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Materials Science at Oregon State University

Using the transmission electron microscope to correlate physical properties and microstructure in micron- and nano-scale systems

Date: Thursday, May 27th
Presenter: Daan Hein Alsem, Ph. D., Hummingbird Scientific


Electron microscopy is an important tool for today?s physical scientist. With the advent of in-situ transmission electron microscopy (TEM) as a more accessible experimental technique it has also become possible to perform experiments while obtaining high magnification images of the internal structure of a material as it evolves. This permits direct correlations to be made between materials processing conditions, microstructure, properties and performance. This approach not only yields deeper understanding of the basic physical processes involved, but also allows rapid exploration of a matrix of conditions and effects. In this talk I will focus on research on small scale mechanical behavior using analytical and in-situ TEM as well as the utilization of in-situ TEM imaging in ambient pressure or liquid environments using a newly developed atmospheric pressure environmental cell.

Adhesion, wear and fatigue are large issues in the reliability of micron-scale structures, so-called microelectromechanical systems (MEMS). Because large surface to volume ratios of components in these devices can cause the governing failure mechanisms as well as the mechanical properties to be different from macro-scale structures, research into mechanical behavior of structural materials at small length scales has become of great importance. I will present work focusing on measuring fatigue and wear behavior of micron-scale polysilicon and finding physical mechanisms for these failure modes using MEMS testing and (in-situ) TEM.

Recently I have focused on work utilizing a newly developed in-situ TEM fluidic experimental platform. This has made it possible to image nano-scale materials in ambient pressure gas and liquid environments with (sub-)nanometer resolution. Specifically, it has allowed direct insight into the development of nano-particle interaction and agglomeration as well as the development of surface layers on Li-ion battery electrode materials during battery charging/discharging. This technique has also been used for nanometer resolution imaging of biological structures in their native liquid environment.