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Computer modeling allows a better understanding of the properties of a material. Changing parameters within a computer program, rather than in a laboratory, permits materials scientists to narrow the scope of their research quickly and efficiently. Here, software developed by Dr. Ju Li, formerly an assistant professor in our department and now at the University of Pennsylvania, helps to visualize the atomic structure of a silicon vacancy, as noted by the green atoms. [see the big picture]
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Understanding a material's properties, and the reason for these properties, is critical in materials science. This "pillar" was created by machining away adjacent material to create a free standing cylinder for compression testing (SEM image, pillar width is 20 μm). Compression tests are performed on these small samples to better understand mechanical properties for use in MEMS and aerospace applications. [see the big picture] Go to Dr. James Williams' research page.
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Atoms can assemble naturally into crystal structures according to the rules of physics. One of the tasks of materials science is to create structures that would not exist in nature, but have much better properties than naturally occurring materials. In the field of electronics, mixing silicon with carbon is desirable since it should result in novel electronic materials with substantially improved properties. However, the solubility of carbon in silicon is very low (~1%). The picture shows the atomic structure of a mixture of 80% silicon and 20% carbon. Theoretical calculations, developed by Dr. Wolfgang Windl, have predicted that a certain arrangement of the carbon atoms (in so-called third-neighbor positions) could create a structure that might be stable enough to be synthesized. Researchers at Arizona State University, using Dr. Windl's calculations, successfully developed this structure in the laboratory. [see the big picture] Go to Dr. Wolfgang Windl's research page.
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Tribology is the science and technology of contacting surfaces in relative motion. MSE is contributing to better understanding of flow processes in this important interdisciplinary field. This figure shows results from an MD simulation using a model crystalline system A (red atoms) sliding on another crystalline system B (blue atoms) at a relative velocity of 1.0 (Lennard-Jones units). The image shows a mechanically mixed layer and a highly disordered zone at the sliding interface. It illustrates, within the limits of computer modeling, how solids can change in both structure and composition through a mixing process resulting from rotational flow, as in fluids. This example shows effects on the nanoscale, but similar flow behavior is expected at size scales ranging up to those encountered in plate tectonics.
[see the big picture] Go to Dr. David Rigney's research page.
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What makes a material strong? Why does it break? Understanding the mechanical behavior of a material is critical when using it in day-to-day applications. By understanding what controls the mechanical properties, such as strength and ductility, materials scientists can tailor the chemical composition and processing of a material to meet a required need. The green lines in the image above represent lines of atomic dislocations in a metal (the red colored regions represent groups of densely packed dislocations). How dislocations migrate in a material is the key to understanding the material's mechanical behavior. Application of this knowledge allows our students and faculty to optimize mechanical properties for a given need--be it an artificial hip or a turbine blade in an advanced jet propulsion system. [see the big picture] Go to Dr. Yunzhi Wang's research page.
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This is a Z-contrast electron microscope image, taken at Oak Ridge National Laboratory by Sergei Lopatin with FEI Corp., of an oxidized mixture of silicon and germanium. The dark area on the right is SiO2, the peanut-shaped blobs on the left are double columns of atoms. The brighter (more yellow) the "peanut," the more germanium is in the respective column. By oxidzing a silicon-germanium mixture instead of plain silicon, a perfect interface is created with the oxide, enabling extremely fast electronic devices such as computer chips. Dr. Windl received jointly with Dr. Duscher (NCSU) the 2004 Nanotechnology Industrial Impact Award for this discovery. [see the big picture] Go to Dr. Wolfgang Windl's research page.
