CVD of Thin Ruby Films on Si(100) and Stainless Steel for Surface Temperature Sensor Applications

Abstract

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 c-Al 2 O 3 and h-Al 2 O 3 , a-Al 2 O 3 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 a-Al 2 O 3 are promising as temperature sensors, they show the typical phosphorescence of ruby, with phosphorescence lifetimes between 2.3 ms at 298 K and 6 ls at 813 K.

Probing and Controlling Photothermal Heat Generation in Plasmonic Nanostructures

“…For the measurements in this thesis, the second decay was the only decay time used to calculate temperatures. This is because the second decay gave more consistent results and its values more closely matched other ruby decay time measurements in literature [38][39][40] . At the time of this writing, it is not yet understood what mechanism causes the initial, faster decay.…”

“…TGPs are metal-doped ceramic materials whose photoluminescence decay time is temperature dependent 37 . These materials have long been used to probe temperatures through optical, non-invasive methods and are typically used in environments with moving surfaces, high temperatures, or where thermocouple attachment is difficult 37,38 .…”

“…The specific phosphor used in the experiments was ruby (Al 2 O 3 :Cr 3+ ). Ruby was chosen because of its excellent sensitivity over the experimental range and because its temperature dependent emission wavelength (694 nm) does not overlap the antenna resonant wavelength (1064 nm) [38][39][40] .…”

“…To reconstitute the α-Al 2 O 3 from the as-deposited Al 2 O 3 , the sample was thermally annealed at 1100° C for 2 hours. This was an important step in the process as the α-Al 2 O 3 has stronger photoluminescence properties than the asdeposited phase (Figure 17), and the α-Al 2 O 3 is the temperature dependent phase of the material 38 . The sapphire substrate was used to allow for perfectly matched thermal expansion coefficients between the film and substrate, thus minimizing film stress and cracking during the annealing process.…”

Two-dimensional cycle-resolved exhaust valve temperature measurements in an optically accessible internal combustion engine using thermographic phosphors

“…Although methods like chemical vapor deposition [15] or solgel-deposition [16] have the ability to produce very thin and homogeneous coatings, the complexity and limited size of the object of interest hinder the application at internal combustion engines. The coating process using a chemical binder involves the mixing of the phosphor powder with the binder and spraying it on the device to be tested via airbrush.…”