Nanoparticles in dielectric matrix for electronics and optics: from the fabrication to the devices

Resume : Nanocomposites containing nanoparticles of the group IB metals such as Au, Ag, Au received a significant interest due to the presence of the surface plasmon resonance effect. In this case diamond like amorphous carbon (DLC) is very good candidate as a nanocomposite matrix material. DLC films received significant attention to their high hardness, wear and corrosion resistance, possibility to vary electrical and optical properties of these films in a wide range. In this study DLC films containing Ag nanoparticles (DLC:Ag) and DLC films with embedded Cu nanoparticles (DLC:Cu) were deposited by reactive high power impulse magnetron sputtering (HIPIMS) ensuring high ion and neutral ratio beneficial for formation of sp3 bonded carbon phase. The maximum of the surface plasmon resonance peak of the absorbance spectra was in 400-500 nm range for DLC:Ag films and in 600-700 nm range for DLC:Cu films. Dependence of position of the surface plasmon resonance peak of nanocomposite films on atomic concentration of the group IB metal and oxygen as well as size of the Ag(Cu) nanoclusters and nanocrystalites was observed. Intensities of the plasmonic peaks increased linearly with metal amount for both DLC:Ag and DLC:Cu films. Surface enhanced Raman scattering (SERS) effect was observed in some films. The dependence of the photovoltaic properties on excitation wavelength and some correlation with position of the plasmonic peak as well as size of the nanoclusters was found.

Resume : Localized surface plasmon resonance (LSPR) and surface enhanced Raman spectroscopy (SERS) are optical effects of metal nanoparticles (NPs) that allow the design of device for optoelectronic applications. Isolated NPs are thermally unstable, tend to aggregate and increase their size by Ostwald ripening affecting the properties of interest. These problems can be solved using a very thin oxide coating to stabilize the NPs morphology. This work presents the synthesis by reactive magnetron sputtering and characterization of ZnO-Au nanocomposite thin films that show localized surface plasmon resonance (LSPR) absorption by Au NPs in the visible region. Thin ZnO-Au films have been synthesized with different gold loadings and under different Ar:O2 gas mixtures. Setting of the reactive deposition conditions and thermal annealing lead to changes in the local chemistry and microstructure and to variations of the optical response. Strong LSPR absorption and related effects such as SERS or improved photoluminescence can be obtained after an annealing process increasing the nanoparticle diameter above 5 nm. Chemical analyses indicate that it is possible to form, in highly oxidizing conditions, NPs with a Au/Au2O3 core/shell structure ascribed to a change of the ZnO matrix from a reducing to an oxidizing character depending on the reactive conditions and the associated chemical defects produced in the ZnO matrix.

Resume : Low Energy Ion Beam Synthesis (LE-IBS) is an original technique that allows obtaining metallic nanoparticles (NPs) assemblies, with controlled size and density, few nm close to the free surface of a hosting oxide matrix. Engineering the optical response and thickness of this matrix film is the key to take simultaneously advantage of spectrally and spatially localized surface plasmon resonance (LSPR) and optical amplification. Indeed, combining TiO2, a high refractive index material, with Ag, known for its excellent plasmonic properties, we obtained a highly enhanced optical response in the visible range. We will present our results on a novel Ag/TiO2 nanocomposite film produced by LE-IBS. TiO2 thin films have been implanted with 3E16 Ag+ ions/cm2 with a kinetic energy of 20 keV. Transmission Electron Microscopy shows the presence of small (3 nm in diameter) Ag NPs close to the surface of TiO2 layer. The obtained films have been optically investigated by means of Raman spectroscopy. In comparison with bare TiO2, the Ag/TiO2 composite film shows up to 20 times higher signal when the exciting wavelength is close to LSPR and the matrix thickness matches the antireflective condition. In addition to the signature of Ag as a collective mode (at about 20 cm-1) and a phonon band (70-160 cm-1), we observe the appearance of an unexpected broad band at about 700 cm-1, probably due to electron-hole excitations and/or Ag-TiO2 coupled modes.

Resume : The concept of nanocrystal (NC) nonvolatile memories (NVM) has been intensively explored in the last decade for CMOS and flexible electronic devices. There, the NCs, which are typically organized in a 2-D array in between dielectrics, act as discrete charge storage nodes and due to quantum effects the trapped charge is retained for a longer time than in conventional floating-gate Flash memories. Such NC-NVMs have the potential for faster operation at low voltage and can sustain a significantly higher number of programming/erasing cycles. In this talk we provide a comprehensive review of NCs synthesis, characterization practices and how they can be manipulated to meet the needs of large scale CMOS integration. Emphasis will be given to the ion-beam-synthesis technique (IBS) by the ultra-low energy (ULE) regime <2keV. ULE-IBS allowed us to realize QDs of different semiconducting materials (Si, Ge) embedded in various insulators (SiO2, Si3N4, Al2O3) for memory applications. Furthemore, the synthesis of semiconductor NCs exhibiting negative conduction band offset with respect to Si substrate will be described. In that direction, emphasis will be placed on our recent findings regarding the synthesis of GaN-NC 2D-arrays formed by radio frequency plasma assisted molecular beam deposition on thin amorphous SiO2 layers. Our latest results will be presented and discussed in terms of device performance and reliability through process optimization.

Resume : Germanium nanocrystals embedded in dielectric materials are discussed as absorbers for third generation solar cells, charge trapping layers for nonvolatile memories, sensitizers of rare earth elements and infrared sensors and emitters. The combination of epitaxial or single-crystalline Ge nanostructured films in combination with high-k materials like ZrO2 grown on Si substrates is of high interest as high mobility channel material for CMOS compatible high-performance transistors. The crystallization of Ge nanocrystals (NC) was studied in ZrO2 and TaZrOx host materials using Ge3.6ZrO2/ZrO2 or GeTaZrOx/TaZrOx superlattices sputtered on Si wafers, which were covered by either SiO2 or Si3N4. The formation of Ge-NCs was analyzed by different analytical methods in order to achieve a better understanding of the nanocrystal-high-k interface. Using pure ZrO2 as host matrix, elongated non-spherical Ge-NCs with insufficient control of shape, size, and spatial distribution were observed on wafers covered by SiO2.1 A Si3N4 cover layer led to the formation of multilayer structures with thin Ge films within the ZrO2 matrix.2 Using TaZrOx as matrix, Ge-NCs with spherical shape and well-defined size were formed in amorphous TaZrOx. In this system, charge trapping phenomena were investigated using metal insulator semiconductor structures with single and double layer storage nodes. A memory window of up to 5 V together with a programming-to-flatband-voltage slope of near 1 could be observed.3 1 P. Seidel, M. Geyer D. Lehninger F. Schneider V. Klemm J. Heitmann, ECS Trans. 53, 237 (2013). 2 S. Haas, F. Schneider, C. Himcinschi, V. Klemm, G. Schreiber, J. von Borany, and J. Heitmann, J. Appl. Phys. 113, 044303 (2013). 3 D. Lehninger, P. Seidel, F. Schneider, V. Klemm, D. Rafaja, J. von Borany, and J. Heitmann, Appl. Phys. Lett. 106, (2015).

Resume : Semiconductor nanocrystals in dielectric matrices are of great interest for a broad range of applications, especially in the field of photon management in solar cells and for non-volatile memories. In this work we investigate the formation of crystalline Ge nanoparticles in superlattice stacks by flash lamp annealing. In detail, amorphous ZrO2/Ge and SiN/Ge superlattices confined by two SiO2 layers on Si were produced by magnetron-sputtering and plasma-enhanced chemical vapor deposition, respectively. Raman and TEM investigations reveal that, depending on the original Ge layer thickness, crystalline Ge nanoparticles with different aspect ratios will be formed under annealing. As shown by electrical measurements, these layers feature large charge trapping capabilities. We compare these two types of layer systems with regard to the formation process of the Ge nanoparticles, the trapped charge density, the memory window and the retention. Finally, the perspectives for non-volatile memories are discussed, if these layer stacks are downscaled to current device dimensions.

Resume : We report on the sensing of volatile organic compounds by polymer multi-layered photonic crystals where one of the component was modified including a nanofiller. All polymer multilayers have been widely investigated as sensing devices but detection on gas and vapor is hindered by contemporary optical and physical requirements. Indeed high transparency, and absence of light scattering needed for the photonic structure and high porosity to allow analytes permeation within the lattice can hardly coexist. We demonstrate detection of environmental toluene vapor concentration below 10 ppm by cellulose acetate-polystyrene multilayers where the optical and physical properties of the latter were modified loading ZnO nanoparticles to increase both its permeability and the dielectric contrast within the lattice but maintaining elevate transparency. Modelling of the multilayers optical behaviour during vapor exposure allowed to extend the detection system to crystalline polymers which have so far been forbidden in photonics application because of their high light scattering properties. As a proof of concept we report on the behaviour of poly (phenylene-oxide)-cellulose acetate multilayer during exposure to two organic volatile compounds which cause poly (phenylene-oxide) amorphous to nano-porous crystalline phase transition.

