Abstract
We report spatially resolved Raman scattering results of polycrystalline monolayer graphene films to study the effects of defects, strains, and strain fluctuations on the electrical performance of graphene. Two-dimensional Raman images of the integrated intensities of the G and D peaks (IG and ID) were used to identify the graphene domain boundaries. The domain boundaries were also identified using Raman images of ID/IG and I2D/IG ratios and 2D spectral widths. Interestingly, the ID maps showed that the defects within individual domains significantly increased for the graphene with large domain size. The correlation analysis between the G and 2D peak energies showed that biaxial tensile strain was more developed in the graphene with large domain size than in the graphene with small domain size. Furthermore, spatial variations in the spectral widths of the 2D peaks over the graphene layer showed that strain fluctuations were more pronounced in the graphene with large domain size. It was observed that the mobility (sheet resistance) was decreased (increased) for the graphene with large domain size. The degradation of the electrical transport properties of the graphene with large domain size is mainly due to the defects, tensile strains, and local strain fluctuations within the individual domains.
Highlights
Large-scale growth of high-quality crystalline graphene is a prerequisite for improving the device performance in graphene-based nanoscale applications
Since the Cu foil underneath the domain boundaries is more vulnerable to the penetration of O2 molecules through defects in graphene, the domain boundaries are distinctly visible as the bright lines in the scanning electron microscope (SEM) images[22]
The electrochemical polishing (ECP) treatment combined with an annealing process suppresses the formation of graphene nucleation sites, resulting in an increase in the domain size[23]
Summary
Large-scale growth of high-quality crystalline graphene is a prerequisite for improving the device performance in graphene-based nanoscale applications. The carrier mobility of polycrystalline graphene tends to decrease for a small domain size, suggesting that the charge transport is influenced by scattering at the domain boundaries[6,7]. Two-dimensional Raman images of the energies, intensities, and/or widths of the D, 2D, and G peaks scanned over a large area of graphene can provide useful information on the spatial distributions of defects, strains, strain fluctuations, etc. Raman mapping measurements were carried out on single-layer graphene samples to investigate the influence of defects, strains, and strain fluctuations on the transport properties in the presence of domain boundaries. We observed that the electrical transport properties of the graphene devices could be affected by the carrier scattering at the domain boundaries and the defects, strains, and strain fluctuations within the individual domains
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