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Abstract: Thermochromic films of VO2 were deposited by DC reactive magnetron sputtering on stainless steel substrate. Complex refractive indexes of VO2 were determined by ellipsometric spectroscopy (0.35–16.5μm) for different film thicknesses. Optical simulations were performed to model the spectral reflectance of the film/substrate system for a film thickness of 100nm and 200nm and to monitor the optical contrast of the thermochromic layers by comparing the spectral reflectance at 25°C and 100°C. The good agreement observed between experimental and theoretical spectra demonstrates the adequacy of the model for predicting the optical properties of the samples. [Copyright &y& Elsevier]

The growth of hydrogenated amorphous carbons (a-C:H) produced by continuous or pulsed discharges of acetylene (C(2)H(2)) in an unbalanced magnetron setup was investigated. At 5 × 10(-3) Torr, only smooth films are obtained, whereas at 5 × 10(-1) Torr using a pulsed discharge some microtextured films are formed if the duty cycle is low. The morphology of these microtextured films consists of nanoparticles, filamentary particles, and particular agglomerates ("microflowers"). This paper presents a study of acetylene gas phase polymerization by mass spectrometry, and a detailed analysis of bulk structure of films by combining three techniques which include IR spectroscopy, Raman spectroscopy, and laser desorption/ionization Fourier transform mass spectrometry (LDI-FTMS). Finally, based on the study of gas phase and film structure, we propose a model for the growth of both smooth and microtextured films.

Thin films deposited on silicon substrate by three different methods of plasma polymerization of acetylene were analyzed by direct laser desorption/ionization Fourier transform mass spectrometry. High-resolution mass spectra showed the presence of carbon clusters and hydrocarbon oligomers in different relative abundances. During unipolar and continuous discharge polymerization of acetylene-hydrogen gas mixtures, quadrupole mass spectra of the plasma constituents showed the presence of molecular species with m/z lower than 100--mainly peaks of C(4)H(2) and C(6)H(2). Films produced had smooth surfaces and the corresponding LDI-FTMS spectra displayed only carbon cluster signals in the positive ion mode and both hydrocarbon and carbon cluster signals (with much higher relative abundance of carbon cluster signals) in the negative ion mode. Alternatively, during bipolar discharge with either higher acetylene gas flux (>40 cm(3)/min) or longer deposition times (>10 min), quadrupole mass spectra of the plasma constituents showed signals corresponding to polycyclic aromatic hydrocarbons (PAH) with m/z higher than 100. SEM pictures of the bipolar thin films demonstrated the presence of "flower" structures and nanoparticles developed on the surface. LDI-FTMS spectra of such thin films showed either total absence or lower relative abundance of carbon cluster signals, compared with hydrocarbon signals., (Copyright 2010 American Society for Mass Spectrometry. Published by Elsevier Inc. All rights reserved.)