Resume : The incorporation of functional nanostructures on glass surfaces results appealing for both, improving the properties of glasses and to develop new ones. A very interesting method to cover large glass areas with single-phase nanoparticles consists of thin film deposition and subsequent annealing. The nanoparticle size, shape and inter-particle distance can be tuned by controlling the initial film thickness and the annealing conditions, providing a simple and low cost method to prepare nanoparticle layers on large areas. In this work, we demonstrate that the method can be applied to obtain complex nanoparticles and dimers co-existing on the same substrate by thin film deposition and annealing. We focus on the system Au/FeOx nanoparticles on silica substrates from different approaches. With this method we fabricated functional nanoparticles exhibiting simultaneously plasmonic and magnetic properties, which can be tuned through the processing parameters.

Resume : Abstract : The structural, electronic and optical properties of cubic praseodymium oxide perovskite PrMnO3 have been calculated using a full-potential augmented plane (FP-LAPW) method within the density functional theory. The exchange-correlation potential was treated with the generalized gradient approximation (WC-GGA) to calculate the total energy. Moreover we use Tran and Blaha’s modified Becke-Johnson (TB-mBJ) exchange potential (plus a local density approximation correlation potential) within the density functional theory to investigate electronic structures and optical properties of PrMnO3. The calculations of the electronic band structure, density of states show that compound has an indirect energy band gap (Γ-Μ). Its optical properties like: the absorption coefficient, dielectric functions, refractive index, reflectivity and energy loss function are also evaluated and discussed in this paper. Keywords: optical properties- electronic band structure- dielectric functions- PrMnO3- mBJ.

Resume : The waveguide-resonance conception of X-ray fluxes propagation is one of the foundation stone of X-ray nanophotonics [1]. The conception, in its turn is an interesting consequence of the total external reflection phenomenon (TER) of X-ray fluxes on a material interface. Appearing of the uniform interference field of X-ray standing wave in all space of planar extended slit clearance formed by two dielectric reflectors located on the interval smaller as half coherence length of the transporting radiation is the conception basis. Periods values of X-ray standing waves are usually higher as the radiation wave length on 2-3 orders owing to TER angle trifle, and its are comparable-sized with periods of optical standing waves appearing in conditions of light fluxes total internal reflection (TIR). The proximity of X-ray and optical standing waves periods gave birth the hopes to fix possible mutual influence of the standing waves fields. Such influence was registered by using the planar X-ray waveguide-resonator (PXWR) with specific construction. Some intensity spatial distribution variation in PXWR emergent beam of CuKa radiation at influence of optical standing wave initiated by laser beam with wavelenght 532 nm has been gained. We suppose that the effect can be base for building of cells been destined for X-ray beam parameters operation. [1] V.K. Egorov, E.V. Egorov. Planar X-ray waveguide-resonator features // Trends in Appl. Spectroscopy. V8. 2010. pp. 67-83.

Resume : A white light emitting device can be obtained by combining blue chips with phosphors from garnet family. The deposition of the phosphors on blue chips is the most important and controversial step in the technology of manufacturing white light-emitting devices. In this study a sol-gel method, simple and with superior potential, was developed to obtain cerium activated terbium aluminum (TAG:Ce) garnet phosphor. The composite material was obtained by incorporate of TAG:Ce powder in poly (methyl methacrylate) (PMMA) matrix. The white light emitting device manufactured by using PMMA-TAG:Ce nanocomposite is presented. The chemical evolution, structure and morphology of the phosphor and composite materials was performed using Fourier Transform Infrared spectrometry, X-ray diffraction, field emission scanning electron microscopy and luminescence spectrophotometer. FTIR spectra confirm the presence of TAG:Ce in PMMA matrix. The XRD results demonstrate the formation of garnet pure phase and confirme that no structural modification occurs for the TAG:Ce structure in the composite. SEM results showed that the TAG:Ce is well dispersed in the PMMA matrix. The optical properties of the composite are similar to the ones observed in the TAG:Ce powder.

Resume : Recently, the study of electronic and optical properties of metallic nanoparticles became one of the most active areas of nanoscience and technology. Wide range of potential applications including energy transfer waveguides, biosensors, imaging and biomedical applications were demonstrated. One of the most active research issues in this field is the study of evolution of electronic energy relaxation processes of laser excited plasmonic nanoparticles; including electron-phonon, and phonon-phonon interaction. In the current research surface plasmon dynamics of Ag and Cu nanoparticles embedded in a diamond like carbon (DLC) matrix were analyzed. DLC:Me films (50 nm in thickness) with different metal filer content were synthesized employing unbalanced magnetron sputtering of metal (Ag, Cu) targets with argon ions in acetylene gas atmosphere. The size of nanoparticles and chemical composition of the films were determined employing XRD, TEM, SEM-EDS and AFM. Optical properties were analyzed with UV-VIS-NIR spectrometer, while ultrafast processes - employing transient absorption spectrometer. The influence of metal content in nanocomposites on relaxation processes of excited (“hot”) electrons in metal nanoparticles was investigated and identified. The investigations revealed evidential metal filer concentration influence on the “hot” electrons relaxation dynamics. Ultrafast laser microstructured and virgin DLC:Me nanocomposite film optical properties were compared.

Resume : We demonstrate a facile but reliable photolithographic technique, which allows the rapid fabrication of highly ordered nanostructure arrays by employing soft transparent polymer films as optical masks for the area-selective exposure of a photoresist upon flood UV illumination. The soft polymer film either contains a monolayer of self-assembled (SAM) colloidal spheres inside at the near surface or has one side replicated from a SAM colloidal layer, in which the confined colloidal spheres or the surface textures can serves as lenses for light focusing. The geometrical feature of the patterns, including the size, pitch, and even the shape, can be finely tuned by adjusting the mask design, exposure time and the thickness of the photoresist layer. Instead of a single usage, the polymer mask can be used numerous times without noticeable distortions in the achieved patterns. The obtained patterns could be used as deposition or etching mask, allowing easy pattern transfer for various applications.

Resume : Façade integrated solar-thermal collectors need to be efficient, with easy maintenance and acceptable from an architectural point of view. This requires a different approach for the glazing, that should get multi-functionality, by simultaneously satisfying pre-requisites related to colour and self-cleaning while preserving the optical properties required by the main functionality. This paper present the development and optimization of complex structures which fulfill the pre-requisites for optimal coatings of the glazing in solar thermal flat plate collectors, by the conjunction of four factors: high transmittance in UV-VIS-IR, low reflectance in VIS-IR, high chemical stability in the working environment and controlled surface energy. The deposition method of SiO2 and TiO2 thin films was based on sol-gel and cold spray which have the advantages to be cost effective, up-scalable and highly reproducible. The antireflection properties can be explained by the double interface. In this case the presence of a un-pair number of high and low refractive index layers will generate two reflected waves which should be out of phase (they partially or totally cancel). If the coating is a quarter wave-length thicknesses and has a refractive index lower than the glass index (1.518) in air, then both reflections are out of phase. The samples where optimize by gold nano-particles insertion in different concentrations in the middle layer which allows to modify the interface properties aiming to improve the transmittance above 90%, antireflective properties and glass maintenance (self-cleaning coatings).

Resume : The production of composites (CMs) with gradient distribution of conductive graphite nanoplatelets (GNPs) in epoxy matrix has been realized due to stratification of the polymer-filler liquid mixture in a centrifuge. It is possible to produce CMs with different gradients of the filler concentration along a certain axis of CM specimen by the variation of filler content (C) in polymer matrix, centrifugal speed (w) (from 3000 to 6000 rot. /min), centrifugation time (t): from the linear decrease of filler concentration along the height of test-tube (at low t) till the sharp stratification of solution (at high t). The separation of particles by size is additionally realized during centrifugation of the GNP-epoxy liquid mixture due to a certain size distribution of GNPs: particles size increases along the centrifugal force, the concentration being increased along the same direction. The comparative analysis of shielding properties (in frequency range of electromagnetic radiation (EMR) 26-37.5 GHz) of epoxy composites containing 5wt.% of GNPs with conventional uniform distribution and gradient distribution of fillers has shown the significant decrease of EMR reflection index and sufficient increase of EMR absorption in gradient composite structures. We have also observed the increase of EMR shielding efficiency SET (attenuation) in gradient structures as compared with usual CMs with the same content of GNPs and shield thickness.

Resume : A solution for non-volatile memory devices is to use Ge nanocrystals (NCs) embedded in high-k oxide matrices, acting as nodes. A good candidate for high-k oxide is HfO2 that makes possible the decrease of the device area and the reduction of the leakage currents, improving the memory properties. We obtain Ge NCs in HfO2 by magnetron sputtering deposition of HfO2/Ge/HfO2 and HfO2/Ge-HfO2/HfO2 trilayer structures on Si substrates and subsequent annealing in a rapid thermal annealing (RTA) processor. For evidencing the memory properties, the structures with different thicknesses of tunnelling oxide, Ge NCs concentration in HfO2 and annealing conditions (temperature and time) were prepared. Electrical and TEM and high resolution TEM (HRTEM) investigations were performed on these structures. The MOS-like capacitors were configured by thermal evaporation of top and bottom Al contacts. C–V characteristics were measured on the MOS-like capacitors at different frequencies between 100 kHz and 1MHz. The C–V characteristics present hysteresis with a flat-band voltage shift of 1.5–3.0 V in the sweeping voltage interval of ±5 V. We show that the largest value is obtained for the MOS-like capacitors with an intermediate layer of Ge (HfO2/Ge/HfO2 structures). The large hysteresis is correlated with the results from the HRTEM investigations showing the presence of Ge NCs and clusters in precise locations close to the tunnelling oxide layer, controlled by RTA processing.

