Silicon carbide (SiC) is a rapidly emerging material for photonic applications, thanks to its exceptional optical properties. To be used as a waveguide, SiC thin films must be deposited directly on silica at low temperature. Amorphous SiC films were deposited by RF magnetron sputtering using a single source of high-purity polycrystalline SiC. A systematic study of the chemical, structural and optical properties of the films was carried out, using a combination of XRD, XPS, SIMS, spectroscopic ellipsometry, Raman spectroscopy and UV-Vis absorption spectroscopy. The aim was to link deposition conditions to film properties. By exploring a three-parameter space (RF power, substrate temperature, pressure), we have demonstrated that RF power is the main parameter which controls the entire deposition process and film properties. By simply adjusting the RF plasma power between 150 and 450 W, it is possible to adjust the refractive index at a wavelength of 1.5 mu m in the range 2.50-2.75 and vary the bandgap from 2.5 to 1.7 eV. This is attributed to a slight variation in film composition, particularly in terms of Si/C ratio and C-C bond concentration.

Transparent electrodes based on emerging nanomaterials like silver nanowire (AgNW) networks have been extensively investigated in the past few years. Thanks to their superior flexibility and versatility in terms of fabrication and device integration, they present an excellent alternative to indium tin oxide. However, the lack of thermal, electrical, and chemical stability requires the encapsulation of the AgNW. This has been performed using thin metal oxide films, graphene, or organic protective coatings. Despite the very promising properties of such nanocomposite approaches and the performance enhancement, more investigation is needed to minimize the loss of optical transmittance upon coating and achieve superior electrical, thermal, and mechanical stability. In the present work, the encapsulation of AgNW networks with aluminum nitride (AlN) coatings is reported for the first time, and it is compared to AgNW/Al2O3 nanocomposites. Thanks to the low thicknesses (<20 nm) and the wide band gap of AlN, the optical transparency is not impacted. Furthermore, the nanocomposite networks demonstrate no failure under electrical and thermal stress conditions (up to 21 V and 400 degrees C respectively), in contrast to the AgNW/Al2O3 nanocomposites, which fail after 15 V and 350 degrees C. In addition, microscratch tests reveal the remarkable mechanical robustness of the nanocomposites, and the electrical stability is further confirmed under accelerated environmental tests, coupled with ex situ characterization by SEM and XPS. The results reported in the present work show that AgNW/AlN electrodes are outstanding candidates for high-performance transparent electrodes.

Two-dimensional (2D) metal nitrides are new emerging materials with potential applications in electronics, energy storage, or conversion efficiency. In this paper, we report the synthesis of molybdenum nitride by nitriding molybdenum disulfide (MoS2) via a 700 °C ammonia (NH3) reactive heat treatment. A well-controlled uniform MoS2 thin film was prepared by atomic layer deposition (ALD). The progressive MoS2 nitriding reaction has been demonstrated and monitored by in situ reflectance measurements. These results have been confirmed by Raman and x-ray photoelectron spectrometry. This method paves the way to a new potential route to the synthesis of Mo nitride obtained from a well-controlled uniform 2D-MoS2 thin film deposited by ALD.

This paper investigates the upconversion luminescence modification of codoped nanoparticles with lanthanides ions based thin films through adding a coating. First, these nanoparticles based thin films composed of Er3+-Yb3+ co-doped anatase-TiO2 are prepared using spin coating technique supported by a design of experiment (DOE) approach with the Hadamard matrix of order 4 to improve the deposition conditions. For the coating step, different thicknesses of Al2O3 layer are realised by thermal atomic layer deposition (T-ALD) onto the surface of Er3+-Yb3+ co-doped anatase-TiO2 nanoparticles based thin films. The results show that the ALD-Al2O3 coating can benefit the luminescence properties of the upconversion nanoparticles based thin films. Thin ALD-Al2O3 (10 nm) coated stack exhibits similar upconversion luminescence as the uncoated nanoparticles based film but insures also their stability. Meanwhile, for 100 nm ALD-Al2O3 coating, enhancement of the upconversion green emission by 98% at the expense of the red emission compared to uncoated sample is observed. This results are promising to be applied in photovoltaics field.

A comprehensive model to predict the stress evolution in a multilayer coating during its use in solar receivers is proposed. The model takes into account residual stress in the coatings, thermal gradient in the structure and high temperature phenomena like oxide scale growth and creep relaxation. The numerical tool developed in this work can help to understand the complex interplay of these phenomena occurring in all the materials involved. Additionally, the present model can be used to assess high temperature data like creep when it is compared with an experimental case.

