A theoretical study of cluster reactivity and the effects of electric field on adatom-surface bond
Akpati, Hilary Chukwuma
Nordlander, Peter J.
Master of Science
We have used the density functional ab initio method to study the reactivity of small clusters (ammonia reacting with GaAs clusters), and the effects of electric field on adatom-surface interactions (H and Al adsorbed on Si(111) surface). In the case of NH$\sb3$ reactivity at various sites of a Ga$\rm\sb5As\sb5$ cluster, a strong correlation is found between the adsorbate-cluster binding energy and charge transfer. Ionizing the bare cluster to a cationic charge state enables multiple chemisorption of ammonia, which is much less favored on a neutral cluster and can be prohibited on a negatively charged cluster. In the case H and Al adsorbed on a Si(111) surface, the influence of an external electric field, such as that present in a scanning tunnelling microscope (STM), on the chemisorption bond is investigated. The changes in charge distributions, vibrational frequencies and adsorbate desorption barriers are calculated as a function of the strength and direction of the electric field. We find that the characteristics of the chemisorption bond can, to a large extent, be controlled through the externally applied field.
Physics; Condensed matter physics; Molecular physics