Resume : Our previous work has shown that the as-grown Si0.32C0.4O0.28 film emits light under excitation at 266 nm. The PL band is centered at ~450 nm and the FWHM is around 202 nm. We use the Si0.32C0.4O0.28 film as the active layer to fabricate a MOSLED. ITO film and Al layer are used as top and bottom electrode, respectively. When the applied voltage is greater than 12 V, the emission of this MOSLED is observable by naked eyes in dark field. Nevertheless, the emission intensity is still low and needs to be improved. In this work, we are going to study the enhancement of EL intensity by Ag particles and/or Ag films. Nano-sized Ag particles could be grown by annealing Ag film and might be used for enhancing LED emission by surface plasma resonance. The average size of Ag nano-particles is controllable by adjusting Ag film thickness, annealing duration as well as annealing temperature. For example, after annealing at 300 degree C for 20 mins, the Ag size increases from 40-60 nm to 60-130nm when the Ag film thickness is increased from 10 to 30 nm. These Ag particles induce surface plasma resonance leading to increase of emission intensity. ITO/Ag/ITO multi-layer is a possible alternative for increasing the LED intensity. Incorporation of Ag layer within ITO film may significantly augment the conductivity of top electrode and thus is potential for increasing the LED intensity. The optimization of EL intensity of SixCyO1-x-y MOSLED will be demonstrated.

Resume : SixGeyO1-x-y has been proved as an initial material to obtain Si and Ge nano-crystals and thus could be used for LED applications. After annealing at 500 degree C for 3h, Si0.23Ge0.25O0.52 thin film comprise 2-8 nm nano-crystals and emits light with excitation at 405 nm. The PL band is centered at 577 nm and the FWHM is around 170 nm. A MOSLED using Si0.23Ge0.25O0.52 thin film as active layer is fabricated. ITO and Al layers are used as top and bottom electrode, respectively. The emission of this LED is observed when a forward bias of +10V is applied. The EL band is centered at 590 nm and the light color is yellow-white. However, the emission of this type of LED is still weak and needs to be enhanced. In this study, we will investigate the effect of top-electrode on the EL of SixGeyO1-x-y LED. ITO/Ag/ITO multi-layer could be used to replace ITO electrode and is potential for increasing the LED intensity. When Ag layer is incorporated into ITO electrode, the effective conductivity of top electrode will be increased and thus might augment the LED intensity. When a 10.8 nm Ag film is incorporated into 90 nm ITO (45 nm / 10.8 nm / 45 nm), effective resistivity of this top electrode is ~9.9*10-5 ohm-cm which is about 18% of that of single ITO film. The decrease of resistivity may lead to enhancement of the EL of LED. In addition, we will use metal mask to control the size and the shape of the top-electrode and study the influence of surface patterned electrode on the emission.

Resume : Degenerate metal oxide nanoparticles are promising systems to expand the significant achievements of plasmonics into the infrared (IR) range. Among the possible candidates, Ga doped ZnO nanocrystals are particularly suited for mid IR. In the present work, we report on the tunable mid IR plasmon induced in degenerate Ga doped ZnO nanocrystals. The nanocrystals are produced by a plasma expansion and exhibit unprotected surfaces. On top of the tunability, the plasmon resonance is characterized by a large damping. By comparing the plasmon of nanocrystals assemblies to that of nanoparticles dispersed in and alumina matrix, we investigate the possible origins of that damping. We demonstrate that it partially results from the self-organization of the naked particles but also from intrinsic inhomogeneity of dopants pointing to strategies to control this behavior common to most metal oxide nanoparticles.

Resume : We present results, obtained by means of an analytic study and a numerical simulation, about the resonant condition necessary to produce a LSPR effect at the surface of metal nanospheres embedded in an amorphous silicon matrix. The study is based on a Lorentz dispersive model for a-Si:H permittivity and a Drude model for the metals. Considering the absorption spectra of a-Si:H, the best choice for the metal nanoparticles appears to be Aluminium , Indium or Magnesium. No difference has been observed when considering a-SiC:H. FDTD simulation of an Al nanosphere embedded into an amorphous silicon matrix shows an increased scattering radius and the presence of LSPR induced by the metal/semiconductor interaction under green light (=560nm) illumination. Further results include the effect of the nanoparticles shape (nano-ellipsoids) in controlling the wavelength suitable to produce LSPR. It has been shown that is possible to produce LSPR in the red part of the visible spectrum (the most critical for a-Si:H solar cells applications in terms of light absorption enhancement) with Aluminium nano-ellipsoids. As an additional results we may conclude that the double Lorentz-Lorenz model for the optical functions of a-Si:H is numerically stable in 3D simulations and can be used safely in the FDTD algorithm. A further simulation study is directed to determine an optimal spatial distribution of Al nanoparticles, with variable shapes, capable to enhance light absorption in the red part of the visible spectrum, exploiting light trapping and plasmonic effects. Experimental studies will include the deposition of this material, measurements of photoconductivity and light transmission-reflection-absorption.

Resume : In this paper we study the in-situ growth of gold nanoparticles (Au-NPs) on ZnO nanorod arrays (NRAs) and the surface plasmon resonance (SPR) effect caused by them. ZnO NRAs were deposited electrochemically and by spray method. Au-NPs were obtained by spin-coating or spraying HAuCl4 in ethanol solution over the nanorod samples. Au-NPs decorated ZnO NRAs were characterized using optical spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and wettability studies. According to XRD, metallic Au-NPs were obtained by both deposition technics. The average size of spherical Au-NPs on ZnO NRAs increases from 45 nm to 70 nm by increasing the HAuCl4 concentration in solution from 0.01 to 0.1 mol/L. There are no visible changes in ZnO NRAs morphology using the solutions with 0.01-0.03 mol/L, partial dissolution of nanorods occurs when using concentrations higher than 0.03 mol/L. The surface wetting properties of ZnO NRAs are highly important to obtain structures with infiltrated Au-NPs by spin-coating technique. In case of nonwetable ZnO surfaces Au agglomerates with the size up to 150 nm are formed on top of nanorod layer while Au-NPs with an average diameter of 40-60 nm formed on hydrophilic ZnO NRA surfaces. Independent of the rods and Au-NP deposition methods, ZnO rods covered with Au-NPs show plasmonic light extinction in the spectral region of 550-570 nm. Extremely thin inorganic absorber sensitised solar cells based on ZnO NRAs with Au-NPs will be discussed.

Resume : Nanocomposite metal/dielectric films consisting of metal objects embedded into an oxide or polymer matrix are widely used as attractive materials for research. They can have interesting optical, mechanical and electrical properties. Technologies used for their preparation strongly influence their resulting properties. Therefore, their structural and morphological properties are often important characteristics which are directly interconnected to their other physical properties. The paper presents computer experiment tools for testing of convenient methods for morphological description of various nanocomposite structures. The goal of the morphological analysis of the 3D nanocomposites is to derive main characteristics as the local metal particle concentration, their size distribution or their spatial distribution using 2D images (e.g. TEM images). The paper focuses on the spatial distribution evaluation. Many morphological methods have been used for 2D structures. Nevertheless, the results presented here show the methods suitable in the case of 3D nanocomposite structure when its objects are more or less randomly distributed in space and have various dimensions. A low metal volume fraction is supposed. A modified hard-sphere method for generation of the nanocomposite structures is used. The computer tool enables a subsequent analysis of electrical properties of the films and their dependence on the morphology.

Resume : Motivated by the idea to manipulate THz radiation for safety control, packaging inspection, chemical composition analysis, we produced via in situ polymerization Epoxy Resin composites filled with multi-walled carbon nanotubes (MWCNT), organoclay and golden nanoparticles (average size 80-100 nm) obtained by reduction of HAuCl4. Two series of samples were fabricated, containing 0.3 and 0.5 wt.% of MWCNT, with different concentration of Au (0.1, 0.5 and 1.0 wt.%). Importantly, for 0.5 and 1.0 wt.% Au composites, large 1-2 microns agglomerates of Au particles were formed on the clay surfaces, percolated then into 200-300 microns clusters. Significant attenuation of THz radiation, at the level of 20-90% was observed by time domain spectrometer for all investigated composites at 0.2-1.5 THz, in favor of samples loaded with 0.5 wt.% of MWCNT. We found that addition of small amount of Au particles (0.1 wt.%) to epoxy/MWCNT leads to sufficient reduction of attenuation ability. The reason is that gold being embedded into epoxy/MWCNT in small concentrations decorates CNT, which might suppress their metallic properties. In contrast, for relatively large Au content (0.5 and 1.0 wt.%) optical density decreases because of plasmonic effects in golden clusters. The significant frequency dispersion of THz transmittance was observed, giving the possibility to propose some of manufactured materials as selectively transparent or, on the contrary, opaque material, depending on the THz slot.

