We present a novel high resolution 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 $\pm 2$ 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 2-dimensional materials such as free-standing membranes or thin films, and for small temperature gradients, the thermal field decays as $T(r) \propto ln(r)$ in the diffusive limit. The case of large temperature gradients within the membranes leads to an exponential decay of the thermal field, $T \propto exp[-A \cdot ln(r)]$. 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.
Thermal analysis of GaN-based photonic membranes for optoelectronics
Universität Bremen（不来梅大学）；MAPEX Center for Materials and Processes, Universität Bremen（不来梅大学材料过程MAPEX中心）；Chalmers University of Technology（查尔姆斯理工大学）；Humboldt-Universität zu Berlin（柏林洪堡大学）；MIT-IBM Watson AI Lab, IBM Research（麻省理工学院-IBM沃森人工智能实验室，IBM研究部）；École Polytechnique Fédérale de Lausanne (EPFL)（洛桑联邦理工学院）
