Surfaces and interfaces in multilayered thin films and nano-composites

Resume : The ABO2 family of delafossite oxide metals host a rich array of bulk materials properties, ranging from ultra-high conductivity to unconventional magnetism [1,2]. I will discuss our angle-resolved photoemission (ARPES) studies of the surface electronic structure of the delafossite oxides (Pd,Pt)(Co,Rh)O2. I will show how a surface polarity triggers a pronounced electron or hole doping, transforming the system from a single-band non-magnetic nearly-free electron metal in the bulk [3] to an itinerant ferromagnet with strong electron-magnon coupling [4], or to a correlated metal hosting a kinetic-energy-coupled inversion symmetry breaking [5] at their surfaces. The latter maximizes the influence of spin-orbit coupling, allowing this oxide surface to develop some of the largest Rashba-like spin splittings that are known. Key collaborators on this work include Veronika Sunko (St Andrews and Max-Planck Institute for Chemical Physics of Solids, Dresden), Federico Mazzola (StA), and Helge Rosner, Pallavi Kushwaha, Seunghyum Khim, and Andy Mackenzie (MPI-CPFS). [1] Ok et al., Phys. Rev. Lett. 111 (2013) 176405 [2] Mackenzie, Rep. Prog. Phys. 80 (2017) 032501 [3] Kushwaha, Sunko et al., Science Advances 1 (2015) e1500692 [4] Mazzola et al., arXiv:1710.05392 (2017) [5] Sunko et al., Nature 549 (2017) 492

Resume : Transition metal oxides with an ABO3 perovskite structure have attracted widespread interest over the last decades, both from academic and industrial points of view. This can be ascribed to their wide range of functionalities that originates from the interplay between lattice, electronic, and magnetic degrees of freedom [1]. Among all perovskites, rare-earth nickelates R3+Ni3+O3 (R=Lu-La, Y) might be considered as a prototypical case because they posses almost all possible degrees of freedom present in these materials. Except for R=La, all nickelates undergo a metal-insulator phase transition at TMI, accompanied by a symmetry lowering from orthorhombic Pbnm to monoclinic P21/n [2,3]. In this P21/n phase, a Ni-site splitting is observed due to the appearance of a breathing of distortion of O6 octahedra yielding a rock-salt pattern of small and large NiO6 groups [4] usually associated with charge disproportionation [5] from 2Ni3+ to Ni(3+?)+ + Ni(3-?)+. At TMI?TN, they undergo an antiferromagnetic transition leading to a quadrupling of the magnetic unit cell and possible collinear or non collinear spin orderings [6]. Finally, the electronic structure is also characterized by strong overlap between O-2p and Ni-3d states yielding large covalent effects [2]. Therefore, nickelates seems to be on the verge of the crossover between dominantly ionic and covalent characters. However, the nature of their ground state is highly debated. Here, we address this problem by performing first-principles calculations on a wide range of nickelates covering the phase diagram. We show that the insulating phase is characterized by a clear-cut split of the electronic states of the two Ni sites, which can be strictly described as being low-spin 4+ and high-spin 2+. At the same time, our simulations reveal a shift of the oxygen-p orbitals toward the depleted Ni cations, that ultimately leads to nearly identical Ni sites from a point of view of integrated charges. The former finding is reminiscent of the ionic-charge disproportionation picture of the rare-earth nickelates originally discussed in the literature while the latter bears similarities with the recently proposed hybridized/covalent electronic configuration involving oxygen-holes. Our results reconcile these two interpretations of the ground state of the rare-earth nickelates and we therefore provide a unified picture allowing to further discuss the role of covalency on their electronic and magnetic properties. By moving to bismuthates A2+Bi4+O3 (A=Ba, Sr) that share many striking properties with nickelates [7-10] but in which Bi cations ensure a strong spin-orbit interaction, we will show that a proper use of strain engineering of their thin film form unlocks an unprecedented oxygen-holes induce Rashba spin-splitting of bands dispersing around the Fermi level. This result paves the way for new functionalities with perovskites and reveals the potential of oxides for applications based on spin-orbitronic. Work supported by the European Research Consolidator grant MINT (Contract 615759). [1] P. Zubko et al, Annu. Rev. Condens. Matter Phys. 2, 141 (2011). [2] M. L. Medarde, J Phys.: Condens. Matter 9, 1679 (1997). [3] G. Catalan, Phase Transitions 81, 729 (2008). [4] M. L. Medarde et al, Phys. Rev. B 78, 212101 (2008). [5] J. M. Alonso et al, J. Am. Chem. Soc. 121, 4754 (1999). [6] J. Garcia-Munoz et al, Phys. Rev. B 50, 978 (1994). [7] R. P. S. M. Lobo et al, Solid State Commun. 98, 61 (1996). [8] T. Thonhauser et al, Phys. Rev. B 73, 212106 (2006). [9] K. Foyetsova et al, Phys. Rev. B 91, 212114 (2015).

Resume : Iron can be found in few types of oxides, which exhibit different magnetic properties in nanometer scale. The most popular, and well described in the literature are magnetite, maghemite, and hematite. There are also iron oxides, which do not exist in the bulk form and can be only fabricated in the nanoscale (ε-Fe2O3, β-Fe2O3). These iron oxides, are rather thermally unstable, but they possess unique properties like giant coercive field (20 kOe) observed at room temperature, the coupling of magnetic and dielectric properties, as well as low saturation magnetization. Here, we present preparation of ε-Fe2O3 by thermal treatment of magnetite. In our case, magnetite nanoparticles were synthesized, with or without presence of silica shell and then, treated with different annealing procedures. Then, transformation to ε-Fe2O3 was studied. The size and morphology of obtained nanostructures were investigated by Transmission Electron Microscopy. Crystalline structure and presence of other iron oxides and especially ε-Fe2O3 phase, was examined by X-ray diffraction. Magnetic properties were studied by Mössbauer. Obtained results show that ε-Fe2O3 phase can be obtained from magnetite nanoparticles coated with silica shell in oxygen rich environment only. The work was partially financed by EU founds via project with contract number POPW.01.03.00-20-034/09-00, POPW.01.03.00-20-004/11-00.

Resume : Research on monoclinic (M1) phase of VO2 has attracted a great of interest for smart coating applications due to its exceptional thermochromic property. Herein, we reported the results using a novel approach to synthesize N-doped VO2(M1) thin films with high purity by heat treatment in NH3 atmosphere. The N dopant in the film can be regulated by varying NH3 concentration during the annealing process. We found that the N atoms are located at the interstitial sites or substitute oxygen atoms, and the V-N bonds in the VO2 thin films increase with NH3 concentration. The metal to insulator transition (MIT) temperature of the VO2 thin film is effectively reduced from 80.0 to 62.9 °C, while the solar modulation efficiency and the modulation efficiency at 2000 nm are 7.36 % and 55.6 % respectively. The band gap of N-doped VO2 thin films related to MIT (Eg1) is estimated to be as low as 0.18-0.25 eV whereas the band gap associated with the visible transparency (Eg2) is about 1.50-1.58 eV. Based on the highly accurate first-principles calculations, the Eg1 of VO2 (M1) is reduced after substituted or interstitial N-doping, while the Eg2 alters with the mode of N-doping in excellent agreement with experimental measurement.

Resume : Gallium selenide (GaSe) is one of the layered chalcogenides which are attracting interests as possible two-dimensional (2D) materials beyond graphene due to their semiconducting properties. Although GaSe is reported to crystallize in four different polytypes which differ in how GaSe layers are stacked via van der Waals interaction, the intralayer structure of GaSe has always been identical; a GaSe layer consists of four atomic layers of Ga and Se stacked in the sequence of Se-Ga-Ga-Se with Ga on top of Ga and Se on top of Se for the in-plane atomic position. Through detailed cross-sectional scanning transmission electron microscopy of GaSe thin films grown on Ge(111) substrate, we had demonstrated that GaSe layers with an unreported structure exist near the film-substrate interface [1]. The GaSe thin films were grown epitaxially on Ge(111) substrate forming van der Waals gap. This result implies that even in van der Waals epitaxy, film structure is greatly affected near the film-substrate interface, possibly, by strain. [1] T. Yonezawa et al., Surface and Interface Analysis, accepted for publication.

Resume : First Principles Phase Diagram calculations were performed for the TMD bulk systems Mo(S,Te)2[1] and W(S,Te)2, using VASP[2] total energy calculations, that include van der Waals interactions[3], as input for ATAT fitting of a cluster expansions (CE). In addition, similar calculations were performed for adsorbed 3-atom thick monolayers on an Al-terminated (0001) saphire substrate[4]. Results of these calculations indicate that: in bulk all formation energies for M_{m+n}(S_{m},Te_{n})2 supercells are positive (indicating a phase separation tendency); but in the adsorbed layer, most formation energies are negative (indicating an ordering tendency). These results suggest that samples which are synthesized in bulk and exfoliated will tend to phase separate, but samples that are synthesized by deposition on a saphire substrate will tend to order; with the caveat that deposition (e.g. CVD) on a substrate often favors the formation of a disordered sample. [1] B.P. Burton and A. Singh, J. Appl. Phys. 120, 155101 (2016) [2] G. Kresse and J. Hafner, Phys. Rev. 47, 558 (1993); G. Kresse, thesis, Technische Universit€tu ua Wien, 1993; B49(14), 251 (1994); G. Kresse and J. Furthm€ller, Comput. Mat. Sci. 6, 15–50 (1996); 54, 11169 (1996); See http://cms.mpi.univie. ac.at/vasp/vasp/vasp.html for VASP Users Guide.17 [3] J. Klimes, D. R. Bowler, and A. Michaelides, Phys. Rev. B 83, 195131 (2011); J. Phys. Condens. Matter 22, 022201 (2010). [2] A.K. Singh, R.G. Hennig, A.V. Davydov, F. Tavazza Applied Physics Letters 2015 107 (5), 053106

Resume : Van der Waals heterostructures have been recognized as a powerful concept to tailor new types of materials with unique material properties (e.g. superconductivity). Within this concept individual building blocks of two-dimensional layers are stacked on top of each other in any desired sequence in order to gain new architectures and properties. However, the number of building blocks is limited to materials which exhibit van der Waals gaps in the bulk structure (e.g. transition metal dichalcogenides). Here we present our approach to synthesize LaSe-VSe2-x heterostructures with varying stacking sequence using a diffusion constrained, kinetically controlled synthesis approach facilitating an amorphous precursor. The ex situ annealed multilayered films exhibited strong c-axis orientation while the adjacent building blocks exhibit incommensurate (in plane) and turbostratic disorder. Quantitative high resolution scanning transmission electron microscopy and XRD of the VSe2-x layers revealed the localized stabilization of the V3Se4 phase which could be further verified by Rietveld refinements. Consequently, these films represent first examples of a bottom up synthesis of chalcogenide van der Waals heterostructures, made of bulk structures that do not form van der Waals gaps in the 3D bulk structure. Furthermore with increasing number of VSe2-x layers the electrical properties systematically changed from semiconducting towards metallic behavior.

Resume : Exploration of the electronics solely comprised of bottom-up synthesized nanowires has been largely hindered due to the complex multistep integration of diverse nanowires. In this research, we report the demonstration of on-demand selective laser integration of secondary heterogeneous branched metal oxide NWs on a primary backbone metal NW in a highly selective manner based on a heater-assisted laser-induced hydrothermal growth (LIHG) process. The most widely studied NWs, silver (Ag) and zinc oxide (ZnO) NWs, are selected as primary backbone and secondary branch NWs respectively. The highly localized and instanteneous temperature elevation by laser irradiation on the primary backbone metallic nanowire generates a nanoscale temperature field followed by a photothermal reaction to selectively grow secondary branch nanowires along the backbone nanowire. A ultraviolet photo-sensor based on the proposed selective laser grown ZnO NW branch on a Ag NW backbone is further fabricated as the simplest form of proof-of-concept for all nanowire electronics and demonstrates its potential as future electronics with compact size, low power consumption, and fast response. Scanning electron microscopy and numerical simulation were employed to analyze the general morphology of hierarchical heterogeneous nanowires and scrutinize the laser polarization effect of the laser utilized in this report on a Ag nanowire with its cross-section respectively. We expect that the proposed process can be further extended to other various material combinations whose hydrothermal growth routes are known. With a broader range of applicable nanowires, the proposed process shows great promise in the bottom-up fabrication of all-nanowire nanoelectronics, such as multifunctional environmental sensors.

