报告时间：2013年8月2日（星期五）上午09:00

报告地点：能源基础楼2楼201会议室

报告人：Tom Wu (吴韬)

Materials Science and Engineering, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia

报告摘要：

As a new paradigm of synthesis, the vapour-liquid-solid (VLS) growth of nanowires has received considerable attention in the past decade due to the vast potential of nanowire-based devices in critical technologies. Indium tin oxide or ITO is the most important transparent conducting oxide, dominating the touch-screen and other emerging electronics markets. In the first part of this talk, I will discuss the synthesis and characterization of single-crystalline ITO nanowires [1]. Recently, we found that at the catalyst/nanowire interface a rare cubic phase of In-Sn-O (ISO) epitaxially forms on top of the conventional bixbyite phase, forming a self-assembled axial nanowire heterostructure (Figure below) [2]. Regarding the synthesis mechanism, we propose that the high chemical pressure of Sn in the liquidus catalyst nanoparticles selectively stabilizes the cubic ISO phase with an unusual equal molar concentration of In and Sn. In the second part of the talk, I will discuss the emergent optical properties of these ITO nanowires. Remarkably, we found that ITO nanowires can emit UV light, exhibiting optical properties different from the bulk counterpart [1]. We argue that as a result of the large surface-to-volume ratio and the high crystallinity of nanowires, the quantum mechanical dipole-forbidden rule in the ideal bulk materials breaks down, thereby allowing the band edge light transition [3]. Overall, our results suggest that the VLS nanowire synthesis departs from the conventional solid-state synthesis routes, giving unprecedented freedom to navigate the phase diagrams and providing new routes towards self-assembled nanomaterials and novel functional devices.

Fig1. SEM image of branched ITO nanowires and HRTEM image of the ITO/ISO interface.

[1] J. Gao, R. Chen, D. H. Li, L. Jiang, J. C. Ye, X. C. Ma, X. D. Chen, Q. H. Xiong, H. D. Sun, and T. Wu, "UV light emitting transparent conducting tin-doped indium oxide (ITO) nanowires" Nanotechnology 22, 195706 (2011). Also in News and Viewsof Nature Photonics 5, 332 (2011).

[2] J. Gao, O. Lebedev, S. Turner, Y. Li, Y. Lu, Y. P. Feng, P. Boullay, W. Prellier, G. van Tendeloo, and T. Wu, "Phase selection enabled formation of abrupt axial heterojunctions in branched oxide nanowires" Nano Letters 12, 275(2012).

[3] Y. F. Li, W. J. Yin, R. Deng, R. Chen, J. Chen, Q. Y. Yan, B. Yao, H. D. Sun, S.-H. Wei, and T. Wu, “Realizing a SnO2-Based Ultraviolet Light-Emitting Diode via Breaking the Dipole Forbidden Rule” NPG Asia Materials 4. E30 (2012).

报告人简介：

Dr. Tom Wu received his B.S. degree from Zhejiang University in 1995 and Ph.D. from the University of Maryland, College Park in 2002. After working as a postdoc in Argonne National Laboratory, Materials Science Division and Center for Nanoscale Materials, he joined the faculty of Nanyang Technological University in 2006, and then moved to King Abdullah University of Science and Technology in 2013. Dr. Wu has authored/co-authored about 140 papers in the field of oxide thin films, nanomaterials and heterostructures (http://www.researcherid.com/rid/A-1158-2012). His research group focuses on designing and synthesizing oxide thin films, nanomaterials and heteostructures, exploring their emergent physical properties, and constructing novel devices in the areas of spintronics, multiferroics, resistive switching memory, and field effect transistors.