A microfabricated amorphous silicon nitride membrane-based nanocalorimeter is proposed to be suitable for an x-ray transparent sample platform with low power heating and built-in temperature sensing. In this work, thermal characterization in both air and vacuum are analyzed experimentally and via simulation. Infrared microscopy and thermoreflectance microscopy are used for thermal imaging of the sample area in air. While a reasonably large isothermal area is found on the sample area, the temperature homogeneity of the entire sample area is low, limiting use of the device as a heater stage in air or other gases. A simulation model that includes conduction, as well as radiation and convection heat loss, is presented with radiation and convection parameters determined experimentally. Simulated temperature distributions show that the homogeneity can be improved by using a thicker thermal conduction layer or reducing the pressure of the gas in the environment but neither are good solutions for the proposed use. A new simple design that has improved temperature homogeneity and a larger isothermal area while maintaining a thin thermal conduction layer is proposed and fabricated. This new design enables applications in transmission x-ray microscopes and spectroscopy setups at atmospheric pressure.

Thermoreflectance thermal imaging microscopy is based on very small change in the surface reflection as a function of temperature. Image shift and instrument drift are limiting factors to obtain accurate and reproducible thermal images. Under large magnification and for devices with sizes on the order of hundreds of nanometers, image registration could significantly encumber accurate thermoreflectance measurements. Additionally, image blurring is an issue because of small sample movements during the measurement. The problem of image registration and defocusing is particularly important during the calibration process to extract the thermoreflectance coefficient of the materials under study. Calibration requires changing the sample temperature with an external stage, which causes significant movement due to heat expansion from the stage. In this work, we discuss how the image registration and defocusing affect accurate measurement and calibration in thermoreflectance thermal imaging. We also show that by incorporating and controlling the position of the sample under test with a closed-loop piezo-stage one can perform accurate and reproducible thermal measurement. Using this setup, we measured the coefficient of thermoreflectance (CTR) of gold at several wavelengths and under different magnifications. We present for the first time thermoreflectance calibration of feature sizes below the diffraction limit, on the order of 200nm.

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