In-situ X-ray Scattering Studies of Oxide Epitaxial Growth Kinetics and Dynamics

University Of Vermont & State Agricultural College, Burlington VT

Investigators

Abstract

PART 1: NON-TECHNICAL SUMMARY X-rays are a powerful tool for exploring materials, capable of measuring atomic structures through diffraction owing to their short wavelength and their ability to penetrate materials without strong absorption. Synchrotrons, among X-ray sources, stand out as the brightest available to scientists. This project employs real-time X-ray scattering to investigate the structure and properties of metal oxides, known for their remarkable electrical and magnetic properties. The researchers aim to unveil the full potential of these materials by closely studying their growth processes, with a specific focus on thin films. Thin films could give rise to properties significantly different to those in the bulk parent compounds from which the films derive. By continuously capturing an evolving X-ray scattering pattern during growth, the team gains insights into the atomic structure of crystalline layers as they assemble from the vapor phase. This understanding is pivotal in creating innovative materials with enhanced or entirely new properties, including the ability to store an electrical charge via a shift in positive and negative ions in the crystal lattice (ferroelectric effect) or generate electrical voltage under deformation (piezoelectric effect). Such effects, along with other more exotic ones, can be tailored through the growth of artificially produced thin films, such as those with alternating layers of two different materials, each only a few atoms thick. The unique properties of metal oxides find applications in electronic memories, detectors, actuators, and energy harvesters. Beyond its scientific impact, the project plays a crucial role in education by offering hands-on training to graduate students and involving undergraduates in cutting-edge research. PART 2: TECHNICAL SUMMARY This project explores fundamental questions surrounding the influence of growth processes on the structure, interfaces, and functional properties of metal oxide thin films. Going beyond the conventional goal of achieving high-quality films, the focus is on uncovering unique growth modes and interfaces that could lead to properties significantly divergent from those observed in the bulk parent compounds. The project integrates complementary measurements of ferroelectric films to establish a feedback loop between synthesis, structural characterization, and resulting material properties, allowing for comparisons with baseline properties of conventional materials. The research plan includes three key pursuits: 1) In-situ study of processes in Pulsed Laser Epitaxy (PLE) to unveil the roles of individual species with disparate surface diffusion rates on growth, 2) Tuning the composition of ferroelectric thin films to engineer domain orientation, bias, and switching behavior, and 3) Dynamic exploration of polarization and domain structure in ferroelectric superlattices as a function of thin film thickness and electrostatic and strain boundary conditions. Utilizing coherent X-ray scattering methods, the project aims to probe spatiotemporal correlations that are not readily accessible by other means, thereby contributing significantly to the intellectual depth of the field. This project is jointly funded by Ceramics Program and the Established Program to Stimulate Competitive Research (EPSCoR). This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.