Instability and Surface Potential Modulation of Self-Patterned (001)SrTiO3 Surfaces

TL;DR

This study investigates how high-temperature annealing affects the surface structure and potential of (001)SrTiO3 crystals, revealing surface chemical self-structuration, potential differences, and the impact of annealing conditions on surface properties.

Contribution

It provides the first detailed analysis of surface potential modulation and chemical self-structuration of (001)SrTiO3 surfaces under various annealing conditions.

Findings

Surface self-organization into SrO and TiO2 regions confirmed.

Contact potential differences align with theoretical predictions but are smaller than ideal.

Surface potential can reverse with high-temperature UHV annealing.

Abstract

The (001)SrTiO3 crystal surface can be engineered to display a self-organized pattern of well-separated and nearly pure single-terminated SrO and TiO2 regions by high temperature annealing in oxidizing atmosphere. By using surface sensitive techniques we have obtained evidence of such surface chemical self-structuration in as-prepared crystals and unambiguously identified the local composition. The contact surface potential at regions initially consisting of majority single terminations (SrO and TiO2) is determined to be smaller for SrO than for TiO2, in agreement with theoretical predictions, although the measured difference below 100 meV is definitely smaller than theoretical predictions for ideally pure single-terminated SrO and TiO2 surfaces. These relative values are maintained if samples are annealed in UHV up to 200 degrees Celsius. Annealing in UHV at higher temperature (400 degrees Celsius) preserves the surface morphology of self-assembled TiO2 and SrO rich regions, although a non-negligible chemical intermixing is observed. The most dramatic consequence is that the surface potential is reversed. It thus follows that electronic and chemical properties of (001)SrTiO3, widely used in oxide thin films growth, can largely vary before growth starts in a manner strongly dependent on temperature and pressure conditions.