. Swayamprabha and S. D. Chavhan J. Mater. Chem. C, 2018,6, 11492

Resume : Nanoscale composite of detonation nanodiamond (DND) and polypyrrole (PPy) as an organic dye is explored as a novel concept for energy generation, using nanodiamond as an inorganic electron acceptor. We present a technology for the composite layer-by-layer synthesis that is suitable for solar cell fabrication. The formation, pronounced material interaction, and photovoltaic properties of DND-PPy composites are characterized down to nanoscale by atomic force microscopy, infrared spectroscopy, Kelvin probe and electronic transport measurements. The data show that DNDs with different surface terminations (hydrogenated, oxidized, poly-functional) assemble PPy oligomers in different ways. This leads to composites with different optoelectronic properties. Tight material interaction results in significantly enhanced photovoltage and broadband (1 - 3.5 eV) optical absorption in DND/PPy composites compared to pristine materials. Combination of both oxygen and hydrogen functional groups on the nanodiamond surface appears to be the most favourable for the optoelectronic effects. Theoretical DFT calculations corroborate the experimental data. Prototype hybrid solar cell demonstrates the functionality of the concept.

Resume : Rare earth (RE) doped silicon host matrices have been broadly investigated to develop light emitting sources for Light Emitting Devices (LEDs). Among all REs, Cerium (Ce) has a high absorption cross section coupled with the 5d-4f transition resulting in an intense blue emission. In the past, Ce3 ions emission has been observed in SiO2 host matrix. However, such a matrix suffers from low Ce3 solubility as well as of aging effect after several current injections. On the other hand, the Si3N4 host matrix is known for its RE higher solubility and has a good electrical current injection due to its smaller band gap than its oxide counterpart. The purpose of this study is to elaborate MOS-LED structure based on Ce3 doped SiOxNy films. The SiOxNy: RE layers are deposited on silicon substrates by using RF magnetron sputtering technique under N2 reactive flow, with a typical thickness of 20-50 nm. A deep investigation is performed to obtain an intense photoluminescence signal according to the Ce and N concentrations. Up to 6 at. % of Ce3 , no saturation of the PL intensity has been observed, demonstrating the absence of Ce clusters and/or silicate phase formation thanks to the nitrogen content. The effect of the matrix composition on current injection in fabricated SiOxNy: RE MOS-LED structures will be presented and the electroluminescence (EL) properties including I-V characteristic and EL spectra will be analyzed. The influence of the nitrogen content on observed EL signal is studied through the conduction mechanisms.

Resume : Silicon-based heterojunction technology (HJT) is one of the most promising candidates for high performance and low cost solar cells with world-record efficiency close to 27% in IBC architecture [1]. The HJT exploits the excellent passivation properties of hydrogenated amorphous silicon (a-Si:H); although, the use of doped a-Si:H has drawbacks such as parasitic absorption and low-thermal budget to cope with back-end metallization. Replacing the p-type a-Si:H with molybdenum oxide (MoOx) is a viable alternative. Optimizing this hole-selective layer is needed; however information on the defect density of states (DOS), linked to oxygen vacancies [2] is still lacking. Layers of MoOx have been deposited by thermal evaporation and post-deposition annealed (PDA). Ellipsometry and RBS analysis confirmed the aimed thicknesses. Photodeflection spectroscopy measurements highlight a peak around 1.5 eV. We associate this phenomenon to polaron absorption [3]. The DOS has been extracted from the deconvolution of the absorption spectra [4], including the polaron contribution. Results reveal a sub-band defect centered 1.1 eV below the conduction band. Albeit the intensity of such peak linearly increases with the PDA temperature, XPS analysis shows oxygen vacancies do not increase with the PDA. [1] K. Yoshikawa et al., Nat. Energy, 2, 2017 [2] K. Kanai et al., Org. Electron., 11, 2010 [3] M. B. Johansson et al., J. Phys. Chem. C, 121, 2017 [4] M. Vaněček et al., Sol. Energy Mater., 8, 1983

Resume : Nowadays, silicon solar cells (Si-SCs) dominate the photovoltaic market. It is important to extend the absorption energy range of the Si-SCs and to cover completely the solar spectrum energy range. Among different solutions considered today, the use of frequency conversion layers is most attractive. In this work, we report on the effect of deposition conditions and post-deposition processing on the structural and optical properties of Er-doped Al2O3 thin films aiming at their up-conversion application. The films were grown on Si substrates kept at 300°C by thermal atomic layer deposition using Er(CpMe)3 and TMA as Er and Al precursors, respectively. The films were subsequently annealed at T=500-1000°C for 10-60 min in nitrogen flow and was studied be means of spectroscopic ellipsometry, FTIR, AFM, TEM and photoluminescence (PL) methods. It was observed that as-deposited and annealed at T<800°C films were found to be amorphous and chemically stable. Annealing at 900°C resulted in the formation of crystallite-like structure that becomes more pronounced after annealing at higher temperatures. Along with this, the formation of Er-silicate phase was observed for some samples. High-temperature annealing enhanced the PL emission from Er3+ ions and quenched PL emission related to host defects (as oxygen vacancies or their complexes). The effect of Er content on Er3+ PL emission as well as the fabrication conditions allowing the chemical composition of Er-doped Al2O3 films to be stabilized are discussed.

