Oxidation Kinetics of Superconducting Niobium and a-Tantalum in Atmosphere at Short and Intermediate Time Scales

TL;DR

This study investigates the atmospheric oxidation kinetics of superconducting niobium and tantalum surfaces over short to intermediate time scales, revealing distinct growth behaviors crucial for improving quantum device fabrication.

Contribution

It provides detailed modeling and analysis of oxidation kinetics for niobium and tantalum, highlighting differences in surface oxide growth regimes relevant to quantum technology manufacturing.

Findings

Niobium oxidation follows inverse logarithmic growth over two weeks.

Tantalum shows a transition between two inverse logarithmic regimes at 1 hour.

Understanding these kinetics aids in better fabrication control for quantum devices.

Abstract

The integration of superconducting niobium and tantalum into superconducting quantum devices has been increasingly explored over the past few years. Recent developments have shown that two-level-systems (TLS) in the surface oxides of these superconducting films are a leading source of decoherence in quantum circuits, and understanding the surface oxidation kinetics of these materials is key to enabling scalability of these technologies. We analyze the nature of atmospheric oxidation of both niobium and a-tantalum surfaces at time scales relevant to fabrication, from sub-minute to two-week atmospheric exposure, employing a combination of x-ray photoelectron spectroscopy and transmission electron microscopy to monitor the growth of the surface oxides. The oxidation kinetics are modeled according to the Cabrera-Mott model of surface oxidation, and the model growth parameters are reported for both films. Our results indicate that niobium surface oxidation follows a consistent regime of inverse logarithmic growth for the entire time scale of the study, whereas a-Ta surface oxidation shows a clear transition between two inverse logarithmic growth regimes at time t = 1 hour, associated with the re-coordination of the surface oxide as determined by x-ray photoelectron spectroscopy analysis. Our findings provide a more complete understanding of the differences in atmospheric surface oxidation between Nb and a-Ta, particularly at short time scales, paving the way for the development of more robust fabrication control for quantum computing architectures.