Resume : We have studied Si quantum dots (QDs) with Doppler broadening mode positron annihilation spectroscopy (PAS). Four samples series were prepared for the study: a 10 nm SiO2 buffer layer was deposited on a Si substrate, after this a superlattice consisting of bilayers of SiO2 and Si-rich layers were deposited up to a thickness of 250 nm, a 30 nm SiO2 capping layers was used. The SiO2 thickness in the bilayer was 2 nm and the Si-rich layer was 1.5, 2.5, 3.5 and 4.5 nm for the different sample series. The thicknesses of the superlattice structure and capping layer were chosen in order to optimize the signal from the superlattice in PAS. The samples were subjected to different annealings and PAS measurements were done after each annealing procedure. The annealing treatments were: 1h in 800 oC in N2 (formation of amorphous Si QDs), 1h in 1150 oC in N2 (formation of crystalline Si QDs) and 1h in 1150 oC (N2) 1h H2 passivation at 500 oC. All samples series show similar behavior after the different annealings. Quite small changes are seen after 800 oC, indicating that the no significant changes in the e annihilation state takes place. After the 1150 oC anneal, the S parameter in the superlattice structure decreases, indicating a reduction in open volume defects. The H2 passivation further decreases the S parameter. The SW-plot shows that the e annihilation state after the passivation process is very close to the Si/SiO2 interface which indicates that passivation is successful.

Resume : In recent years particular attention has been devoted to Silicon nanocrystals and nanowires, a powerful class of nanostructures which is opening new substantial opportunities for optoelectronics and photovoltaics. These nanostructures are zero- and one-dimensional materials with diameter from few to some tenths of nanometers. They present unique size dependent electronic, optical and transport properties that are intrinsically associated with their low dimensionality and quantum confinement effect. In particular we have performed several ab-initio calculations in the framework of Density Functional Theory and Many-Body Perturbation Theory for free and matrix embedded Si nanocrystals and for Si and Si-Ge nanowires. Among the different results we will concentrate, here, on Si nanocrystals. The opportunity of doping and codoping of Si nanocrystals embedded in different matrices or passivated by H or OH groups will be considered in order to tune their transport and/or optical and electronic properties. Moreover we will show how the interaction between different Si nanocrystals is a promising route to foster the establishment of third generation photovoltaics due to multiple exciton generation.

Resume : Conventional flash memories suffer from storage-density, speed and operating-voltage improvement issues. As an alternative, the nanocrystal (NC) memories have the potential of operating at lower voltages and higher speed coupled to a better robustness and fault-tolerance. Two NC manufacturing solutions have been explored so far: deposition techniques and low-energy ion-implantation with thermal annealing. Due to high dose requirements, this last method shows severe limitations for mass production. Plasma Immersion Ion Implantation (PIII) can be a competitive alternative with its high-throughput in the low-energy and high dose regime. In this work we demonstrate the fabrication of a shallow 2-D layer of Si-NCs by pulsed PIII in SiO2 films. The effect of energy and dose on NC formation is investigated by TEM. NC population characteristics can be finely controlled by properly adjusting the PIII parameters. C(V) measurements of MOS capacitors show memory windows up to 2V for a 4 keV implantation energy and high Si ion dose. For particular PIII conditions, significant 10-years memory windows are extracted from charge retention measurements at room and high (90 °C) temperatures. Similar PIII processing of HfO2 layers gives rise to interesting structures with Si NCs embedded in SiOx cap-layer on top of a high-k tunnel oxide. This attractive method can also be used in various applications such as optoelectronic or photovoltaic devices.

Resume : Hybrid systems composed of silicon and silver nanocrystals (Si-NCs and Ag-NCs) are of considerable interest in photon conversion solar cells. In fact, due to their plasmonic properties, Ag-NCs strongly increase the photoluminescence emission intensity of Si-NCs placed in their vicinity, allowing in principle to solve the problem of their low PL yield. In this work we have developed an original method based on Ultra-Low-Energy Ion-Beam-Synthesis (ULE-IBS) to synthetize double layers of Si-NCs and Ag-NCs in dielectric matrices. First, a 2D layer of Si-NCs is obtained by Si+ ultra low energy ion implantation followed by high temperature thermal annealing. Then, Ag+ ions are implanted in the same matrix and crystalline Ag-NPs are formed. The influence of the intermediate annealing following the Si implantation on the final structure of the double layers (investigated by HREM and EFTEM) and on their optical properties (PL emission) will be presented. The results obtained in the case of a simple sequential Si and Ag implantation (without intermediate annealing) have been compared with those obtained in the case of RTA and furnace annealing and with different ambient (inert, oxidizing, forming gas). We will discuss the conditions that are necessary to recover the matrix integrity and finally to control the synthesis of both Si an Ag nanocrystals.

Resume : Many recent studies focus on the formation and the characterisation of silicon nanoclusters (Si-nc) embedded in silica matrix. Such systems have plenty of possible applications: photovoltaic cells, memory devices, waveguide amplifiers… Nevertheless the use of Si-nc in optoelectronic and non-volatile memory devices requires an accurate control of the characteristics of the clusters (size, distribution, composition, nature of the interface between clusters and matrix…) where properties are highly dependent on structural characteristics. In present work, we propose an innovative study of SiOx and rare-earth (RE) doped SiOx fabricated by RF magnetron sputtering by atom probe tomography. In the case of Si-nc embedded in silica, phase separation processes have been investigated for different supersaturations in SiOX, different annealing times and temperatures, and for different thicknesses of SiOX and SiO2 layers. It has been observed that the thickness of the layers and supersaturation drastically change the decomposition process, sometime from spinodal-like decomposition to classical growth of particles. The results obtained on RE doped samples evidenced a strong influence on dopant element on the phase separation phenomena of silicon excess and redistribution of dopants. The deep analyses carried out have allowed evidencing the formation of Si nanoclusters correlated to RE silicates phases. In the two case, structural results where discuss in relation with optical properties.

Resume : Silicon nanoparticles potentially enable new applications in silicon based optoelectronics and photovoltaics. Single layers of nitrogen free Si rich oxides with varying Si excess concentrations were deposited by PECVD [1,2] followed by a subsequent high temperature annealing to induce phase separation. The structural properties of the layers are investigated by plane view TEM using high resolution as well as energy filtered TEM. At low Si excess, isolated single crystalline Si particles with low density are observed indicating an incomplete phase separation. An increase of Si excess leads to larger Si particles along with an increased intrinsic crystal defect density. Furthermore, we find a transition point near SiOx=0.4, where the isolated Si particles merge into a continuous network. In addition we study the influence of annealing conditions and find negligible differences that are indicative of fast phase separation on the timescale of seconds and significantly slower particle growth due diffusion processes. The importance of the results is discussed in the context of transport properties that affect a possible Si nanocrystal device performance. [1] Laube et al. JAP, 116, 223501 [2] Gutsch et al. BJnano submitted

Resume : Given the dominant role of silicon (Si) in electronics, the observation of localized surface plasmon resonance (LSPR) in phosphorus (P)-doped Si nanocrystals (NCs) [1] is very promising for the integration of plasmonics with Si technology. We review progress in the emerging field of Si-NC plasmonics. On the experimental side, it is shown that LSPR also occurs to boron (B)-doped Si NCs [2]. LSPR is found in the energy regions of 0.26-0.40 eV and 0.09-0.13 eV in B- and P-doped Si NCs, respectively. The LSPR frequency increases with the dopant concentration, highlighting the remarkable tunability of LSPR in doped semiconductor NCs. It looks that B-doped Si NCs are better positioned for practical use than P-doped Si NCs. On the theoretical side, it is shown that these results can be understood using a simple Drude model in spite of strong quantum confinement, due to the efficient coupling between quantum oscillators corresponding to the excitation of the carriers brought by the dopants [3]. Possible reasons why LSPR is presently not found at energies higher than 0.4 eV are discussed, including the effect of structural relaxation induced by the doping of Si NCs [4]. [1] D. J. Rowe et al, Nano Lett. 13, 1317 (2013). [2] S. Zhou et al, ACS Nano, DOI: 10.1021/nn505416r. [3] X. D. Pi and C. Delerue, Phys. Rev. Lett. 111, 177402 (2013). [4] X. D. Pi, Z. Y. Ni, D. Yang, and C. Delerue, J. Appl. Phys. 116, 194304 (2014).

Resume : The energy transfer (ET) processes between rare earths are very attractive for different applications, such as lighting, photovoltaics and silicon microphotonics. In particular, ET has been proposed in Er-containing materials for realizing efficient photonic devices at 1.54 um inside the telecommunication window. We propose the introduction of Bi as a sensitizer for Er in Si-compatible materials, such as Er-Y oxides and Er-Y silicates. These compounds permit to dissolve very high amounts of optically active Er ions (up to 10^22 at/cm^3) without clustering, by replacing Y in substitutional positions. The interaction between Bi and Er has been investigated through the optical and structural properties of oxides and silicates. In particular, it has been found, by performing conventional TEM and analytical STEM-EDX and STEM-EELS, that some Bi ions precipitate in nanoparticles only in the silicate host after thermal treatment under different atmospheres. Their chemical and structural properties will be discussed. In addition, optical measurements have demonstrated the presence of some dispersed Bi ions acting as sensitizers for Er only when they are in the 3 oxidation state. Bi3 oxidation state is favored in Er-Y oxides, thus determining the best Bi-Er coupling with an increase of the Er effective excitation cross section by more than three orders of magnitude. These results demonstrate that Bi-doped Y-Er compounds are efficient materials for photonic applications at 1.54 um.

