Probing Strain and Doping along a Graphene Wrinkle Using Tip-Enhanced Raman Spectroscopy

Wrinkles are unavoidable byproducts of graphene growth during chemical vapor deposition. They form because of the different thermal expansion coefficients of graphene and the underlying substrate. Micrometer-sized wrinkles are known to affect the electronic properties of graphene due to their shape and the strain variations they create. However, as graphene finds more applications in nanoscale devices, it is necessary to investigate the physical and electronic nature of wrinkles of nanometer dimensions. Here, we analyze the strain distribution and doping of a graphene wrinkle having 1.9 nm width using tip-enhanced Raman spectroscopy (TERS) in ambient conditions. We imaged the wrinkle through TERS mapping of the graphene Raman peaks and found that anisotropic strain and varying p-doping occur along the length of the wrinkle. Furthermore, we mapped the electronic Raman scattering (eRS) from the Au(111) that manifests as a broad background continuum in the Raman spectra. We found a strong correlation between the TERS images of the graphene wrinkle and the eRS of the Au(111) substrate. Our work demonstrates that the as-fabricated physical and electronic properties of nanometer-sized features, such as wrinkles, can be probed and studied in detail with TERS which is essential for nanodevice characterization.