Recently, the latest research results of the graphene research group of the Advanced Carbon Materials Research Department of the National Materials Research Institute of the Institute of Materials Science of the Chinese Academy of Sciences were published. The related paper was published online on February 16th in Nature-Communication.

Grain boundaries are ubiquitous defects in large-area graphene films prepared by chemical vapor deposition (CVD) methods. An in-depth understanding of the effects of grain boundaries on the electrical and thermal properties of graphene is important for the development of graphene-based electronic, optoelectronic and thermoelectric devices.

“Although the current research on the influence of single grain boundary on the properties of graphene is more, the influence of grain size on the electrical and thermal properties of graphene on the macroscopic scale is still unclear. The main reason is based on traditional precipitation (nickel matrix) or The CVD growth method based on the surface adsorption growth (copper matrix) mechanism cannot regulate the grain size of graphene in a wide range, and it is difficult to prepare small-grain graphene having a grain size smaller than the electron and phonon mean free path (about 1 μm). "The first author of the thesis, Ma Teng, a doctoral student at the Institute of Metals, told the Journal of the Chinese Academy of Sciences.

The graphene research group used a metal platinum plate with moderate carbon content as the growth matrix, and developed a CVD method based on the principle of “precipitation-surface adsorption growth”. The control of graphene nucleation density was achieved only by changing the precipitation temperature. A high-quality single-layer polycrystalline graphene film having a grain size ranging from ~200 nm to ~1 μm and uniformly blended at a grain boundary is prepared.

On this basis, the research group also obtained the influence of grain size on the electrical conductivity and thermal conductivity of polycrystalline graphene and the grain boundary resistivity (~0.3 kW·μm) and grain boundary thermal conductivity (~3.8×109). Wm-2K-1), found that reducing the grain size can result in a significant decrease in thermal conductivity, but has less effect on conductivity.

Ma Teng pointed out that according to the influence law research group, when the grain size of graphene is reduced from 1 mm to 5 nm, the thermal conductivity can be attenuated by 300 times, and the conductivity is only 10 times. Left and right, and the rate of change of thermal conductivity and electrical conductivity as a function of grain size is higher than that of a typical semiconductor thermoelectric material. The above results can provide useful guidance for the electrical and thermal properties of graphene by grain size engineering and its application in the fields of electronics, optoelectronics and thermoelectrics.

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