C. Sella

Preparation, characterization and properties of sputtered electrochromic and thermochromic devices

Abstract The interest in electrochromic materials has increased in the last few years because of their applications in a wide variety of optical modulation devices including smart windows for solar control in the architectural and automotive sectors and flat panel displays. Thermochromic coatings which reduce the transmission of solar energy as the temperature rises can prevent overheating and find application in the thermal control of buildings, satellites and spatial equipements. This article reports on the optical and structural properties of RF sputtered thin films of WO 3 and VO 2 for electrochromic and thermochromic devices.

Structural and magnetic properties of Fe/Ni and Fe/Co multilayers

Fe/Ni and Fe/Co multilayers (ML) have been deposited by dc triode sputtering, with a layer thickness (t) in the range 1–10 nm. For t≳4 nm both metals are in crystalline form (bcc Fe, fcc Ni, hcp Co). For t<2 nm one has a single‐phase structure (fcc in Fe/Ni ML, bcc in Fe/Co ML) which can be explained by assuming the presence of a 1‐nm‐thick mixed layer at the interfaces. This interfacial mixing affects the magnetic properties. The basic difference between the two systems is the fact that while Fe‐Ni interfacial alloys are magnetically soft those of Fe‐Co are hard which leads to different magnetic behavior. Furthermore, the Fe layers are better crystallized in our samples than those prepared by rf magnetron or ion‐beam sputtering.

Corrosion resistance of amorphous hydrogenated SiC and diamond-like coatings deposited by r.f.-plasma-enhanced chemical vapour deposition

Abstract This paper reports on the properties and corrosion resistance of amorphous hydrogenated carbon and amorphous hydrogenated SiC films deposited by r.f.-plasma-enhanced chemical vapour deposition at low temperatures (below 200 °C). SiC coatings were prepared from SiH 4 -CH 4 gas mixtures. Hydrogenated diamond-like coatings were deposited from classical CH 4 -H 2 mixtures. The influence of various deposition parameters was investigated. Microstructural and mechanical properties of the films were studied (density, hydrogen content, nanohardness, internal stress, critical load and friction coefficient). Two examples of corrosion resistance are given: (1) the corrosion resistance and biocompatibility of SiC and diamond-like coatings deposited on metal implants (Ti alloy) (the corrosion resistance is evaluated through potentiodynamic polarization tests in biological media; the biocompatibility of coated and uncoated metals is compared using differentiated human cell cultures); and (2) the corrosion resistance of SiC-coated magnesium in chloride-containing boric borate buffer at pH=9.3 evaluated from anodic polarization curves and scanning electron microscopy studies.

Low cost selective absorber based on a FeAl2O3 cermet film

Abstract The absorber-reflector tandem configuration is used for the realization of a selective absorbing surface for the photothermal conversion of solar energy. The infrared reflector consists of a stainless steel substrate, covered or not with a W or Mo thick film. The visible absorbing function is realized by a thin, low cost, FeAl2O3 cermet film. The cermet films are prepared by rf cosputtering onto a rotating stainless steel substrate. The target consists of a circular Al2O3 plate covered with small discs, the concentration varying with the Fe disc number. The optical properties of the thin FeAl2O3 films are studied as a function of the Fe volume fraction from 0.2 to 0.9. The dielectric function is calculated from the reflectivity and transmittivity measurements in the 300–50000 nm spectral range. The films exhibiting the required selective properties (high absorptivity in the visible, high transparency in the infrared) are selected. A sandwich, composed of a thin Al2O3 antireflecting film, the cermet film (with adequate thickness and composition) and the reflecting substrate, exhibits a good selectivity for the photothermal conversion at low and middle temperatures ( α = 0.95; e(300 K ) = 0.06; e(700 K ) = 0.14 ).

Microstructure and growth mechanism of Pt Al2O3 co-sputtered nanocermet films studied by SAXS, TEM and AFM

The physical properties of nanocermets are related mostly to their morphology. In this contribution, we present the microstructural and morphological evolution of co-sputtered Pt Al2O3 granular films with thickness, metal concentration and thermal annealing. These investigations are achieved by grazing angle X-ray reflectometry, transmission electron microscopy and atomic force microscopy. The experimental results show that (i) the diameter of platinum clusters increases as a function of film thickness, annealing temperature and metal concentration and (ii) a columnar growth is observed whose morphology also depends on the previous parameters and on the growth direction.

