Effect of Non linearity Between Raman Shift and Laser Power on the Thermal Conductivity of Graphene Measured by Micro-Raman Spectroscopy

Confocal micro-Raman spectroscopy has been demonstrated to be an efficient method for the measurement of the thermal conductivity of graphene. It relies on the experimentally established near-linear dependence of the Raman peak shift on temperature. In earlier literature studies, the magnitude of the thermal conductivity was determined directly from the experimental data of the Raman peak shift as a function of the power of the laser. On the basis of the general principles of heat transfer at the continuum level we suggest that as the direct result of graphene's strongly negative temperature-dependent thermal conductivity, the temperature and associated Raman peak shift at the sample's center where the measurements are made should exhibit a strongly nonlinear, rather than a linear, dependence on the power of the laser. Such non-linearity was demonstrated analytically for the general experimental conditions encountered in practice. A reassessment of a set of literature data to take this effect into account indicated that the thermal conductivity values for single-layer graphene at or near ambient temperatures could be some 40% higher than those originally reported.