Abstract. Optical properties of transparent polymer thin films, produced by spin-coating on silicon and constituted of polycarbonate ͑PC͒, poly͑methyl methacrylate͒ ͑PMMA͒, and PC/PMMA, were investigated with regard to integrated thermo-optical ͑TO͒ device applications. Refractive index dependences on wavelength, temperature, and film composition were measured by spectroscopic ellipsometry with a dedicated autocontrolled heater setup, in the ranges of 400 to 800 nm, 25 to 85°C and 0 to 100 wt % PC, respectively, with determination of Cauchy and Lorentz-Lorenz parameters. Within these intervals, thermomechanical compatibility and pronounced index contrast of around 0.12 between PC and PMMA, as well as their TO coefficients one order of magnitude higher than that of silica, allow convenient tailoring for specific TO requirements. In addition, wide-range fine-tuning of refractive index variation is found to be facilitated by the weak dependence of isothermal dispersion curves and TO coefficients on film composition.
Polytetrafluoroethylene (PTFE)-like films, produced by electron beam (e-beam) deposition, have shown higher hydrophobicity than those deposited by RF sputtering under similar deposition rates. It was found that this results from both surface chemical composition and nano-roughness. X-ray photoelectron spectroscopy measurements revealed that larger moieties of CF 2 and CF 3 groups were present to reduce surface energy in the e-beam deposited films. RF sputtering led to a higher degree of PTFE target fragmentation producing a different perfluorinated film on the Si substrate. Scanning electron microscopy and atomic force microscopy measurements revealed a much larger rms roughness on the film surfaces produced by e-beam (25.13 nm, at 20 mA) than those by RF sputtering (2.42 nm, at 100 W), and allowed a broad power spectrum density analysis with determination of the j B wetting parameter. In addition, the e-beam deposited films presented a linear increase of contact angle with applied electron current in the range under study (5-20 mA). This allows easy water repellency adjustment, up to 159 ± 2°. For a superhydrophobic state with self-cleaning, a micropyramid structure was wet etched on the Si wafer, followed by PTFE deposition, and a very low contact angle (163 ± 2°) and hysteresis was attained (\3°). These first results indicate that e-beam PTFE deposition with adjustable hydrophobicity may become a useful technique for integrated production with present Si microelectronics technology and for Si solar cells.
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