Nanoscale distribution of strains and defects in graphene transferred onto polymethylmethacrylate

Graphene has attracted a wide interest over the last decade and deeper understanding of formation of defects and strains controlling its properties is one of the major goals. One of the commonly used methods for transferring graphene on a substrate of interest utilizes polymethylmethacrylate (PMMA) as a temporary support. While several studies demonstrated that the length scale of strain can be as small as a few nm for graphene on SiO₂ substrates [1], the strain coherence length and distribution of defects on a nanoscale for graphene laying on PMMA remains poorly understood. Here we present tip-enhanced Raman Spectroscopy (TERS) study of single layer graphene on top of PMMA. Our results provide a clear experimental evidence that the locations of defects correlate with topological features of PMMA, which on the other hand replicates topological structure of copper foil. We found that the strain is anisotropically distributed with a length scale varies from tens hundred nm.
1. Teague, M. L. et al. Nano Lett. 2009, 9, 2542