Resume : The driving force in molecular electronics within the past decades has been to shift organic-based thin-film devices from basic research to the application level. In this talk, a few strategies toward the realization of organic layers with well-defined structural features are outlined, specifically by leveraging on the self-assembly process during film deposition. In the first place, we show how large area molecular junctions of outstanding robustness can be realized using molecular metal-terpyridine complex oligomers, whose electronic structure at the interface with the metal contact is elucidated by electrical and spectroscopic means.[1,2] In the second part, the so-called giant surface potential (GSP) effect is explored, and a computational model is provided to predict GSP for a number of systems studied experimentally. We identify short-range van der Waals interactions as the driving force behind the anisotropic molecular orientation promoting GSP, and show how this effect influences the energy levels responsible for charge transport, which is important for the design of organic semiconductors and devices.[3] [1] Zoi Karipidou, Barbara Branchi, Mustafa Sarpasan, Nikolaus Knorr, Vadim Rodin, Pascal Friederich, Tobias Neumann, Velimir Meded, Silvia Rosselli, Gabriele Nelles, Wolfgang Wenzel, Maria A. Rampi, Florian von Wrochem, Ultrarobust Thin-Film Devices from Self-Assembled Metal-Terpyridine Oligomers, Adv. Mater., 28, 3473-3480 (2016). [2] Velimir Meded, Nikolaus Knorr, Tobias Neumann, Wolfgang Wenzel, Florian von Wrochem, Structural origins of the cohesive energy in metal-terpyridine oligomer thin-films, Phys. Chem. Chem. Phys., 19, 27952 (2017). [3] Pascal Friederich, Vadim Rodin, Florian von Wrochem, Wolfgang Wenzel, Built-in potentials induced by molecular order in amorphous organic thin films, ACS Appl. Mater. Interfaces, 10, 1881 (2018).

Resume : In reality, few materials are perfect. Imperfections abound and in the limit of the very small scale can have disastrous effects, especially on device performance (in say a transistor). Here lies a challenge for materials science: to engineer a 2D material in which edge effects are not detrimental to transport as the channel width shrinks below 20 nm. Here we discuss possible 2D materials with highly anisotropic band structure and edge structure and chemistry such that fabrication of ribbons for devices can be done reliably and reproducibly with few imperfections to enable to production of high performance 2D devices with sub-20 nm dimensions. Transition metal trichalcogenides (TMTs), like MX3 (M=Ti, Zr, Hf; X=S, Se, Te) and In4X3 (X=Se, Te), are possible candidates for a semiconductor channel for a field effect transistor (FET) on the scale of a few nanometers. The band structure of titanium trisulfide (TiS3) [1] and In4Se3 [2] are both found to be highly anisotropic, consistent with transport measurements. With promising low electron and hole effective mass and high carrier mobility along the quasi 1D chains, TMTs also have band gaps comparable to that of silicon (1.1 eV): ~ 1 eV for TiS3; a direct band gap of about 1.3 eV and an indirect gap of about 0.6 eV for In4Se3. [1] H. Yi, et al. Applied Physics Letters 112 (2018) 052102 [2] Ya. B. Losovyj, et al., Applied Physics Letters 92 (2008) 122107

Resume : Since the discovery of two dimensional (2D) graphene, people have been inspired to explore other 2D-layered materials because of the gapless nature of graphene [1]. Among them, 2D transition metal dichalcogenides (TMDCs) and black phosphorus (BP) have attracted great interests for their wide range of optical bandgap from near IR to visible wavelength, structural stability, high photoluminescence and large exciton binding energy [2]. Here, we fabricate MoS2/BP 2D heterostructures possessing relative p/n junction. We measure ultraviolet photoelectron spectroscopy (UPS) to determine the energy levels of individual materials, and perform microbeam scanning photoelectron microscopy (SPEM) to obtain local energy level alignment of 2D heterostructures. We also execute photoemission electron microscopy (PEEM) to visualize the dynamics of photogenerated electrons. From this study, we can obtain a submicron-resolution energy level alignment and spatial information of ultrafast electron dynamics such as charge generation, separation, and transfer occurring at 2D heterojunction. This study will visualize local and fast events of charge carrier motion governed by energetics between layered materials. Furthermore, the results has a great impact on the application of 2D material-based optoelectronic devices. [1] Deng, Y.; Luo, Z.; Conrad, N. J.; Liu, H.; Gong, Y.; Najmaei, S.; Ajayan, P. M.; Lou, J.; Xu, X.; Ye, P. D. Black Phosphorus–Monolayer MoS2 van der Waals Heterojunction p–n Diode. ACS Nano 2014, 8, 8292-8299. [2] Cha, S.; Sung, J. H.; Sim, S.; Park, J.; Heo, H.; Jo, M.-H.; Choi, H. 1s-intraexcitonic dynamics in monolayer MoS2 probed by ultrafast mid-infrared spectroscopy. Nature Comm. 2016, 7, 10768.

Resume : Black Phosphorus (BP) has emerged to be one of the most exciting 2D materials, due to its extraordinary properties [1]. However, in order to use BP in modern day devices, one has to deal with the lack of stability under ambient conditions. Combining BP with other 2D materials in so-called van der Waals (vdW) heterostructures [2] can offer solution for this important surface degradation problem. It has been experimentally shown, that BP encapsulated with hexagonal boron nitride (h-BN) becomes resistant to oxidation and exhibit excellent electrical properties. However, little is known about the encapsulation impact on the vibrational properties of BP. Therefore, we present an extensive ab initio study of few layer BP encapsulated with h-BN which we compare to experimental findings. Our studies reveal that the structural and electronic properties, as well as the frequency of optical phonons are layer dependent. Both non-encapsulated and encapsulated black phosphorus layers, exhibit anomalous evolution of these phonon frequencies, showing a red-shifted trend. However, the encapsulation significantly increases this trend. Very recently an elusive peak located above the 4 cm -1 A g1 has been reported [3]. By symmetry considerations, we give a theoretical explanation for this new experimental result. All the aspects presented in this communication are compared to experimental findings. The work was supported in part by PL-GRID Infrastructure, and computing facilities of the ICM of the University of Warsaw. MB is funded by the NCN grant no. UMO-2016/23/D/ST3/03446.

Resume : High energy and low signature properties are the future trend of solid propellants. As a promising oxidizer, hexanitrohexaazaisowurtzitane (CL-20) is expected to reach above goals due to its high energy and halogen-free molecular structure. However, the high pressure exponent hinders the application of CL-20 in solid propellants. It has been reported that the addition of efficient catalysts into oxidizers can decrease their thermal decomposition temperature so that the pressure exponent of solid propellants is reduced as well. Currently, the development of effective catalysts to improve the thermal decomposition properties of CL-20 still remains challenging due to its complex multi-step decomposition process. Of late, three-dimensional hierarchically ordered porous carbon (3D HOPC) is attractive as catalyst for CL-20 thermal decomposition due to its plentiful exposed catalytic sites, shortened diffusion paths and space-confining effect. Herein, nanostructured CL-20/HOPC composites are synthesized through solvent evaporation dispersion process, and CL-20 is successfully space-confined into the porous carbon scaffold as nanocrystals. A significant improvement of the thermal decomposition properties of Cl-20 is achieved with tunable exothermic peak temperature ranging from 174.8 to 245 oC, and enhanced thermal decomposition kinetics with a low activation energy of 115.3 KJ/mol compared to 165.5 KJ/mol for the bulk counterpart. All these features indicate that 3D HOPC is a superior catalyst for CL-20 thermal decomposition. This work is also valuable for exploring high-performance carbon-based catalysts for nitroamine explosives based solid propellants.

Resume : Multilayer metal-isolator (MIM) nanolaminate TiAlN / Ag and Al2O3 / Ag coatings up to 500 nm thick were deposited by PVD method. The thickness of the layers varied from 1 to 80 nm. The layers had a nanocrystalline or amorphous structure. Phase interfaces were perfect without mixing. Spectral reflectance characteristics in the IR, visible and UV regions were measured in full reflection mode on a Shimadzu SolidSpec-3700 spectrophotometer. Previously, it was shown that these multilayer nano-laminate coatings had an anomalously low thermal conductivity of the order of 1-2 W / mK. The influence of layer thickness on the electronic structure of individual layers and the features of plasmon resonance are investigated. Multilayer coatings had a very high (85 - 88%) reflection coefficient ,which correlates well with excellent heat reflectivity of the systems under study in the near IR region . On the basis of the data obtained and the Drude-Lorentz model, the optical constants of the coatings were calculated by the matrix transfer method. The IR and UV cutoff levels can move along the spectrum depending on the parameters of the plasmon excitation, determined by the thicknesses and the number of layers of nanolaminates. The influence of the coating architecture on their electronic structure and optical properties is discussed. Acknowledgement: The work was carried out in frame of the project RSF No. 14-12-00170-P.

Resume : The multilayer antimonene nanoribbons with room temperature orange light emission uniformly distributed on InSb was synthesized by the plasma-assisted process that has been utilized for synthesis of multilayer graphene, germanene, violet phosphorene, and arsenene. The formation mechanism could be interpreted by thermodynamics, in which the variations of Gibbs free energy (ΔG) of reactions result in the selectivity of reactions. The ~2.03 eV bandgap of multilayer antimonene nanoribbons was estimated by a photoluminescence (PL) measurement. The bandgap opening was caused by the quantum confinement effect of the nanoribbon structure and the turbostratic stacking of antimonene layers. The attractive two-dimensional (2D) material, whose band structure is proper for applications of transistors and light-emitting diodes was first synthesized.

Resume : Polymer solar cells (PSCs) have received significant attention due to their unique advantages, including inexpensive fabrication, light weight and flexibility. Despite, interface interactions and charge separation can be problematic in PSC fabricated by P3HT:PCBM materials and this issue might reduce the photovoltaic performance. As well known, the work function and the surface property of thin films can be effectively tuned by the self-assembled monolayer (SAM). Also, the interface controlling to form a homogeneous thin films and enhance the quality of their interfaces on solar cells is simply possible by the SAM treatment. In this research, we investigated inverted type polymer solar cells with three different boronic acid derivatives SAMs treated compact-TiO2 electron transporting layer. The treated and untreated compact-TiO2 surfaces were characterized by UV-Vis Spectroscopy, XRD, AFM and Kelvin Probe Force Microscopy for the determination of structural, morphological and electrical properties. According to photovoltaic characterization results, interface modification between polymer and TiO2 layers is employed to obtain a promising device performance of 2.8%. This study shows a potential method to enhance the power conversion efficiencies of PSCs by the control of interface property between inorganic and organic materials in polymer solar cells.

Resume : Graphene is an allotropic form of carbon with a unique property portfolio (considered to be the hardest material, high thermal conductivity, good transparency, inert material, etc.) allowing it to be used in various types of applications (mechanical protection, gas barriers, thermal barriers, biocompatibility, solar cells, LCDs, OLEDs, nanocomposites, etc.). In the graphene technology, one of the major problems is represented by the possibility of transferring the graphene from the copper substrate, where is grown by CVD method, on another substrate (SiO2/Si, Au, flexible, etc). In this work we report a graphene transfer process (monolayer or multilayer) from a copper substrate to a gold substrate or another type, to allow further processing and developed different types of applications. The graphene transfer process involves the use of a PMMA film, corrosion of the copper substrate in acid-hydrogen peroxide solutions, in the presence of hexane and at room temperature without contamination of the graphene film. The final stage is a classic "fishing" stage of the graphene film from cleaning water with the substrate where is transferred. The quality of the transferred graphene was studied from morphology and chemical structure point of view. The spectrometry (Raman and FTIR) and microscopy (SEM) showed the lack of impurities, confirming the total removal of the PMMA layer and not affecting the quality of the grafhene layer. The etching medium of the substrate does not induce the presence of other functional groups.

