Abstract
Monolayer hexagonal boron nitride (hBN) tunnel barriers investigated using conductive atomic force microscopy reveal moiré patterns in the spatial maps of their tunnel conductance consistent with the formation of a moiré superlattice between the hBN and an underlying highly ordered pyrolytic graphite (HOPG) substrate. This variation is attributed to a periodc modulation of the local density of states and occurs for both exfoliated hBN barriers and epitaxially grown layers. The epitaxial barriers also exhibit enhanced conductance at localized subnanometer regions which are attributed to exposure of the substrate to a nitrogen plasma source during the high temperature growth process. Our results show clearly a spatial periodicity of tunnel current due to the formation of a moiré superlattice and we argue that this can provide a mechanism for elastic scattering of charge carriers for similar interfaces embedded in graphene/hBN resonant tunnel diodes.
Highlights
Hexagonal boron nitride has emerged as one of the most widely investigated[1] two-dimensional (2D) materials (2DMs) since the initial isolation of graphene.[2]
Heterostructures based on the two crystals represent a new class of functional electronic materials.[3−9] For example, graphene mounted on the atomically flat surface of Hexagonal boron nitride (hBN) has a much higher carrier mobility due to the reduction of potential fluctuations encountered in early graphene devices fabricated on SiO2.1,10−12 When the crystal lattice of graphene is overlaid on hBN, an additional physical property emerges, namely the formation of a hexagonal moiré fringe pattern with an associated superlattice potential which leads to pronounced changes in the in-plane magnetoconductivity of graphene through the formation of mini-bands and small energy gaps.[3,5,8,13−18] Moiré patterns might be expected when hBN layers are placed or grown on graphene/graphite
There have been very few reports of the formation of such structures[19−21] these interfaces form an integral part of graphene/hBN resonant tunneling diodes and related van der Waals heterostructures.[4,19,22−24] In particular, hBN tunnel barriers have been exploited to produce resonant tunneling transistors with gate-controlled negative differential conductance.[22,25−29]
Summary
Hexagonal boron nitride (hBN) has emerged as one of the most widely investigated[1] two-dimensional (2D) materials (2DMs) since the initial isolation of graphene.[2].
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