Curvature analysis of single layer graphene on the basis of extreme low-frequency Raman spectroscopy

Abstract

Single layer graphene (SLG) sheets offer exciting optical and electronic properties, as well as excellent mechanical performance, which are desirable for countless potential applications in ultrathin optical, electronic, and mechanical devices. Typically, the mechanical properties of SLG are extrapolated from few layer graphene (FLG) systems in most existing experimental studies, despite the fact that the environmental mechanical response of SLG is quite different from FLG. Raman spectroscopy is one of the most versatile and nondestructive experimental techniques to probe graphene samples. Here, we provide direct experimental evidence for the vibrational behavior of SLG and its response to high pressure conditions (0-10 GPa) via Raman spectroscopy including the extreme low-frequency Raman region (5-250 cm-1). Artificial introduction of the curvature of the SLG sheets causes van Hove singularities within the range of Fermi energies (EF). The radius of curvature ρ can be predicted via a comparison of the shear mode and the breathing mode of SLG with the squash mode and the radial breathing mode of single wall carbon nanotubes (SWNTs). Furthermore, an additional polarization analysis further confirms similar low frequency modes of SLG and SWNTs under pressure. This direct investigation of SLG mechanical properties improves the quality of the available mechanical data, which is required for the design of new graphene-based nanocomposites and the development of electronic or mechatronic devices.