Resume : Mesoporous Germanium (Ge) nanostructures have attracted rapidly increasing attention over the last few years. Due to its unique optical properties related to its near-infrared (NIR) and visible light emissions, mesoporous crystalline Ge opened up new opportunities for next generation optoelectronic and biomedical applications. The samples were fabricated by bipolar electrochemical etching of Ge wafer in HF-based electrolytes. In our previous work, high resolution scanning transmission electron microscopy (HRSTEM) provided strong evidence that NIR originates from the size reduction of the nanocrystallites. However, there are still many questions to be revealed concerning the size-related emission of the nanocrystallites. In this work, we will show some results obtained by Raman spectroscopy. This one is a very sensitive technique that allows studying the physical properties of nanostructures. Among these properties, we will focus on the study of the size effects of the nanocrystallites of Ge and their distribution on the phonon modes, a new phonon-confinement model was developed to extract the size of the core and the crystallites for different etched times. The results were compared with the atomic force microscopy and Scanning transmission electron microscopy measurements.

Resume : Group-III (Al, In & Ga) nitrides and their doped alloys are engineered into various energy profiles and super-lattices for optimizing material’s performance and improving efficiencies. Our work is based on QM/MM methodologies (developed at Daresbury in collaboration with UCL) to model the electronic structures of native defects and impurity centres in III-nitride materials and their interfaces. At this stage, two-body interatomic potentials are used and intrinsic point defect energies of AlN, as well as Schottky and Frenkel defect energies, are calculated for the system. Our results agree well with earlier work, upon which we will build by applying DFT and quantum mechanics calculations for further modelling on the system. This work is extended to study the properties of elementary defects and their complexes in solid solutions of these nitrides and their interfaces with a view of gaining insights into the work of relevant optoelectronic devices.

Resume : Rh-Mn-Sb and Ir-Mn-Sb ternary systems are expected to present half-metallic magnetic Heusler alloys attractive for spintronics and magnetoelectronics. So far, there have been limited experimental investigations in these systems. In this study, Rh2MnSb, Mn2RhSb and their Ir analogues were prepared as epitaxial thin films by sputtering and their growth, structure, morphology and magnetic properties were investigated and compared employing a wide range of complementary characterization techniques. The films were prepared on MgO(001) substrates at temperatures up to 750°C in an Ar plasma at 2 Pa in an UHV chamber with two types of thickness; 20 nm and 500 nm. In terms of resulting structure, morphology and properties, they manifested a remarkably tight relation to growth temperature. Up to 400°C, prepared samples of all types of compositions displayed a nanocrystalline multiphase structure with indistinct morphology. On the other hand, above 400°C every temperature increase by 100°C resulted in formation of a particular material. Also, it seems that the Sb melting temperature, 630.5°C, represented an important threshold with regard to the growth temperature. Rh2MnSb and Ir2MnSb showed well defined ferromagnetic behavior with Curie temperatures spanning between 300 and 350 K. In the Mn2RhSb and Mn2IrSb case, their magnetic character was more complex and deserves further attention and investigation.

Resume : Research on novel lead-free pyroelectric thin films is triggered by their promising integrability in CMOS processes and application in environmental friendly infra-red sensors. High precision characterization of such materials is a key challenge in development of new pyroelectric materials. In this study, we report on the characterization of pyroelectric thin films and piezo-composites, in particular the analysis of the pyroelectric response and micro- and nanoscale thermal analysis, by using an advanced laser-based stimulation technique. We identified wide band gap semiconductor thin films fabricated by PVD and CSD processes, including Aluminum nitride and Scandium doped Aluminum nitride, as model materials for pyroelectric sensors due to their excellent dielectric properties and CMOS compatibility. We will report on the physical origin of the pyroelectricity in AlScN. By high frequency stimulation of a quantum cascade infrared-laser we measured with high spatial resolution through thickness polarization of integrated samples similar to the Laser Intensity Modulation Method. These results are complemented by thermal simulation for fundamental thermal analysis down to the nanoscale. Our novel laser-based measurement system is an essential step forward for precise material characterization in research, and quality control on industrial scales for optimized device reliability.

