Raman Topography and Strain Uniformity of Large-Area Epitaxial Graphene

Abstract

We report results from two-dimensional Raman spectroscopy studies of large-area epitaxial graphene grown on SiC. Our work reveals unexpectedly large variation in Raman peak position across the sample resulting from inhomogeneity in the strain of the graphene film, which we show to be correlated with physical topography by coupling Raman spectroscopy with atomic force microscopy.We report that essentially strain free graphene is possible even for epitaxial graphene.Graphene exhibits extraordinary electronic properties including an unusually high mobility of the charge carriers. 1 While significant progress toward understanding the properties of graphene has resulted from studying graphene flakes mechanically exfoliated from bulk graphite, 2 these small flakes (< 100 µm 2 ) are most suited for studying the fundamental science of graphene, and are not practical for the development of graphene-based technologies. Alternatively, the sublimation of silicon (Si) from silicon carbide (SiC) to form epitaxial graphene is a promising route for the production of wafer size graphene films. 3 -45678 9 However, rapid characterization and precise control of properties of epitaxial graphene over a wafer-size area are yet to be achieved. Micro-Raman spectroscopy is a rapid, highresolution optical characterization technique that yields important information on the thickness, the charge carrier density, and the strain of epitaxial graphene. 10,11,12,13 However, no studies of Raman topography, the two-dimensional mapping of Raman spectrum over large-area epitaxial graphene, have been carried out to date.

Wafer-scale graphene on 2 inch SiC with uniform structural and electrical characteristics

“…The peak shifts are quite similar for the two lines and are comparable to those reported in the literature [14]. The small shift of the peaks is probably induced by different strain or doping across the sample [18][19][20]. Here, we consider that strain is the main cause of the peak shift.…”

Correlating Raman Spectral Signatures with Carrier Mobility in Epitaxial Graphene: A Guide to Achieving High Mobility on the Wafer Scale

“…2,3 Peaks fit using two Lorentzian functions are categorized as a transition layer (T), which are further categorized as a thickness transition, or a strain state transition of monolayer graphene. 16 Because EG C is much thicker than EG Si , atomic force microscopy (AFM) is utilized to measure EG C thickness. Layer stacking in EG C and EG Si is identified using the 2D peak full width at half maximum, and component fitting.…”

“…Of the characterization techniques used for layer thickness determination, 13 ,14,15, -16,17,18, 19 Raman spectroscopy is arguably the simplest and fastest, especially for exploring monolayer EG on SiC(0001) (referred to as EG Si )and EG layer stacking on SiC(000-1) (referred to as EG c ). [15][16][17][18][19] Characterization of EG via Raman spectroscopy requires fitting the 2D Raman peak. 15,16,20 Raman spectra of EG Si fit by one or four Lorentzian functions are characteristic of monolayer or bilayer graphene, respectively.…”

“…[15][16][17][18][19] Characterization of EG via Raman spectroscopy requires fitting the 2D Raman peak. 15,16,20 Raman spectra of EG Si fit by one or four Lorentzian functions are characteristic of monolayer or bilayer graphene, respectively. 15 Figure 1a demonstrates layer thickness evaluation for monolayer and bilayer EG Si via Lorentzian fitting of the 2D Raman spectra.…”

Uniaxial strain in graphene by Raman spectroscopy:Gpeak splitting, Grüneisen parameters, and sample orientation

“…The Grü-neisen parameters for the vibrational modes of graphite and graphene under biaxial strain were calculated by first principles, yielding excellent agreement with the thermomechanical properties of graphite. 19 Recently, changes to the Raman spectra were reported due to the presence of stress in graphene, [20][21][22][23][24][25] but the inferred strains disagreed by a factor of 5 or more for similar Raman shifts. 20,[22][23][24] Furthermore, no significant difference was seen between the cases of uniaxial and biaxial strain, 20,23,24 in contrast with theory, and the opening of a band gap at the K point was suggested, 20 again in contrast with the theory for small strains.…”