Fabien Capon

On the deactivation of the dopant and electronic structure in reactively sputtered transparent Al-doped ZnO thin films

We report on the possible origin of electrical heterogeneities in 4 at% Al-doped ZnO (AZO) reactively sputtered films. It is found through the Zn L3 and Al K edge x-ray absorption near-edge structure that a fraction of the Al dopant is deactivated by its positioning in octahedral conformation with oxygen. This fraction as well as the conductivity, optical bandgap and c-axis parameter of ZnO wurtzite are all found to depend on the sample position during deposition. The present results suggest the formation of a metastable Al2O3(ZnO)m homologous phase that degrades the electrical conductivity.

Thermochromic effect in NdNiO3−δ thin films annealed in ambient air

The synthesis of NdNiO3 perovskite structure was achieved by soft post deposition annealing of initially amorphous thin films reactively sputter deposited on silicon substrates. The physical measurements were fully consistent with the properties expected for the thermochromic NdNiO3 phase. Upon heating, the optical transmission that was correlated with the electrical properties decreased in the infrared domain showing a thermochromic effect in this optical region. The metal–insulator transition temperature was found to be −68 °C for the specimen tested and the jump in resistance at the transition was 1.4 orders of magnitude. The state-of-the-art methods that normally involve an annealing at a high oxygen pressure (200 × 105 Pa) or epitaxial stabilization were considerably improved in this work by the use of dc sputtering and the optimization of the deposition conditions. Therefore, the novel soft process proposed here opens up numerous research possibilities.

Cation size effect on the thermochromic properties of rare earth cobaltites RECoO3 (RE: La, Nd, Sm)

RECoO3 (RE: rare earth) perovskite thin films have been deposited at room temperature by direct current co-sputtering and subsequent annealing in air at 923 K during 1 day. The effect of the octahedra tilts on the optical properties has been tracked decreasing the RE cation size. The bending and stretching vibrational modes of the CoO6/2 octahedra give information on the Co–O distances and the Co–O–Co angles which determine the Co–O overlap integral and hence the electric properties of these perovskites. Transmittance measurements in the 1.42–100 μm wavelength range show a high transparency at room temperature. When temperature increases, an optical screening effect depending on the RE3+ ionic radii (i.e., Co-O-Co angles) and resulting from the electrical behaviour occurs. At the wavelength of 8 μm, the transmittance drops from about 90% at room temperature to 50% at the temperature of 516, 600, and 640 K for LaCoO3, NdCoO3, and SmCoO3, respectively.

Thermochromic effect at room temperature of Sm0.5Ca0.5MnO3 thin films

Sm0.5Ca0.5MnO3 thermochromic thin films were synthesized using dc reactive magnetron co-sputtering and subsequent annealing in air. The film structure was studied by x-ray diffraction analysis. To validate the thermochromic potentiality of Sm0.5Ca0.5MnO3, electrical resistivity and infrared transmittance spectra were recorded for temperatures ranging from 77 K to 420 K. The temperature dependence of the optical band gap was estimated in the near infrared range. Upon heating, the optical transmission decreases in the infrared domain showing a thermochromic effect over a wide wavelength range at room temperature.

Hyperspectral imaging as an analytical tool for thin single and multilayer oxides characterization: A laboratory study

Characterization of deposited thin oxide layers using conventional laboratory techniques such as ellipsometry and Fourier transform infrared spectroscopy (FTIR) requires long sampling time. The hyperspectral technology with a high acquisition rate appears to be an interesting solution for high throughput quantification. To check its capability for this purpose, we develop an analysis protocol in the laboratory using this device to measure thin oxide layers. In this paper we study the acquisition setup regarding the incidence angle in reflection mode, the relation of layer thickness and measured signal to enable the quantification and identification of deposited Al2O3 and SiO2 thin films. Analysis results from FTIR, hyperspectral camera and ellipsometry are presented along with calculations based on Fresnel equations. Measured results correspond with the expected theoretical spectra. The study of the detection sensitivity also extends to multilayer oxide. Overall, the capability of the hyperspectral camera to detect nanometric oxide layers is demonstrated. With this conclusion and in combination with its many advantages, the hyperspectral camera could be used for dynamic analysis of oxide layer.

Evolution of structural and physical properties upon annealing of sputter-deposited Zr0.84Y0.16-O2 films incorporating copper and palladium nanoparticles

Me-incorporated Zr0.84Y0.16 oxide thin films (Me: Cu or Pd) were synthesized by magnetron co-sputtering. The film structural evolution due to metal content increase was shown: Me-doped nanocrystalline yttria stabilized zirconia (YSZ); Me-doped amorphous oxide; metal nanoparticles embedded in the amorphous oxide matrix. Annealing for 2 h at 300°C in air promoted copper oxide formation and the segregation of very fine Pd particles. XANES analysis at the Cu-K edge showed that Cu is bonded to oxygen and Zr(Y) in Cu-doped amorphous oxide; this state was not affected by the thermal treatment. XANES and resistivity analyses indicated that the Cu nanoparticles likely have oxidized surfaces while the Pd-containing films showed only minor chemical changes after annealing.