Interface Energy Coupling between β-tungsten Nanofilm and Few-layered Graphene

We report the thermal conductance induced by few-layered graphene (G) sandwiched between beta-phase tungsten (beta-W) films of 15, 30 and 40 nm thickness. Our differential characterization is able to distinguish the thermal conductance of beta-W film and beta-W/G interface. The cross-plane thermal conductivity (k) of beta-W films is determined at 1.69-2.41 Wm(-1)K(-1) which is much smaller than that of alpha-phase tungsten (174 Wm-1K-1). This small value is consistent with the large electrical resistivity reported for beta-W in literatures and in this work. The beta-W/beta-W and beta-W/G interface thermal conductance (G(W/W) and G(W/G)) are characterized and compared using multilayered beta-W films with and without sandwiched graphene layers. The average G(W/W) is found to be at 280 MW m(-2)K(-1). G(W/G) features strong variation from sample to sample, and has a lower-limit of 84 MW m-2K-1, taking into consideration of the uncertainties. This is attributed to possible graphene structure damage and variation during graphene transfer and W sputtering. The difference between G(2W/G) and G(W/W) uncovers the finite thermal resistance induced by the graphene layer. Compared with up-to-date reported graphene interface thermal conductance, the beta-W/G interface is at the high end in terms of local energy coupling.