Resume : Materials with a tailor-made spectral optical response that can be switched or modulated in a controlled way using heat, light, or magnetic fields are of paramount interest for the development of active optical and photonic devices, such as smart windows or all-optical switching components. As a result a timely research line has been opened to develop dielectric hosts with embedded nanoparticles that show switchable polaritonic/plasmonic properties based on phase transitions, such as the solid-liquid. However in this context the broadly used plasmonic noble metal nanoparticles are not suitable for these applications since their solid-liquid phase transition takes place at high temperatures (>960 ºC). Therefore there is a quest for the study of other elements that can combine a polaritonic/plasmonic response with a low enough melting point. \\ We have reported the observation of optical resonances in solid bismuth (Bi) nanoparticles (NPs) embedded in an amorphous Al2O3 matrix in the near ultraviolet to near infrared range [1] that have an interband transition-related polaritonic origin[2]. In addition, Bi has a low melting point (270ºC), and a metallic behavior in the liquid state that allows plasmonic effects. Based on these properties, very recently we have demonstrated spectrally-selective thermo-optical switching in germanate glasses doped with Bi-NPs [3]. In our presentation we will show how this phenomenon can be controlled in order to design tailored metamaterials with a switchable optical response. The role of the embedding matrix and substrate (refractive index), size, shape and distribution of the Bi-NPs on the metamaterials switching properties will be discussed. [1 ] Toudert et al., J. Phys. Chem. C 116, 20530 (2012) [2] Toudert, Nanotechnology Rev. 3, 223 (2014) [3] Jiménez de Castro et al., Appl. Phys. Lett. 105, 113102 (2014)

Resume : Carrier-carrier and carrier-phonon scattering in semiconductors involves multiple physical processes which become seriously modified in nanocrystals. In particular quantum confinement strongly affects properties of hot carriers, enhancing their effective lifetime – by reduction of phonon emission, and promoting impact excitation rates – by enabling multiple exciton generation and energy transfers to the outside of the nanostructure. In my presentation, I will discuss some results of investigations of these effects in Si and Ge nanocrystals embedded in large bandgap solid state matrices, and in particular: 1. Carrier multiplication in Si nanocrystals. Here I will present results as obtained by calibrated ultrafast transient absorption and advanced photoluminescence quantum yield spectroscopies. I will also discuss the on-going investigations of spectral modification of emission induced by the carrier multiplication process. 2. Energy recycling processes for hot carriers in Si nanocrystals, enabled by interplay between impact excitation and Auger recombination of multiple excitons in the same nanocrystal. 3. Energy diffusion within an ensemble of Si nanocrystals, leading to peculiarities in exciton characteristics. 4. Excitation of Er emitters by hot carriers optically generated in Si nanocrystals, demonstrating that this energy transfer path can successfully compete with phonon emission. [1] M.T. Trinh et al., Nature Photonics 6, 316-321 (2012). [2] S. Saeed et al., Nature Communications 5:4665 (2014) [3] F. Priolo, T. Gregorkiewicz, M. Galli, and T. Krauss, Nature Nanotechnology 9, 19 (2014) [4] S. Saeed et al., NPG Light: Science and Applications, to appear March 2015

Resume : The ion-shaping technique can be seen as a novel route for downscaling the engineering of embedded NPs with a precision that is barely reachable with standard techniques. Its importance relays in its unique capability to control both the morphology and the spatial orientation of metallic nanoparticles embedded within an amorphous host matrix. In the first part of this talk the fabrication of a model system and the potentialities offered by the ion-shaping technique will be reviewed. We show that the ion-shaping is not limited to the transformation into prolate nanorods and/or nanowires, but that depending on the initial size of the NPs, several new classes of ion-shaped NPs can also be obtained: i) facetted-like NPs, ii) nanowires growing from a facetted core or iii) chromosome-like NPs. In parallel, the thermal-spike model - implemented for three-dimensional anisotropic and composite media - is used to correlate the fraction of the nanoparticle that is molten and the deformation path followed by the NPs during the irradiation. Besides, EELS is used to study Localized Surface Plasmon Resonances (LPSR) in ion-shaped metallic nanoparticles with a nanometer-scale spatial resolution. Finally, optical spectra are simulated using a specifically developed Auxiliary Differential Equations-Finite Difference Time Domain (ADE-FTDT) code whereas EELS spectra and maps are simulated using the MNPBEM toolbox. This work demonstrates the possibility to use ion irradiation as tool for the controllable fabrication of a whole family of plasmonic nanostructures with topologically tunable optical properties. These ion-beam shaped composite media have potential applications spanning from plasmonic photovoltaics to bio-sensing.

Resume : Ordered metallic nano-particles can exhibit unique properties of light scattering, confinement and absorption, prominent for a vast number of applications (energy harvesting, bio-sensing, surface enhanced Raman spectroscopy etc). However, deposition of such arrays over macroscopic surfaces remains challenging. Among various methods known for the fabrication of metal nano-particles, we chose the solid-state dewetting of very thin metallic films. This technique alone results in randomly distributed islands with an important size distribution. But if the metal layer is deposed on a patterned surface, the dewetting results in the arrays of metallic nano-particles. In this contribution, we demonstrate how nano-imprint process combined to silver dewetting leads to an innovative, simple and scalable approach for fabrication of silver nano-particles arrays. It allows us to drastically increase the fabrication scalability and obtain the 8×8 cm2 sample. Moreover, this new technique can be applied on substrates of any type (for example: wafers, glass plate or plastic substrate). We prove the excellent organization of our silver nano-particles array showing both order and uniform size distribution. We control the size and organization of particles with the initial thickness of the silver film and the period of patterns. Finally we investigate the optical properties of these nano-particles and in particular the impact of the organization.

Resume : A great interest lies in developing a light source that is integrated on-chip for the emergent Si photonics circuits. Among the explored approaches, use of Er ions has the advantages of stable and low-noise operation at the telecommunication 1.54 μm region. However in the traditionally amorphous silica and related materials the Er amount that can be dispersed without inducing optical deactivation is limited to about 10^20 Er/cm. This work propose an extensive study on Er-based rare earth compounds that permit to dilute very high number of emitters, upto 10^22 Er/cm3, in a dielectric media totally compatible with Si platform. In particular, mixed rare earth (RE) disilicates will be discussed as good host candidates. The high solubility is due to the similarity of crystalline structure of the constituent silicates, then Er can substitute the other RE in the same atomic sites. An accurate description of Er-Er interactions is reached. Moreover the role of sensitizers, such as Yb or Bi, will be taken into account to increase the optical efficiency at 1.54 μm upto three orders of magnitude. Finally we successfully propose an efficient coupling between Er ions in such compounds and the optical modes of a photonic crystal cavity realized in SOI. The photoluminescence of Er in the nanocavity is enhanced by the Purcell effect and the increased extraction efficiency. Very high excited population has been estimated, by making the material very promising as high gain medium.

Resume : Silicon-based waveguides show potential for applications in e.g. inter-core optical communication and data manipulation, in the form of devices such as waveguide amplifiers, but also as possible laser sources. A particularly promising device architecture is provided by the slot waveguide geometry, in which a thin SiO_2 slot is inserted into a silicon waveguide as proposed by [Martinez, A. et al, Nano Lett. (2010), 10, 1507.]. Due to the refractive index contrast, the electric field amplitude polarized normal to the slot plane is enhanced inside the slot, which improves both absorption and emission efficiency of embedded luminescent structures. We incorporate both Erbium ions via ion beam implantation and size-controlled Silicon nanocrystals via sputtering using a superlattice approach into such a slot. The silicon nanocrystals act as Erbium sensitizers. The 1.54 µm Erbium emission is studied in dependence of nanocrystal size and annealing conditions. Most efficient pumping of the Erbium luminescence is found for Si nanocrystal sizes in the range of 3 nm, and elevated post-Er-implantation annealing temperatures of 1000 °C. Furthermore it is shown that the sample structure induces a dependence of the Erbium luminescence intensity on the polarization direction of the exciting laser light, where polarization normal to the slot layer enhances Erbium emission intensity.

Resume : Advanced integrated photonic devices will include active metamaterials in which plasmonic and photonic modes will be used to manipulate the light in nanoscale dimensions. Efficient, robust, and optically modulated nanoscale light emitters with high color purity are required as active building blocks for these metamaterials. A single ultrathin layer (few nanometers thick) formed by Er ions coupled to Si nanoparticles or nanostructures (NSs) is suitable for such a purpose, since RE ions provide a robust emission that can be enhanced by using the Si NSs as sensitizers. However, it is necessary to investigate the potential of these nanoscale systems for light emission and modulation. // In this work we report the light emission properties of ultrathin (< 8 nm) hybrid Er-Si NSs layers, in which all the Er ions are located at few nm of the Si NSs in order to obtain unprecedently high sensitization efficiency. Clear IR Er light emission from an ultrathin layer containing less than 2.5% of an atomic monolayer of Er under near-ultraviolet and visible excitation. Moreover it is found that the emission of the Er-Si NSs layers shows a complex non-linear behaviour as a function of the excitation photon flux. We will discuss how these Er-Si NSs layers possess a high functional versatility, and can be used as efficient nanoscale near IR light sources the emission of which can be modulated optically.

