Understanding the interplay of surface structure and work function in oxides: A case study on SrTiO3

Tianyu Ma,Ryan Jacobs,John Booske,Dane Morgan

doi:10.1063/1.5143325

Abstract

The work function is one of the most fundamental surface properties of a material, and understanding and controlling its value is of central importance for manipulating electron flow in applications ranging from high power vacuum electronics to oxide electronics and solar cells. Recent computational studies using Density Functional Theory (DFT) have demonstrated that DFT-calculated work function values for metals tend to agree well (within about 0.3 eV on average) with experimental values. However, a detailed validation of DFT-calculated work functions for oxide materials has not been conducted and is challenging due to the complex dipole structures that can occur on oxide surfaces. In this work, we have focused our investigation on the widely studied perovskite SrTiO3 as a case study example. We find that DFT can accurately predict the work function values of clean and reconstructed SrTiO3 surfaces vs experiment at about the same level of accuracy as metals when direct comparisons can be made. Furthermore, to aid in understanding the factors governing the work function of oxides, we have performed systematic studies on the influence of common surface features, including surface point defects, doping, adsorbates, reconstructions, and surface steps, on the work function. The relationships between the surface structure and work function for SrTiO3 identified here may be qualitatively applicable to other complex oxide materials.

Highlights

The work function, which is a fundamental electronic property of a material surface, is defined as the energy required to move an electron from the Fermi level to the vacuum level.[1]
Density Functional Theory (DFT) calculations were used to assess the accuracy of oxide work functions for which both the experimental surface structure and work function are known, using perovskite SrTiO3 as a case study example
These results support the fact that DFT-Heyd–Scuseria– Ernzerhof (HSE) methods can provide accurate work functions for at least one complex oxide system (SrTiO3), and additional detailed comparisons are needed to assess if this agreement extends to other systems

Summary

Introduction

The work function, which is a fundamental electronic property of a material surface, is defined as the energy required to move an electron from the Fermi level to the vacuum level.[1]. Controlling electronic transport across interfaces is important for engineering electrocatalytic materials,[11] solid-state Schottky or Ohmic junctions,[12,13] and efficient charge transport in oxide electronics and solar cells.[14]

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