Magnetic studies in multilayer Ni‐C films

Multilayer Ni‐C films have been prepared using dc triode sputtering with a fixed C layer of 2 nm thick and with a Ni layer varying from 3 to 10 nm thick. The C layer is amorphous and the structure of the Ni layer is hexagonal for 3 nm thick but becomes fcc when the thickness is above 6 nm. The magnetization is strongly reduced which is attributed to the presence of nonmagnetic layers at each interface. These layers could be Ni3C. FMR indicates an easy perpendicular axis for t(Ni)>20 nm, but for t(Ni)<7 nm, the films develop an easy plane anisotropy. The Hc and the linewidth increases for t(Ni)<7 nm. Annealing at 473 K in vacuum leads to an increase in 4πM, indicating that C atoms are segregating out of the Ni layer and that the Ni film crystallizes better. The perpendicular anisotropy also develops strongly after annealing. The results are discussed.

PtAl2O3 selective absorber coatings for photothermal conversion up to 600°C

Abstract PtAl 2 O 3 cermet films (Pt volume fraction 0.18–0.53) have been deposited on optically polished glass substrates by co-sputtering using composite targets. The optical transmittance and reflectance in the range 300–3000 nm and the electrical conductivity have been measured. The electrical percolation and the optical cross over occur around 0.43 Pt volume fraction. Cermet films with a composition close to this percolation threshold show a good solar spectral selectivity which can be improved when they are overcoated by an Al 2 O 3 film. Solar absorptances greater than 0.95 and emittances of about 0.14 have been obtained. These selective absorbers deposited on stainless steel show a good stability up to 400°C in air. Between 400 and 600°C, the diffusion of certain elements of the substrate into the coating and their oxidization contribute to the degradation of the optical properties. Coatings deposited on iron, nickel, cobalt base superalloy substrates are stable over 600°C and appear to be attractive for collector applications operating at high temperatures and under a high concentration of solar flux.

Differences in the optical and photoelectrochemical behaviours of single-crystal and amorphous ferric oxide

Abstract The photoelectrochemical properties of n-type semiconducting ferric oxide (Fe2O3) were investigated using samples prepared by two different techniques: a flux-grown single crystal and a sputtered compound were used as electrodes in a photoelectrochemical cell. The transition mode, the band gap and the flat-band potential were determined by studying the photocurrent and the impedance of the electrode. The results show that the photoelectrochemical behaviours of the two compounds are very different.

Structural and magnetic properties of the Ti/Fe multilayers

The structure and magnetic properties of the rf-sputtered Fe/Ti multilayers with the fixed Ti-layer thicknesses (series 1: tTi=1 nm and series 2: tTi=2 nm) and the variable Fe-layer thicknesses (1 nm⩽tFe⩽6 nm) have been studied by the high-angle x-ray diffraction, transmission electron microscopy, conversion electron Mossbauer spectrometry and vibrating sample magnetometer. The results show that Fe layers with thicknesses less than 1 nm are alloyed forming an amorphous TiFe2 phase. As the Fe-layer thickness increases, the iron-rich crystalline Fe–Ti alloy is formed at the interface and, finally, the pure crystalline α-Fe and Ti layers appear in the center of the individual subsystems. The spin orientation in Fe layers is then strongly aligned in the film plane. However, in the interfacial region, perpendicular spin orientation is evidenced. This perpendicular magnetic anisotropy is associated to the Fe-rich alloy at the interface and is discussed in terms of reduced symmetry effects on the band structure ...

Structural investigation of Pt–Al2O3 co-sputtered nano-cermet films studied by small angle X-ray scattering, grazing angle X-ray reflectometry, TEM and AFM

Abstract The physical properties of nanocermets are related mostly to their morphology. In this contribution, we present the microstructural and morphological evolution of co-sputtered Pt–A1 2 O 3 granular films with thickness, metal concentration and thermal annealing. These investigations are achieved by grazing angle X-ray reflectometry (GAXR), small angle X-ray scattering (SAXS), transmission electron microscopy and atomic force microscopy. The experimental results show that: (1) the diameter of platinum nanoparticles increases as a function of film thickness, annealing temperature and metal concentration; and (2) a columnar growth is observed whose morphology is depending also on the previous parameters and on the growth direction.