Resume : Components that form an eutectic composition and have low inter solubility are more preferred for a magneto-granular structure in semiconductor-ferromagnet systems. In that case simultaneous components crystallization of an eutectic melt during the cooling takes place. This leads to the specific fine-dispersed structure creation. The ultra-high alloy supersaturation leads to a significant supercooling of all phases, and causes metastable crystallization. These factors leads to a synergistic effect, contributing to nanostructuring for granular structure creation. In this work the interaction in the CdAs2 ? MnAs system is investigated. CdAs2 is a semiconductor with a band gap 0.9 eV (1.14 eV at 0 K), and has considerable anisotropic of optical and electric properties. It is crystallized in the tetragonal structure (space group I4122) with the unit cell parameters: a=7.954 Å, c=4.678 Å. In order to choose optimal compositions and synthesis parameters for grained structures, we have studied phase equilibrium in the CdAs2 ? MnAs system using a set of physicochemical methods. CdAs2?MnAs system was investigated by X-ray powder diffraction (XRD), differential thermal analysis (DTA), optical and scanning electron microscopy (SEM). Differential scanning calorimetry (DSC) of the samples was carried out in a Q20 system (TA Instruments) at heating and cooling rates from 6 to 18 °/min in temperature interval 0-100 °C. The DSC curves showed the structural transformation effect from hexagonal to orthorhombic modification of the ??? MnAs. The curve clearly shows the reversible thermal effect. CdAs2?MnAs system phase diagram was investigated by DTA, X-ray and SEMThe eutectic coordinates are 94 mol.% CdAs2 and 6 mol.% MnAs, with Tmelt=614 °C. This work received financial support from the Ministry of Education and Science of the Russian Federation (Subsidy Grant Agreement no. 075-02-2018-210 dated November 26, 2018, unique identifier of the agreement RFMEFI57818X0266).

Resume : The ability to have a tunable band-gap that extends part of the ultraviolet (UV) region makes group-III nitrides, and in particular Al_(1-x) Ga_x N, suitable for many applications. Some of which are the production of blue LEDS and lasers, as well as high-electron mobility transistors. The resistance to radiation is of utmost importance in the semiconductor industry. In this work we explored the channeled along the c-axis implantation of Argon, an inert element, in ~500 nm thick films of AlGaN grown on c-Al2O3 substrates. By increasing the energies of implantation the strain of the implanted volume, suggested as being the driving force for crystallographic defects, can be evaluated as function of depth using high resolution X-ray diffraction (XRD). Calling upon computer simulations based on the dynamical theory, combined (0002), (0004) and (0006) 2theta-omega radial symmetrical reflections show that increasing implantation energy results in increased lattice-parameters in the implanted region. The thicker strained regions arising from higher energies of implantation are, therefore, followed by higher density of defects. Comparison between channeled and random implantation directions is also discussed in terms of accumulated strain and crystal damage .

Resume : By molecular imprinting in polymers, we prepared chemical sensorsfor selective determination of genetically significant oligonucleotides. These included 5’ TATAAA 3’ (T thymine and A – adenine) [1] and 5’ GCGGCGGC 3’ (G-guanine, C-cytosine) [2] hexa- and octanucleotide, respectively. For that, by electrochemical polymerization we synthesized and simultaneously deposited on electrodes molecularly imprinted polymer (MIP) films rich in sequence-defined hexakis- and octakis(2,2’-bithien-5-yl) hybridizing probes. With the density functional theory (DFT) modeling, synthetic procedures developed, and isothermal titration calorimetry (ITC) quantifying, the A-, C-, G- or T-substituted 2,2’-bithien-5-yl functional monomers capable of Watson-Crick pairing with the template consisting of the target oligonucleotide or its peptide nucleic acid (PNA) analog of pre-programmed nucleobase sequences were designed. For transduction of oligonucleotide recognition into a useful analytical signal, we applied piezoelectric microgravimetry (PM), capacitive impedimetry (CI), and surface plasmon resonance (SPR) spectroscopy under either stagnant-solution or flow-injection analysis (FIA) conditions. The hexakis- and octakisnucleotide chemosensors discriminated one- and two-nucleotide-mismatched oligonucleotides, respectively at room temperature. Using EIS, we determined the target oligonucleotide with the 200 pM limit of detection. With the EIS determined apparent impact factor of ca. 4.0, the octakis chemosensor discriminated 5’ GCGGCGGC 3’ from Dulbecco’s modified Eagle’s medium interferences. 1. Bartold, K., et al., ACS Appl. Mater. Interfaces 2017, 9, 3948. 2. Bartold, K., et al., ACS Appl. Mater. Interfaces 2018, 10, 27562.