Resume : Advanced structural composites consisting of a ceramic Al2O3 matrix, a ductile metallic Niobium phase and dispersed ZrO2 nanoparticles are characterized by high wear resistance, excellent high-temperature properties, and high fracture toughness and are therefore attractive for numerous technical applications. In this context, a key point is related to the state of the materials surface because it strongly influences specific properties such as optical behavior, wettability and tribological performance. Regarding a functionalization of surfaces, laser-induced periodic surface structures (LIPSS) gained rapidly increasing interest in the recent past. LIPSS can be fabricated on almost all types of materials when irradiating the materials surface near its ablation threshold. The present study deals with the selective formation of LIPSS on the surface of Al2O3-ZrO2-Nb composites by taking advantage of the different light absorption behavior of ceramics and metals. The structuring process was realized using a fs-laser (λ = 1025 nm, τ = 300 fs, frep = 1 kHz) with laser peak fluences between F = 0.23-0.40 J/cm2. The laser processed surfaces were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and infrared spectroscopy (ATR-FTIR). The influence of the LIPSS on the wettability and the tribological performance of the composite surface was evaluated by water contact angle measurements and sliding experiments, respectively.

Resume : Plasmon spectroscopy was first used to analyze the nanoscale films surface of the transition metals. A detailed analysis of the plasmon energy loss spectra of primary electrons in the 50-600-eV range for surface layers of nanoscale mono- and multilayer thin-film systems Ni/Cu/Cr/Si(001); Ni/Cu/V/Si(001) and V/Si (001), obtained by electron-beam deposition in a super-high vacuum of 10-7 Pa. The samples were irradiated with Ar+ ions with a current density of 5 μA/cm2 and an energy of 600 eV at doses of 2⋅1017 and 12⋅1017 ion/cm2 and were kept in an atmosphere of atomically pure oxygen for 24 hours. The averaged values of the energy of the surface (Es) and bulk (Eb) plasmons and their ratio Eb/Es, the concentration of the conduction electrons participating in plasma oscillations, and the relative change in interplanar distances are calculated. The peaks of the surface and bulk plasmons observed in the nickel spectrum are localized at lower loss energies than it follows from the model of a homogeneous, isotropic plasma of the set of s and d electrons in accordance with the classical theory of collective excitations in a solid. Concentration of the conduction electrons is substantially reduced. In the case of vanadium, the maximum number of valence electrons participates in collective vibrations. The concentration of such electrons is most strongly reduced for the surface, which may be due to the structural features of the surface layers. After ion bombardment, the electron concentration for nickel decreases noticeably, probably because of the formation of radiation defects and the relaxation of the crystal lattice of the "expansion" type, and for vanadium of the "compression" type.

Resume : Holographic display has been considered as an ultimate technology to display realistic 3D images without any special glasses. To achieve the high quality holographic display, there are several major issues to be overcome. Display characteristics of LCDs are mostly determined by the orientation of liquid crystal (LC) molecules and the mutual interaction between PI alignment films and LC molecules at the interface. Thus alignment control at the molecular level is important for realizing high performance LCDs. In general, the PI film is rubbed with a roller covered with a cloth typically rayon or cotton, causing the outer layer of the rubbed PI film to become oriented. This rubbing process changes the topography of PI surface and induces the anisotropic orientation of PI molecules along the rubbing direction. However during a rubbing process, excess friction induced molecular-alignment defect, disclination, and light leakage around the scratched PI surface, which reduces the image quality such as contrast ratio and luminance of holographic display. Among several variables of rubbing process, the contact impression can be a key factor and applied to a currently existing manufacturing process because it is simple and compatible. In this study, we examine the effects of the contact compression that is a key factor in controlling LC alignment, on the image quality of holographic displays. Analytical techniques such as atomic force microscopy (AFM) and IR dichroism were employed for determining the nano-scale structures of rubbed PI films. Also the electro-optical performance of the LC cells was determined by measuring the voltage-transmittance (V-T) and response time. We could observe the degree of molecular orientation of PI film through the measured the dimension of groove and dichroic ratio (DR). Finally, the LC cells made from rubbed PI films showed homogeneous planar LC alignment in the parallel direction with respect to the rubbing direction. It is expected that the undesirable rubbing defects can be reduced effectively by choosing an appropriate contact impression. These results could easily be applied to 3D holographic display mass-production lines by simply changing the condition of the rubbing process.

Resume : We report on the growth of self-assembled epitaxial spinel-perovskite nanocomposite thin films using a sputtering technique. The fabrication of epitaxial nanocomposite thin films using sputtering is a promising technology for low cost and large area memory devices. Herein we explore the effect of annealing and sputtering conditions such as working pressure, Ar:O2 ratio, and sputtering power on the structure, morphology, and magnetic properties of BiFeO3-CoFe2O4 nanocomposite thin films. Vertically aligned nanocomposites, consisting CoFe2O4 grown as epitaxial pillars in a BiFeO3 matrix, were observed by x-ray diffraction and scanning electron microscopy under optimum growth conditions. The magnetic hysteresis loops of these nanocomposites showed a strong out-of-plane anisotropy originating from shape anisotropy of the pillars and magnetoelastic anisotropy of the CoFe2O4, but the latter was dominant. The physical properties of these nanocomposites were dramatically changed by modulating the growth conditions, which affected the growth rates and strain states. Finally, we provided a mapping that summarizes the structure and magnetic anisotropy changes that occur with growth rate, for optimizing synthesis conditions for epitaxial oxide nanostructures.

Resume : Printed electronics, which manufactures electronic circuits and devices using printing technologies, has attracted the attention of many researchers. This technology directly prints base materials with conductive ink, etc., thereby greatly simplifying the manufacturing processes of electronic circuits and devices. Furthermore, the use of plastics as substrates allows the ready manufacture of flexible devices that can fulfill contradictory needs; for example, the realization of flexible organic electroluminescence displays could result in compact or upsized screens for smartphones. The ongoing active study of flexible devices is expected to lead to the development of a high-performance transparent conductive film exhibiting high flexibility and elasticity. The indium tin oxide thin film in general use today is not suitable for flexible devices because the fragile thin film is susceptible to bending stress and is produced using high-temperature vacuum treatment. Our research has focused on the use of highly flexible and conductive poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) to produce a flexible organic transparent conductive film by applying the PEDOT/PSS onto a polyethylene naphthalate substrate using an inkjet printer. However, the surface of the organic transparent conductive film used for printing technologies must be uniform during printing, and the characteristics of the produced thin film must be improved for this thin film to have practical uses. This study examined treatment methods for the production of a PEDOT/PSS thin film using dimethyl sulfoxide (DMSO) as a polar solvent, with the aim of further improving the characteristics of the thin film. The resistivity of the PEDOT/PSS thin film was lower and the homogeneity of the film surface was higher when the thin film was dipped into DMSO, a polar solvent, than when the thin film was dipped into ethylene glycol, the polar solvent we used in our previous studies. The electrical characteristics of the PEDOT/PSS thin film was also improved using DMSO as the polar solvent. We found that the characteristics of the PEDOT/PSS thin film were further improved by applying the polar solvent onto the thin film using a printer rather than dipping the thin film into the polar solvent. However, the low viscosity of DMSO makes it difficult to use with a printer, so this study investigated the use of a polar solvent mixture of DMSO and ethylene glycol. The DMSO content affected the characteristics of PEDOT/PSS the thin film. In conclusion, for the application of a polar solvent onto a PEDOT/PSS thin film using a printer, lowering the viscosity of the polar solvent is an effective way to increase the homogeneity of the film surface and to improve the electrical characteristics of the thin film. These results will be useful for the practical application of flexible devices manufactured using only inkjet printing.

Resume : Two-dimension (2D) materials, such as transition metal dichalcogenides (MoS2, WSe2, etc) and semi-metal (graphene, Bi2Se3, etc) have been widely studied for their potential in the next-generation nanoelectronic and spintronic devices. 2D MoS2 has an intrinsic wide bandgap (monolayer ~ 1.8eV) to exhibit high on/off ratio which leads to reduce off-current of MOSFETs. Recently, a 2D Bi2Se3 topological insulator with bandgap of 0.25eV has triggered new opportunities for TFET devices. In this work, a low temperature photoreaction method is proposed to implement the photo exposure treatment on the surface of MoS2 and Bi2Se3 for the surface modification of materials. These factors of impact mechanism could be built up from both materials analysis and electrical results. At first, MoS2 and Bi2Se3 were deposited on the silicon substrate with SiO2 film grown by the method of thermal oxidation and physical vapor deposition (PVD), respectively. After photoreaction process, the peak distance between E2g and A1g of MoS2 Raman spectrum is changed from 25.56 cm-1 (larger than 5 layers thickness) to 23.35 cm-1 (3 layers thickness). Similarly, the contact angle of Bi2Se3 film could be obviously changed more than 40% after the surface treatment. The hydrophobic property of Bi2Se3 film is tended to the hydrophilic behavior due to photoreaction effect. Finally, the I-V characteristics of materials could be to evaluate the potential impact of contact resistance due to its interface characteristics of material surface modification.

Resume : Graphene is a promising material for application in solar energy, because it has a unique set of properties (such as transparency, high conductivity and good mechanical properties). Thus, the research of graphene interaction with metals is interesting. In our previous works, we have studied the system "bcc Fe / Graphene" and "hcp Ti / Graphene". In these works, we performed the research of the system "fcc Pt / Graphene". Processes of structural transformation in the surface layers of Pt under the influence of a free surface and graphene monolayer were the object of our theoretical study. LAMMPS software was used for molecular dynamics (MD) simulation. Model of Pt monocrystal with different crystallographic orientations (001), (011), (111) of free surface was created for MD simulation. This model has been simulated before and after the graphene coating for two temperatures: 300K and 400K. Dependence of atoms distribution in depth on the surface, the radial distribution function in the surface planes, and the dependence of interplanar distances on depth were determine and analyzed. Total and axial stresses were calculated for all systems and for the systems' components separately (for each surface layers). Grapheme relief for crystallographic orientations (001), (011), (111) was obtained. Conclusions about dependence of structure relaxation on the packing density of planes and temperature were made. Comparison of the results for the system "bcc Fe / Graphene", system "hcp Ti / Graphene" and "fcc Pt / Graphene" was conducted.

Resume : Doping of LiNbO3 (LN) due to diffusion of metal ions during high temperature annealing is used for its properties modification. However, the issues of the spatial distribution of dopants, crystal properties spatial changes caused by the dopants and annealing conditions, as well as the role of point defects in the diffusion processes were studied insufficiently. We present results of structural, optical, electrophysical studies of LN crystals annealed in the presence of Cu, Fe, Co ions. Cu ions have the largest diffusion coefficient and are clearly pronounced in optical spectra in states 1 and 2 . XRD studies showed the formation of an inhomogeneous layer containing nanoparticles (1-3 nm) and compounds of other compositions and structures near annealed LN surfaces. Optical spectra were recorded with a 20 μm step along the diffusion direction, while the probe light was propagating perpendicular to it. The profiles of dopant spatial distribution in different directions depending on annealing conditions were determined, diffusion process parameters and the role of point defects were defined. The temperature changes in the electrical conductivity of LN doped with Cu differ from those of un-doped crystals and depend on LN polarization vector direction relative to the diffusion one. The mechanisms of metals diffusion in LN and the mathematical model of the observed processes were discussed. The work was supported by the Ministry of Education and Science of Ukraine (project DB/MEZHA).

Resume : We report the web-like structured silver nanowires (AgNW) bundle networks by dewetting liquid thin films to produce highly transparent electrodes. Such AgNW-web structures were formed by dewtting the thin films of AgNW suspension in a mixture of isopropyl alcohol (IPA) and ethylene glycol (EG) on hydrophobized coating substrates by using meniscus-dragging deposition (MDD) technique. Length and diameter of the AgNW bundles and the open space area in the AgNW-web network can be finely controlled by varying contact angle, EG concentration, and coating parameters of the MDD process. The formation of such AgNW-web structures was well analyzed by calculating dewetting and drying times of the liquid thin films. The transparent thin films with AgNW-web structures exhibit the superior optical and electrical properties compared to the electrodes with random network of AgNW, which is well described by the high ratio of DC to optical conductivity and percolation theory in a two-dimensional matrix model. Our simple coating technique enables the deposition of AgNW-web network with high optical transparency, flexibility, and stretchability directly on rigid or plastic substrates.

