Imaging electron flow and quantum dot formation in MoS2 nanostructures

TL;DR

This paper uses a cooled scanning probe microscope to image electron flow and quantum dot formation in MoS2 nanostructures, revealing details about scattering sources and quantum confinement at low temperatures.

Contribution

It demonstrates a novel imaging technique to visualize electron flow and quantum dots in MoS2, providing insights into scattering mechanisms and quantum dot characteristics.

Findings

Electron flow decays exponentially from the edge.

Bullseye Coulomb blockade patterns indicate quantum dots.

Quantum dot size and position estimated using capacitive modeling.

Abstract

Among newly discovered two-dimensional (2D) materials, semiconducting ultrathin sheets of MoS2 show potential for nanoelectronics. However, the carrier mobility in MoS2 is limited by scattering from surface impurities and the substrate. To probe the sources of scattering, we use a cooled scanning probe microscope (SPM) to image the flow of electrons in a MoS2 Hall bar sample at 4.2 K. Capacitive coupling to the SPM tip changes the electron density below and scatters electrons flowing nearby; an image of flow can be obtained by measuring the change in resistance between two contacts as the tip is raster scanned across the sample. We present images of current flow through a large contact that decay exponentially away from the sample edge. In addition, the images show the characteristic "bullseye" pattern of Coulomb blockade conductance rings around a quantum dot as the density is depleted with a back gate. We estimate the size and position of these quantum dots using a capacitive model.