Resume : Atomically thin, magnetic materials have recently gained a lot of attention in the field of two-dimensional (2D) materials [1]. Single magnetic layers with critical temperature above room-temperature are extremely attractive for fundamental studies and could potentially be the basis for a new class of information storage. Probing the magnetic order of the 2D systems by conventional experimental means is very challenging. However, it is well known, that even in the single layer limit, semiconducting two-dimensional materials strongly absorb light. Therefore, optical spectroscopy is a good method for their characterization. In order to shed light on the intriguing phenomena of 2D magnetism, we present theoretical investigations of the optical properties of the layered material MnPS3, which is one important example from the large family of transition metal phosphorus trisulfide (MPS3)[2]. Our study reveals, that the interband absorption spectrum, which is proportional to the imaginary part of the dielectric function, is very similar for different possible magnetic order of MnPS3. On the other hand, the calculated effective masses of electrons and holes do depend on the magnetic order, which is reflected in the binding energy of excitons in the studied systems. In addition, our studies reveal that the Hubbard correction (U) in the DFT U approach can have a crucial impact on the prediction of the optical and electronic properties of the investigated structures. MB is funded by the NCN grant no. UMO-2016/23/D/ST3/03446. [1] M. Gibertini et al., Nat.Nanot. vol. 14, p. 408 (2019). [2] M. Evain et al., J. of Solid State Chem. vol. 7, p. 244 (1987).

Resume : GaN based nanowires has been intensively investigated for their promising potential in high-efficiency lightning technologies. As the advantages of being dislocation and strain-free, zero quantum-confined stark effect on m-planes, and improved light extraction efficiency, core-shell InGaN/GaN multi-quantum well (MQS) have been demonstrated on GaN nanowires for LEDs and laser applications [1]. Nevertheless, the point defects incorporated in GaN core can migrate and further be incorporated into InGaN/GaN quantum-wells [2]. Here, we report the luminescent properties of core-shell structures of InGaN/GaN MQS grown on GaN-based nanowires with AlGaN undershell. The GaN core nanowires growth was performed by using continuous-flow mode in metal organic chemical vapor deposition (MOCVD). An AlGaN shell was coaxially grown on the GaN nanowires by MOCVD, followed by five pairs of InGaN/GaN quantum shells. For comparison, samples without and with low In incorporation (3%) of InGaN undershell were prepared with the same growth conditions, respectively. Cathodoluminescence (CL) was used to probe the emission at different penetration depths and positions of the nanowires to assess the luminescent properties. The photoluminescence (PL) spectra of the nanowires show an obvious degradation of the defect-related yellowish emission by using AlGaN undershells. The CL maps evidence a significant improvement of the emission intensity along the nanowire, which is ascribed to the reduction of point defects incorporation into the InGaN/GaN MQS structures. This comprehensive investigation has shown that the coaxial InGaN/GaN MQS with AlGaN undershell grown on GaN nanowires can provide a promising approach for realizing highly efficient nanowire-based optoelectronic devices.

Resume : Graphene transferred onto spatial, three-dimensional (3D) structures is a new approach for improving the efficiency of optoelectronic and photovoltaic devices. Spatial structure enlarges active surface for optical or chemical phenomena relative to bulk, conventional substrates. Furthermore, such spatial structures also enable graphene’s modification from both sides. We investigated the novel three-dimensional AlGaN-based microcolumns as a substrate for transferred graphene. These spatial structures are analogous to the nanowires, however they are stable and stiff, with controllable shape, length and distance between them. This features eliminate the high rate of defect observed in graphene deposited on inhomogeneous nanowires [1]. For these reasons, it is possible to avoid such high level of graphene degradation. Moreover, allows to determine graphene’s behaviour, such as strain presence, and quality characteristics in two cases, i.e. when graphene is free-standing layer on the microcolumn surfaces and when is freely suspended between them. In this work, graphene was grown by chemical vapor deposition (CVD) and transferred onto 3D AlGaN-based microcolumns which in turn were grown by metalorganic vapor phase epitaxy (MOVPE). Quality of graphene was revealed by Raman spectroscopy and electron microscopy (SEM) observations. Hall measurements were investigated in order to evaluate the electrical properties. Raman spectroscopy showed close dependence between distance and tips (conical or flat) type of microcolumns and properties of graphene. [1] Kierdaszuk et al., Carbon N. Y. 128 (2018). Acknowledgments: This work was supported by National Science Centre (NCN) within the OPUS10 2015/19/B/ST7/02163 project.

