Modified numerical method for thin film thermal conductivity calculation with micro-raman spectroscopy

Thin film materials have recently drawn a great attention for their wide range of applications in nano- and micro-scale devices. To overcome thermal issues associated with these devices, thin film materials must be thermally characterized since they do not have the same thermal properties as their bulk counterparts. Various analytical and experimental techniques are used to find thin film thermal conductivities. Micro-Raman spectroscopy is a preferred technique among other optical thermal conductivity measurement techniques due to its non-destructive and non-contact nature. However, the thermal size effects originating from both localized heat generation from Raman laser and phonon scattering at boundaries cause erroneous estimation of the thermal conductivities with the current methods. In this study, the gray phonon Boltzmann transport equation (BTE) is used to simulate the real conditions during the Raman experiment. Thermal conductivities from the developed virtual Raman experiment are then compared with a simple slab model in which the deduction of thermal conductivity in sub-micron thicknesses is calculated using the reduced BTE heat flux through the slab, resulting from phonon directional energy densities. Due to the frequency independence of single phonon mode in the gray BTE model, our method stays ahead of most theoretical methods in calculation time while giving adequate agreement with the literature data. The results show that the results from the developed model are in a good agreement with the slab model results as well as literature values.