In this work, a simple, low temperature (T < 300 degrees C) procedure suitable to increase the efficiency of solar cell and optoelectronic devices through reducing the mismatch with solar spectrum in the infrared range is proposed. TiO2 co-doped with rare earth ions is a promising candidate for its use in optical field due to the possibility to expand the spectral absorption range. Here, pure and Er3+-Yb3+ co-doped anatase-TiO2 nano-spherical particles (diameter < 50 nm) with high surface area (125.7 m(2)/g and 140.6 m(2)/g for the pure and co-doped, respectively), good crystallinity are prepared by hydrothermal-assisted sol-gel method, followed by their dispersion and deposition as thin films. The nanoparticles are characterized by studying their structural, morphology, surface chemical compositions and photoluminescent properties. From the dispersion study, results showed that the optimal conditions were obtained for co-doped TiO2 at operational pH = 3 and with 20 min as a suitable duration of ultrasonication. The co-doped TiO2 nanoparticles showed excellent upconversion properties (green and red emissions) at room temperature under 980 nm excitation. To extend this result towards optoelectronic and photonic applications, the upconversion nanoparticles are deposited at the surface of n-type (100) Si wafer using a spin-coating process. From scanning electron microscopy, it is observed that the entire surface of substrate is covered with a uniform film composed of compact arrangement of small nanoparticles with a good adhesion on Si surface, also the resulting 750 nm thick TiO2:Er-Yb film maintained the upconversion luminescence phenomena.

The efficiency of the superconducting radio frequency cavities composed of Nb required the deposition of thickness-controlled multilayer coatings of superconductor-insulator-superconductor (S-I-S) on the internal surfaces of the cavities. Herein, we report the plasma-enhanced atomic layer deposition of carbon-free NbN (50 mu m thick), followed by a thermal treatment, to obtain the superconducting layer in the S-I-S structure. Using (tert-butylimido)-tris(diethylamino)-niobium as the niobium precursor and H-2 and NH3 plasma as reactive gasses, the deposition and annealing parameters were optimized by studying their effects on the film properties (crystallinity, density, and composition). We demonstrated that the superconducting critical temperature (Tc) can be improved after thermal annealing up to 13.8 K, a value compatible with the targeted application. In addition to the expected densified layers and increased grain size, we observed a partial transformation of the oxide present in the as-deposited layer into niobium oxynitride, which could indicate the origin of the improvement of the superconducting properties. With low carbon and oxygen impurity concentrations in the films, this study contributes to the understanding of the relationship between the structure, composition, and superconductivity in NbN.

Porous hollow PtNi/C nanoparticles (NPs), an highly active electrocatalyst for the oxygen reduction reaction (ORR)1, were successfully synthesized on different carbon supports. The latter plays an essential role in the NPs synthesis, providing a way to control their morphology and Ni content. The physico-chemical properties of the different carbon supports were crucial during accelerated stress tests simulating start-stop events at a PEMFC cathode (i.e. step potentials between 1.0 and 1.5 V vs. RHE) and were discussed by the means of identical-location transmission electron microscopy (IL-TEM) and electrochemistry (see. Figure 1). It was observed that electrocatalysts supported on graphene nanosheets and carbon xerogel suffer from NPs detachment and carbon complete corrosion while COsurf forms on carbon blacks supports (i.e. incomplete oxidation of the surface). The degradation of the carbon support resulted in mass activity and specific activity losses, as the result of the increase of the resistance of the catalytic layers (ΔR k). Figure 1

Plasma enhanced atomic layer deposition (PE-ALD) of aluminum nitride (AlN) thin films often utilizes NH3 or a mixture of N-2 and H-2 as a plasma source. However, the possibility of separating the activation step from the nitridation step by using H-2 alone as the plasma source has never been explored. In this paper, we study the deposition of MN by PE-ALD by using trimethylaluminum, H-2 plasma and NH3 for deposition temperatures below 400 degrees C. The self-limiting ALD growth was achieved between 325 degrees C and 350 degrees C. As a comparison, AIN was also deposited by thermal ALD (T-ALD), where surface reactions between TMA and NH3 occurred with reasonable growth rates only at temperatures above 400 degrees C. The PE-ALD films showed low oxygen (1.5 at.%) and carbon contaminations (1 at.%). The T-ALD films contained carbon (5 at.%) mainly attributed to the presence of C-Al bonds that was insignificant in PE-ALD films. The flow rate of H-2 used in H-2 plasma was found to have a significant impact on the preferred orientation of MN films, where higher H-2 flow rate promoted the (002) preferred orientation. Besides, the electrical resistivities were probed to be 1085 cm, as expected in an insulating material. As an example, AlN was used to infiltrate porous sintered silicon carbide (SiC). Both AIN deposited by PE-ALD and by T-ALD operating with exposure mode deposited at 400 degrees C were attempted. Even though, there is a greater risk for TMA precursor to decompose at 400 degrees C, infiltration of MN was more successful by T-ALD operating with exposure mode.

