报告时间：4月27号周一上午9:30
地点：教十一318（分析测试中心会议室）
Imaging Processes in Liquid Media with Electron Microscopy at Nanoresolution
Haim H. Bau
Dept. Mechanical Engineering and Applied Mechanics
University of Pennsylvania, Philadelphia, USA
bau@seas.upenn.edu
Since its invention, the electron microscope has facilitated numerous advances in a plethora of disciplines ranging from materials science, physics, and chemistry, to biology. Traditional electron microscopy must be carried out, however, in a high vacuum environment that does not allow for real time imaging of processes in liquid media. Consequently, traditional electron microscopy has been restricted to painstaking, “postmortem,” after the fact investigations of dry or frozen samples without any guarantee that an image is captured at the “right” moment. Static images also do not provide information on process dynamics, and the sample preparation may adversely impact the structure of the object to be studied. The ability to image dynamic processes in liquid media is certain to be transformative, lead to new discoveries, and provide a better understanding of many important processes at the nanoscale. To overcome the limitations of traditional electron microscopy, there has been a growing interest in recent years in developing means to image samples in real time in their native liquid environment and observe processes in situ as they take place. We briefly survey recent efforts pertaining to wet electron microscopy and then describe in greater detail the work of our group with a custom-made, micro-fabricated liquid cell dubbed the nanoaquarium. The nanoaquarium sandwiches a thin liquid layer, ranging in thickness from tens of nanometers to a few microns, between two thin, electron-transparent, silicon nitride membranes. The liquid cell is hermetically sealed from the vacuum environment of the electron microscope. The thin liquid layer allows one to image entities suspended in the liquid in transmission mode with high resolution. We describe briefly the interactions of the electron beam with water (radiolysis) and its implications; the study of nucleation, growth, and migration of gas nanobubbles; the imaging of diffusion limited aggregation of nanoparticles and formation of colloidal crystals; the electron-beam-induced formation and growth habit of gold crystals; and the study of morphological instabilities during electro-deposition of copper. The talk concludes with a description of the patterning of nanowires, using the electron beam as a pen without a need for a mask.
http://bau.seas.upenn.edu/
