Toward Functionalized Ultrathin Oxide Films: the Impact of Surface Apical Oxygen

TL;DR

This paper demonstrates that surface apical oxygen significantly influences the electronic structure of ultrathin transition metal oxide films, affecting their potential for nanoscale electronic device applications.

Contribution

It reveals the crucial role of surface apical oxygen in altering the electronic properties of ultrathin SrVO₃ films, challenging the idealized stoichiometric surface assumption.

Findings

Surface apical oxygen persists even in ultrahigh vacuum.

Presence of apical oxygen creates an electronically dead surface layer.

Oxygen alters band filling and electron correlations in the film.

Abstract

Thin films of transition metal oxides open up a gateway to nanoscale electronic devices beyond silicon characterized by novel electronic functionalities. While such films are commonly prepared in an oxygen atmosphere, they are typically considered to be ideally terminated with the stoichiometric composition. Using the prototypical correlated metal SrVO$_3$ as an example, it is demonstrated that this idealized description overlooks an essential ingredient: oxygen adsorbing at the surface apical sites. The oxygen adatoms, which persist even in an ultrahigh vacuum environment, are shown to severely affect the intrinsic electronic structure of a transition metal oxide film. Their presence leads to the formation of an electronically dead surface layer but also alters the band filling and the electron correlations in the thin films. These findings highlight that it is important to take into account surface apical oxygen or -- mutatis mutandis -- the specific oxygen configuration imposed by a capping layer to predict the behavior of ultrathin films of transition metal oxides near the single unit-cell limit.