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Design of Semiconductor Nanostructures for Next-Generation Electronic, Sensor and Energy-Harvesting Devices

时间:2017-08-11 11:09 点击:
报告人:Johnny C. Ho
报告时间:2017年8月14日上午11:00-12:00
报告地点:南校区G楼118报告厅
报告简介:
In this presentation, I would summarize and discuss the recent progress in our research group, emphasizing the development of various nanostructured materials for different technological application. In the past decade, due to intriguing physical properties, one-dimensional (1D) semiconductor nanowires (NWs), especially III-Sb materials, have attracted attention as fundamental building blocks for next-generation electronics, optoelectronics, photovoltaics and so on. Although various device structures based on GaSb nanowires have been realized, further performance enhancement suffers from uncontrolled radial growth during the nanowire synthesis, resulting in non-uniform and tapered nanowires with diameters larger than few tens of nanometres. Here we report the use of sulfur surfactant in chemical vapour deposition to achieve very thin and uniform GaSb nanowires with diameters down to 20 nm. In contrast to surfactant effects typically employed in the liquid phase and thin-film technologies, the sulfur atoms contribute to form stable S-Sb bonds on the as-grown nanowire surface, effectively stabilizing sidewalls and minimizing unintentional radial nanowire growth. When configured into transistors, these devices exhibit impressive electrical properties with the peak hole mobility of ~200 cm2V-1s-1, better than any mobility value reported for a GaSb nanowire device to date. These factors indicate the effectiveness of this surfactant-assisted growth for high-performance small-diameter GaSb nanowires.
Also, we develop an extremely simple method to prepare oxygen evolution reaction (OER) catalysts, exhibiting excellent activity and superior OER stability in alkaline conditions. The OER catalysts are composed nanomaterials of mixed Ni-Fe oxides or hydroxides that can be easily obtained by in-situ reactive dip-coating of nickel foams in a Fe3+-containing aqueous solution. The as-prepared composites can give an overpotential value of 210 mV under a current density of 10 mA cm−2 in 1 M KOH aqueous solution and there is not any obvious degradation in OER activity even after 50 hour’s chronopotentiometry measurement at a current density of 50 mA cm−2. We as well work on the design and development of a hierarchical hydrogen evolution reaction (HER) electrocatalyst constructed from microporous nickel foam and well-assembled bimetallic nickel-molybdenum (NiMo) nanowires, which are capable to deliver current densities as comparable to those of the state-of-the-art Pt/C catalyst at low overpotentials and even larger current densities at higher overpotentials (> 124 mV).  This binder-free 3D hydrogen evolution (HER) cathode catalyst displays the excellent stability, without any decay of the current density observed after long-term stability tests at a low current density of 10 mA cm-2 and a high current density of 50 mA cm-2. By pairing this NiMo 3D cathode with a NiFe-based anode, a water electrolyzer can be achieved with a stable current density of 10 mA cm-2 for overall water splitting at a voltage of ~1.53 V, indicating that the water splitting can be indeed realized without any performance sacrifice by using earth abundant electrocatalysts.
 
报告人介绍:
Dr. Johnny C. Ho received his B.S. degree with high honors in Chemical Engineering, and M.S. and Ph.D. degrees in Materials Science and Engineering from the University of California, Berkeley, in 2002, 2005 and 2009, respectively. From 2009 to 2010, he worked as a post-doctoral researcher in the Nanoscale Synthesis and Characterization group (Materials Science Division) at Lawrence Livermore National Laboratory, California. Currently, he is an Associate Professor in the department of Materials Science and Engineering at City University of Hong Kong. He has published more than 110 journal articles till now, including 3 Nature Materials, 1 Nature Communications and many others. His current research interests focus on the synthesis, characterization, integration and device applications of nanoscale materials for various technological utilizations, including electronic, sensor, photonic and energy harvesting applications (http://www.ap.cityu.edu.hk/personal-website/johnny/site_flash/index.html).