The aim of the present study is to evaluate the possibility of improving crystalline quality of AlN deposited on Si (111) substrates by implementation of substrate patterning. Growth on flat Si (111) substrates was conducted to investigate influence of deposition parameters on the growth behavior and quality of resulting AlN films. This investigation showed that SiC buffer layer is required to suppress disorientation of the AlN layer, optimum growth temperature is about 1260°C, Al-rich conditions favor more rapid coalescence of the nucleation island while N-rich conditions lead to the formation of a smooth surface. Transposition of the resulting AlN growth recipe on to patterned Si (111) substrates revealed reduction of the stress in AlN, bending of the threading dislocations and formation of a dislocation free area in the overgrown region. For the formation of a continuous layer on silicon pillars, we propose a novel technique based on the decrease of the mean free path of gaseous species leading to localized growth of AlN on the top of the pillars. Such continuous layer exhibit lower crack density compared to that on a flat substrate. Thus, the growth of AlN on pillar patterned Si substrate is seen to be a promising way for the further improvement of the AlN films quality.

A library of binary PtRh thin-film electrocatalysts was obtained by potentiostatic co-electrodeposition of Pt4+ and Rh3+ on a gold wire in a capillary cell, the capillary separating on the one hand the Pt4(+) compartment and on the other hand the Rh3+ compartment. More specifically, this capillary cell enables to hinder the mobility of the ions from the one compartment to the other, thereby creating a continuous gradient of concentrations of Pt4+ and Rh3+ in the solution along the gold wire; as a result, the surface of the gold wire substrate witnesses crossed gradients of Pt4+ and Rh3+ during the electrodeposition, and countless PtRh compositions can be generated on the surface of a single sample. The feasibility of the protocol was confirmed by electron probe microanalysis and sections of the film (with lengths of 1 mm) were subsequently accessed by cyclic voltammetry. The results demonstrate the potential of this approach to perform compositional studies in a single piece of substrate and open new perspectives of studies in catalysis and electrocatalysis with a relatively low-cost and time-saving approach.

ZnO thin films are interesting for applications in several technological fields, including optoelectronics and renewable energies. Nanodevice applications require controlled synthesis of ZnO structures at nanometer scale, which can be achieved via atomic layer deposition (ALD). However, the mechanisms governing the initial stages of ALD had not been addressed until very recently. Investigations into the initial nucleation and growth as well as the atomic structure of the heterointerface are crucial to optimize the ALD process and understand the structure–property relationships for ZnO. We have used a complementary suite of in situ synchrotron x-ray techniques to investigate both the structural and chemical evolution during ZnO growth by ALD on two different substrates, i.e., SiO2 and Al2O3, which led us to formulate an atomistic model of the incipient growth of ZnO. The model relies on the formation of nanoscale islands of different size and aspect ratio and consequent disorder induced in the Zn neighbors’ distribution. However, endorsement of our model requires testing and discussion of possible alternative models which could account for the experimental results. In this work, we review, test, and rule out several alternative models; the results confirm our view of the atomistic mechanisms at play, which influence the overall microstructure and resulting properties of the final thin film.

Al2O3 thin films with thickness between 2 and 100nm were synthetized at 250°C by thermal atomic layer deposition on silicon substrates. Characterizations of as-deposited and annealed layers were carried out using ellipsometry, X-ray reflectivity, and X-ray photoelectron spectroscopy. A silicon-rich SiOx layer at the interface between Si and Al2O3 was introduced in the optical models to fit the experimental data. Surface passivation performances of Al2O3 layers deposited on n-type float-zone monocrystalline silicon were investigated as a function of thickness and post-deposition annealing conditions. Surface recombination velocity around 2cm.s−1 was measured after the activation of the negative charges at the Si/Al2O3 interface under optimized annealing at 400°C for 10min. The evolution of the interface layer and of the material properties with the thermal treatment was studied.

A complementary suite of in situ synchrotron X-ray techniques is used to investigate both structural and chemical evolution during ZnO growth by atomic layer deposition. Focusing on the first 10 cycles of growth, we observe that the structure formed during the coalescence stage largely determines the overall microstructure of the film. Furthermore, by comparing ZnO growth on silicon with a native oxide with that on Al2O3(001), we find that even with lattice-mismatched substrates and low deposition temperatures, the crystalline texture of the films is dependent strongly on the nature of the interfacial bonds.

The growth of zinc oxide thin films by atomic layer deposition is believed to proceed through an embryonic step in which three-dimensional nanoislands form and then coalesce to trigger a layer-by-layer growth mode. This transient initial state is characterized by a poorly ordered atomic structure, which may be inaccessible by X-ray diffraction techniques. In this work, we apply X-ray absorption spectroscopy in situ to address the local structure of Zn after each atomic layer deposition cycle, using a custom-built reactor mounted at a synchrotron beamline, and we shed light on the atomistic mechanisms taking place during the first stages of the growth. We find that such mechanisms are surprisingly different for zinc oxide growth on amorphous (silica) and crystalline (sapphire) substrate. Ab initio simulations and quantitative data analysis allow the formulation of a comprehensive growth model, based on the different effects of surface atoms and grain boundaries in the nanoscale islands, and the consequent ...

