Date of Award

Spring 1-1-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Applied Physics

First Advisor

Ahn, Charles

Abstract

This dissertation reports on developments in quantum materials synthesis and characterization, with an emphasis on the study of superconducting nickelates through molecular beam epitaxy (MBE) and real-time synchrotron hard X-ray data analysis. The work elaborates on the developments in MBE synthesis, real-time characterization, and strategic materials design, and leads to the discovery of a nickelate superconductor. High resolution X-ray diffraction measurements were taken at the Advanced Photon Source, Argonne National Laboratory.The dissertation reports on the development of real-time analysis frameworks for both synthesis and characterization. This includes dynamic MBE source flux calibration techniques using RHEED and the shutter-control method, as well as data analysis approaches for real-time crystal truncation rod (CTR) intensity analysis from synchrotron data. The dissertation then introduces the aluminum-based reduction method for infinite-layer nickelate synthesis, which provides precise control over oxygen content through control of aluminum coverage via real-time electronic and atomic structure characterization using synchrotron MBE facilities. This technique circumvents calcium hydride post-annealing treatment and reduces surface contamination. The synthesized thin films are comprehensively characterized using CTR, diffraction X-ray absorption near edge structure (dXANES) and scanning transmission electron microscopy (STEM). The dissertation then discusses the discovery of superconducting Nd1-xEuxNiO2. Europium is introduced as a rare-earth dopant as part of a strategic material design approach. It maintains chemical compatibility during synthesis and achieves hole doping through a Ni-3d Eu-4f self-doping mechanism. The Eu substitution produces a superconductor with a transition temperature of 21K and unusual magnetic properties, expands the family of superconducting nickelates and provides new insights into oxide superconductivity.

Download

Share

COinS