Metal-Induced Gap States at Well Defined Alkali-Halide/Metal Interfaces

TL;DR

This study investigates metal-induced gap states at alkali-halide/metal interfaces using spectroscopic techniques and ab initio calculations, revealing thin, localized states formed by metal proximity.

Contribution

It provides direct experimental and theoretical evidence for the existence and characteristics of metal-induced gap states at insulator/metal interfaces.

Findings

MIGS observed as an extra peak below the bulk edge

MIGS are as thin as one monolayer

Ab initio calculations support localized MIGS

Abstract

In order to search for states specific to insulator/metal interfaces, we have studied epitaxially grown interfaces with element-selective near edge X-ray absorption fine structure (NEXAFS). An extra peak is observed below the bulk edge onset for LiCl films on Cu and Ag substrates. The nature of chemical bonds as probed by X-ray photoemission spectroscopy and Auger electron spectroscopy remains unchanged, so we regard this as evidence for metal-induced gap states(MIGS) formed by the proximity to a metal, rather than local bonds at the interface. The dependence on the film thickness shows that the MIGS are as thin as one monolayer. An ab initio electronic structure calculation supports the existence of the MIGS that are strongly localized at the interface.