Resume : Recent developments in the field of microcapsule have led to a renewed interest in the manipulation of liquid-liquid (Liq.-Liq.) interfaces. In most cases, double-emulsion system has been exploited with subsequent solidification of the materials in middle phases resulting in the solid shell of the microcapsule. However, so far, very little attention has been paid to the role of control of the spatial position. Because it is technically challenging to possess diverse functions with spatially controlled position and there exists trade-off relationship between simple fabrication process and multi-functions of capsules. Therefore, it is imperative to develop versatile and multi-functional capsule with new chemistry for precisely controllable properties including size, porosity, stability, spatial position and shell composition by facile means of experimental methods. In this work, we combine these two techniques: the microfluidics and metal-phenolic chemistry, as promising tools for designing versatile hollow functional microcapsule. By taking advantages of both techniques, it is available to fabricate multiple functional capsules with spatially controlled position by simply utilizing Liq.-Liq. interfacial reaction of metal-phenolic chemistry. It is expected that this approach makes a major contribution to research on the role of the spatially sequential combination of various functional capsules.

Resume : The organization of well-controlled three-dimensional (3D) structures from individual building blocks such as graphene nanosheet or carbon nanotube has scientific and technological importance since it can impart advanced physical properties compared to their bulk counterparts. In particular, for a number of practical applications including electrode, supercapacitor, sensor, fluid absorber, energy damping, thermal insulator and catalysis, it is essential to fabricate well-defined 3D graphene structures with high surface area. While progress toward creation 3D porous graphene materials, previous efforts have placed severe restrictions on their wide-spread utilization because it is hard to create regularized and ordered structures with controlled dimensions, shapes, and morphologies. To overcome these challenges, multiphasic fluid mixtures such as emulsions droplets and bubbles have been investigated as alternative templates for generating well-defined 3D structures. However, it still remains a critical challenge to direct the construction of graphene nanosheets into suitable structures with low density, high uniformity in dimensions and controllable structural motifs. Therefore, we report a new class of building block, GO-shelled hollow sphere, by using microfluidic gas-in-oil-in-water compound bubbles as templates and study their stability.

Resume : After the discovery of graphene prepared by peeling graphite off using scotch tape, many methods are proposed and actually have used to prepare graphene film such as thermal decomposition of silicon carbide (SiC), and chemical vapor deposition (CVD) method. However the CVD method requires metal catalyst (Cu, Ni), and films are required to transfer onto insulating substrates for device fabrications. Another interesting method employs pencils and paper. Paper sheet drown using a lead pencil is irradiated by femtosecond laser, and graphitic materials remain on the paper sheet [1]. In this presentation, yet another method using pulsed laser deposition (PLD) in carbon oxide[2] will be proposed. Although carbon dioxide (CO2) is product after hydrocarbon combustion in oxygen atmosphere, interestingly, CO2 can be an oxidant in certain situations. We show direct growth of graphene on insulating substrates in 100% CO2 environment, and observed the layer by layer growth on stepped edge of insulating substrate. The direct growth can be a large advantage over other common methods because of excluding the necessary process of transferring the graphene on insulating substrate. Stepped substrates and carbon target were placed face to face in CO2 atmosphere with the distance of 40 mm in nitrogen, oxygen and carbon dioxides. Carbon films were examined by Raman spectroscopy with the exciting laser wavelength of 785 nm and surface morphology was observed by atomic force microscopy (AFM). Target surface was irradiated with a wavelength of 532 nm generated at the repetition rate of 2 Hz, which was reduced by a slow Q-switched YAG laser system[3]. Carbon film prepared in nitrogen seems to be diamond like carbon (DLC) or amorphous carbon, and often showed ripples on the film surface, which often occurs on preparing DLC film due to an internal stress. Strong oxidizability in oxygen atmosphere did not allow the film growth at high substrate temperature. Oxidizing environment prepared by carbon oxides offers optimal environment for graphene growth. We will show details of AFM and Raman spectra at our presentation. [1] S. Kaneko, Y. Shimizu, T. Rachi, K. Sato, M. Ushiyama, S. Konuma, Y. Itou, H. Takikawa, G. Tan, A. Matsuda, M. Yoshimoto: Jpn. J. Appl. Phys. 55 (2016) 01AE24. [2] S. Kaneko, T. Ito, C. Kato, S. Tanaka, S. Yasuhara, A. Matsuda, M. Yoshimoto: ACS Omega 2 (2017) 1523. [3] S. Kaneko, Y. Shimizu, and S. Ohya, Jpn. J. Appl. Phys. 40 4870 (2001).

Resume : Crystalline structure, surface morphology, absorption and photoluminescence spectra of the composite consisting of InSe and ZnSe micro- and nanocristalites, are studied in this work. The composite material was obtained by thermal annealing of InSe plates in Zn vapours, at 870K, lasting from 0.5 hours up to 12 hours. As a result of thermal annealing in Zn vapours, the InSe lattice transformation takes place with formation of In2Se3 phase and ZnSe compound. The ZnSe nanoformations are formed at both InSe surface and volume, as a result of chemical bonds created by the Zn atoms, intercalated between Se-In-In-Se elementary packings, with the Se atoms. Released In atoms coagulate as islands. The ZnSe-InSe composite properties were studied by XRD method, SEM microscopy, Raman, absorption and photoluminescence (PL) spectroscopies. PL spectra consist of a wide band which covers the blue-NIR spectral range. The PL band deconvolutes into elementary curves which correlate well with PL spectra of both InSe and ZnSe compounds.

Resume : Photoactive self-cleaning TiO2 thin films on glass substrates have high potentiality for practical applications such as mirrors, window glasses, windshields of automobiles, and so on. The photoactive self-cleaning property of the surface allows water to spread completely across the surface rather than remain as droplets, thus making the surface anti-fogging and easy to wash. Wang et al. have studied the photogeneration of a highly amphiphilic titanium dioxide surface. Machida et al. have also reported the effect of SiO2 addition on super-hydrophilic property of TiO2 photocatalyst. Watanabe et al. has reported TiO2 photocatalyst and its application. In this works, TiO2 nano particles (TNP, P25, Degussa, Germany) was used to prepare coating solutions. The mixing ratio of TNP in coating solution was controlled from 2 to 10 wt%. Ethanol and distilled water were mixed to use as a solvent for TNP coating solution. The titanium isopropoxide (TIPP, C12H28O4Ti, 98+%, ACROS, USA) used in the TiO2 sol (T-sol) source was mixed and stirred at room temperature. Using the prepared coating solution, TiO2 layer was coated on glass substrate using the dip coating method. The microstructure and porosity of the TiO2 thin films were examined using field-emission scanning electron microscopy (FE-SEM) and Brunauer–Emmett–Teller (BET). Optical and surface wetting properties were measured using UV-Visible spectrophotometer and contact angle measurement system. Additionally, the photoactive degradation property of TiO2 thin films was characterized using artificial fingerprint oil under UV irradiation.

Resume : The continuous development of nanotechnology requires the design and optimization of high-engineered materials for widespread applications. In this sense, one of the most versatile strategies is the growth of hybrid heterostructures combining different properties (e.g., optical, magnetic, catalytic) into a single entity. Interestingly, the functionality of such nanostructures can be tailored by the synergic combination of the diverse properties of each counterpart. One example is the gold-magnetite system, where magnetite nanoparticles are used as T2 contrast agents in magnetic resonance imaging (MRI) and nano-heaters in magnetic hyperthermia. On the other hand, gold particles can be imaged by X-ray computed tomography. Moreover, gold nanoparticles are able to generate heat by the absorption of light due to their unique surface plasmon resonances (photo hyperthermia). In this work we will show different strategies to tune the size and morphology of Au-Fe3O4 nanostructures based on thermal decomposition approaches, ensuring an intimate contact between both phases. In fact, exploring the reaction parameters allows us to understand the reaction mechanism and thus to control the final morphology of the nanostructures. The magnetic and optic properties of the nanoparticles are rather dependent on the size and morphology of the nanostructures. Finally, the nanostructrures were transferred to aqueous media in order to be tested as theranostic agents (MRI, hyperthermia).

Resume : Two-dimensional structures of transition metal dichalcogenides (TMD) are already accepted as promising basis for novel optoelectronic devices advances. Although the properties of the atomic-thin MoS2 films were intensively studied in the last years, the intentional control of the properties of the MoS2 based structures still requires better understanding about a relationship between the technological conditions and the parameters of the structures. Our study is focused on a development of the predictable growth of MoS2 films by sulphurisation of metallic precursor. In this report, we present an original technology for synthesis of uniform large area (from 100 to 250 mm2) crystalline MoS2 films with predictable thickness. The MoS2 thin films were obtained by sulphurisation of metallic molybdenum thin film precursors in atmospheric pressure chemical vapor deposition (CVD) system. Si/SiO2 wafers were used for the substrates. We experimentally related the thickness of the Mo precursor with the number of MoS2 sheets based on the analysis of Raman shift spectra. We demonstrate that the intensities of the A1’ and E’ lines of the Raman shift spectra can be used as more sensitive scale for detection of the number of MoS2 sheets. In addition, we experimentally evaluated the absorption coefficient and the band gap for the CVD MoS2 multi-sheet films. Our results suggests new technological approaches to control the parameters of the CVD MoS2 films in the photonic devices

Resume : Perovskite solar cells are gaining attention in the field of photovoltaic technology because of its high efficiency and applicability by easy processes [1]. Mesoscopic or planar heterojunction solar cells based on organometallic halide perovskite show promising photovoltaic performance. Recent studies show that solar cells based on this material have high power conversion efficiency (over 20%) [2]. Many researchers have investigated to increase the efficiency of perovskite solar cells by using different metal oxides or hole transport material or modifications with different dopants [3]. In this study, effect of lithium dopant on efficiency of planar solar cells with compact-TiO2 layer was investigated. Lithium doped compact-TiO2 solution with different ratios was coated on FTO coated glass surface at 450°C by spray pyrolysis method. In order to investigate the surface of doped and undoped compact-TiO2, AFM technique was used. Perovskite solution prepared by lead iodide and methylammonium iodide with ratios of 1.23M:1.23M in γ-butyrolactone was coated onto the surface via spin-coating using solvent washing method. P3HT solution in chlorobenzene with concentration of 2% was chosen as hole transport material and coated to the surface at 4000 r.p.m. for 40 seconds via spin coating. Coated surfaces were heated at 85°C for 15 minutes. Prepared solar cells were then characterized by using solar simulator. Results show that lithium doped perovskite solar cells have better efficiency values than undoped perovskite solar cells.

Resume : Considerable evidence exists demonstrating the spin filtering response of chiral molecules to electron beams. Strong spin filtering effects can even be observed for electrons transmitted through a few monolayers of non-helical chiral molecules. [1] Two different types of chiral molecules were employed for the experiments reported here, each one with its corresponding enantiomers. 1,2-Diphenyl-1,2-ethanediol (DPED), possesses two chiral centres. This molecule binds to Co through its -OH groups but only physisorbs weakly on Cu. (1,2)-Diphenyl-ethylene-diamine (DPEDA), has a similar atomic configuration, with the -OH groups being substituted by amines (-NH2), which form strong bonds also with Cu. The electronic structure of the DPED molecules adsorbed on Co and Cu, is investigated using x-ray absorption. The DPEDA molecules on Co are characterized using ultra violet photoemission. Significant differences in the molecular and substrate electronic states associated with the molecule's helicity are detected. [2] These are discussed in the context of the spin polarization of the Co substrate, and the spin filtering effects observed for DPED in the monolayer range [1]. This work is supported in Spain by the Mineco (MAT2013-47869-C4-3-P and FIS2016-74893-P) and in Poland by the NCN (2011/03/D/ST3/02654). [1] M. Á. Niño, I. A. Kowalik, F. J. Luque, et al., Adv. Mater. 2014, 26, 7474. [2] F. J. Luque , M. Á. Niño, M. J. Spilsbury, et al., Chimia, 2018, to be published.

