American Vacuum Society - 51st International Symposium, Anaheim, CA, 11/14 - 11/19/04 (poster)

J. Sun (UNH), H. Mönig, J. Wells, Ph. Hofmann (Univ. of Aarhus, Denmark), and K. Pohl (UNH)

Bismuth is a group V semimetal with a very low density of states at the Fermi level.
However, a small distortion of its rhombohedral (A7) bulk structure would give a cubic lattice, which should be a good metal.
In view of this close relation between structure and electronic structure it is not surprising that the surfaces of Bi are very different from the bulk material.
They are good, two-dimensional metals with an electronic structure governed by spin-orbit coupling.^{1-3}
The changes in the geometric structure which lead to these interesting properties are totally unknown.
We have studied the surface structure of clean Bi(111) and the mean-square displacement of the surface atoms by low energy electron diffraction (LEED).
Experimental and theoretical diffraction intensities are analyzed for sample temperatures of 140, 171, 218, 268, and 313K.
The optimization of the structural and nonstructural parameters is carried out by minimizing a R-factor with the quadratic tensor model algorithm.
This results in an excellent agreement between the experimental and calculated data and R-factors of less than 0.1 are obtained.
Moreover, the short termination of the bulk on the surface is confirmed.
The temperature-dependent relaxations of the first layer distances and the atomic vibrations in the surface region are discussed.

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