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

We present a novel contactless technique for thermal conductivity determination and thermal field mapping based on creating a thermal distribution of phonons using a heating laser, while a second laser probes the local temperature through the spectral position of a Raman active mode. The spatial resolution can be as small as 300 nm, whereas its temperature accuracy is +/- 2 K. We validate this technique investigating the thermal properties of three free-standing single crystalline Si membranes with thickness of 250, 1000, and 2000 nm. We show that for two-dimensional materials such as freestanding membranes or thin films, and for small temperature gradients, the thermal field decays as T(r) proportional to ln(r) in the diffusive limit. The case of large temperature gradients within the membranes leads to an exponential decay of the thermal field, T proportional to exp[ -A center dot ln(r)]. The results demonstrate the full potential of this new contactless method for quantitative determination of thermal properties. The range of materials to which this method is applicable reaches far beyond the here demonstrated case of Si, as the only requirement is the presence of a Raman active mode. (C) 2014 AIP Publishing LLC.