Locality and lateral modulations of quantum well states in Ag(100) thin films studied using a scanning tunneling microscope

TL;DR

This study uses low-temperature scanning tunneling microscopy to examine how quantum well states in Ag(100) thin films are modulated laterally by defects and surface steps, revealing local variations over nanometer scales.

Contribution

It provides detailed experimental insights into the lateral modulation of quantum well states in Ag(100) films caused by interface defects and surface steps, supported by a simple wave diffraction model.

Findings

QW states modulate over ~5 nm near interface defects

QW states are unaffected up to 1 nm from surface steps

Modulations are explained by electron wave diffraction

Abstract

We investigate Ag(100) thin films epitaxially grown on a Fe(100) substrate using a low-temperature scanning tunneling microscope. Fabrication of a wedge structure by evaporating Ag through a shadow mask allows us to observe systematic evolution of quantum well (QW) states for layer thicknesses varying from 3 to 16 monolayers (ML). Close inspection of differential conductance spectra and images reveal significant modulations of QW states in the lateral directions, presumably due to the local defects at the Ag/Fe interface. The area where QW states are modulated extends over ~ 5 nm. In clear contrast, near a surface atomic step, QW states exhibit negligible changes at least up to 1 nm away from the step, leaving unmixed the two sets of neighboring QW states belonging to different thicknesses. The results are discussed in terms of a simple electron wave diffraction model.