Raman spectroscopy as probe of nanometre-scale strain variations in graphene

Abstract

Confocal Raman spectroscopy has emerged as a major, versatile workhorse for the non-invasive characterization of graphene. Although it is successfully used to determine the number of layers, the quality of edges, and the effects of strain, doping and disorder, the nature of the experimentally observed broadening of the most prominent Raman 2D line has remained unclear. Here we show that the observed 2D line width contains valuable information on strain variations in graphene on length scales far below the laser spot size, that is, on the nanometre-scale. This finding is highly relevant as it has been shown recently that such nanometre-scaled strain variations limit the carrier mobility in high-quality graphene devices. Consequently, the 2D line width is a good and easily accessible quantity for classifying the crystalline quality, nanometre-scale flatness as well as local electronic properties of graphene, all important for future scientific and industrial applications.

Ab initio calculation of the G peak intensity of graphene: Laser-energy and Fermi-energy dependence and importance of quantum interference effects

“…Despite this apparent simplicity, the Raman spectrum yields a large amount of information on, amongst others, doping, strain, inter-layer interaction, and the underlying substrate [1][2][3][4] . To understand the influence of these quantities on the Raman spectrum of graphene, considerable effort has been made to understand the shape [5][6][7][8][9] , width [10][11][12][13] , height [14][15][16] , and position 11,[17][18][19][20][21] of the G and 2D peaks. While a clear picture for the 2D peak has been established 6,12,22,23 , a corresponding simple picture for the G peak is still missing.…”

Spatial Control of Laser-Induced Doping Profiles in Graphene on Hexagonal Boron Nitride

“…In particular, the small full width at half maximum (FWHM) of the graphene 2D line of around 17 cm −1 is an indication of the high crystal quality and local flatness of the encapsulated graphene sheet. 12,22 A scanning force microscopy (SFM) image of the Hall bar is shown in Figure 1e. Comparison with a scanning Raman microscopy image (Figure 1f), showing the intensity of the prominent Si Raman line at 520 cm −1 (see spectra in Figure 1d), reveals the high spatial resolution of our optical setup.…”

Perfecting the Growth and Transfer of Large Single-Crystal CVD Graphene: A Platform Material for Optoelectronic Applications

“…Aside from microscopy techniques, a quantitative measure of the quality and cleanliness of transferred graphene is the analysis of the 2D peak in the Raman spectrum of graphene [15], [16]. In particular, the width of the 2D peak Γ (2D) is an indicator of strain variations within the laser probe spot, which can also be responsible for charge carrier scattering, and hence is a major limitation of electronic mobility.…”