Resume : Twisted bi-layer graphene(tBG) is different physical properties depending on the twisting angle, therefore accurate angle control and clean interlayer are essential to fabricate tBG. Generally, methods of fabricating tBG is by stacking two exfoliation graphene flakes from HOPG. Although using CVD synthetic tBG is effective to research and develop devices of tBG, it is very difficult to directly synthesize tBG of desired twist angle. When fabricating tBG by transferring two CVD synthetic single layer graphene, the polymer support layer used in the transfer process is trapped and interferes with interlayer interaction. We report the direct transfer of CVD synthesized graphene from catalysts for twisted bi- and multi-layer graphene with accurate twist angle and clean interlayer. As a result of our previous research, graphene synthesized on hydrogen-terminated germanium is the single crystal and extremely weak adhesion between graphene and underlying substrate. So we can easily pick up graphene from the catalyst by placing materials, which have moderate adhesion with graphene on graphene. The van der Waals interactions between 2D materials such as graphene and graphene or hBN and graphene are sufficient adhesion to pick up graphene from the catalytic substrate. Thus, we were able to fabricate twisted bi-layer graphene with varying twist angles by placing graphene at a controlled angle onto synthesized graphene. In addition, through repeated pick and place, we can fabricate the twisted multi-layer graphene. Moreover, through pick and place using hBN instead of graphene, we easily fabricated van der Waals heterostructure of hBN encapsulated graphene. This approach can be a suitable method for fabricating controlled twist angle van der Waals heterostructures.

Resume : Wearable and flexible pressure-strain sensors that are attachable on human skins or body has extended their applications of conventional pressure sensors to a much wider range such as monitoring of physiological signals, electronic skin, human–machine interactions, artificial limb implants. To be applicable in such broader spectrum, a wearable strain-pressure sensor should be able to accurately detect subtle body signals from external stimuli in an extensive sensing range from pulse signals to knee joint bending. Furthermore, they must exhibit high reliability and reproducibility after repeated mechanical strain. Herein, flexible and wearable pressure-strain sensors for human motion detection are introduced. Two sensors are based on graphene composites such as rGO (Reduced Graphene Oxide)-SWCNT composite coated fabrics and MoS2/Graphene foam/Ecoflex hybrid nanostructures. Sensing performance and reliability at different points such as fingertip, finger joint and wrist for electronic gloves are presented. Sleepiness prevention test at eye rims and nape is also presented. The fabricated sensors showed potential in practical applications such as a human motion sensor to detect drowsiness and an array type tactile sensor. These sensors can be applicable for personalized physiological monitoring, prosthetic hand and leg, car securities, smart shoes and chairs, etc. In addition, a multifunctional EMI shielding skin with excellent EMI shielding effectiveness (SE) and pressure sensing performance are also introduced.

Resume : Two dimensional (2D) post-transition metal chalcogenides is an emerging group of promising materials for high-performance electronic and optoelectronic devices [1-2]. However, the synthesis of this group of 2D materials with a lateral dimension of > 50 µm has been a challenge [3-4]. In this work, we present a simple way to synthesis 2D indium sulfide (In2S3) from sulfurization of the surface oxide layer of melted indium metal. 2D In2S3 is determined to feature p-type semiconducting behavior with a direct bandgap of ∼2.9 eV, potentially offering the broad detection range from UV to visible blue light region. The 2D In2S3 based photodetector exhibits a very high photoresponsivity of 8364.4 AW-1 with an excellent external quantum efficiency of 3.7067×104% and a detectivity of 4.4205 × 1010 Jones. The synthesis technique is facile, scalable, and holds promise for creating atomically thin semiconductors at wafer scale. Furthermore, the impressive optoelectronic properties of 2D In2S3 represent it as a suitable candidate for future generation optical and electronic devices.

Resume : The physical properties of two-dimensional (2D) materials depend strongly on the number of layers [1], [2]. Hence, methods for controlling their thickness with atomic layer precision are highly desirable, yet still too rare, and demonstrated for only a limited number of 2D materials [3]. Here we present a simple and scalable method for the continuous layer-by-layer thinning that works for a large class of 2D materials, notably the germanium-based 2D materials. It is based on a simple oxidation/reduction process, which selectively occurs on the topmost layer. Through a combination of atomic force microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and X-ray diffraction experiments, we demonstrate this layer-by-layer thinning method on germanium arsenide (GeAs), germanium sulfide (GeS) and germanium disulfide (GeS2). Our strategy, which we believe could be applied to other classes of 2D materials upon proper choice of the oxidation/reduction reagent, could pave the way for the realization of 2D material-based devices, such as electronic or opto-electronic ones, where a precise control over the number of layers (hence over the material’s physical properties) is needed. [1] S. Z. Butler et al., ACS Nano, vol. 7, no. 4, pp. 2898–2926, 2013. [2] X.-L. Li et al., Adv. Funct. Mater., vol. 27, no. 19, p. 1604468, 2017. [3] Y. Liu et al., ACS Nano, vol. 7, no. 5, pp. 4202–4209, 2013.

