Disorder and screening in decoupled graphene on a metallic substrate

Abstract

Graphene on a dielectric substrate exhibits spatial doping inhomogeneities, forming electronhole puddles. Understanding and controlling the latter is of crucial importance for unraveling many of graphene's fundamental properties at the Dirac point. Here we show the coexistence and correlation of charge puddles and topographic ripples in graphene decoupled from the metallic substrate it was grown on. The analysis of interferences of Dirac fermion-like electrons yields a linear dispersion relation, indicating that graphene on a metal can recover its intrinsic electronic properties.

Physics of a disordered Dirac point in epitaxial graphene from temperature-dependent magnetotransport measurements

“…It has been theoretically studied and experimentally confirmed that close to the Dirac point, as a consequence of disorder, the carrier density landscape is extremely inhomogeneous and electron-hole puddles form [4][5][6][7][8][9]. Classically, the low-field Hall coefficient in the presence of both electrons and holes is given by…”

“…(4) and (5), as shown in the figure (dashed lines), where the disorder potential strength s and the mobility ratio μ e /μ h are extracted from the fitting. ∼30 STM/STS [9] can be made based on the theory [4] assuming that the electronic potential energy of disordered graphene follows Gaussian statistics, which give the probability of finding the local potential within a range dV about V ,…”

“…2), giving potential fluctuation strengths s = 12.7, 10.2, and 31.3 meV, and prefactors α which translate into mobility ratios of electrons to holes μ e /μ h = 2.04, 1.85, and 2.36, for the devices CD1, CD2, and UV1, respectively. Table I shows comparisons of the potential fluctuations, due to electron-hole puddles, between the values deduced from our magnetotransport measurements and those found in the literature [5][6][7][8][9], where most of the characterizations are based on STM. Table I also includes the disorder strength (15 ± 1 meV) from our analysis of the published data for SiC/G samples exposed to aqueous-ozone (AO) processing [21], which results in high mobility and extremely low p-type doping with an effective carrier density n eff,0 = −4.0 × 10 10 cm −2 (negative sign for holelike behavior) from Hall measurements.…”

“…Of particular significance are the effects of disorder potentials on electrical transport properties [4] due to the lack of screening at very low carrier densities. Microscopically, the fluctuating electrostatic potential breaks up the intrinsically homogeneous charge distribution into electron-hole puddles [5][6][7][8][9]. This effect is recognized to mainly originate from unintendedly introduced charged impurities, whose type, spatial distribution, and density also depend on the sample environment, device fabrication techniques, and particularly graphene synthesis and treatment processes.…”

Quantum capacitance and compressibility of graphene: The role of Coulomb interactions

“…A random potential, arising in real graphene samples due to charged impurities and corrugations, manifests itself in formation of electron-hole puddles [4,18,[21][22][23] and qualitatively changes graphene physics at low carrier densities near CNP. Disorder has been proposed as a source of the observed nonvanishing compressibility and quantum capacitance of graphene at CNP [8,[23][24][25][26][27][28][29].…”