Grain boundaries in chemical vapor deposition-grown graphene

Chemical vapor deposition (CVD) is the most perspective method for producing large-area graphene. The produced graphene sheet is a patchwork of crystallites with random orientation separated by grain boundary (GB) regions. The GBs will have a decisive role in defining the electrical transport properties of graphene films. Their structure may vary from fully periodic to completely disordered depending primarily on the synthesis temperature and substrate used for CVD. The chapter mainly focuses on the experimental findings on graphene grown by CVD under a very wide range of experimental conditions (temperature, pressure hydrogen/hydrocarbon ratio, gas flow velocity, and substrates). The most frequently used methods for atomic-scale characterization of GB structures, their possibilities and limitations, and the alterations of the GBs in CVD graphene during investigation are discussed. The effects of GB disorder on electrical and thermal transport are reviewed and the relatively scarce data available on the chemical properties of the GBs are summarized. GBs are complex-enough nanoobjects that it may be unlikely that two experimentally produced GBs of several microns in length could be completely identical in all of their atomic-scale details, but despite this, certain generalized conclusions may be formulated, which may be helpful for experimentalists in the interpretation of results and in planning new experiments, which could lead to a more systematic picture of GBs in CVD graphene and to a better understanding of ways to improve its electrical transport properties.