Resume : In the world, energy demand is constantly increasing. Therefore, environmental problems and the limited availability of fossil fuels require sustainable and renewable energy sources to be demanded. Solar photovoltaic (PV) technology, which is used to convert photon energy directly into electricity, provides an environmentally friendly and renewable energy path [1]. The utilization of highly transparent antireflection coating (ARC) in solar cells provides an important approach to reduce or suppress reflection losses, to increase the amount of light entering the PV device and hence, to enhance the power conversion efficiency of solar cells. Light losses transmitted through a transparent medium caused by reflection can be reduced by antireflective (AR) film coatings [2]. These coatings can also be used for future large scale applications by a variety of techniques including spraying, physical vapour deposition and sol-gel coating. In this study, we aimed to increase the light transmittance value of the glass on glass/ITO/PEDOT:PSS/P3HT:PCBM/Al polymer solar cell. AR films were prepared in the range of 1-3 μm by initiated chemical vapour deposition (iCVD) coating technique and the films obtained were characterized by XPS, AFM, UV-Vis, FT-IR and SEM techniques. The light transmittance values of these films were compared. 1.5 μm AR film provided a light transmittance of 91.5 %, whereas 3 μm AR film provided 93 % a light transmittance. The light transmittance values of bare glass is 90 %. According to photovoltaic characterization results, AR film coating by CVD is a promising technique to enhance the photovoltaic (PV) performance of P3HT:PCBM polymer solar cells. [1] Fuwen Zhao, Shuixing Dai, Yang Wu, Qianqian Zhang, Jiayu Wang, Li Jiang, Qidan Ling, Zhixiang Wei, Wei Ma, Wei You, Chunru Wang, Xiaowei Zhan, 2017, Single‐Junction Binary‐Blend Nonfullerene Polymer Solar Cells with 12.1% Efficiency, Advanced Materials, 29-18. [2] Ömer Kesmez, Esin Akarsu, H. Erdem Çamurlu, Emre Yavuz, Murat Akarsu, Ertuğrul Arpaç, 2018, Preparation and characterization of multilayer anti-reflective coatings via sol-gel process, Ceramics International, 44, 3183-3188.

Resume : Titanium dioxide, as a promising photocatalyst, has received much interest due to its potential applications for environmental remediation, especially for purification of water and decomposition of organic compounds. However, UV light irradiation is required in order to perform photocatalysis because of the relatively wide band gap (3.2 eV) of TiO2. Moreover recombination of created electron-hole pair reduce efficiency as well. To expand the application field and improve photocatalytic performance, the development of TiO2 which efficiently responds to visible light has been investigated and a great progress was shown in case of TiO2 immobilisation on noble metal (Ag, Pt, Au) particles and their doping into the TiO2. In this study, less costly metals were used as an alternative solution for visible light driven photocatalysis. Layered M/TiO2 films with high electron affinity metals (M = Ni, Cu, Nb, W) were prepared by pulsed DC reactive magnetron sputtering technique on glass substrates in two-steps deposition process. The photocatalytic activity of obtained structures was compared and evaluated by the photodegradation test of methylene blue dye in water under the UV and visible light irradiation. The films were characterized by ultraviolet-visible light spectrophotometer (UV-vis), X-ray diffractometer (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscope (XPS). Various M/TiO2 interfaces were analysed, compared and discussed in the paper.

Resume : Surface modification is usually applied for optimizing the wear resistance or other properties such as biocompatibility of many industrial devices. The most sophisticated application is for medical implants or surgical tools. Recently, there has been an intense research effort focused amorphous carbon (a-C) as an ideal potential material for obtaining high wear and corrosion resistance of protective coatings. For a-C:H coatings deposited on metallic substrates, the main problem is their the poor adhesion to the substrate. The coatings may peel off owing to high compressive residual stress. To enhance the adhesion of a-C:H coatings, metallic nanoparticles are inserted into the a-C:H structure. To date, the research conducted on the a-C:H coatings has been focused mainly on enhancing the mechanical properties. In the presented paper, the goal was not only to enhance mechanical properties, however also maintain the high biological features of the pure a-C:H material. Wear mechanisms operating at the nanoscale may directly influence on biomechanical properties of the coatings. In the research, the biomechanical properties of the a-C:H coatings reinforced by different crystallites have been characterized. The optimal biomechanical properties were found for the a-C:H implanted by Ag-Pt crystallites. This coating has been selected for the detailed analysis by TEM technique. Acknowledgement Research project was financed by the National Science Centre (abbr. NCN) No:2015/17/N/ST8/00020

Resume : Vertical stacks of layers of 2D materials opens interesting and promising ways for development of novel electronic and photonic devices for diverse practical applications. Specific combinations of several layers of different materials into an integrated multilayer construction are typically required aiming to acquire desired functional properties of the devices. Typically it is highly challenging task to develop an approach for manufacturing of a vertically stacked constructions by a direct growth of 2D materials one on the top of another because the conditions of a synthesis of an atomic-thick material layers are frequently non-compatible. The problem of compatibility of the growth conditions can be completely eliminated by a bottom-to-up method that is based on a mechanical transfer of the 2D materials from a growth substrate on the top of of the construction. However, in this case, there is a great risk of mechanical damages produced by the supporting frames in the functional layers during the transfer process. This study aims to quantitatively describe a relationship between the thermal softening of a polymer layer that is used as a transfer frame and the density and the type of defects in a graphene layer placed on a substrate of a model device. Cracks, tears and residuals were analyzed with atomic force microscope, optical microscope and Raman spectroscopy. Model device was analyzed by measuring it’s electrical parameters.

Resume : Vertically stacked (VS) atomic-thin layers of two-dimensional (2D) materials are accepted as highly interesting constructions for development of electronic detectors of external influence, including electromagnetic radiation (THz, IR, Vis, UV light), chemical interaction, mechanical forces and ambient temperature. Conversion of external influence into electrical response highly depends on the charge transport mechanisms in VS multi-layered construction, based on van der Waals contact between metal and 2D material layer. For large area 2D materials, grown by a chemical vapor deposition (CVD) method, it is highly important to identify influence of defects of an atomic-thin layer on the properties of the contacts, between the VS layers. Therefore, we studied dependences of local tunneling current on the probe pressing force by scanning probe microscopy (SPM) in samples with graphene and molybdenum disulfide (MoS2) on a thick metal film. Based on SPM experiments in laboratory ambient, we obtained force-distance and current-force dependencies under applied constant bias. We obtained an asymmetry in the current-force curves with respect to the polarity of the applied bias for all samples. The current-voltage characteristics were dependent not only on the probe pressing force but also on the defects, revealed by topography image of the surface. In addition, we have analyzed how local tunneling current depends on the material and the number of layers in tested structures.

Resume : The emission of electrons from surfaces has been studied intensively from a material science perspective in relation to technical applications. Essential are the nature of the exciting particle, the occurring processes of electron excitation as well as the chemical and electronic properties of the surface under consideration. Focussing on electron-induced processes, the ratio between electrons that are elastically reflected from a surface and emitted secondary electrons, that are generated within a material, strongly depends on the kinetic energy of the impinging electrons, their impact angle and the considered emission angle. Furthermore, the external electric and/or magnetic fields affect the trajectory of both the impinging and emitted electrons. All these parameters must be considered when performing simulations to predict electron cloud build up or when tuning surface properties to reduce such an effect. We present experimental approaches and results on the analysis of electron yield of copper-based materials at low kinetic energy (0-1500 eV) or weak external DC magnetic fields as well as measurements on the energy distribution of emitted electrons which can be used to simulate electron cloud build-up phenomena in proton accelerators. We will also discuss the influence of chemical surface modification and the effects induced by the electron irradiation dose to mitigate electron cloud formation.

Resume : Glasses containing rare-earth ions are frequently used materials in optics and photonics due to their sheer number of properties and advantages. Holmium as a dopant has a vast range of applications due to its photoluminescence in visible as well as infrared region around 2 µm. Enhancement of its photoluminescence can be achieved by addition of d-block metals. Previously, our research group has achieved significant success in preparing optical amplifiers by doping erbium containing glasses with silver using the ion exchange method, which leads to creation of planar waveguides, and ion implantation. In this contribution, we extend our research onto holmium and explore the possibility of enhancing its photoluminescence with silver or copper. We prepared a silicate glass containing holmium and ytterbium, other components were sodium, zinc and aluminium oxides. Prepared glasses were doped with silver and copper using ion exchange and ion implantation methods, which lead to creation of surface layers containing these metals. Prepared samples were studied from various viewpoints: concentration and distribution of copper and silver, as well as oxidation states of copper and silver. Finally, the effect of silver and copper in various oxidation states on photoluminescence in infrared region was evaluated. We have determined that silver has a positive effect on photoluminescence of holmium in infrared region. However, this enhancement is order of magnitude lower that in glasses with erbium. Copper, which has been previously used to enhance the photoluminescence of erbium, had no verifiable effect on photoluminescence of holmium in glass used in this work.

Resume : In this study, we analyzed several nanostructured multilayers of noble metals (Ag and Au) ultra thin films, having thickness values in the range 10 – 100 Å and deposited onto glass substrates by radio frequency magnetron sputtering (rfMS) technique. Low dimensions of the nanostructured multilayers are essential in miniaturized optical systems. Nevertheless, these ultra-thin films are not easily achieved because of difficulty in controlling the accuracy of the nanoscale film. A comparative analysis was conducted in measuring the thickness of the corresponding Ag and Au ultra thin films, using low coherence light interferometry and stylus profilometry methods. The effect of deposition conditions on the structural properties of these ultra thin films were discussed based on XRD and XPS results. AFM technique was used to investigate the surface morphology of the obtained films. Transmittance spectra (in double-beam configuration) were recorded in the 190 nm – 3000 nm wavelength range and, from these, optical constants were obtained for the Ag and Au thin films. Optical properties of these oxide films, in the near infrared (NIR) spectral range, were described by the Drude free electron model. The electrical conductivity was measured using the four-points method. These ultra thin nanostructured multilayers with small dimensions present interest for advanced technologies to be integrated in the micro and nanosatellites. *This research is supported by the National Authority for Research and Innovation in the frame of STAR programme - contract 178/2017 and ELI 17/2018.

Resume : Results of electron microscopic analysis of the structure and phase composition of the ultradispersed diamond, obtained by various methods, are presented. Diamond, obtained by detonation synthesis, is represented in the form of flake-like aggregates, composed by independent particles with different degrees of length of contact between them. Results of microdiffraction studies allows to conclude that the basic component of the product of detonation synthesis is cubic diamond containing certain lonsdaleite fraction. Diamond, obtained by shock-wave treatment of graphite, is presented in the form of plates of different degrees of continuity. Most particles or their fragments are biphased and have predominant content of lonsdaleite. Diamond, obtained on the basis of the initial carbon of a different structural state, is usually similar to diamond, which was formed by the shock-wave graphite-diamond transformation, contains a component with microdomain substructure and dense aggregates of perfect single-crystalline grains. Diamond, synthesized by quasi-hydrostatic compression of graphite, mainly has a form of plane-parallel plates. Developed surface of the particles has a microrelief in the form of a chevron due to the development of the graphite-diamond martensitic transformation.

