Tailoring the Physicochemical Properties of Nb Thin Films via Surface Engineering Methods

Area of Science:

• Materials Science
• Surface Science
• Quantum Computing

Background:

• Niobium (Nb) thin films are crucial for superconducting qubits.
• Surface oxide layers significantly impact Nb film properties and device performance.
• Controlling oxide layer characteristics is key to enhancing qubit functionality.

Purpose of the Study:

• To investigate the structural and chemical properties of niobium oxide layers modified by CMP and ANAB.
• To understand the oxidation gradients and hydrogen incorporation within these oxides.
• To assess the impact of these modifications on oxygen surface exchange and interfacial layer behavior.

Main Methods:

• Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) for structural analysis.
• Scanning TEM, Energy-Dispersive X-ray Spectroscopy (EDS), and X-ray Photoelectron Spectroscopy (XPS) for chemical composition.
• Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) for depth profiling and isotopic labeling (¹⁸O₂).
• Density Functional Theory (DFT) calculations for interfacial behavior.

Main Results:

• CMP and ANAB processing yield significantly thinner and smoother Nb oxides compared to native oxides.
• An oxidation gradient (Nb⁵⁺ at the surface, suboxides near the interface) was identified.
• Engineered oxides exhibit enhanced resistance to oxygen surface exchange.
• An interfacial layer of hydrogen-containing species was detected and observed to migrate.
• DFT calculations confirm hydrogen segregation at the Nb oxide/metal interface.

Conclusions:

• Surface modification techniques (CMP, ANAB) effectively control Nb oxide properties for qubit applications.
• Understanding oxidation gradients and hydrogen incorporation is vital for optimizing Nb-based superconducting devices.
• The interfacial hydrogen layer plays a critical role in oxide stability and device performance.