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2012 - 11th Annual NC State Summer Undergraduate Research Symposium
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Session Time :
8/1/12 3:00 PM - 8/1/12 4:14 PM
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Content Area : NC State Independent Researchers
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Lead Student Presenters : Fangkai Yang
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Abstract Title : Simulation of Five-fold Twins Formation in Nanocrystalline Diamond Films
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Abstract :
Formation of twins in nanocrystalline metals plays a critical role in their physical properties, such as electrical and mechanical performance. For example, recent experiments show that introduction of nanotwins in ultrafine-grained metals can produce an unusual combination of ultrahigh strength and high ductility. In micro-electronic industries, twins in nano-scale grains can change the grain-boundary structure and atomic-diffusion behavior along the boundary. Stepped sites produced by twin boundaries can also provide lower energy barriers for intermediates to bind on and improve catalytic efficiency. In this project, simulation of a five-fold twin in a diamond thin-film was performed. The coordinates of carbon atoms in a five-fold twin were developed, according to the diamond crystal structure and mirror-reflection relationship of twin planes, as the original state for simulation. Hydrogen atoms were attached to the boundary carbon atoms to eliminate dangling bonds. The perfect diamond structure with the same number of carbon and hydrogen atoms was used for comparison. After simulation, several goals were accomplished as follows:
1. The defect energy was calculated using the Brenner potential.
2. The angle distribution of five-fold twins was determined, corresponding to the equilibrium structure.
3. The secondary defect (dislocation) structure along the grain boundaries of five-fold twins was explored.
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Mentor and/or Co-Author : Jay Narayan
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