Abstract
The exceptional electronic properties of monatomic thin graphene sheets triggered numerous original transport concepts, pushing quantum physics into the realm of device technology for electronics, optoelectronics and thermoelectrics. At the conceptual pivot point is the particular two-dimensional massless Dirac fermion character of graphene charge carriers and its volitional modification by intrinsic or extrinsic means. Here, interfaces between different electronic and structural graphene modifications promise exciting physics and functionality, in particular when fabricated with atomic precision. In this study we show that quasiperiodic modulations of doping levels can be imprinted down to the nanoscale in monolayer graphene sheets. Vicinal copper surfaces allow to alternate graphene carrier densities by several 1013 carriers per cm2 along a specific copper high-symmetry direction. The process is triggered by a self-assembled copper faceting process during high-temperature graphene chemical vapor deposition, which defines interfaces between different graphene doping levels at the atomic level.
Highlights
Graphene, a simple two-dimensional honeycomb arrangement of sp2-hybridised carbon atoms, is hailed for its exceptional electronic environment, forcing charge carriers to propagate analogous to relativistic massless particles[1]
Single-layer graphene was prepared on commercial Cu foils at growth temperatures of 1020 °C, following a pulsed chemical vapor deposition (CVD) method, which prevents the formation of multilayer patches at the nucleation centers as described in an earlier work[17]
The inclination of the (111) direction with respect to the surface normal is directly visible in the k-photoemission electron microscopy (PEEM) pattern in Fig. 1b, showing a high-index vicinal (111) cut of the copper’s Fermi surface as developed after graphene removal by a mild Ar+ ion sputtering followed by 300 °C annealing in ultra-high vacuum (UHV)
Summary
A simple two-dimensional honeycomb arrangement of sp2-hybridised carbon atoms, is hailed for its exceptional electronic environment, forcing charge carriers to propagate analogous to relativistic massless particles[1]. Heterogeneous properties majorly widen the options for electronics and for experiments on exciting fundamental physics: 1D grain boundaries between different honeycomb lattice orientations can be exploited to achieve variable bandgaps for optoelectronics in otherwise semi-metallic graphene[2], to tune carrier mobilities[3], or to introduce spin degrees of freedom[4]. Supporting metallic surfaces are rich playgrounds for these concepts, offering the prospect of large scale production of high-quality graphene via chemical vapor deposition (CVD). Metals may exhibit coexisting surface terminations with different interaction potentials and the potential to trigger variations in graphene doping[13]. They allow the formation of graphene with different crystallographic orientations[14], different kinds of grain boundaries between domains, and domains with various doping levels[15,16]. The general concept of this work, which avoids any lithography processing steps, can be extended towards other chemical vapor deposited 2D systems of current interest such as semiconducting transition metal dichalcogenides, e.g. MoS2, insulating hexagonal boron nitride (h-BN) monolayers, and respective hybrid structures
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