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Unformatted text preview: January 28, 2009 Condensed Matter Physics/Physics-335 Assignment #2Diffraction Due on Moday February 8, 2010 @ 12:30PM sharp (Suggestion: start immediately working on this assignment it is a bit more difficult than it looks. This is particularly the case for Problem #4). Problem #1 (10 marks) Low-energy electron diffraction (LEED) experiments are carried on to study molecular adsorption of molecular nitrogen (N 2 ) and argon (Ar) on the surface of a graphite single crystal. In the regime of vapor pressure considered, 75% of N 2 and 25% of Ar are adsorbed on the (hexagonal) crystalline surface of graphite. The N 2 molecules and Ar atoms organize themselves with the two-dimensional lattice structure shown below. We are assuming that in the range of adsorption temperature considered, the N 2 molecules are spinning rapidly, so that their elongated ellipsoidal molecular shape can be forgotten, and N 2 molecules can be represented by spherical objects. We take the relative form factor of Ar, objects....
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