Oxidation of deposited Au_n (n = 2-13) on SiO₂/Si: Influence of the NaOH(aq) treatment

Au cluster anions consisting of 2-13 atoms were soft-landed on native-oxide-covered Si wafers. Reaction of soft-landed clusters with an atomic oxygen atmosphere was studied using X-ray photoelectron spectroscopy (XPS). Au₅, Au₇, and Au₁₃ turned out to show pronounced inertness for Au-oxide formation. When the samples with deposited Au clusters were treated with aqueous NaOH, the inert Au₅, Au₇, and Au₁₃ clusters became reactive towards Au-oxide formation, whereas the other originally reactive clusters became inert. This result can be interpreted in terms of electronic modification of Au clusters by Na, which was also evidenced by Au 4f and Na 1s core level shifts.