Boron Nitride is a promising group 13–group 15 compound material that exhibits various interesting properties like wide band gap, chemical stability, attractive mechanical properties and other. The growth behavior of this material has not been investigated in sufficient details to tailor properties of the resulting films. In this work we present the results on the growth of turbostratic boron nitride (t‐BN) thin films at a relatively high growth rate of 3 μm/h with the aim to investigate the potential use of boron trichloride in combination with ammonia as precursors for growth. Deposition experiments were conducted in a vertical cold wall high temperature chemical vapor deposition reactor in the temperature range 1000°C–1700°C depending on the substrate used. Templates of w‐AlN (0001), 4° off‐cut 4H‐SiC (0001), Cr (110) and W (110) were employed as substrates for the BN growth. As‐grown BN layers were characterized by Scanning Electron Microscopy, X‐Ray Diffraction, Electron Diffraction and Raman Spectroscopy. The results indicate that temperature and N/B ratio have a great influence on the crystallinity of the deposited films. For AlN and SiC substrates, a temperature of 1600°C and N/B ratio in range between 3 and 7.5 were identified as the best parameters for the growth of a 2 μm thick t‐BN layer with a spacing between basal planes of about 3.36 Å compare to the 3.33 Å spacing between basal planes of hexagonal or rhombohedral BN (h‐BN or r‐BN). For Cr and W substrates which have a lower mismatch with h‐BN (1 and 8.8 %), layers of t‐BN were deposited at much lower temperature (1000°C–1150°C) with a spacing between basal planes of 3.5 Å and morphology similar to that observed on SiC substrates. We obtained t‐BN layers with in plane strong disorder but out of plane orientation (c‐axis normal to the surface).

The impact of the carbon structure, the aging protocol, and the gas atmosphere on the degradation of Pt/C electrocatalysts were studied by electrochemical and spectroscopic methods. Pt nanocrystallites loaded onto high-surface area carbon (HSAC), Vulcan XC72, or reinforced-graphite (RG) with identical Pt weight fraction (40 wt %) were submitted to two accelerated stress test (AST) protocols from the Fuel Cell Commercialization Conference of Japan (FCCJ) mimicking load-cycling or start-up/shutdown events in a proton-exchange membrane fuel cell (PEMFC). The load-cycling protocol essentially caused dissolution/redeposition and migration/aggregation/coalescence of the Pt nanocrystallites but led to similar electrochemically active surface area (ECSA) losses for the three Pt/C electrocatalysts. This suggests that the nature of the carbon support plays a minor role in the potential range 0.60 < E < 1.0 V versus RHE. In contrast, the carbon support was strongly corroded under the start-up/shutdown protocol (1.0 < E < 1.5 V versus RHE), resulting in pronounced detachment of the Pt nanocrystallites and massive ECSA losses. Raman spectroscopy and differential electrochemical mass spectrometry were used to shed light on the underlying corrosion mechanisms of structurally ordered and disordered carbon supports in this potential region. Although for Pt/HSAC the start-up/shutdown protocol resulted into preferential oxidation of the more disorganized domains of the carbon support, new structural defects were generated at quasi-graphitic crystallites for Pt/RG. Pt/Vulcan represented an intermediate case. Finally, we show that oxygen affects the surface chemistry of the carbon supports but negligibly influences the ECSA losses for both aging protocols.

Thermal Atomic Layer Deposition was used to deposit Al2O3 layers with thickness ranging from 2 to 100nm for surface passivation of silicon solar cells. Various characterization techniques were used to evaluate the chemical, physical and optical properties of the layers and interfaces. Minority carrier lifetime around 2ms was measured for an optimal thickness of 15nm for as-deposited layers on high resistivity n-type silicon substrate. An annealing step at 400°Cincreases lifetime up to 5.7ms for the same structure.

Abstract AISI 441 ferritic stainless steel is a good candidate for metallic interconnects of solid oxide fuel cells (SOFCs). In this alloy, the minor elements Ti and Nb are used to stabilise the ferritic structure but their influence on steel durability is not well understood. This study focuses on the early stages of oxidation (24 h) at 800°C of AISI 441 under 5%H2O in O2 following the cathodic SOFCs conditions. The typical duplex oxide scale, composed of a (Mn,Cr)3O4 spinel top layer and a Cr2O3 rich sublayer is observed, with oxide nodules growing in places. These objects, in the micrometre range in size, are studied by FIB tomography. The analyses reveal a complex structure and a development strongly linked to the presence of niobium and/or titanium compound(s) in the subjacent substrate.