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Abstract:
Cesium, hydrogen and oxygen adsorption on beryllium clusters are studied using restricted Hartree-Fock (RHF) calculations and ab initio relativistic effective core potentials. The clusters are taken as cylindrical plugs from beryllium wafers. Cs(-), H(-) and 0-to-substrate internuclear distances are optimized. For each system numerous low-lying electronic states are investigated and Mulliken electron populations analyzed. RHF calculations show that Be19, with three layers of atoms, is too small to adequately model the Be surface, while Be33, a five-layered system, and Be45, a seven-layered system, are more accurate representations of the bulk metal. The emitted electron is clearly seen as vacating a molecular orbital which is localized in the surface layer of the cluster, thereby giving further credence to the model. RHF calculations are completed for Pbl and Bil semiconductor clusters. Blue shifts in optical spectra and geometry changes are shown to be due to quantum size effects. Scanning tunneling microscopy is used to investigate the nature of colloidal particles in the 15 nm diameter size range. Images show a near monodispersion of small gold clusters. A model of the STM tip as a polyatomic crystalline surface is shown to correctly explain observations of anomalous long range order.
| Limitations: |
 APPROVED FOR PUBLIC RELEASE |
| Description: |
Final rept. 1 Jul 87-30 Jun 90 |
| Pages: |
121 |
| Report Date: |
APR 91 |
| Contract Number: |
AFOSR-87-0302 |
| Report Number: |
A609542 |
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