HYPERPOLARIZABILITIES OF SI CLUSTERS - MODEL-CALCULATIONS TO INTERPRET 2ND-HARMONIC GENERATION FROM SIO2 SI(111) INTERFACE/

We have evaluated molecular hyperpolarizability beta of Si clusters ei ther with or without a dangling bond normal to Si(111) surface, and di scussed the results in relation to the second-harmonic-generation (SHG ) measurement from SiO2/Si(111) interface. The simplified sum-over-sta tes calculation and missing-orbital analysis are extended to handle an open shell system, i.e. a dangling bond. In the presence of the dangl ing bond, beta is caused by charge-transfers from the cluster interior to the dangling bond, while its absence by hydrogen termination great ly reduces beta. This is consistent with the experiment that SHG is re duced by termination of interfacial Si atoms by annealing under hydrog en ambient. (C) 1997 Elsevier Science B.V.