Resume : One of the most important problem in an Electrochemical Hydrogen Compressor (EHC) is the membrane, due generated pressure in the catholic chamber where the hydrogen is reduced at high pressure. For this reason, we are working in alternative membranes based on Sulfonated Poly (Ether-Ether ketone) (SPEEK). It has been demonstrated that incorporation of halloysite nanotubes (HNT) improvement mechanical properties in the membranes, likewise, this membrane need it improve its proton conductivity for this motive we add the phosphotungstic acid (PWA). In this investigation, we work in the synthesis of composite membranes baseline SPEEK with different sulfonation degree (SD). In addition these membranes were characterized mechanically for tensile test and it was observed the membrane with SD = 0.7 has the better tensile strength (TS = 29 MPa) in comparison with other SD. However it observed this SD increase the water uptake resulting in a deformation of the membrane. Three different membranes were prepared baseline on SPEEK with SD=0.7 [S70 (unmodified), S70/HNT15 (With HNT) and S70/(0.3PWA+0.7HNT)15 (With HNT impregnated of PWA)], and present excellent ionic properties to be used in an EHC.

Resume : In the sensors industry the non-lead piezoelectric materials with strong piezoelectric response are the key for future devices. Lead free (Ba1?xCax)(ZryTi1?y)O3 (BCZT) with a value of longitudinal piezoelectric coefficient d33 up to 650 pC/N in bulk, is a promise candidate for piezoelectric related devices. Heterostructure of inorganic piezoelectric materials within a PVDF matrix deposited on flexible substrate can be used in wearable pressure sensors. In this work we report the functional properties of the BCTZ/PVDF thin films and heterostructures of BCTZ nanoparticles into a PVDF matrix obtained by laser tehiques. The heterostructures of BCZT/PVDF were deposited by Pulsed Laser Deposition (PLD) and Matrix Assisted Laser Evaporation (MAPLE) techniques on Kapton substrates. The influence of deposition parameters on the properties of heterostructures were carried out. The functional properties of of the BCTZ/PVDF structures were investigated by Spectroscopic Ellipsometry, PFM and dielectric spectroscopy. Crystallinity and quality of surface were investigated by XRD, AFM and HR-TEM techniques.

Resume : Microwave antennas developed for space industry must be able to operate in harsh environments, where the mechanical and temperature stresses are high. In order to protect the microwave antennas, various coating techniques and materials were developed. In this work, we report the properties of heterostructures of Al2O3/SiC and Yttria stabilized zirconia YSZ and Silicon carbide SiC obtained by PLD. The multilayer structures were on silicon and alumina substrates. A parametric study on the influence of deposition parameters was carried out. The crystalline properties and topography of multilayers were studied by XRD, AFM and SEM techniques. The effect of temperature variation on optical properties of heterostructures was studied by spectroscopic ellipsometry in the 23-300 C range of temperature. The influence of mechanical stress during the launch in space, the micrometeorites impact and the effect of radiation was theoretical studied on the obtained heterostructure. Acknowledgements: This work was supported by a grant of the Ministry of National Education and Scientific Research, RDI Programe for Space Technology and Avanced Research - STAR, project number 168/20.07.2017.

Resume : Zinc oxide has been investigated for gas sensor applications in recent years. The properties of zinc oxide can be tuned by doping, surface modification and mixing with other metal oxides. However, the improvement of selective detection of gases is a challenging task. In this investigation, an attempt was made to improve the selectivity of zinc oxide-based humidity sensor by fabrication of a dual layer device. Dual aluminum oxide and zinc oxide layers were used to detect humidity at room temperature. First nanocrystalline zinc oxide layer (~40 nm) coated on an insulating substrate followed by coating an aluminum oxide layer (20 nm) was coated by a sol-gel process. The films were calcinated more than 550 deg C for 3 hours. The sensing behavior of these films was investigated for different humidity concentrations and it was found that the aluminum oxide coated zinc oxide has a greater sensitivity than pure zinc oxide. The improvement was estimated to be 30% while the other sensing characteristics such as response speed and recovery speed were improved. The dual layers were characterized in SEM, XRD, and electrical property measurements. The sensing properties of this dual layer on other gases such as hydrogen and ammonia was investigated. In this paper, the experimental results of these tests will be presented and the effect will be interpreted.

Resume : The effects of microstructure and crystalline orientation on the surface segregation behavior and oxygen surface exchange properties of La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF) thin films are investigated. The LSCF films were deposited using pulsed laser deposition (PLD) technique on gadolinia-doped ceria (GDC)-buffered YSZ single crystal substrates having (100) and (111) orientation, and their microstructural evolution upon long-term annealing at 800 degC and 900 degC in air was examined in detail. Using the isotope exchange depth profile method utilizing secondary ion mass spectrometry (SIMS), it was found that as-grown LSCF thin films which are dominantly (110)-oriented exhibited much more enhanced oxygen surface exchange properties compared to (100)p.c. (pseudocubic)-oriented LSCF thin films; however due to the highly polar nature of (110) surfaces they also exhibited a stronger tendency for surface segregation. By contrast, (100)p.c. (pseudocubic)-oriented LSCF thin films epitaxially grown on (100) GDC stabilized by pre-annealing exhibited exceptional stability against surface segregation. These results have implications toward tailoring the performance of cathode surfaces by understanding the dependence of cation segregation on driving forces such as surface chemistry and microstructure.

Resume : ALD is based on sequential and self-limiting surface reactions enabling growth of laminated layers of almost any composition and layer thickness. Thin films made by ALD are common in MEMS devices, and depending on the stage where those are applied, they might be exposed to large temperature variations during subsequent processing. Thermomechanical properties of ALD Al2O3-TiO2 (ATO) nanolaminates, grown from TiCl4/TMA and H2O at 200 °C with varying bilayer thickness, were studied here in situ during annealing. In HTXRR data, the superlattice peak indicates quality and interface sharpness of the nanolaminate; the onset of layer mixing is detected from the decrease of peak intensity. The discrete sublayers mixed here already below 450°C. In-situ curvature measurement showed only moderate changes detected upon heating of the structure up to 500°C and back to room temperature. With HTXRD it was found that anatase crystallized first at ~650 °C and rutile at ~725 °C, while corundum appeared at ~900 °C. For most laminates rutile and corundum remained as major phases, only in thickest bilayer there were signs of Al2TiO5/Ti3O5. Combining HTXRD/HTXRR with in-situ curvature measurements help to find processing window for ATO nanolaminates, where depending on application little to no changes in thermomechanical properties are needed. Not only this is useful for MEMS applications where thermal budget influences the usability of the material, but similar methodology can be used to study other laminate structures as well.

Resume : Dynamic processes at the liquid/solid interfaces are of key significance across broad areas of technological interest, such as solidification, liquid-phase epitaxial growth, wetting, liquid-phase joining, crystal growth, and lubrication [1,2]. Many studies have been reported with the indirect evidence of density fluctuations at liquid/solid interfaces on the basis of X-ray scattering methods [3], atomic force microscopy (AFM) [4] and with the support of atomistic simulations [5]. Transmission electron microscopy (TEM) can, in principle, allow us to observe dynamic processes directly, yet to date such investigations are scarce due to the exceptionally high need of an elegant microscope and a suitable system that enables to see liquids, solids and their junctions simultaneously. Hence, due to the lack of direct experimental observations at the atomic-scale and also for the intricacies of tackling such challenging systems, much confusion still exists regarding the atomistic understanding of the dynamic processes at the liquid/solid interfaces. Bismuth (Bi) bulk metal has a low melting point of 544.4 K and the melting temperature of its nanoparticles can be low even to room temperature due to size effects. As such, Bi is an ideal model material to track electron-beam induced nucleation and growth. Hence we take this unique system comprising of the formed Bi droplets on crystalline SrBi2Ta2O9 support and by manipulating electron doses within the TEM we probe such a liquid/solid interface. In this work, we observe the in-situ atomic-scale behavior of fabricated Bi droplets segregated on SrBi2Ta2O9 by using aberration corrected transmission electron microscopy. We demonstrate ordered interface and surface structures for the droplets on the oxide at the atomic-scale and unravel a nucleation mechanism involving droplet coalescence at the liquid/solid interface. We identify a critical diameter of the formed nanocrystal in stabilizing the crystalline phase and reveal lattice induced fast crystallization of the droplet at the initial stage of the coalescence of nanocrystal with droplet. Further sequential observations show the stepped coalescence and growth mechanism of the nanocrystals at the atomic-scale. Interestingly, in contrast to the rapid coalescence of two liquid droplets, the coalescence of a nanocrystal with a liquid droplet takes place via a clear step-migration mechanism. These results offer insights into the dynamic process at liquid/solid interfaces, which may have implications for many functionalities of materials and their applications [6,7]. The capability of performing such in-situ atomic-scale observations of dynamic processes of liquid droplets at a liquid/solid interface using advanced transmission electron microscopy represents a significant step forward in understanding liquids, solids and their interactions at the atomic-scale. These findings provide detailed dynamic information at the Bi/SrBi2Ta2O9 liquid/solid interface at atomic-scale, and should help to advance our general understanding of dynamic process in other liquid/solid interfaces. References [1] SH Oh et al, Science 310 (2005) p. 661. [2] OG Shpyrko et al, Science 313 (2006) p. 77. [3] H Reichert et al, Nature 408 (2000) p. 839. [4] S Biggs and P Mulvaney, J. Chem. Phys. 100 (1994) p. 8501. [5] GC Sosso, et al, Chem. Rev. 116 (2016) p. 7078. [6] J Li, Z Wang, FL Deepak, ACS Nano 11 (2017) p.5590. [7] J Li, J Chen, H Wang, N Chen, Z Wang, L Guo, FL Deepak, Adv. Sci., 2018, 1700992; DOI:10.1002/advs.201700992.

Resume : Hard X-ray photoelectron spectroscopy (HAXPES) uses X-rays in the 2-10 keV range to excite photoelectrons, which are used to non-destructively probe the local chemistry and electronic structure of materials. It is particularly useful as it can be applied to bulk as well as structured samples. HAXPES is a powerful technique for the study of buried layers and interfaces in multilayer thin film stacks and composite materials. This information is not accessible by standard XPS, which uses soft X-rays and is very surface sensitive. Up to now HAXPES was only available at synchrotron sources, which provide the necessary intense, high energy X-rays. This work presents a new laboratory-based instrument capable of delivering monochromated hard X-rays with an energy of 9.25 keV and a focused 30x45 μm2 X-ray spot, giving excellent energy resolution of <0.5 eV. The instrument behaviour and capability is showcased by experimental results from reference as well as technologically relevant systems, including TiO2 bulk samples and multilayer metal oxide structures used in transistors. Measurements including shallow and deep core levels, Auger lines, and valence bands will be presented, including comparison of valence data with theoretical density of states calculations. Ultimately, this spectrometer presents an alternative to synchrotron-based endstations and will help to expand the number and range of HAXPES experiments performed in the future.

