# Strained single-crystal Al2O3 grown layer-by-layer on Nb (110) thin films

## TL;DR

This study demonstrates the layer-by-layer growth of single-crystal Al2O3 on Nb (110) films, revealing initial lattice clamping with tensile strain and subsequent relaxation, providing insights into epitaxial oxide film growth.

## Contribution

It presents a detailed analysis of the epitaxial growth process of Al2O3 on Nb (110), including strain behavior and growth modes, which was not previously characterized.

## Key findings

- Initial Al2O3 grows with tensile strain near 10%.
- Strain relaxes as film thickness increases beyond 5 nm.
- Despite lattice mismatch, strain remains surprisingly isotropic.

## Abstract

We report on the layer-by-layer growth of single-crystal Al2O3 thin-films on Nb (110). Single-crystal Nb films are first prepared on A-plane sapphire, followed by the evaporation of Al in an O2 background. The first stages of Al2O3 growth are layer-by-layer with hexagonal symmetry. Electron and x-ray diffraction measurements indicate the Al2O3 initially grows clamped to the Nb lattice with a tensile strain near 10%. This strain relaxes with further deposition, and beyond about 5 nm we observe the onset of island growth. Despite the asymmetric misfit between the Al2O3 film and the Nb under-layer, the observed strain is surprisingly isotropic.