Strongly correlated electron materials and functional materials with reduced dimensions
Research on correlated electron materials enriches our understanding of solid
state physics and offers a route toward novel useful devices. Many unique
properties of strongly correlated electron materials originate from the
competition of different degrees of freedom, which usually results in complex
phase diagrams and stabilizes multiple phase coexistence at the sub-micron scale.
Integration of multiple functionalities of correlated electron materials thus
requires controlling and understanding their properties on the single or few domain
level. Specifically, this project involves synthesis of transition metal chalcogenide and oxide
nanostructures, fabrication and characterization of nanodevices, and examining various types of phase
transitions at the nanoscale using scanning probe, optical and in situ scanning and transmission
electron microscopes.
Photovoltaics and thermoelectrics of semiconductors
Theoretical as well as experimental studies have demonstrated the great promise
that semiconductors especially nanostructures hold for energy applications.
We examine photon-carrier and phonon-carrier interactions in semiconductor thin films and nanostructures, targeting
fundamental problems in their photovoltaic and thermoelectric applications. Specifically, we study group III-nitride alloys and oxide semiconductors for broad-spectrum photovoltaics, and highly mismatched semiconductor alloys and heterojunctions for high-ZT themoelectrics. Our work also heavily involves numerical modeling of charge behavior and device performance of various photovoltaic and thermoelectric structures. This research is partially in collaboration with the Solar Energy Materials Research Group at the Lawrence Berkeley National Lab.
Materials Interfaces and Composites
We have strong research interest and effort in electronically and mechanically dynamic phenomena ocurring at the interface between dissimilar materials. These phenomena involve some of the most fundamental processes in materials physics, such as atomic diffusion, phase segragation, charge transfer and scattering, and electron-phonon interactions. Using a number of advanced in situ microscopic and spectroscopic techniques, we try to understand these processes, and look for ways to engineer them for synergistic materials properties that cannot be found in any of the constituents alone.
A poster (PDF) describing our recent research activities.
Enhancing thermoelectric power factor with highly mismatched isoelectronic doping; Phys. Rev. Lett., 104, 016602 (2010).
Determining surface Fermi level pinning position of InN nanowires using electrolyte gating; Appl. Phys. Lett., 95, 173114 (2009).
Thermoelectric Effect across the Metal-Insulator Domain Walls in VO2 Microbeams. Nano. Lett., 9, 4001 (2009)
Sublimation of GeTe nanowires and evidence of its size effect studied by in situ TEM. J. Am. Chem. Soc., 131, 14526 (2009).
Strain engineering and one-dimensional organization of metal-insulator domains in single-crystal VO2 beams. Nature Nanotech., 4, 732 (2009). (cover highlight)
When Group III - Nitrides Go Infrared: New Properties and Perspectives. J. Appl. Phys., 106, 011101 (2009).
Modulating Surface Electron Accumulation in InN by the Electrolyte Gated Hall Effect. Appl. Phys. Lett.; 93, 262105 (2008)
Effects of Surface States on Electrical Characteristics of InN and InGaN. Phys. Rev. B, Rapid Commun.; 76, 041303(R) (2007).
Gate Coupling and Charge Distribution in Nanowire Field Effect Transistors. Nano Lett., 7, 2778 (2007).
