CVD of Thin Ruby Films on Si(100) and Stainless Steel for Surface Temperature Sensor Applications
Surface temperature measurements are crucial in many applications; one promising approach is the use of thermographic phosphors. The temperatures of surfaces coated with such a material can easily be detected by measuring and evaluating the luminescence. In the present study, the CVD of chromium-doped aluminum oxide films (ruby) on Si(100) and stainless steel substrates is investigated with respect to this application. Films are deposited in a cold-wall reactor from oxygen and the acetylacetonates of aluminum and chromium under pressures between 200 hPa (200 mbar) and 240 hPa, and at temperatures between 1273 K and 1473 K. The growth of aluminum oxide, containing 1 % chromium, is confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) spectroscopy. While films grown at 1273 K are mainly γ-Al2O3 and θ-Al2O3, α-Al2O3 films are grown at higher temperatures. The films are analyzed by laser excitation with regard to the temperature-dependent luminescence. The films consisting of mainly α-Al2O3 are promising as temperature sensors, they show the typical phosphorescence of ruby, with phosphorescence lifetimes between 2.3 ms at 298 K and 6 μs at 813 K.
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