Optical temperature measurements on thin freestanding silicon membranes

We report on a contactless, all-optical method to derive thermal properties of 340 nm thin, 640×640 μm(2) wide, freestanding silicon membranes. Exploiting the temperature dependent optical transmissivity of 4×10(-3)/K between 300 and 470 K, we are able to measure the temperature of the membrane with millikelvin thermal, micrometer lateral, and nanosecond temporal resolution. Experiments such as the decay of a transient thermal grating with spacings between 5 and 30 μm, measured in first order of diffraction, as well as heat diffusion in a statically heated membrane are reported in this letter. For the latter case an example of a nanostructured membrane by means of focused ion beam milling is given.