Resume : Strain engineering is a powerful strategy for manipulating the physical properties of manganite films because delocalization of the crucial Mn eg electrons is closely coupled to the lattice degrees of freedom. So far, most previous experiments on the strain effects have been conducted under in-plane biaxial strain by using various single crystal substrates. However, an elongation of in-plane lattice always accompanies by a shrinkage of out-of-plane lattice, or vice versa, according to the elastic model. Therefore, the biaxial strain inevitably increases the Jahn – Teller distortion, which plays a key role against delocalization of the eg electrons. To compensate such a negative influence due to the biaxial strain, in this work we demonstrate that the compressive out-of-plane lattice, which is due to the tensile in-plane lattice, can be elongated by helium doping through the magnetron sputtering technique. Accordingly, the metal-insulator transition temperature (TMI) increases appreciably under helium doping. We tried two processes to obtain He-doped manganite films. One is inversely-sputtering the manganite films under Helium atmosphere. (001)-oriented La0.7Sr0.3MnO3 (LSMO) films of 30 nm were grown on SrTiO3 (STO) with substrate temperature Ts = 750°C through magnetron sputtering. The obtained films were post-annealed for 3 h at 900°C in pure argon. Then the films were sent back to the vacuum chamber and placed at the cathode. Finally, He discharge was triggered under appropriate He pressure and electric voltage, so that He can penetrate into the films. The content of the implanted helium was determined by the He-discharge time (tdis). The other way is deposition of manganite films using co-sputtering method under He-Ar mixed atmosphere. La0.7Ca0.3MnO3 (LCMO) films with same orientation and thickness were grown on STO at room temperature in the mixture of Ar, O2 and He. Proportion of helium was set at several values to control the He- content in the films. After the deposition, the films were post-annealed for 3 h at 900°C in pure oxygen to obtain epitaxial films. The orientation and quality of the films were examined by X-ray diffraction (XRD). Particularly, evolution of the out-of-plane lattice is a direct reflection of the He-content. Electrical resistivity of the films was measured by a standard four point-probe method. For the former method, with increasing the He-discharge time, TMI increases from 172 K for the as-grown film to at least 300 K for tdis = 20 min, clearly indicating the He-doping effect. With further increasing tdis to 30 min, TMI falls back to 250 K, might related to degradation of the film quality due to over discharge. However, it is unexpected that the XRD patterns show little change for the He-inversely-sputtered LSMO films, suggesting that the He injection depth is quite small . Because resistivity measurement is sensitive to the surface layer. To obtain uniformly-He-doped films, we tried co-sputtering method.The He-undoped LCMO film shows the shortest out-of-plane lattice c = 3.823 Å. With increasing He content in the mixed gases, the c-axis increases through 3.834 Å under 0.5, to 3.845 Å under 1.5. The He-undoped LCMO film displays a resistivity peak at TMI = 260 K. As the c-axis is expanded under He-doping, TMI rises correspondingly to 266 K and 279 K. Helium implantation by using the co-sputtering method effectively elongates the out-of-plane lattice, which in turn regulates TMI in manganite films. To understand the He doping effect on TMI, we consider the double-exchange model along with Jahn-Teller (JT) distortion for the Mn3 ions. JT distortion removes the orbital degeneracy and leads to an energy splitting (Δ) between dx2-y2 and d3z2-r2 orbitals. By elongating the out-of-plane lattice in tensile strained films, He implantation compensates the JT distortion. Accordingly, delocalization of eg electrons as well as DE interaction must be enhanced, eventually resulting in an elevated TMI. In summary, helium implantation has been realized in manganite films by using Ar/He co-sputtering method. It offers a viable means to control the out-of-plane lattice parameter and the transport properties in the films. Controlling a single-axis gives rise to new possibilities for manipulating functionality of materials.

Resume : Nonlinear optical nanostructured materials are gaining increased interest as optical limiters for laser safety applications. Many nanomaterials are known to suffer from reduced limiting efficiencies at high light fluences due to photo-induced degradation. Here we report the nonlinear optical properties of ferrite core/shell nanoparticles dispersed in toluene, and demonstrate their robustness for ultrafast (femtosecond) optical limiting. The effective two-photon absorption (2PA) coefficient is found to show a non-monotonic dependence on the shell thickness, with a maximum value obtained for thin shells. In view of the local electric field confinement, this indicates that core/shell might be an advantageous morphology for improving the nonlinear optical properties. These nanoparticles exhibit excellent optical limiting performance with effective 2PA coefficients in the range of 10^-12 cm/W, and optical limiting threshold fluences in the range of 1.7 J/cm^2, for 100 fs laser pulse excitation. These values are comparable to or better than that of many of the recently reported optical limiting materials. The consistency of open aperture Z-scan data recorded at intensities as high as 35 TW/cm^2 indicates the high optical damage thresholds of the nanoparticles, ensuring their robustness. The high photostability combined with the remarkable nonlinear optical properties make these ferrite core/shell nanoparticles excellent candidates for ultrafast optical limiting applications.

Resume : Shell coating of magnetic nanoparticles is important for avoiding strong interparticle interactions and providing biocompatibility in various applications such as medical imaging, drug delivery and cancer treatment by magnetic hyperthermia. Here we investigate the effect of silica-coating on magnetic and structural properties of 8 nm maghemite particles, studying two different shell thickness values (t = 4 and 17 nm) as well as uncoated (bare) particles. A larger exchange-bias field is found for the coated particles (Heb,sil ~ 110 Oe) compared to bare (Heb,bare ~ 60 Oe), while x-ray diffraction reveals a positive correlation between microstrain in the maghemite cores and the thickness of the (amorphous) silica shells. The effect of annealing in air is studied in both sample types. After annealing of the bare nanoparticles at 350ºC, electron microscopy evidences the onset of particle coalescence, while magnetometry indicates the persistence of a strongly interacting system of small (~ 8 nm) particles together with a slightly reduced exchange-bias field (0.9 Heb,bare) and a reduction in magnetization (to around 80 % of its initial value); diffraction peak widths also become sharper, pointing to reduced structural disorder. The heat treatment in the silica-coated particles results in the loss of exchange-bias at a lower (annealing) temperature in the thicker than in the thinner shell particles – e.g., after annealing at 800ºC this field has reduced to 20 % (90 %) of its initial value in the t = 17 nm (t = 4 nm) sample – together with the appearance of a non-saturating component in the low-temperature field dependence, which is more prevalent in the thicker shell particles. Notwithstanding, electron microscopy, small-angle x-ray scattering and temperature-dependent magnetization curves indicate that the silica coating prevents the coalescence of the magnetic cores for annealing up to 850 ºC, while the observed maghemite diffraction peak in the thick shell sample does not sharpen such as to indicate a significant alleviation of strain by the annealing, and the silica remains amorphous. We suggest that a thermally-activated diffusion of Fe ions into the silica shells is responsible for the non-saturating component and we attribute the differences in the annealing behavior between the t = 4 nm and t = 17 nm samples to a larger degree of microstrain induced by the thicker shells in the latter sample, which causes its maghemite cores to be less stable to thermal treatment than those of the thinner shell sample. Thus, contrary to our expectation, the results of the study suggest that the thinner silica shells protect better than the thicker shells.

Resume : Barium hexaferrite (BaFe12O19 - HF) nanoplatelets display a high uniaxial magnetocrystalline anisotropy with an easy axis that is perpendicular to the platelet. This unique property gives them tremendous potential in innovative applications, for example, in the magneto-mechanical eradication of cancer cells. As the nanoplatelets adopt a distinct structure and composition, which are significantly different to the bulk, they can be considered as novel structural variations of hexaferrite stabilized on the nanoscale. For example, the structure of the normally used nanoplatelets (~ 50 nm wide and 3 nm thick) can be represented by a SRSRS stacking sequence, where S and R represent a hexagonal (BaFe6O11)2- and a cubic (Fe6O8)2+ structural block, respectively. The weak point of the HF nanoplatelets is their modest saturation magnetization, MS. The MS can be effectively increased by coating them with a shell of soft-magnetic maghemite (M). Given the cubic S block termination of the platelets, layers of M, with a cubic spinel structure, can be easily grown epitaxially, forming a sandwiched M/BHF/M platelet structure. As the two phases are magnetically exchange-coupled the formed composite nanoplatelet homogeneously magnetizes like a single-phase particle. In the lecture the evolution of the structure and the magnetic properties with the growth of the HF nanoplatelets, as well as the synthesis and the magnetic properties of the composite nanoplatelets, will be presented.

Resume : As is known, magnetic flux is quantized in superconductors. Scanning superconducting quantum interference device (SQUID) microscopy (SSM) is a powerful technique to observe one by one the quantized magnetic flux, which is so-called vortex. In this talk, observations of unconventional magnetic flux quantum in multilayered superconducting thin films by SSM are presented. Bi-based superconductors exhibit strong anisotropy and ellipsoidal vortex is known to exist when the magnetic field is applied parallel to ab-plane. We have succeeded in fabricating high quality non c-axis oriented Bi-2212 thin films by MOCVD technique and observing vortices with large aspect ratio in them by SSM. The films are expected to be applied to terahertz devices instead of bulk single crystals. Further, we will report on the first observation of fractional, i.e. non-integer vortices in a bilayer thin film of s-wave Nb superconductor. SSM has highly sensitive and quantitative measurement capability to distinguish between fractional and normal vortices. The bilayer structure is an artificial multicomponent superconductor composed of conventional one. The magnetic flux is no longer quantized as it is destroyed by the existence of an inter-component phase soliton (i -soliton). Part of this work was supported by JSPS Kakenhi Grant 15K06449, 15K05997 and 16K06275 and TIA collaborative research program ?Kakehashi?. Nanofabrication Platform of NIMS and CRAVITY of AIST are also acknowledged.

Resume : An experimental investigation is performed into the mechanical and fracture characteristics of metallic glass materials. The experimental results show that the plastic flow stress and strain rate sensitivity coefficients change with strain and strain rate. With the increase of strain rate, both the plastic flow stress value and the strain rate sensitivity coefficient increase. The surface morphology of the fractured section can be observed by scanning electron microscopy. It can be seen that the broken section has a dimple-like structure. The appearances, and densities of the dimple structure depend on the strain rate, the doping elements, and the annealing temperature. Finally, the deformation mechanism of the metallic glass materials is discussed. The results can be useful for the application of tools and microsystem.

Resume : The work function of oxide heterostructures is of central interest for many applications as well as for the understanding of the electronic properties of multilayers. In this work we investigate epitaxially grown BaO-SrTiO3 heterostructures and compare the in-situ measured work functions with the values predicted by density functional theory (DFT). The BaO films were grown with monolayer precision by PLD on reduced SrTiO3 (001). For the DFT calculations we employed the corresponding slab-geometry unit cells and considered different doping scenarios including niobium impurities and oxygen vacancies. The work functions were measured in-situ using a thermoelectronic converter [1]. This technique allows to characterize samples with surface areas of several square millimeters, while simultaneously resolving the work function at different locations. The work function of the grown bilayer was measured in reference to the work function of platinum. We investigated samples capped by BaO films with thicknesses of 0-9 unit cells and found a reduction of the work function of up to 2 eV. This trend was predicted to a satisfactory degree by our DFT calculations. Quantitative differences might originate from the sensitivity of the calculation to the amount and kind of electronic doping. [1] R. Wanke, W. Voesch, I. Rastegar, A. Kyriazis, W. Braun, J. Mannhart, MRS Bull. 2017, 42, (7), 518–524.

Resume : The interface junction of composites is key to their fundamental properties and enhanced performance in many technologies. However, this is difficult to probe experimentally and is largely ignored in recent theoretical examinations of photocatalysts composed of TiO2 rutile-anatase composites. Computational advances permit detailed modeling of the structural, electronic and optical properties of composites. In this contribution, we focus on a model system of mixed-phase rutile-anatase TiO2 and use density functional theory (DFT) to interrogate the key structural feature, namely, the rutile–anatase interface. We discuss its relationship to and effect on photogenerated charge localization, bulk band alignments, and defect formation. The interfacial region is disordered and distinct from rutile and anatase and contains low coordinated Ti sites and oxygen vacancies, both drivers of charge localization. The relaxations of the interface upon formation of excited electrons and holes determine the final location of charges which cannot always be predicted from bulk band alignments. We also investigate rutile modified with varying thickness of anatase and vice versa to explore the influence of the interface region in different realisations of this phase junction. Finally, the adsorption of carbon dioxide at these interfacial models is investigated to examine if CO2 adsorption can be promoted. A detailed understanding of the interfacial phase junction between two materials thus lays the foundation for directed synthesis of highly active and efficient composite photocatalysts.

Resume : Venkatasubramanian et al. reported that epitaxial superlattices (SLs) of Bi2Te3 and Sb2Te3 exhibit outstanding thermoelectric figure of merit (ZT) of 2.4 at room temperature. However, the initially reported high-quality SL can hardly be reproduced and a thorough investigation of structural and physical properties is missing. Here we report our results in order to reproduce such SLs using molecular beam epitaxy. XRD and TEM measurements of various produced films showed the presence of satellite reflections which could be attributed to the additional periodicity introduced by the sharply defined SLs thus verifying the high quality of the obtained films. To investigate the thermal stability of the obtained SLs in situ and ex situ heating experiments were performed by TEM and XRD. Heating the samples resulted in a significant reduction of the SL reflections initialized at sites with defective SLs as a result of the anisotropy of the diffusion coefficient. The obtained SLs exhibit reduced thermal lattice conductivity compared to the bulk components. However, the electrical properties for the MBE produced SLs significantly deviate from the results reported by Venkatasubramanian et al. It is assumed that the electrical properties are hampered by charge carrier compensation effects due to the stacking of a p-type Sb2Te3 and n-type Bi2Te3 layers which should be a general concern in producing such SLs.

