Atomic and Electronic Structures of Aluminum Clusters, Solid Buckminsterfullerene, and Interfaces of Aluminum on Gallium ARSENIDE(110)
Abstract
The energetics and structure of Al clusters containing 13, 19, and 55 atoms are studied using the Car-Parrinello method. It is found that the structural energy differences between small cluster and bulk structures are surprisingly small, indicating that the icosahedral-fcc structural transition can occur very early in Al clusters. Simulated annealing studies for 13- and 55-atom cluster show that the distortions from the ideal structures are substantial. For a 13-atom Al cluster, a slightly distorted icosahedron is the lowest energy structure. For a 55-atom Al cluster, several inequivalent but energetically nearly degenerate structures are found, which is likely to lead to floppiness at finite temperatures as well as a low melting point. The origin of this near -degeneracy is traced to the short range of the effective interatomic interactions. We have carried out ab-initio structure optimization and quantum molecular dynamics simulations for solid C_{60}. The symmetry-unconstrained optimization results in a nearly ideal buckminsterfullerene structure. The T = 0 ^circK structure consists of alternating single and double bonds, but this distinction becomes blurred at relatively low temperatures. The intermolecular interactions are so weak that the individual C_{60 } molecules can rotate at relatively low temperatures. At high temperatures vibrations cause large distortions, but the cage structure is still preserved. Atomic structure of Al on GaAs(110) is studied using ab-initio molecular dynamics. For a chemisorbed Al atom, a three-fold coordinated site is preferred and its binding energy is 3.4 eV. The surface potential barrier for Al migration is 0.7 eV. Dimer -like structure and cluster formation are more stable than separate adsorption of Al atoms. The Al cluster we have studied interacts strongly with the GaAs substrate. The reason for the absence of Fermi level pinning in cluster deposition is explained.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1991
- Bibcode:
- 1991PhDT........49Y
- Keywords:
-
- ATOMIC STRUCTURE;
- BUCKMINSTERFULLERENE;
- GALLIUM ARSENIDE(110);
- Physics: Condensed Matter