Resume : Two types of photonic structures grown by MBE on c-ZnO substrates were studied. The first one is composed of 5 pairs of ZnO/ZnMgO layers (60/50 nm), the central ZnO microcavity (300 nm) and 5 bilayers on top. The second one is a superlattice (SL) structure composed of 80 pairs of thin ZnO/ZnMgO layers (1.5/1 nm). Layer thicknesses were checked using cross-sectional Scanning Electron Microscope (SEM) mapping. The Mg contents in the ZnMgO layers has been determined to ~40% in the SL using Rutherford backscattering spectrometry and numerical simulations of the spectra. The Mg contents in the thick photonic structure were ~15%. High-Resolution X-ray Diffractions measurements revealed that both studied structures are wurtzite without precipitates of foreign phases. Their crystallographic quality is perfect as satellite lines up to the 8th order confirmed the existence of highly periodic superlattices. Reciprocal space mapping allowed to calculate the lattice constants and revealed that the structures are strained, however, partial relaxation has been found in the case of the SL with high Mg contents. The observed spatial distribution of the emission in low-temperature SEM-CL maps revealed transient regions between the substrate and strained ZnMgO/ZnO structures of quenched emission due to generation of misfit defects. Acknowledgements. The work was supported by the NCN project DEC-2018/28/C/ST3/00285 and also DEC-2014/15/B/ST3/04105

Resume : Due to their unique electrical, thermal, mechanical, optical and other properties, carbon nanotubes have attracted attention of scientists from every part of the world. For instance, the ability to conduct thermal or electrical energy in a significantly more efficient way than copper made us believe that we have finally created materials able to follow the rapid pace of the development of the civilization. Silicon and other classical materials operate close to their theoretical limits, therefore their successors have to step in shortly for us to continue the technological progress. Unfortunately, the promising performance of individual carbon nanotubes has been found to be not easily scalable and their macroscopic networks present inferior properties. One of the key underlying reasons is that these ensembles are formed from a plethora of carbon nanotubes of different types. To tackle this problem, these carbon nanotube blends have to be sorted first into highly-defined fractions. Recently, a range of sorting methods have been developed for this purpose, but most of them either require expensive infrastructure or they have a very tedious and iterative nature [1]. Herein, we would like to present our results how this can be achieved in a much more convenient way that is based on a single step aqueous two-phase extraction method [2,3]. To demonstrate the application potential of these sorted materials, we will also show how to make thin free-standing films from them based on any type of nanocarbon [4,5]. [1] D. Janas, Towards monochiral carbon nanotubes: a review of progress in the sorting of single-walled carbon nanotubes, Materials Chemistry Frontiers 2 (2018) 36-63. [2] E. Turek, T. Shiraki, T. Shiraishi, T. Shiga, T. Fujigaya, D. Janas, Single-step isolation of carbon nanotubes with narrow-band light emission characteristics, Scientific Reports 9 (2019) 535. [3] E. Turek, B. Kumanek, S. Boncel, D. Janas, Manufacture of networks from large diameter single-walled carbon nanotubes of particular electrical character, Nanomaterials 9 (2019) 614. [4] D. Janas, M. Rdest, K. Koziol, Free-standing films from chirality-controlled carbon nanotubes, Materials & Design 121 (2017) 119-125. [5] D. Janas, G. Stando, Unexpectedly strong hydrophilic character of free-standing thin films from carbon nanotubes, Scientific Reports 7 (2017) 12274.

Resume : In recent days, taste sensing have been an important issue in terms of, detecting food quality or sensing various chemical substances from specific materials. This kind of taste sensor mainly uses 2-Dimensional materials such as graphene for sensing rather using lipids or other biological substances. The aim of using 2D materials rather lipids is for longer use; bio-substance based taste sensors have very high selectivity and sensitivity but the life span of the device is short and it is sensitive to external atmosphere. For long term use and daily usage, 2D material based sensors have the advantage to bio-based sensors. Here in, we report graphene based taste sensors graphene decorated with gold for glucose sensing and nafion spin coating on graphene for pH sensing. Graphene is the main source of sensing and the decorated materials help to enhance selectivity by absorbing or penetrating the target material. Gold is well known to have selectivity to glucose and nafion has the ability to selectively penetrate cations. Gold is decorated with e-beam deposition; which thickness is about 2nm. On the other hand, nafion is spin coated onto a graphene transferred substrate.

Resume : Three-dimensional (3D) graphene is a porous structure comprised of multilayers of graphene. In this work, we study the feasibility of chemical vapor deposition grown 3D graphene to operate as a resonating nanoelectronic device. The electrostatic operation of 3D graphene is first demonstrated under steady electrostatic field, followed by its dynamic excitation. Our analysis show that electrostatic operation of 3D graphene results in highly compliant mechanical behavior due to sliding of the graphene layers under the influence of the electrostatic field. We also found that the electrostatic dynamic excitation of the 3D graphene yields wide bandwidth frequency response due to significant energy dissipation. As a results, 3D graphene is highly attractive material for high-end nanoelectronics applications, such as resonating sensors (e.g., accelerometers and force sensors), electronic components (e.g., electromechanical band pass filters), micro/nano-electromechanical (MEMS/NEMS) resonators, and more.

