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(Color online) Calculated contrast of a multilayer structure consisting of GaAs, single-layer graphene, PMMA, and air as a function of the wavelength of the incident light and the thickness of the PMMA layer. The color sensitivity of the human eye was taken into account. The black lines indicate the layer thicknesses of the PMMA resists with molecular weights of 50 k, 600 k, and 950 k used in this work. The left inset shows schematically the calculated multilayer structure. The contrast without the sensitivity of the human eye is presented in the right inset.
(Color online) Optical microscope images of single-layer (SLG) and few-layer graphene (FLG) on GaAs (a) without PMMA resist, (b) with a PMMA 600 k layer, and (c) with a PMMA 50 k layer spin-coated on top of the graphene flake. (d) FLG and SLG parts of the graphene flake indicated in (c). (e) A map of the Raman signal of the area marked in (d). FLG areas with high intensity of the G peak are displayed in yellow and SLG parts in dark yellow, respectively.
(Color online) Raman spectroscopy measurements of (a) SLG on GaAs covered by PMMA 50 k, 600 k, and 950 k and (b) SLG on GaAs without PMMA resist and PMMA 50 k on GaAs without graphene. A non-linear background as shown in the inset of (b) is subtracted in the measurements presented here. Curves are offset by a constant value for better visibility.
(Color online) (a) Magnetotransport measurements of FLG on GaAs at different temperatures and zero gate voltage UG . (b) Magnetoresistance at B = 0 T and T = 300 mK as a function of UG .
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