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.

Current societal challenges, such as climate change and resource depletion, highlight an unprecedented need for disruptive innovation in materials science. Significant breakthroughs are expected in multinary materials whose efficient exploration necessitates dedicated strategies. The exploration of a refractory high entropy alloy Nb-Ti-Zr-Cr-Mo is proposed here as test case for a new strategy. Based on the proven methodology of mixture design and on combinatorial thin film metallurgy, the composition space is explored by a limited number of chosen gradients to build an alloy library comprising hardness and ductility, two antagonistic properties. The workflow is showcased here by studying the properties of the as-grown graded film, which presents wide amorphous domains and contrasted mechanical properties. This experimental dataset then trains machine learning models to provide continuous predictions of the alloy properties over the entire composition space. We show that optimal alloy properties are expected close to the binary edges of the quinary.

This work investigates the 3C-SiC heteroepitaxial growth on silicon substrates having a wide variety of orientations, i.e. (100) on axis and 2°off, (111), (110), (211), (311), (331), (510), (553) and (995). All the 3C-SiC layers were grown using the same two-step CVD process with a growth rate of 2 μm/h. According to X-ray diffraction characterizations, direct heteroepitaxy (layer having exactly the same orientation as the substrate) was successful on most of the Si substrates except for (110) one which was the only orientation leading to obvious polycrystalline deposit. Each layer led to a specific surface morphology, the smoothest being the ones grown on Si (100)2°off, and (995) substrates. None of these layers cracked upon cooling though those grown on Si (111), (211) and (553) substrates were highly bowed.

Tantalum nitride (TaN) ultra-thin films deposited by Atomic Layer Deposition (ALD) are efficient diffusion barriers for copper interconnects embedded in silica matrix. The present paper reports a methodical investigation of the first stages of TaN ALD growth on either dense SiO2 or nanoporous SiOCH surfaces. The deposited TaNx phases, film microstructure, chemistry and resistivity were characterized at different steps of ALD growth (from 0 to 160 ALD-cycles). While a granular morphology combining orthorhombic-Ta3N5 (o-Ta3N5) and cubic-TaN (c-TaN) was obtained on SiOCH, a continuous film mainly composed of o-Ta 3 N 5 was found when deposited on dense SiO2. In both cases, TaNx films were not completely-crystallized. The electrical behavior is shown to be mainly driven by film morphology rather than by the intrinsic conductivity of the deposited phases. Growth modes on both surfaces are then discussed in terms of surface chemical reactivity: two growth timelines are proposed to explain the observed phenomena (film continuity, deposited phase, conductivity). As this methodical approach shows the major interest for a deposition on SiO2 substrate, a surface functionalization of SiOCH has also been performed. It was determined that a 3 nm-thick SiO2 layer capping the SiOCH surface is enough to recover the required properties for optimal TaN deposition.

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.

The deposition of epitaxial superconducting (Nb,Ti)N thin films is addressed with a new approach, using a chemical vapor deposition technique with in situ production of precursors. Both classic and reactive CVD process are optimized toward (i) the control of crystal structure of the deposited films and (ii) the control of stoichiometry and thus of superconducting properties. Films are chararcterized using thermodynamic, structural, and electrical characterization tools. Precession electron diffraction and electron backscatter diffraction techniques provide the phase and orientation mapping of the films down to the nanometer scale. We demonstrate that the cubic phase (structure with the most prominent superconducting properties) is the thermodynamically stable phase under classic CVD from 800 degrees C up to 1300 degrees C. The hexagonal (Nb,Ti)N is formed via a "nitridation like" process under reactive CVD, up to 1200 degrees C. The composition of the films is controlled by the chemistry of the gas phase, whereas the thickness is regulated down to less than 10 nm due to the low growth rate that can be achieved. This technique allows for the control of the superconducting properties of the films, through the control of Ti composition.

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).

Undoped and nitrogen doped TiO2 thin films were deposited by atomic layer deposition on planar substrates. Deposition on 3D-architecture substrates made of metallic foams was also investigated to propose architectured photovoltaic stack fabrication. All the films were deposited at 265 °C and nitrogen incorporation was achieved by using titanium isopropoxide, NH3 and/or N2O as precursors. The maximum nitrogen incorporation level obtained in this study was 2.9 at. %, resulting in films exhibiting a resistivity of 115 Ω cm (+/−10 Ω cm) combined with an average total transmittance of 60% in the 400–1000 nm wavelength range. Eventually, TiO2 thin films were deposited on the 3D metallic foam template.

