MSE 298 Seminar: Understanding the Role of Defects for Tuning Optical and Thermal Properties of Oxides

Abstract: Defects are well known to drastically affect the thermal and optical properties of materials. For example, point defects (vacancies and impurities) and grain boundaries can scatter phonons causing potentially detrimental reduction of thermal conductivity. Recently we have also shown that substitutional dopants can alter the phonon spectra even at low concentrations. However, defects are crucial for many light emission applications. Thus, their concentrations and length scales must be carefully considered. I will pressnt our ongoing work aimed at understanding the role of point defects and grain boundaries on the thermal conductivity, optical absorption and luminesce in oxides systems. We will also discuss a recently developed ceramic laser welding procedure. It relies on focusing light on interfaces to ensure an optical interaction volume to stimulate linear/nonlinear absorption processes causing localized melting rather than ablation. The key is the interplay between linear and nonlinear optical properties and laser energy-material coupling. We show that tuning of the grain sizes and defect concentrations is important for successful laser joining.

Bio: Garay is a professor in the department of mechanical and aerospace engineering and the materials science and engineering program at the Jacobs School of Engineering at UC San Diego. He is also the associate dean for research in the Jacobs School. He received his B.S. in mechanical engineering and his M.S. and Ph.D. in materials science and engineering from UC Davis. His research focuses on materials processing, property measurements and the integration of materials in devices. The application spaces are in optical devices, magnetic devices and thermal energy storage/management. He is also particularly interested in understanding the role of the length scale of nano-/micro-structural features on light, heat and magnetism. Garay is on the editorial advisory board for applied physics letters and is a deputy editor for AIP Advances.