A novel high resolution contactless technique for thermal field mapping and thermal conductivity determination: Two-Laser Raman Thermometry

摘要

We present a novel high resolution contactless technique for thermalconductivity determination and thermal field mapping based on creating athermal distribution of phonons using a heating laser, while a second laserprobes the local temperature through the spectral position of a Raman activemode. The spatial resolution can be as small as $300$ nm, whereas itstemperature accuracy is $\pm 2$ K. We validate this technique investigating thethermal properties of three free-standing single crystalline Si membranes withthickness of 250, 1000, and 2000 nm. We show that for 2-dimensional materialssuch as free-standing membranes or thin films, and for small temperaturegradients, the thermal field decays as $T(r) \propto ln(r)$ in the diffusivelimit. The case of large temperature gradients within the membranes leads to anexponential decay of the thermal field, $T \propto exp[-A \cdot ln(r)]$. Theresults demonstrate the full potential of this new contactless method forquantitative determination of thermal properties. The range of materials towhich this method is applicable reaches far beyond the here demonstrated caseof Si, as the only requirement is the presence of a Raman active mode.