Electron Transport at the Nanometer‐Scale Spatially Revealed by Four‐Probe Scanning Tunneling Microscopy

Abstract

Electron transport at the nanometer-scale is the key to novel applications of nanomaterials in electronic and energy technologies. Due to the restricted dimensionality, one of the distinctive characteristics of nano-systems is their transport properties critically depend on structural details. Therefore, an important requirement for transport research of a specifi c nanomaterial system is to examine structures and properties in a coherent manner. In this regard, four-probe scanning tunneling microscopy (STM), which combines four independently controllable STMs with a scanning electron microscope (SEM) in the same cryogenic environment, is uniquely useful for probing electron transport on multiple length-scales and revealing how transport is coupled to the electronic and structural properties down to the atomic scale for individual nanomaterials. By utilizing this unique tool, extensive research has been undertaken to explore aspects of nanotransport, which include (a) intertwined electronic and structural phase transitions in surface supported two-dimensional structures, (b) effects of atomic defects and interwire coupling on the electronic and transport properties of ultra thin quantum wire systems, (c) grain boundary resistances in copper nanowires with one-to-one correspondence to the grain boundary structure, (d) defect scattering effects in two-dimensional electron gas systems, and (e) evaluation of transport behaviors of individual semiconductor nano-junctions and nanodevices. In this paper, transport measurement techniques are fi rst introduced with a four-probe STM and then the recent progress on its applications is reviewed with a focus on the spatially resolved electron transport at the nanometerscale. The goal is to stimulate further advancement and utilization of techniques capable of characterizing materials properties at the nanometerscale to facilitate the exploration of the great promise of nanoscience and nanotechnology.

Atomic-Scale Mapping of Thermoelectric Power on Graphene: Role of Defects and Boundaries

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Dual-probe spectroscopic fingerprints of defects in graphene

“…Such setups have been achieved experimentally [23][24][25][26][27][28] and the recent progress is reviewed in detail in Refs. [29,30]. State-of-the-art experimental techniques [24,31] allow for tip separations down to 50-100 nm.…”

Hidden quantum mirage by negative refraction in semiconductor P-N junctions

“…Since the most popular 2D semiconductors have isotropic low-energy dispersion, Fermi surface matching can be satisfied by appropriately tuning the Fermi energy, so that the hidden quantum mirage can be detected by the well-developed multiprobe scanning tunneling microscopy (STM), which has already been used to characterize the non-local responses of many systems [30] such as two-dimensional thin films [31] and graphene [32,33] with nanoscale resolution. We consider a twodimensional PNJ connected to two STM tips, one located at R 1 in the N region and the other at R 2 in the P region.…”