New frontiers in the application of complex functional oxide thin films

Affiliation: Materials Science and Engineering, University of California, Berkeley

Speaker: Dr. Lei Zhang

Title: New frontiers in the application of complex functional oxide thin films

Abstract:
Complex oxide thin films that possess properties such as piezoelectricity, ferroelectricity, magnetism and multiferroics are candidates for the next-generation non-volatile memory, low-power electronics and sensing devices. Gaining a fundamental understanding of intrinsic material properties and influence of the engineering knobs will ultimately enhance the device performance based on complex oxide thin films. Through this presentation, two examples will be used to illustrate how material properties can be manipulated to achieve the desired functionalities in two different application fields. In the first part of my talk, I will focus on leveraging strong electron-electron correlation in correlated metals, SrVO3 and CaVO3, to develop a new type of transparent conductors which can be used in display and photovoltaic applications beyond conventional wide band gap semiconductors. It will be shown that high carrier effective mass originating from the mass renormalization in a typical metal-to-insulator transition is essential to strike a delicate balance between the mutually exclusive properties of high electrical conductivity and optical transparency. In the second part, I will focus on new material opportunities for the renaissance of fields of pyroelectric energy conversion and solid state cooling enabled by the capability of engineering and designing high-quality pyroelectric thin films. These applications require materials with large pyroelectric coefficient, represented by the change of spontaneous polarization with temperature variation. Using electrothermal test platforms which are microfabricated for thin-film geometry to extract phase-sensitive pyroelectric current, it will be shown that by positioning a material close to a polar-to-nonpolar phase boundary in Bi1-xLaxFeO3 quaternary system, the pyroelectric properties can be significantly enhanced.

Biography:
Lei Zhang is a postdoctoral fellow with Prof. Lane W. Martin at the University of California, Berkeley. Lei was a graduate research assistant in Prof. Roman Engel-Herbert’s group and obtained his Ph.D. in Materials Science and Engineering from the Pennsylvania State University in 2017. His current research interests include thin film epitaxy, characterization and nanofabrication of complex oxides, and their applications in transparent conductors, pyroelectric energy conversion and low-power electronics. He is the recipient of 2017 Chinese Government Award for Outstanding Self-Financed Students Abroad and 2016 Materials Research Society Graduate Student Gold Award.