GOALI: Structural and Topological Controls on Viscoelasticity and Relaxation Processes in Chalcogenide Glass-Forming Liquids

University Of California-Davis, Davis CA

Investigators

Abstract

NON-TECHNICAL DESCRIPTION: Chalcogenide (non-oxide alloys or compounds containing sulfur, selenium or tellurium) glasses are an important class of materials with wide-ranging applications in the areas of photonics, telecommunication, memory storage, photovoltaics and environmental remote sensing. A fundamental understanding of the dynamical processes associated with the temperature- and composition- dependent flow behavior of the parent melts or liquids from which these glasses are derived, is crucial in all stages of their industrial production. This project aims to provide unique knowledge regarding the connection between the "microscopic (atomistic)" and the "macroscopic" aspects of the dynamical behavior of chalcogenide liquids for the very first time, using a combination of cutting-edge characterization techniques. This knowledge is key to the optimization of the chemistry and processing parameters of these materials for improved and novel functionality, thereby enabling their application in modern transformative technologies with strong societal impact. Scientifically, this work impacts materials science, physical chemistry, and solid-state physics. The interdisciplinary nature of this work transfers knowledge between fields and provides students with unique opportunities for intellectual growth. Graduates typically find employment in both academia and in glass and semiconductor industry. The impact of this project in terms of education and outreach is in three major areas: (1) participation by students in research, (2) active and tight-knit collaboration with industry (Corning, Inc.) where students are mentored and gain understanding of industry priorities, and (3) dissemination of knowledge about glass science and technology to the broader scientific community. The research findings are embedded into special topics courses that are offered to students in materials science, chemistry, and other related fields; and they contribute to campus programs for women and minority students and to the recruitment of promising students from underrepresented and economically-disadvantaged groups. TECHNICAL DETAILS: The dynamical processes in supercooled glass-forming liquids, associated with their viscous flow, structural relaxation and annealing near the glass transition, control all aspects of the processing and technological utility of the resulting glasses and glass-ceramics. However, surprisingly enough, little is known regarding the connection between the atomic structure, its connectivity and topology and the temperature dependence of the flow behavior of chalcogenide liquids. Historically, therefore, much of the approach for designing new chalcogenide glasses has been largely empirical and lacked the predictive power needed for their compositional optimization and processing methods. This GOALI project brings together investigators with complementary expertise and common interests from UC Davis (Sen, PI) and from Corning Incorporated (Aitken, co-PI), to investigate the effects of structural connectivity and topology on the temperature dependence of the viscoelastic behavior and relaxation processes in supercooled chalcogenide (sulfide and selenide) liquids, using a unique combination of state-of-the-art oscillatory parallel-plate rheometry, dynamical nuclear magnetic resonance (NMR) spectroscopy and differential scanning calorimetry measurements. Predictive atomistic models of structure-relaxation-viscous flow relationships, built on the basis of the results obtained in this project, may enable the optimization of the chemistry, synthesis, and processing parameters of these complex materials for a wide range of modern technological applications. The focus of this project, namely how and why, the various aspects of the atomic structure control the temperature dependent viscoelasticity, relaxational behavior and related phenomena in chalcogenide glass-forming liquids is in itself crosscutting materials research. The breadth, flexibility and interdisciplinary nature of this project prepare the students with powerful experimental skills and research experience in both academic and industrial settings that may open many future career opportunities. It also enriches the graduate education and training experience through numerous scientific interactions between the collaborating scientists and participating students. 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.