A simple method to produce biobased iridescent pigments from cellulose nanocrystal (CNC) films is reported. The process consists of forming nanostructured films from a CNC liquid-crystalline suspension and an appropriate dry grinding. The features of the iridescent pigments are described; they have a flake-like morphology with a thickness of 25 μm. However, because of the presence of sulfate groups, thermal degradation and high redispersion in water occur, which affect the iridescent property of these biobased pigments. To overcome such limitations, two post-treatments are proposed. The sulfate ester groups are removed from the iridescent pigments with vacuum overdrying. The mass loss of iridescent pigment in water is reduced with an increase of the ionic strength in the aqueous medium by NaCl addition. These post-treatments have proven to be efficient and engineered pigments based on CNC films can be used to add anticounterfeiting features to packaging manufactured by classical paper techniques or extrusion.

Synthesis of thin niobium nitride (NbN) layers by High Temperature Chemical Vapor Deposition (HTCVD) is presented and the crystallographic orientations are investigated during heteroepitaxial growth on (0001)Al2O3, (0001)AlN template and 112¯0Al2O3. The HTCVD NbN layers are ex-situ characterized by means of X-ray diffraction (XRD) methods, Raman spectroscopy and Transmission Electron Microscopy (TEM). Depending on the deposition temperature, hexagonal NbN or fcc (face-centered cubic) δ-NbN is obtained. Orientation relationships between the fcc δ-NbN layer with respect to the substrates are given. We discuss the role of an AlN layer as a possible protective layer of the sapphire for the synthesis of fcc δ-NbN.

AlN epilayers were grown on c-plane Sapphire substrates using High Temperature Halide Chemical Vapor Deposition (HTCVD). Introduction of low temperature nucleation layers (NLs) prior to the high temperature AlN (HT-AlN) layers was investigated. It was found that NLs stabilizes the epitaxial growth. NL deposition conditions were optimized to improve the quality of AlN epilayers. Increasing nucleation layer deposition temperature from 650 to 850 degrees C as well as the growth temperature of AlN epilayers from 1200 to 1400 degrees C improves the structural quality and surface morphology. X-ray diffraction of theta/2 theta scan confirms that AlN layers deposited on NLs are (0002) oriented and X-ray rocking curve measurement shows FWHM values as low as 864 arcsec for (0002) plane. Surface steps and specular morphology were observed for such AlN epilayers. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

There is a growing interest in producing tantalum nitride (TaN) thin films for various industrial applications. For example, in microelectronics, the development of IC technology is driven by the need to increase both performance and functionality while reducing power and cost. This goal can be achieved by several solutions among which the introduction of architecture enhancements such as 3D integration. The most challenging step is the deposition of a conformal, continuous, and adherent diffusion barrier. In this work, atomic layer deposition (ALD) of TaN thin films is explored using the combination between the thermodynamical behavior of the precursor, mass transfer in the reactor, and the operating conditions. TaN thin film deposition on very complex shape substrates, such as nanodots, TSV, silicon nanowires, and carbon nanotubes, has been evaluated.

Austenite/ferrite phase transformations in Fe-xCu-10Ni alloys, 0<x<15 (mass%), are studied under two different cooling conditions, ice-brined quenching or slow cooling in the dilatometer. The influence of copper addition and cooling rate on the microstructure of the alloys is studied. Metallographic examinations of quenched samples show that metastable transformations occur during cooling. As for Fe-Ni alloys, it is impossible to stabilize the high temperature phase (γFeNi) in the Fe-Ni-Cu alloys. Dilatometry measurements of the γ → α transformation temperature with a cooling rate of 2°C/min also indicate a metastable phase formation despite the low cooling rate. For all alloys, a mixture of massive and lath ferrite is observed, one being predominant depending on the cooling conditions and composition. It is shown that the cooling rate has nearly no influence on the microstructure of alloys with a small amount of Cu unlike the alloys containing more Cu. In all alloys containing Cu, nanometric γCu precipitates, much finer in the quenched samples, are detected in the ferrite grains.

The photochemical reduction of metal precursors under UV light has been studied to produce noble metal nanoparticles. Depending on the metal (Pt, Au or Ag) and precursor (chlorinated or nitrate) natures, different 1-step or 2-step photolytic or photocatalytic reduction mechanisms have been investigated. These mechanisms yield simple all-inorganic methods to generate metal nanoparticles in liquid medium and disperse these particles at the surface of various kinds of supports. Depending on the metal particle and support natures, different functionalities can arise from such easy and low-cost photometallisation methods.