ABSTRACT
A critical challenge for the development of alternative energy resources is the inability to fabricate efficient and inexpensive energy conversion and storage devices. Any solution technologies rely on advanced functional materials. Understanding how materials grow, function, and transform dynamically at nanometer or atomic level
is essential. In the first part of my talk, I will present our recent study on the phase transformation dynamics of copper sulfide nanocrystals. Copper sulfide has been studied extensively for solar cell applications and there are a number of phases with the Cu:S ratio close to 2:1. Cu2S transforms from low- to high-chalcocite phase at 376 K (bulk). An understanding of the microscopic mechanisms of structural transformations is critical for controlling the metastability of the material and the long-term performance of the solar cell devices. We have been able to directly observe structural fluctuations within a single copper sulfide nanorod using an aberration-corrected transmission electron microscopy (TEM). We observed trajectories of structural transformations in individual nanocrystals with atomic resolution, which reveal an unprecedented level of details on the fluctuation dynamics, including nucleation, phase propagation, and pinning of structure domains by defects. The clear influence of the surface and interface energies on nucleation and pinning phenomena suggest strategies for stabilizing particular metastable structures. In the second part of the presentation, I will show our studies of growth trajectories of individual nanocrystals in solution using a microfabricated liquid cell operating in a TEM. In situobservation of the dynamic growth of individual nanocrystals is expected to advance our understanding of nanocrystal growth mechanisms and future control of the solution processing of materials.
References:
H. Zheng*, J. B. Rivest, T. Miller, B. Sadtler, A. Lindenberg, M. F Toney, L-W. Wang, C. Kisielowski, A. P. Alivisatos, “Observation of transient structural transformation dynamicsof a single Cu2S nanorod” Science 333, 206 (2011).
H. Zheng, R. K. Smith, Y. W. Jun, C. Kisielowski, U. Dahmen, A. P. Alivisatos,“Observation of single colloidal platinum nanocrystal growth trajectories” Science 324, 1309 (2009).
H. Xin, H. Zheng* “Fluctuations during solution growth of Bi nanoparticles” In preparation.
H-G., Liao, H. Zheng*, “Growth of PtFe Nanoparticles & Surfactant Effects” In preparation.
郑海梅简历
郑海梅博士的研究领域属原位电子显微学在材料科学研究中的应用，特别是纳米和原子尺度的晶体生长和相变。共发表论文及专著40篇（部）, 包括四篇Science, 一篇 Nature Materials, 合著著作一部。被引用次数共约3000次。在国际学术会上做报告几十次。
工作经历
2010至今，Staff Scientist & Principle Investigator，劳伦斯伯克利国家实验室材料科学部。
2006－2010，Postdoctoral Researcher，劳伦斯伯克利国家实验室美国国家电镜中心；加州大学伯克利分校化学系。
2005－2006，Postdoctoral Researcher，加州大学伯克利分校物理系。
1997－1999，讲师，天津大学材料科学与工程系。
教育背景
2004年，美国马里兰大学（University of Maryland, College Part), 材料科学与工程系，博士学位
1997年天津大学材料科学与工程系，硕士学位
1992年重庆大学材料科学与工程系，学士学位 |