Resume : Rare earth (RE) doped silicon oxide thin films have emerged as promising materials for future Si-based light emitting devices. Among all RE ions, Cerium (Ce) is of particular interest since Ce3+ is characterized by an electric dipolar allowed 5d-4f transition leading to emission in the violet-blue. In this contribution, we investigate the structural and optical properties of Ce-doped SiO(1.5) thin films by means of photoluminescence (PL), Raman spectroscopy, scanning transmission electron microscopy (STEM) and atom probe tomography (APT). We observe strong blue luminescence at room temperature. By investigating the optical properties as a function of annealing temperature, we found that the Ce-related PL exhibits a complex behavior independently of the Ce content in the films. For annealing temperatures up to 500°C, the Ce-related PL increases as a result of a reduced density of non-radiative recombination centers. From 500°C up to 900°C, the Ce-related PL strongly decreases. Both STEM and APT measurements demonstrate the formation of superimposed Ce-rich and Si-rich clusters. The decreasing Ce-related PL is thus due to concentration induced quenching. For annealing temperatures larger than 900°C, the Ce-related PL increases. The structural characterizations show that a phase separation occurs between pure Si nanocrystals and Ce-rich clusters of stoichiometry close to Ce2Si2O7. This compound contains Ce3+ ions thus explaining the increased Ce-related PL at high temperatures.

Resume : During the last decades, silicon integrated photonics has attracted much interest due to the increasing demand of optoelectronics devices compatible with the existing technology. Several routes have thus been explored to circumvent the limitations of bulk silicon. Rare-earth (RE) ions incorporated silicon nanocrystals in silica (SiO2) system is one of the most promising route to obtain light from Si-based materials. However, the light emission in such system is strongly dependent on the microstructure such as clustering or distribution of rare earth in host materials. In this work, we investigate the structure of Ce-doped SiOx and Er-doped SiOx films containing Si nanocrystals using the atom probe tomography (APT). Such technique provides a 3D chemical mapping of the analyzed material at the atomic scale. It has been observed that a thermal annealing at 1100°C leads to the formation of Si nanoclusters and RE-rich clusters. Surprisingly, these two clusters are collected to each other. This is related to a demixing of the RE-silicon rich phase observed at annealed temperatures lower than 1100°C in order to form a well detected silicate phase. Moreover this microstructure has then been correlated to the optical emission of rare earth ions and Si nanocrystals obtained by the measurement of steady state photoluminescence.

Resume : Rare earth (RE)-doped oxides are attractive thanks to the narrow intra-atomic transitions and intense luminescence they exhibit in adequate coordination environment (3+ oxidation state). Different methods have been used to obtain RE-doped thin films, such as chemical and physical vapor deposition and/or doping by ion implantation. Nevertheless, these techniques do not allow the accurate control of the RE inter-ion distance. As a consequence, RE clustering may occur, which quenches their optical emission. To avoid this effect, we have employed a technique that combines electron beam evaporation with the so called delta-doping approach, which allows the control of the RE inter-ion distance along the growth direction with less than 1 nm resolution. Thin films were deposited onto a crystalline silicon substrate and consist in a Tb/SiO2 superlattice with sub-nm-thick Tb layers. Transmission electron microscopy was used to image the superlattice structure. To investigate the control of the RE inter-ion distance in the growth direction, different SiO2 thicknesses were studied. Moreover, an annealing process was carried out for 1 h in N2, at temperatures ranging from 700 to 1100 °C. Photoluminescence experiments reveal narrow-line emissions from Tb3+ ions in all samples, with an intensity variation depending on the oxide thickness. Finally, the incorporation of Al in different spatial configurations produced an enhancement up to one order of magnitude in the luminescence intensity.

Resume : Recently, very stable and efficient light-emitting diodes (LEDs) based on Si-nanocrystals (SiNCs) embedded in a solid matrix were fabricated [1]. Light extraction efficiency from such structures could be strongly enhanced by reducing the internal reflection phenomenon. This can be realized by random or periodical patterning of the slab surface. In the latter approach, two-dimensional (2D) photonic crystal (PhC) with properly-designed dimensions is prepared on the top of the light-emitting layer. Then, the previously trapped modes, now referred to as leaky modes, are diffracted into surroundings under specific angles of extraction [2]. In our study, we fabricated a series of samples composed of 2D PhCs etched on the surface of SiO2 layers embedded with light-emitting SiNCs. The PhCs were formed by periodically ordered columns of various heights and lattice constants possessing square and hexagonal symmetries. Dimensions of the PhCs were computed by Rigorous coupled-wave analysis method [2]. We have measured photonic band diagrams for all the samples and showed that the photoluminescence of SiNCs is extracted with very high efficiency within large spatial angle (e.g., extracted with up to 11-fold enhancement in the direction normal to the sample plane). This original study can be applied to improve the SiNCs-based LEDs. [1] F. Maier-Flaig et al., Nano Letters 13, 475-480 (2013); [2] L. Ondic et al., Appl. Phys. Lett. 102, 251111 (2013); L. Ondic et al, Sci. Rep. 2, 914 (2012)

Resume : The annealed SixGeyO1-x-y film comprises Si and Ge nano-sized poly-crystals and could be used for emission applications. Due to quantum confinement, the emission related to these nano-crystals is wavelength-tunable by adjusting particle size. In our previous study, we confirmed the peak of PL band is tunable from 430 to 600 nm. The result indicates that this material is potential as a sensitizer to transfer its energy to rare-earth ions such as Er3 leading to emission in the IR range. We have grown Er doped SixGeyO1-x-y film and confirmed the annealed film emit light in both visible and IR range. The PL band in the visible range is related to nano-crystals and the IR-PL centered at 1530 nm is originated from Er ions. In this study, we are going to investigate optimization of IR emission by different method such as by controlling Er concentration in the films. According to some literature, when the Er concentration is higher than 2%, concentration quenching seems important resulting in the weak IR emission at 1530 nm. We will use mechanical gauge and adjust growth condition to control Er concentration for optimization of IR emission. The influence of Si/Ge nano-particles including the average-size and the quantity on the IR emission will be also investigated. Additionally, in order to further analyze the energy transfer mechanism between RE ions and Si/Ge nano-crystals, we will study Pr doped in SixGeyO1-x-y thin films. More details will be discussed.

Resume : The understanding and control of electromagnetic interactions and charge transfer between a 2D electronic layer (graphene, dichalcogenide) and an assembly of metallic nanocrystals (NCs) are of great interest for multiple electronic, optical or plasmonic applications. So far, we have developed a specific architecture called “three scales – three dimensions” (3S-3D) that offers a new approach to modulate and analyze simultaneously electro-optical and transport properties. The most crucial parameter of this architecture, i.e. the distance between the NCs and 2D systems, can be finely controlled at the nanometer scale by using low energy ion implantation. This accuracy allows a progressive tuning from electric field polarization to charge transfer for both transport properties and light scattering enhancement over a large perfectly flat area. However, before developing any application it is necessary to check a key step, namely that the electrons are able to pass through the nanoparticle assembly embedded in the dielectric. We carried out a transmission electron microscopy (TEM) study, varying the parameters of low energy ion implantation to tune the distance to the interface and the density of Ag nanoparticles embedded in SiO2 and SixNy. The transport measurements made on developed devices show that conduction is possible under certain conditions. The I-V and R-T characteristics provide the physical mechanisms involved in the electron transport through such NPs metallic assemblies.

Resume : Si nanocrystals embedded in SiO2 multilayer structures (MLs) are fabricated and characterised with the goal of exploring the formation of nanocrystals (NCs). MLs provide both narrower size distributions, as well as extra control knobs during the fabrication of solid state Si NCs embedded in a SiO2 matrix; most of all the nanolayer thickness of substoichemetric SiO2 is associated with control over the NC size. During this research, MLs were fabricated using a radio-frequency sputter deposition system with subsequent furnace annealing. Characterisation of the Si NCs was performed by photoluminescence and (high-resolution) transmission electron microscopy. In our study we explore the enhanced control over NC size and concentration and the effect it has on the optical quality of NCs. We observe that with our fabrication methods NC size is not directly controlled by the nanolayer thickness, and explore the effect of buffer layer thickness on NC formation.

Resume : The realization of silicon nanocrystal (SiNC) based tandem solar cells is of great interest because of their possibility to extend their performance. The adjustment of the nanocrystals size with quantum confinement can modify the optical bandgap to better catch the sunlight. An interesting possibility would be to manufacture and control the size of silicon nanocrystals (NC) in a silicon carbide matrix [1,2,3]. The studied samples have been sputtered by using silicon carbide (SiC) and silicon targets on various substrates. The working pressure has been optimized and the silicon quantity inside the thin films tuned by changing the growth parameters. The samples were analyzed for different annealing temperatures mainly using microscopy, infrared absorption, Raman and UV-visible spectroscopy and Auger spectroscopy. Silicon nanocrystals appear for silicon-rich thin films. The nature and size of the Si NC were studied using Raman spectroscopy coupled to a simple phonon confinement model [4]. The SiNCs observed for silicon poor samples remain amorphous which is not the case for silicon rich samples that exhibit a non-negligible part of crystalline silicon. The diameter of the SiNC was evaluated using the confinement model. [1] D. Song et al., Thin Solid Films 516 3824–3830 (2008). [2] D. Song et al., Solar Energy Materials & Solar Cells 92 474–481(2008). [3] Rena Gradmann eyt al., Phys. Status Solidi C 8, No. 3, 831–834 (2011). [4] P. Miska et al., J. Phys. Chem. C 114, 17344 (2010).

