Study of the Substrate-Induced Strain of As-Grown Graphene on Cu(100) Using Temperature-Dependent Raman Spectroscopy: Estimating the Mode Grüneisen Parameter with Temperature

Abstract

The strategy of using the thermal expansion of a copper single crystal can provide an approach to produce homogeneous strain along the basal plane to study the strain characteristic of graphene with temperature. Using an in situ Raman measurement under an ultrahigh vacuum (UHV) environment, the ability to remove contaminations allowed the direct observation of the strain property in as-grown chemical vapor deposited graphene (CVD-graphene) with temperature on a Cu(100) substrate. In this study, the strain coefficients of the G and G′ bands with temperature were investigated from the in situ temperature-dependent Raman spectra of the asgrown CVD-graphene on the Cu(100) single crystal under UHV. By eliminating the minor contributions of the lattice expansion and anharmonic phonon-scattering effects, we were able to estimate the strain coefficient of the G and G′ bands of graphene over a wide temperature range from 100 to 800 K. On the basis of the strain coefficients and the correlation map of the G-and G′-band frequencies, we made a reasonable presumption that a uniaxial-like strain is exhibited in graphene on Cu(100). For a correction to the magnitude of the uniaxial strain, the mode Gruneisen parameters at room temperature are estimated to be about ∼1.8 for the G bands, in reasonable agreement of the literature values. This strategy made it possible to estimate the temperature-dependent mode Gruneisen parameters of the G and G′ bands for the first time.

Spectroscopic evaluation of charge-transfer doping and strain in graphene/ MoS2 heterostructures

“…The frequencies of the two major Raman peaks in graphene (G and G' peaks) and in MoS2 (E' and A' peaks) are influenced by charge transfer doping and strain, and correlation analysis between the two modes offers a way to decouple their effects. [15][16][17][18][19][20][21][22] That is, by plotting the frequencies of the G' (E') band against the G (A') band in graphene (MoS2), one can establish the extent of strain versus doping in each layer. In addition to Raman peaks, monolayer MoS2 exhibits strain-and dopingdependent photoluminescence (PL) emission, offering an additional means to study the interaction between graphene and MoS2.…”

Liquids relax and unify strain in graphene

“…Use of supporting substrates facilitated its exploitability and prompted the development of the vast variety of graphene-based devices, such as field effect transistors 4 , transparent conducting electrodes 5 , gas and pressure sensors 6,7 , DNA single-molecule detectors, to name a few 8,9 . Although being widely adapted for the fabrication of current graphene-based devices and technologies, solid substrates largely affect graphene due to doping and induced strain, and thus hinder graphene's intrinsic properties [10][11][12][13][14][15][16][17][18] . The effect is even more prominent for CVD (chemical vapour deposition)-grown graphene samples, in which numerous inhomogeneities, inevitably caused by the growth and transfer processes, result in a wide variability in the band structure (and thus Raman signature) 12,13,15,16,[18][19][20][21][22][23] not only from sample to sample, but also from spot to spot within a single graphene sample.…”

“…Although being widely adapted for the fabrication of current graphene-based devices and technologies, solid substrates largely affect graphene due to doping and induced strain, and thus hinder graphene's intrinsic properties [10][11][12][13][14][15][16][17][18] . The effect is even more prominent for CVD (chemical vapour deposition)-grown graphene samples, in which numerous inhomogeneities, inevitably caused by the growth and transfer processes, result in a wide variability in the band structure (and thus Raman signature) 12,13,15,16,[18][19][20][21][22][23] not only from sample to sample, but also from spot to spot within a single graphene sample. Here we study graphene supported by liquids, namely graphene at liquid/air and liquid/liquid interfaces, which provide well-defined interfacial boundaries, unlike solid/air interfaces.…”

“…In this work we demonstrate that liquids can be a standalone support for graphene and allow for important insights into intrinsic properties of graphene that are difficult to access otherwise. By applying confocal Raman spectroscopy to CVD-grown graphene free-floating at water/air and water/liquid interfaces, we found that graphene supported by liquid(s) undergoes very small to zero strain and doping effect, posing stark contrast with "conventional" solid-supported graphene, known to always be subjected to strain and doping [10][11][12][13][14][15][16][17][18] . Additionally, statistical analysis of graphene Raman peaks showed that also the variations of strain and doping values across a graphene sheet are significantly smaller when supported by liquids, owing to more homogeneous and molecularly defined graphene-liquid interface, as opposed to a graphene-solid interface.…”

Graphene-enhanced Raman scattering on single layer and bilayers of pristine and hydrogenated graphene

“…It was shown that the substrate significantly affects the graphene layer 19,20 . The effects of the substrate may include doping 21 , strain 22 , and/or mixing of electronic states 23 . The easiest approach to study the effect of the substrate is a comparison of the behavior of single-layer graphene and turbostratic graphene bilayer on SiO 2 / Si substrate 24 .…”