Advances in thermal wave based microscopy

Abstract
We analyze the dependence of ac signal obtained in scanning thermal microscopy (SThM) using a Wollaston thermal probe, on thermophysical properties of the sample. The amplitude and phase sensitivities to the specific heat c and to thermal conductivity k of the sample are computed with a finite element software, in a range of k values from 0.18 Wm^-1K^-1 (typical insulator, PMMA) to k=2200 Wm^-1K^-1 (diamond). We find that the SThM signal is sensitive only to k, to an extent that favors insulating materials. Moreover, the signal is sensitive at least to the same extent to the tip/sample thermal resistance, that reduces drastically the dynamic range. We define a crossover frequency separating two frequency ranges, isothermal and adiabatic. The model is validated by measuring temperature profiles along an upscaled wire, using a thermographic camera and lock-in image processing.