Resume : Many products in health-care and customer sectors promote silver nanoparticles (AgNPs) to exploit their strong antibacterial efficiency. The huge surface-volume ratio of these NPs facilitates the silver release (dissolved Ag), leading to an increased toxicity for organisms. In this work a new method is developed and applied to assess the bio-available Ag released in buffered water from layers with AgNPs embedded in silica (SiO2) films. Two approaches were used to elaborate these nanocomposite structures: (I) low energy ion beam synthesis using an implanter modified to work at low energies; (II) combined sputtering and plasma enhanced chemical vapor deposition by using the plasma of an axially asymmetric RF discharge. Both techniques allow fabricating a single layer of AgNPs embedded in SiO2 films at controlled nanometric distance from the free surface. By using fluorometry, the short-term toxicity of silver released from embedded AgNPs to the photosynthesis of Chlamydomonas reinhardtii was used to determine the bio-available Ag released from nanocomposites structures in liquid media. The structural analyses performed by TEM and optical measurements reveal that the properties of AgNPs embedded in SiO2 layers are preserved even after immersion in liquids. This study shows that, even embedded in dielectric/glass matrix, Ag release systematically takes place, mainly by Ag+ diffusion. This release can be modulated by the distance between the embedded NPs and free surface.

Resume : The properties of nanocomposite materials are nowadays widely studied aiming at a large spectrum of applications. In particular, nanostructures containing a layer of silver nanoparticles (AgNPs) embedded in silica matrix close to the free surface have a strong potential for plasmonic devices. The main advantage of these structures is the possibility to manipulate, localize and enhance the electromagnetic field at their surface. To guarantee the performance of plasmonic structures when integrated in devices one needs to characterize their dielectric response during the elaboration phase. A good way is to use reliable non-destructive diagnostic methods. In this work we present a fully predictive model appropriate for the interpretation of ellipsometric spectra recorded on plasmonic structures. It is based on the quasistatic approximation of the classical Maxwell-Garnett formalism, however accounting for the electronic confinement effect through the damping parameter. Samples were elaborated by using: (i) low energy ion beam synthesis and (ii) combined sputtering and plasma polymerization. The model allows extracting from the experimental ellipsometric spectra the characteristics of the NPs population: average size, surface density and distance of the AgNPs layer from the matrix free surface. Comparison with results obtained from transmission electron microscopy confirms the applicability of this method. The limits of the proposed diagnostic method are also discussed.

Resume : It is of great interest for several electro-optical applications to perform band gap engineering with Si nanocrystals (Si NC) embedded in SiC. Therefore the control of the Si NC size and distribution is crucial. The suitability of a multilayer (ML) structure for Si NC size control is investigated by varying both the stoichiometric SiC barrier thickness and the Si-rich SiC well thickness between 3 nm and 9 nm and comparing them to single layers (SL). All layers were deposited by plasma enhanced chemical vapour deposition (PECVD) and afterwards subjected to a thermal anneal at 1000-1100°C for crystal formation. Grazing incidence X-ray diffraction (GIXRD) was used to determine the mean Si NC size. Fourier-transform infrared spectroscopy (FTIR) was applied to gain inside into the structure of the Si-C network and UV-Vis measurements were performed to investigate the absorption coefficient and to estimate the bandgap. All this characterisation methods yield bulk information about the entire sample area and depth. We discovered that the influence of the ML structure on the Si NC size, on the Si-C network and on the absorption properties is small and that the key parameter for the structural and optical properties is the overall Si content in the samples. We attribute this behaviour to interdiffusion of barrier and well layers. Since the produced Si NC are inside the target size of 2-4 nm we propose to use the Si content to adjust the Si NC size in future experiments.

Resume : The nuclear low-lying isomeric level in 229Th isotope is the unique exception in nuclear physics. This level has uncharacteristic low energy value of 7.8±0.5 eV located in the region of vacuum ultraviolet. However, the isomeric transition energy has been measured indirectly, while the direct registration of the transition is very difficult and has not been successful yet. One of the approaches of exciting the isomeric nuclear transition implies placing of 229Th ions into crystals such as LiCaAlF6, CaF2, and Na2ThF6. Synthesis of these crystals with the desired purity is a challenging and resource consuming problem. In the present work we propose an original technique for preparation of thorium sub-monolayer thin films embedded into the CaF2 matrix based on conjoint use of atomic layer deposition (ALD) and electron beam evaporation (EBE). It was found that atomic layer deposition of Th on the CaF2 surface provide formation of thorium fluoride island films with band gap energy about 7 eV. The XPS analysis showed that the resulting film without CaF2 coverage layer after annealing in UHV condition leads to the restoration of thorium up to pure metal. At the same time annealing of thorium fluoride film coated by 5 nm thickness CaF2 film does not change the chemical state of thorium atoms but change its band structure. The origin of the observed thorium films formation and the results on the investigation of Th films embedded into the CaF2 matrix by XPS and REELS are discussed.

Resume : A dielectric matrix with embedded Si-nanoparticles show luminescence, which depends on nanoparticles size, concentration, and matrix type. Ion implantation followed by thermal annealing was identified as a powerful method to form such nanoparticles. It has also been shown that implantation parameters, such as the fluence and flux of incident ions, play an important role for the achieved nanoparticles size and their distribution. In this work, 40 keV Si-ions are implanted into a SiO2-layer on-top of a Si-substrate by varying fluence in a range of 3.75×1016 – 1.5×1017 ions/cm2 (corresponding to 5 – 20 atomic %), and using a constant flux of 1.2×1013 ions/cm2/s. The as-implanted samples are annealed in N2-gas at 1,000 and 1,100 oC to activate the Si diffusion and the nanoparticles nucleation processes. Furthermore, hydrogen-passivation is employed in order to reduce the non-radiative defects. The aim is to optimize the synthesis of Si-nanoparticles with spherical shape and about 2 – 10 nm-diameter. The luminescence properties are measured by spectrally resolved photoluminescence including time-decay measurements, while X-ray diffraction, atomic force microscopy, electron microscopy, and ion beam analysis techniques are used to characterize the nanoparticle formation process. The optical and physical properties are mutually analyzed in order to explain the characteristics of Si-nanoparticles. Keywords: Silicon-nanoparticle (SiNP), Ion implantation

Resume : Percolating systems provide a wide range of applications in totally different areas of science, from analyzing transport in porous media, epidemic spreading to nanocomposite materials. Randomly deposited nanoparticles (RDN) were produced [1], which exhibit quantized conductance even at room temperature. Nanocomposite materials are investigated by using continuum percolation models. In this context, the model of 2D overlapping disks has been successfully applied for RDNs [2]. This types of systems exhibit metal-insulator transition (MIT) [3] and the system conductance obeys a power law beyond the percolation threshold. However, tunneling regime is still controversial. Percolating systems of this kind have been investigated by semi-classical transport models [2,3]. Our approach is based on coherent transport calculations which employs an efficient scattering formalism [4]. We discuss the charge localization phenomena and the behavior of the system conductance around the percolating threshold, with a particular focus on the MIT transition. The approach serves a guiding tool for the design of tunable nanocomposite materials. [1] A. Sattar, S. Fostner and S. A. Brown, Phys. Rev. Lett. 111, 136808 (2013) [2] S. Fostner, R. Brown, J. Carr and S. A. Brown, Phys. Rev. B 89, 075402 (2014) [3] S. Das Sarma, E. H. Hwang, and Qiuzi Li, Phys. Rev. B 88, 155310 (2013) [4] T. L. Mitran, G. A. Nemnes, L. Ion and D. Dragoman, J. Appl. Phys. 116, 124316 (2014)

Resume : There is substantial interest in developing new classes of semiconductor materials exploiting the properties of group V semimetal bismuth. These include materials for development of optoelectronic, thermoelectric and electronic devices such as laser diodes, light emitting diodes and solar cells. The effect on the growth kinetics of the dilute GaAsBi and InAsBi nanostructures, caused by incorporating Bi in GaAs and InAs, was examined at different temperatures. The formation of well-ordered metallic Bi/III-V was obtained and the Bi adsorption on GaAs surface was studied. Structural properties of dilute III-V bismide nanostructures were studied by scanning electronic microscopy (SEM) and atomic force microscopy (AFM). These analyses established that the nucleation and growth mechanism of dilute III-V bismide was carried out under a 3D mode. At low growth temperature, a Bi-induced nanoline structure in the InAsBi surface was observed. The main reason to stabilize the nanolines was found to be the large atomic size of Bi. The obtained results have shown a new window for III-V nanowires growth with bismuth as a catalyst.

