Normalization procedure for obtaining the local density of states from high-bias scanning tunneling spectroscopy

TL;DR

This paper introduces a normalization method to accurately extract the local density of states from high-bias scanning tunneling spectroscopy, addressing challenges posed by large voltages and tip height variations.

Contribution

The authors develop a normalization scheme that accounts for the effects of high bias and in-plane momentum, improving the accuracy of local density of states measurements in STM.

Findings

The scheme effectively corrects for tunnel barrier effects at high bias.

It accounts for in-plane momentum in the current analysis.

Validated on field-emission resonances with well-defined momentum.

Abstract

Differential conductance spectroscopy performed in the high bias regime -- in which the applied voltage exceeds the sample work function -- is a poor measure of the local density of states due to the effects of the changing tunnel barrier. Additionally, the large applied voltage oftentimes makes constant-height measurement experimentally impractical, lending constant-current spectroscopy an advantageous edge; but the differential conductance in that case is even further removed from the local density of states due to the changing tip height. Here, we present a normalization scheme for extracting the local density of states from high bias scanning tunneling spectroscopy, obtained in either constant-current or constant-height mode. We extend this model to account for the effects of the in-plane momentum of the probed states to the overall current. We demonstrate the validity of the proposed scheme by applying it to laterally confined field-emission resonances, which appear as peak-shaped spectroscopic features with a well-defined in-plane momentum.