Resume : In this talk, we will review the composites based on porous silicon functionalized with Ag or Ni with a variety of morphology of the guest phase (0D-3D) obtained by electrochemical methods and its applications in sensors, optoelectronics and biomedicine. Some features and problems of detecting and characterizing a guest phase in a porous matrix will be highlighted, as well as the ways to solve it. The possibilities of design the morphology of metal clusters on the por-Si surface by controlling the properties of it (morphology, porosity and wettability) are shown using Ag as a guest material. Silver clusters of various dimensions were obtained depending on the characteristics of por-Si: 0D - spherical, triangular clusters, 1D - filled by metal pore channels, 2D - layers, 3D - dendrites, and also fractal aggregates). Our findings showed that the composition of adsorption centers on the por-Si surface (adsorption centers exhibiting the properties of an acid or a base of Lewis or Brønsted) strongly depends on the technological conditions and may significantly affect on the nature of the interaction with the “guest” substance. A proposed technological approach allows obtaining a composite material “Ag-por-Si” with a designed morphology of silver clusters in one cycle of electrochemical processing of single-crystal Si. The influence of the synthesis conditions of introducing Ni into por-Si on electrical properties of "Ni-por-Si" composite and its changes under special gas atmosphere by impedance spectroscopy is discussed.

Resume : The combination of semiconducting and piezoelectric properties in materials e.g. ZnO, III-Ns and other III-Vs, has given rise to unique physical phenomena such as controlling the characteristics of a semiconductor device with applied stress. This was coined as the piezotronic effect. Piezotronic sensors exhibit strain gauge factors orders of magnitude larger than piezoresistive sensors. Here we demonstrate an extremely high piezotronic sensing capability of GaAs NW ensemble Schottky diodes. The measured piezotronic sensitivity of our device, i.e. the Schottky barrier height change with pressure, was about 7800 meV/MPa. This is an order magnitude higher than record numbers obtained with optimized structures of ZnO – a material 10 times more piezoelectric than GaAs. We explore the underlying device physics and explain the high sensitivity. We identify three main contributors, related to the nanoscale characteristics and growth method of the NWs: i) pressure focusing – the nanowire ensemble geometry results in pressure applied to the top electrode to be focused/enhanced in the nanowires, thus increasing the actual stress acting on them; ii) the nanowires are mostly depleted, a result of geometry and nominally undoped growth. This means that the entire length of the NW becomes piezo-active and susceptible to exhibit the piezotronic effect; iii) our analysis suggests that current is flowing primarily through the top facet of the nanowires, which is piezo-active, and therefore no competing current routes which are not-piezo-active are holding back performance. We believe that these analysis and results will serve as future guidelines for designing superior pressure sensors through established semiconductor technology.

Resume : Functional polymeric coatings have recently attracted much attention for sensor applications due to their tunable chemical and physical properties, and their ability to be deposited on low-cost substrates. Conventional wet process that involves solvents films suffer from wetting and material compatibility issues, limitation of solid flat substrates. As a subset of Chemical Vapor Deposition (CVD) methods, initiated-CVD (iCVD) overcomes many of these limitations, enable the use of any materials with complex geometries as substrates with a fine control of film properties during deposition. In this study we investigate the applicability of polymer film functionalization by binding of selected fluorescent nanoparticles using various pre- and post-polymerization methods that are compatible with iCVD technique for biological and chemical sensing applications. Here, we present fabrication of copolymer coatings via iCVD using poly(glycidyl methacrylate) (pGMA) as the main functional polymer which was selected due to epoxy group in its structure. Functionalization is achieved via epoxy ring opening reactions which can be done pre- and post-polymerization to incorporate fluorescent nanoparticles including various dyes and quantum dots (CdSe, CdTe etc.) to either monomers or polymers. By detailed structural and optical characterization of fabricated functional polymer films, the feasibility and effectiveness of various pre-and post-polymerization functionalization methods are reported.

Resume : Human skin allows us to perceive various shapes and textures, changes in temperature, and varying degrees of contact pressure. An artificial skin with such sensory capabilities is often referred to as sensitive skin, smart skin, or electronic skin (e-skin). Significant progress in the development and advancement of e-skin has been achieved in recent years, in which particular emphasis has been placed on mimicking the mechanically compliant yet highly sensitive properties of human skin. Important considerations for the development of e-skin are the choice of materials used in its fabrication and the ability to confer the mechanical properties of human skin (low modulus, stretchability and flexibility) into its artificial counterpart. Recently developed nano-materials have been tried to apply for the fabrication of the devices mimicking E-skin. Among those are carbon nanotube, graphene, and organic based materials such as conducting small molecules and conductive polymers. While naturally occurring human skin has the ability to repair itself after incurring mechanical damage, this property has yet to be fully realized in e-skin. For artificial skin, the ability to repair both mechanical and electrical damage would be highly advantageous for practical applications. In this study, highly conductive and reversible conductor structure is formulated by combining Ga-based liquid metal, especially the eutectic alloy (EGaIn: 75 wt.% Ga, 25 wt.% In) on the matrix of Ag nanowires (NWs). With this structure, conductivity of 630 S/cm is maintained with no applied strain. The hybrid conductor showed high mechanical flexibility, with the percentage change in its resistance being small (12.5 % at bending radius: 0.5 mm). This percentage change in the resistance was much smaller that for the conductor without Ag-NWs (25.4 %). Moreover, the hybrid conductor showed excellent bending recovery performance at 50°C for 10 mins.

