Nano Lett., Just Accepted Manuscript
DOI: 10.1021/nl5028167
Publication Date (Web): October 15, 2014
Copyright © 2014 American Chemical Society
The electrical performance of graphene synthesized by chemical vapour deposition and transferred to insulating surfaces may be compromised by extended defects, including for instance grain boundaries, cracks, wrinkles and tears. In this study we experimentally investigate and compare the nano- and micro-scale electrical continuity of single layer graphene grown on cm-size single crystal copper with that of previously studied graphene films, grown on commercially available copper foil. The electrical continuity of the graphene films is analysed using two non-invasive conductance characterization methods: ultra-broadband terahertz time-domain spectroscopy and micro four-point probe, which probe the electrical properties of the graphene film on different length scales; 100 nm and 10 µm, respectively. Ultra-broadband terahertz time-domain spectroscopy allows for measurement of the complex conductance response in the frequency range 1-15 terahertz, covering the entire intraband conductance spectrum, and reveals that the conductance response for the graphene grown on single crystalline copper intimately follows the Drude model for a barrier-free conductor. In contrast, the graphene grown on commercial foil copper shows a distinctly non-Drude conductance spectrum that is better described by the Drude-Smith model, which incorporates the effect of preferential carrier backscattering associated with extended, electronic barriers with a typical separation on the order of 100 nm. Micro four-point probe resistance values measured on graphene grown on single crystalline copper in two different voltage-current configurations show close agreement with the expected distributions for a continuous 2D conductor, in contrast with previous observations on graphene grown on commercial copper foil. The terahertz and micro four-point probe conductance values of the graphene grown on single crystalline copper shows a close to unity correlation, in contrast with those of the graphene grown on commercial copper foil, which we explain by the absence of extended defects on the microscale in CVD graphene grown on single crystalline copper. The presented results demonstrate that the graphene grown on single crystal copper is electrically continuous on the nano-, micro-, as well as intermediate scales.
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