Resume : Microcavities are well known in photonics for their ability to create a localization of the electromagnetic field inside engineered defects of photonic crystals (PhCs). This localization is of great attraction even in the world of optoelectronics due to the possibility to modify the behaviour of emitters contained where the field is confined. The use of polymers make it easy to produce PhCs and cavities while the use of polymer/inorganic nanocomposites makes it possible to have passive matrices that host photoactive materials. In this work is reported the preparation and optical characterization of an all-polymer 1-D microcavity composed by a photoactive nanocomposite’s defect layer sandwiched between two DBRs made of polyvynilcarbazole and cellulose acetate. The nanocomposite is formed by CdSe/CdS core-shell nanorods dispersed in a polystyrene matrix. By using the conceptually simple technique of spin coating a very high quality PhC composed by 101 different layers has been realized. Preliminary results show a marked sharpening of the PL spectra respect to the one of bare NCs passing from about 24 nm of full width at half maximum to roughly 2.4 nm. The reduction of a factor 10 of the width is accompanied by a spectral redistribution of the emission dependent upon the direction of propagation of the light. This cavity is a prototype that reveals the potentiality of these structures as platform to study other effects like for example lasing.

Resume : The integration of non-reciprocal functions, such as optical isolators, on photonic platforms is still a great challenge. Indeed classical magneto-optical (MO) materials required to obtain the non-reciprocity need a high crystallization temperature (~ 700 °C), which is incompatible with integration technologies. To overcome these difficulties, a composite approach was proposed using magnetic nanoparticles (CoFe2O4) embedded in a silica matrix. The nanoparticles are prepared through a co-precipitation method, then dispersed in water, and finally added to a sol-gel preparation of silica precursors. Composite layers are obtained through the coating of this preparation on classical substrates followed by a soft thermal treatment (~ 100 °C). This approach has previously enabled to produce on-glass integrated MO converters with a working wavelength of 1,5 µm, in the telecom spectral range. But, the low merit factor (magnitude of the MO effect divided by absorption) of the nanoparticles was a main drawback. In this study, using spectral MO and absorption spectroscopic measurements combined with XMCD spectroscopy, it is shown that the spectral merit factor of these NP can be modulated by the size of the nanoparticles and/or by the localization of Co2+ ions in tetra or octahedral site of the spinel structure of CoFe2O4. Furthermore, depending on the size and on the orientation of the nanoparticles in the matrix obtained during the coating, the MO hysteresis loop can be tuned.

Resume : AFM current-force spectroscopy is performed on few-layer arrays of colloidal nanoparticles fabricated by convective self-assembly. Thiol and phosphine based molecules (MUDA, 11-MercaptoUndecanoic Acid) and TDSP, Tris (4,6-Dimethyl-3-sulfonatophenyl) phosphine) are used as ligands [1]. The contact-AFM current spectra are interpreted in terms of resistor networks representative of the particle arrangement, using Hertz sphere model for the interparticle contact within the lattice. The size scale of AFM makes the approach suitable for characterizing the individual junction by transition voltage spectroscopy (TVS) and is therefore a method complementary to macroscopic measurements [2,3]. The results are validated by comparing the predicted Young modulus to values found by molecular dynamics. A potential role of Coulomb blockade is discussed [4]. Colloidal assemblies of large-gap semiconductor nanoparticles provide a low-cost route to resistive strain gauges for touch-sensitive panels on flexible substrates. [1] H. Moreira, J. Grisolia, N.M. Sangeetha, N. Decorde, C. Farcau, B. Viallet, K. Chen, G. Viau, and L. Ressier, Nanotechnology, 2013, 24(9), 095701 [2] Jeremy M. Beebe, BongSoo Kim, J. W. Gadzuk, C. Daniel Frisbie, and James G. Kushmerick, PRL, 97, 026801 (2006) [3] E. H. Huisman, C. M. Guedon, B. J. van Wees, S. J. van der Molen, NANO LETTERS 9 (11), 3909 (2009) [4] K. H. Mueller, J. Hermann, G. Wei, B. Raguse, G. Baxter, and T. Reda, Phys. Rev. B, 66, 075417 (2002)

Resume : We report on the development of a free nanoparticles NPs generator coupled to a Pulsed Laser Deposition (PLD) set-up allowing stacks of NPs or NPs embedded in a co-deposited matrix. This process uses two lasers, respectively, a Nd-YAG laser for NP synthesis and an excimer laser for the PLD matrix. Intrinsic particularities of the process, a very narrow metallic-NP size distribution centered on 3-5 nm is confirmed by HRTEM and AFM. In this paper, we will focus on metallic vanadium (V-NPs) stacks encapsulated between two Al2O3 protective layers. These original materials were chosen to synthesize VO2 films after thermal treatment. VO2 presents a first order insulator (ins) to metal (met) transition exhibiting at 68°C, under external stimuli such as heating, strain or electrical voltage, an abrupt change in its resistivity and near-IR transmission. Due to the high porosity of these specific architectures (of about 50% of the single crystal) and the high chemical reactivity of the NPs, VO2-NPs are synthesized by V-NPs oxidation under 3.10-2 mbar O2 pressure, annealing at 300°C during 10 min. The VO2-NPs phase synthesis is substrate-independent: VO2-NPs stacks are obtained on c-Al2O3, MgO or glass substrates. Based on optical transmission and electrical measurements, VO2-NPs-stacks exhibit behavior close to continuous VO2 thin films. VO2-NPs-stacks present a lower transition temperature (50°C) and a larger hysteresis (20-30°C), confirming the specificity of these films.

Resume : The synthesis of plasmonic nanocomposites is reported by chemical vapor deposition using a single-pot process, where adjusting the time-programmed deposition cycles is used as an approach to grow embedded non-coalescent nanoparticles into continuous matrices. The reliability of this approach is demonstrated by the growth of plasmonic nanocomposites with intimate interface between both phases. The structure of the obtained nanocomposites was assessed by scanning and tunnel electron microscopy. The surface plasmon resonance (SPR) in these composites was investigated as a function of the architecture parameters of the nanocomposite coating. We report on a tunable SPR in the entire visible spectrum by adjusting the composition and size of the nanoparticles, and the composition of the matrix. Here, the involvement of various host matrices will be reported.

Resume : Optical materials with semiconductor nanoparticles within dielectric matrices are of interest for construction of non-linear optical elements, selective filters, spectral converters, etc. In the present work, we concern the glasses with PbS and PbSe fabricated by the two-step technique on the basis of silicate glass matrix and report the recent studied using the SANS technique (which has been applied for this type of glasses for the first time). A proper understanding the structure of material, size of particles and spectral features need to control optical functionality of glasses. SANS is efficient non-destructive technique allowing a wide range of structural models in the size range from atomic clusters to submicron size. The glasses in this study were synthesized from a mixture of glass-forming oxides and chalcogens at 1400оС, but the nucleation and growth of PbS/Se particles have occurred by the secondary heat treatment. SANS curves were recorded in the range of scattering factors 0.005-0.5 Ǻ-1. Principal features in the scattering appear at Q 0,01-0,1 Ǻ-1 for the glasses with nanoparticles in contrast with a blank glass matrix. For the lowest Q (QR<<1), where R the radius of particles, the Gunier analysis (a model of isolated spheres) reveals that the particle size depends weakly on heat treatment steps and fits the values of 4-5nm. An analysis in the full range evidences formation more complicated structures promoted by late heat treatment steps (aggregates, fractal).

Resume : Light emitting Si nanocrystals (Si-NCs) in solid matrices offer certain advantages for optoelectronic applications, however, generally their external quantum efficiency is limited to about few percent. One of the recent approaches to overcome this problem is based on plasmon-induced enhancement of Si-NCs emission due to their interaction with metal nanostructures. To achieve the significant enhancement an effective near-field coupling is required between Si-NCs and nearby metal nanoparticles. Thus, the effect of Si-NCs emission enhancement is of strong local nature which is defined by localized type of the plasmons involved. In turn, weaker interest is focused on utilization of delocalized (propagating) plasmons for the enhancement of Si-NCs luminescence, which might be realized by means of 1D-periodic metal structure. The present work is devoted to the investigation of resonant interaction between propagating surface plasmon polaritons (SPP), induced by light diffracted from 1D-periodic metal structure, and silicon nanocrystals in silicon dioxide matrix. In order to define the geometrical parameters of metal structure, which are suitable for resonant interaction, theoretical calculations of directional emissivity for the SiNCs were performed. Angle-resolved reflectance spectroscopy was used to determine the main parameters of light-excited SPP. Photoluminescence measurements were done to study the dependence of enhancement level on the structural parameters of the samples.

Resume : In the past decades, there was an increasing interest in the unique structure and properties of metal and semiconductor nanoparticles, since the small dimensions are leading to a tremendous change of their physical properties. One of the actual problems in this field is to develop novel low-voltage phosphors having high efficiency and chemical stability. Many research groups have started to study ZnO nanostructures formation using ion beam synthesis in SiO2 matrix and thermal oxidation. It has been found that if the annealing temperature exceeds 800 °C, ZnO bonding starts to break down, and Zn2SiO4 (willemite) forms. The present study is focused on the structural and photoluminescence properties of willemite nanophase formed in the SiO2 by means of ion implantation and subsequent 900 °C, 1 hour annealing in air or dry N2 atmosphere. Willemite is a well-known luminescent material, that can emit blue, green or red light depending on rare earth and transition metal ions being incorporated. Quartz glasses were chosen as well-known reference in order to reveal the role of host matrix. X-ray diffraction data, optical absorption and photoluminescence spectra confirm the formation of willemite nanophase. PL excitation spectra demonstrate the contribution of silica electronic states and point defects, thus suggesting interphase energy transfer mechanism. Temperature broadening of the green PL band reveals the role of phonon-assisted processes.