Thickness-dependent Local Surface Electronic Structures of Homoepitaxial SrTiO3 Thin Films

TL;DR

This study uses low-temperature STM/STS to explore how the surface electronic structures of SrTiO3 thin films depend on thickness, revealing defect density variations and surface reconstructions related to growth conditions and film thickness.

Contribution

It provides detailed atomic-scale insights into the surface electronic structures of homoepitaxial SrTiO3 films and how these structures vary with film thickness and preparation conditions.

Findings

Disordered surface after annealing at 1000°C in low oxygen pressure.

Surface reconstructions observed on homoepitaxial films.

Defect density decreases with increasing film thickness.

Abstract

We have investigated the atomically-resolved substrate and homoepitaxial thin film surfaces of SrTiO3(001) using low-temperature scanning tunneling microscopy/spectroscopy (STM/STS) combined with pulsed laser deposition (PLD). It was found that annealing at 1000 oC in an oxygen partial pressure of 1*10-6 Torr, which is a typical annealing treatment for the preparation of SrTiO3 substrates, unexpectedly resulted in a disordered surface on an atomic scale. In contrast, homoepitaxial SrTiO3 thin films grown on this disordered substrate exhibited (2*2) surface reconstructions. The differential conductance spectra, dI/dV in STS measurements, revealed a number of surface defects in a 10-unit-cell-thick SrTiO3 film, but much fewer in a 50-unit-cell-thick film. These results indicate that the defect density in the film strongly depends on the film thickness, suggesting non-uniform stoichiometry along the growth direction.