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NUE 2003-2004

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Graphite Spiral

This image shows a growth spiral on the surface of a natural graphite crystal from Namibia. There is also a self-assembled array of micro-scale growth hillocks (low hills) at the corners of the spiral's steps. A possible (and as yet unverified) mechanism for the formation of these growth hillocks is based on impurities. As illustrated in the animation, imagine that there are impurities on the surface of the graphite that are mobile (free to diffuse around the surface).

Growth of the graphite takes place primarily at the steps of the spiral. As carbon atoms attach at the steps, the steps develop kinks which appear to move along the step as carbon atoms attach at the kinks. The advancing kinks and steps move the impurities out of the way (crystallization purification) and tend to concentrate the impurities at the spiral corners. As the concentration of the impurities increases at the corners, they interfere with the spiral growth.

Eventually they can "pin" the step at the corner. As the pinned impurities eventually get covered in carbon layers they could nucleate screw dislocations (atomic-scale defects), which could lead to hillock formation at the step corners.

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About This Animation

Investigators:

Dr. John A. Jaszczak
Department of Physics, Michigan Technological University
Houghton, Michigan

Dr. John Rakovan
Geology Department, Miami University
Oxford, Ohio

Animator:

Dr. Susan E. Hill

Animation Usage

  1. "Monte Carlo Simulations of Surface Phase Transitions and Morphology Dynamics"
    The 2004 PhD dissertation presented by Da Gao, MTU physics graduate student, included this animation.
  2. Surprises in Natural Graphite: Beauty from Defects
    The MTU Physics Colloquium presented by Dr. John A. Jaszczak on January 22, 2004 included this animation.
  3. The same presentation was given at Drexel University's Materials Science & Engineering Department on September 3, 2003.

© 2003 Michigan Technological University