Gold Nanoclusters at the Interface Au/GaAs(001): Preparation, Characterization, and Plasmonic Spectroscopy

Resumo

Local plasmons of gold nanoclusters formed at Au/GaAs interface are observed and investigated. The gold nanoclusters are prepared by thermal annealing of thin Au films deposited on GaAs(001) surface. In order to prevent chemical interaction between Au and GaAs at high temperatures, a thin layer of GaN is formed on GaAs substrate surface by chemical nitridation in hydrazine sulfide solution prior to deposition of Au. Typical shapes and sizes of Au nanoclusters are obtained from STM characterization of samples in ultrahigh vacuum followed by measuring and calculating their optical reflectivity spectra. In general, the reflectivity spectra of Au/GaAs samples reveal two resonant peaks at the energies about 1.55 and 2.15 eV. The former peak dominates for oxidized GaAs(001) substrates, while the latter peak is clearly visible for nitridized GaAs substrates. Theoretical analysis of the optical spectra of Au/GaAs interface using a model of Au nanospheroids allows us to assign the reflectance peak at 2.15 eV to local plasmons of Au nanoclusters which look like oblate islands on a Au/GaAs(001) sample. In turn, the peak at 1.55 eV is assigned to plasmons of Au nanoclusters prolate perpendicularly to the surface of GaAs crystal in whose near-surface region these Au clusters are buried.