Dissimilar gold nanoclusters at GaAs(0 0 1) surface: Formation chemistry, structure, and localized plasmons

Abstract

A procedure is developed for controlled creation of Au nanoclusters by annealing of a gold film deposited onto GaAs(0 0 1) crystal surface. The nanoclusters of Au are formed at GaAs surfaces covered by either a natural oxide layer or a monolayer of gallium nitride. Surface morphology of the Au/GaAs structures with Au nanoclusters is characterized by scanning probe diagnostics and localized plasmons of the nanoclusters are investigated by optical reflection spectroscopy. In annealing Au film dissimilar gold nanoclusters are found to occur on oxidized or nitridized GaAs(0 0 1) surface via chemical transformation or recrystallization of Au film, respectively. Gold nanoclusters of the two types cause resonant peaks in optical reflectance spectra at the energies of 1.6 eV and 2.15 eV. Using the data of optical spectroscopy and their theoretical analysis we assign the former peak to localized plasmons of prolate Au nanoclusters buried into GaAs crystal near its surface. Another peak at 2.15 eV is attributed to plasmons of oblate Au nanoislands appearing on nitride overlayer which prevents any chemical contact of Au with GaAs bulk. The asserted existence of Au nanoclusters in the bulk of GaAs crystal near its oxidized surface is expected to be helpful in elucidating the nature and structure of Ohmic Au-GaAs contacts.