Resume : Magnetic skyrmions are topologically distinct spin textures with quasi-particle like behavior and can be manipulated with very low electric currents [1]. This makes them interesting for low-power information technologies [2], where data is encoded in topological charges, instead of electronic charges as in conventional semiconducting devices. We demonstrated that inhomogeneous charge currents in magnetic multilayers can generate skyrmions at room temperature in a process that is remarkably similar to the droplet formation in surface-tension driven fluid flows [3]. Micromagnetic simulations reproduce key aspects of this transformation process and suggest a possible second mechanism at higher currents that does not rely on preexisting magnetic domain structures [4]. Using this approach, we demonstrated that the topological charge gives rise to a transverse motion on the skyrmions, i.e., the skyrmion Hall effect [5], which is in analogy to the ordinary Hall effect given by the motion of electrically charged particles in the presence of a magnetic field. This work was supported by the U.S. Department of Energy, Office of Science, Materials Sciences and Engineering Division. [1] W. Jiang, et al., Phys. Rep. 704, 1 (2017). [2] A. Hoffmann and S. D. Bader, Phys. Rev. Appl. 4, 047001 (2015). [3] W. Jiang, et al., Science 349, 283 (2015). [4] O. Heinonen, et al., Phys. Rev. B 93, 094407 (2016). [5] W. Jiang, et al., Nature Phys. 13, 162 (2017).

Resume : New materials concepts to enhance magnetoelectric effects (i.e., control of magnetism with voltage) are presented. First, a drastic reduction of coercivity (by 32%) is observed at room temperature in relatively thick nanoporous Cu-Ni and Co-Pt films prepared by micelle-assisted electrodeposition by subjecting these films to the action of an electric field [1]. The voltage is applied across an electrical double layer using a non-oxidative liquid electrolyte (propylene carbonate with Na+ solvated species). Ab-initio calculations indicate that the effect is mainly due to changes in the magnetic anisotropy energy at the surface of the pore walls. Further enhancement of the magnetoelectric effects is accomplished in nanoporous Co-Pt lithographed microdisks with controlled incorporation of oxygen in their structure. A pronounced reduction of coercivity (88%) and a remarkable increase of saturation magnetization (300%) are observed upon subjecting the micro-disks to voltage using the aforementioned electrolyte. In this case, the origin of the drastic changes in the magnetic properties of the micro-disks is two-fold: (i) ?pure? magnetoelectric effect due to charge accumulation at the surface of the pore walls and (ii) magneto-ionic effect, where voltage-driven O2- migration promotes the partial reduction of CoO to Co. The obtained results are appealing for a wide range of fields such as energy-efficient spintronic devices. [1] A. Quintana et al., Adv. Funct. Mater. 2017, 27, 1701904.

Resume : Magnetic refrigeration based on the magneto-caloric eect is one of the best alternatives to compete with vapor-compression technology. The viability of a magnetic refrigeration system for magnetic cooling can be tested by exploiting materials in various forms, ranging from bulk to nanostructured materials.In order to achieve a wide refrigerating temperature range in magnetic refrigeration, we study in this paper a 100 nm-thick Gd-Co alloys based multilayer stack. The stack is made of four individual Gd-Co alloy layers with dierent values of concentration and Curie temperature ( TC). A magnetic entropy change associated with the second order magnetic phase transition was determined from the magnetic isotherms. Moreover, the relative cooling power (RCP) of the studied Gd-Co based multilayer is enhanced compared to the one of bulk Gd, and reach a value 200 J/kg. Such enhancement of the RCP is not due to an enhanced maximum variation of entropy, but is due to a much broader magnetic entropy peak.This study demonstrates the potential of nanostructured Gd-Co multilayer stack for magnetic cooling applications

Resume : The application of organic materials in spintronic devices has received a great deal of attention recently. Although a great number of transport, electronic, and magnetic measurements was reported for various molecular spin-valves, very little is known about the effect of organic-material/ferromagnetic interfaces on the magnetic anisotropy energy. In this report, the effect of an organic capping layer on the magnetic anisotropy of hexagonal close-packed cobalt (0001) will be presented. Experiments, accomplished by the ferromagnetic resonance spectroscopy (FMR) and superconducting quantum interference device magnetometry (SQUID), have proven that the surface energy of Co film could be significantly increased at the cobalt/organic interface and direct an equilibrium magnetization perpendicular to the film plane. The origin of the effect has been attributed to the redistribution of the charge at the interface, induced by the interaction between the hydrocarbon frontier orbitals and the Co 3d band. It consequently results in the formation of strong dipoles at the metal film surface, which affects the charge configuration of the surface atoms and significantly changes the magnitude of the surface energy.

Resume : Metal?organic frameworks (MOFs) are emerging as a unique type of porous and organic/inorganic hybrid materials.1 This is because they can be simply self-assembled from their corresponding inorganic metal ions/clusters with organic linkers, and can be straightforwardly characterized by various analytical methods. Specifically, lanthanide-based MOFs2 are appealing candidates as optical sensing materials because of their narrow emission and high color purity resulting from the lanthanide emitters. The guest molecules in the host MOF influence the light absorption and emission profile of the lanthanide ion. Among the bottlenecks, improving sensitivity, selectivity, stability and reusability are key challenges to bring these materials to the level of practical implementation. We will show that self-assembling lanthanide building-blocks with octacyanometallates give robust microporous MOFs which have highly hydrophilic channels containing a large amount of water molecules.3 Combined photoluminescence and impedance spectroscopy studies allowed us to demonstrate that the europium-based MOF behaves as a highly effective and reliable humidity sensor, enabling dual-mode humidity detection.4 Furthermore, the solubility of specific carbon dots (CDs) within the growth media of our MOFs afforded the synthesis of CDs@MOFs composites through a one-pot synthesis. This enabled us to design a multi-luminescent material which gives opportunities for multimolecular sensing applications. We will discuss its synthesis, characterization and sensing properties. 1. Y. Cui, B. Li, H. He, W. Zhou, B. Chen and G. Qian, Acc. Chem. Res. 49, 483 (2016). 2. C. Pagis, G. Rothenberg and S. Tanase, ACS Catalysis 6, 6063 (2016). 3. Y. Gao, R. Broersen, W. Hageman, N. Yan, M.C. Mittelmeijer-Hazeleger, G. Rothenberg and S. Tanase, J. Mater. Chem. A 3, 22347 (2015). 4. Y. Gao, P. Jing, N. Yan, M. Hilbers, H. Zhang, G. Rothenberg, S. Tanase, Chem. Commun. 53, 4465 (2017).

Resume : Understanding the behavior of metal organic molecules on appropriate support is a critical element to increase their efficiency in many different applications (1,2). Phthalocyanines (Pcs) are square planar organic molecules with the chemical formula (C32H16N8 ) that consist of four isoindole units linked by Nitrogen atoms and can accommodate a metal atom in their central cavity. Combining scanning tunneling microscopy (STM) experiments with density functional theory (DFT) calculations, we studied the growth behavior of Iron(II) phthalocyanines (FePcs) on Al2O3/Ni3Al(111) substrate at monolayer and multilayer coverage. The oxide template has regular stoichiometric defects (oxygen vacancies) that induce a strong modulation in the potential energy surface and cause the formation of a FePc molecular layer with a regular hexagonal arrangement, avoiding defects, and a well defined chirality. However, increasing coverage, the growth of multilayers has been observed before the first layer is complete. Moreover, the second layer was found to exhibit a different chirality with respect to the first one. In presence of Cu clusters deposited on the alumina template, that likely fill the oxygen vacancies of the defected alumina, the potential energy surface allows the FePc molecules to fully cover the oxide template and form long range ordered structure with almost square unit cell, as in the case of FePc assemblies on different substrates (3). References: (1) A. B. Sorokin, Chem. Rev. 113 8152-8191 (2013) (2) M. Ince, J.H. Yum, Y. Kim, S. Mathew, M. Grätzel, T. Torres, M. K. Nazeeruddin, J. Phys. Chem. C 118 17166–17170 (2014) . (3) Z. H. Cheng, L. Gao, Z. T. Deng, N. Jiang, Q. Liu, D. X. Shi, S. X. Du, H. M. Guo, and H.-J. Gao, J. Phys. Chem. C, 111, 9240-9244 (2007)

Resume : The cellulose nanofiber (CNF) hydrogels formed a highly transparent film and the transmittance was above 75% in the range of visible wavelength with a film form. The clarity of the CNF film was unique compared with the normal cellulose paper in analytical chemistry due to the enhanced efficiency in the detection. The highly transparent substrates enabled the direct observation of the flowing channels rather than the reflection from the paper surface. Channels were connected to silicone tubing using a stainless steel bridge. Thickness of a CNF microfluidic device consisting of three layered channels located vertically. Two streams of aqueous dye solutions flew through the separate microfluidic channels and met at a junction making a laminar flow of the two streams through the CNF microfluidic channels. We found out that the CNF based open-channel microfluidic devices could produce the same diffusion-limited co-flows as reported in conventional PDMS open-channel microfluidic devices. For the prevention of liquid penetration through the channel surface, the inside of the channel was coated with silicone elastomer. The fibrous structure of the channels disappeared and a new nonporous surface was formed after the coating inferring the uniform coating of the surfaces.

Resume : Liquid thin films can generate intriguing flow regimes and under specific conditions, lead to disintegration and de-wetting with the formation structures of submicron feature size. This concept has been well utilized as a non-lithographic route for creating meso-scale structures, where the structures can be ordered by guiding the instability pathway using a template. We show that patterns present on the surface of a polymer thin film (Polystyrene) on a flat substrate can result in an ordered dewetted morphology under certain specific conditions. The pre-patterned polymer thin film undergoes pattern directed rupture along the thinnest parts of the film when the initial local thickness over these zones is reduced to a limiting thickness (< 10 nm). In addition, depending on the periodicity of the imprinted patterns, the wavelength of the corresponding instability must be lower than the width of the patterned grooves. A morphology phase diagram is constructed which indicates a transition from the surface tension induced flattening to the ordered pattern directed rupture. The versatility of this technique is shown in its ability to form myriad of aligned meso-patterns starting from a simple grating structure on the film surface. We further extend this concept to a Polystyrene-Poly(methylmethacrylate) bilayer with a patterned polymer-polymer interface, where the instability is more complex due to coupled deformation of multiple, confined interfaces. This leads to creation of exotic patterns such as submerged, embedded and core shell structures, which are beyond the capability of standard lithography methods. The morphology of the evolving patterns is controlled by several parameters including the initial film thickness, pre-pattern amplitude, duration of dewetting and wettability of the stamp used for pre-patterning the film. The evolution can be interrupted at any intermediate stage thereby achieving patterns on demand, which are spatially ordered as well as significantly miniaturized as compared to features obtained from dewetting of a flat film of same initial thickness.

Resume : Carbon nanotubes (CNTs) are among the most mature nanoparticles that are being used in composites, due to their high values for strength and conductivity. The dispersion of the CNTs in a composite, however, is challenging. To overcome the problem of increased viscosity by melt-mixing with polymers, aqueous CNT suspensions have been explored. Nevertheless, hydrophobic surface of the CNTs makes them no-dispersible in water. Many water soluble polymers are able to disperse CNTs in water. Among all, cellulose as a versatile biopolymer is a suitable candidate. Additionally, cellulose derivatives in the form of water soluble polymers (e.g. carboxymethyl cellulose -CMC-) or aqueous suspension of nanoparticles (nanocellulose) were shown as very efficient materials to disperse and stabilize CNTs in water. Another advantage of using these systems is the ability to exploit the potential of colloidal assembly between CNTs and cellulose. By removal of water from cellulose–CNT hybrid dispersions, a stable hydrogel is formed. The gel can then be utilized to build wide range of complex structures with various functionalities and properties. Hereby, we investigate how cellulose derivatives (in particular CMC and nanocellulose) can assemble with CNTs in water. Then, the properties of the composites using these dispersions are shown. The advantages of using these dispersions in making composites will also be discussed.