Resume : Energy harvesting by nature-driven bio-compatible and bio-degradable materials responding to biomechanical activities has received great attention to develop an alternative energy source for next generation portable biomedical devices [1]. Among various energy harvesting materials, piezoelectric nanogenerators (PNGs) are considered as the best renewable green energy sources for harvesting mechanical/bio-mechanical energy into electricity. Organic or inorganic materials based PNGs are very much incompatible and, considered as e-wastes for their high toxicity and complex synthesis methods [2]. Spider silk (SS) fibers having remarkable protein sequence structure contain nature’s most outstanding mechanical properties and unrivalled elasticity along with biocompatibility and biodegradability. Here, using piezoresponse force microscopy (PFM), we report for the first time structure-dependent piezoelectric response of the SS at the molecular level and confirm that SS fiber shows vertical piezoelectric coefficient of ~0.36 pm/V. The fabricated SS based bio-piezoelectric nanogenerator (SSBPNG) provides excellent output performance and high energy conversion efficiency ~66%. The fabricated SSBPNG generates an output voltage of ~21.3 V and output current of ~0.68 μA, with instantaneous peak power density of ≈4.56 μW/cm2 under cyclic external mechanical pressure. The SSBPNG device is bio-compatible and ultra-sensitive towards physiological signal monitoring such as arterial pulse, coughing, swallowing responses which can further be useful for various possible potential e-health care monitoring applications. Keywords: Spider silk, Vertical piezoelectricity, Bio-piezoelectric nanogenerator, Self-powered, Biomedical sensor. References 1. Z. L. Wang, et. al, Science 312, 242-246 (2006). 2. S. K. Karan et. al, Nano Energy 49, 655-666 (2018).

Resume : Flexible sensors are essential components in electronic devices in various applications. High-performance, self-powered sensor is a highly interesting topic for a wide range of applications in artificial intelligence, prosthetics, automotive, and human-machine interactions. Triboelectric devices can be used as self-powered sensors for detecting mechanical stimuli. Self-powered sensors using triboelectric effect have been developed, but they have shown limitations such as bulky spacers, arch shapes and 3D structures, impeding flexible and thin structures. Here, we propose zinc oxide nanorods (ZnO NRs) grown on microscale curvature surfaces of carbon-fiber-reinforced plastics (CFRPs) having large surface areas for developing spacer-free, ultrathin, highly sensitive, and flexible triboelectric sensor (TESs), that is, mechanical sensors that allow measurement of deformations using triboelectrically-generated voltages. By fabricating hierarchical micro-nanostructures using novel methods, the TESs proposed are highly sensitive and ultrathin owing to maximized surface area and space-saving design. CFRPs having flexibility and microscale curvature surfaces can also detect tensile strains and have impact-sensing capability. Therefore, the self-powered TESs using CFRP composite with hierarchical micro-nanostructures are expected to find numerous applications in various fields.

Resume : Metal Organic Frameworks (MOFs) are promising materials for a wide range of applications (like optics, electronics, gas sensing and energy storage) because of their high surface area, versatility, and chemical stability. MOFs are hybrid porous systems in which periodic arrangements of metal clusters are connected by organic ligands. Among all MOFs, MIL-101 and MIL-88 are two framework isomers built from the same precursors a trivalent metal center (mainly Cr) and a terephthalate ligand but with different connectivity. There are few examples of MIL films, which were carried out either through deposition techniques like Langmuir Blodgett and spin-coating, or through the solution growth (4 - 11 days of reaction) on gold substrates prefunctionalizated with self-assembled monolayers. This contribution proposes a fast synthetic route for the direct growth on Si of Fe-MIL films with different morphology, crystallinity and surface coverages depending on the experimental conditions. Isolated crystals of MIL-101 were directly grown from solution whereas carboxylates-based SAMs were used to obtain homogenous film consisted of MIL-88 crystals embedded in a Fe2O3 matrix. Thermal desorption experiments proved that isolated MIL-101 crystals are able to distinguish nitrobenzene from toluene. Finally, reported results showed that it is possible to integrate 3D porous MIL networks on Si surfaces to develop hybrid devices suitable for sensing applications.