03/03/2025
By Stephen Margiotta

The Francis College of Engineering, Department of Electrical & Computer Engineering, invites you to attend a Master’s thesis defense by Stephen Margiotta on “Developing Crystalline NBN Superconductors on Gan by Sputtering: Insights into Structure, Electrical Properties, Thermal and Radiation Stability." 

Candidate Name: Stephen Margiotta
Degree: Master’s
Defense Date: Wednesday March 12 2025
Time:From 11 a.m. to 1 p.m.
Location: Saab Emerging Technologies & Innovation Center - LaTorre Conf. Room 245, North Campus
Thesis/Dissertation Title: Developing Crystalline NBN Superconductors on Gan by Sputtering: Insights into Structure, Electrical Properties, Thermal and Radiation Stability.

Advisor: Anhar Bhuiyan, Ph.D, Department of Electrical & Computer Engineering, University of Massachusetts Lowell
Committee: Joel Therrien, Ph.D, Department of Electrical & Computer Engineering, University of Massachusetts Lowell
Committee: Hualiang Zhang, Ph.D, Department of Electrical & Computer Engineering, University of Massachusetts Lowell

Brief Abstract: In the rapidly evolving field of quantum computing, niobium nitride (NbN) superconductors have emerged as an integral material due to it’s unique structural properties, including a high superconducting transition temperature, exceptional electrical conductivity, and compatibility with advanced device architectures. This work investigates reactive DC magnetron sputtering of NbN on GaN, β-Ga2O3, and Al2O3 substrates with a focus on GaN. Samples deposited on GaN underwent high temperature annealing, gamma radiation, and neutron irradiation with the structural, electrical, and superconducting properties of NbN examined. The as-deposited cubic δ-NbN (111) films exhibited a high intensity distinct x-ray diffraction (XRD) peak, a high superconducting transition temperature (Tc) of up to 13.93 K, and an atomically flat surface. Annealing at 500 °C and 950 °C for varying durations revealed notable structural and surface changes. High resolution scanning transmission electron microscopy (STEM) indicated improved local ordering, while atomic force microscopy (AFM) showed reduced surface roughness after annealing. X-ray photoelectron spectroscopy (XPS) revealed a gradual increase in the Nb/N ratio with higher annealing temperatures and durations. High-resolution XRD and STEM analysis showed lattice constant modifications in δ-NbN films, attributed to residual stress changes following annealing.