Extraordinary Thermal Conductivity of Graphene: Prospects of Thermal Management Applications

We have recently discovered experimentally that suspended graphene, which is an individual sheet of sp²-hybridized carbon bound in two dimensions (2D), reveal an extremely high thermal conductivity. The measurements were performed using a non-contact optical technique developed by us on the basis of Raman spectroscopy. A large number of graphene flakes were suspended across trenches in Si wafers and attached to heat sinks. The flakes were heated by the focused laser light in the middle of the suspended portion of graphene. The amount of laser power dissipated in graphene and corresponding local temperature rise were determined from the integrated intensity and spectral position of graphene’s Raman G mode. The position of the G peak as a function of the sample temperature was measured independently allowing the use of micro-Raman spectrometer as a “thermometer”. The experimental thermal conductivity values were in the range of ∼ 3000–5300 W/mK near room temperature (RT) and depended on the graphene flake sizes. The thermal conductivity of graphene is the highest among all materials known to date. In this review work we will describe the details of our measurement procedure and explain theoretically why the 2D thermal conductivity of graphene is higher than that of bulk graphite provided that the size of graphene flakes is sufficiently large. Our theory, which includes the phonon-mode dependent Gruneisen parameter and phonon scattering on edges and defects, gives results, which are in excellent agreement with the experiment. Superior thermal properties of graphene are beneficial for the proposed graphene electronic devices, and may pave the way for graphene’s thermal management applications.