Synthesis And Heat Transport Properties Of Reduced Graphene Oxide Films

Graphene sheets, a new class of atom thick two-dimensional (2D) carbon nanostructure, possess excellent thermal conductivity, high mechanical properties and low density, which is very promising for heat management applications in micro-devices. Although there are many reports on the intrinsic thermal conductivity of graphene, few work has been done on thermal transport properties of the films assembled by the graphenes. It is urgent to investigate the controllable preparation, heat transport properties of graphene-based films for their applications as heat dissipation materials in the microelectronic devices.In this work, graphene oxide (GO) was prepared by a modified Hummers method, and free-standing GO films were fabricated by vacuum filtration. The effects of reduction methods and addition of carbon nanotubes on the microstructure and thermal conductivity of the reduced graphene oxide (RGO) films were investigated.(1) The GO films were reduced by three reduction methods to form free-standing RGO films:HI acid, thermal annealing by sandwiched between two stacked Si wafers and two-step (HI acid reduction followed by thermal annealing). The orientation degree and the density of GO films after reduction is decreased caused by the generated interspaces in the RGO films. The thermal conductivity of the GO films after reduction is enhanced due to the increase in the content of nonoxygenated carbon, which can achieve 373 W/mK.(2) The GO films were thermally reduced by a hot-pressing technique. The obtained RGO film maintains the original high flexibility and integrity, and even has improved ductility and strength. The pole figures show that the orientation degree of GO film after reduction is enhanced and is increased with the increasing of the pressure. The XRD measurements show that the d-spacing (d002) is decreased and the average graphite-like domains height (Lc) is increased after reduction, and the higher pressure lead to smaller d002 and larger Lc. The density and the in-plane thermal conductivity of the GO film after reduction can achieve 1.96 g/cm3 and 2423 W/mK, respectively.(3) The carbon nanotubes (CNTs)/GO composite films were fabricated by vacuum filtration, and the effects of addition of carbon nanotubes (CNTs) on the microstructure and thermal conductivity of the RGO films were investigated. It is found that the CNTs are severely aggregated in the GO films, resulting no significant positive impact on the thermal conductivity of the resultant RGO films.