Homogeneous Large-Area Quasi-Free-Standing Monolayer\nand Bilayer Graphene on SiC

Abstract

In\nthis study, we first show that the argon flow during epitaxial\ngraphene growth is an important parameter to control the quality of\nthe buffer and the graphene layer. Atomic force microscopy (AFM) and\nlow-energy electron diffraction (LEED) measurements reveal that the\ndecomposition of the SiC substrate strongly depends on the Ar mass\nflow rate while pressure and temperature are kept constant. Our data\nare interpreted by a model based on the competition of the SiC decomposition\nrate, controlled by the Ar flow, with a uniform graphene buffer layer\nformation under the equilibrium process at the SiC surface. The proper\nchoice of a set of growth parameters allows the growth of a defect-free,\nultrasmooth, and coherent graphene-free buffer layer and bilayer-free\nmonolayer graphene sheets which can be transformed into large-area\nhigh-quality quasi-free-standing monolayer and bilayer graphene by\nhydrogen intercalation. AFM, scanning tunneling microscopy, Raman\nspectroscopy, and electronic transport measurements underline the\nexcellent homogeneity of the resulting quasi-free-standing layers.\nElectronic transport measurements in four-point probe configuration\nreveal a homogeneous low resistance anisotropy on both μm and\nmm scales.