Dynamic secondary ion mass spectroscopy of Au nanoparticles on Si wafer using Bi3+ as primary ion coupled with surface etching by Ar cluster ion beam: The effect of etching conditions on surface structure

Wet-chemically synthesized Au nanoparticles were deposited on Si wafer surfaces, and the secondary ions mass spectra (SIMS) from these samples were collected using Bi₃⁺ with an energy of 30 keV as the primary ions. In the SIMS, Au cluster cations with a well-known, even-odd alteration pattern in the signal intensity were observed. We also performed depth profile SIMS analyses, i.e., etching the surface using an Ar gas cluster ion beam (GCIB), and a subsequent Bi₃⁺ SIMS analysis was repetitively performed. Here, two different etching conditions (Ar₁₆₀₀ clusters of 10 keV energy or Ar₁₀₀₀ of 2.5 keV denoted as "harsh" or "soft" etching conditions, respectively) were used. Etching under harsh conditions induced emission of the Au-Si binary cluster cations in the SIMS spectra of the Bi₃⁺ primary ions. The formation of binary cluster cations can be induced by either fragmentation of Au nanoparticles or alloying of Au and Si, increasing Au-Si coordination on the sample surface during harsh GCIB etching. Alternatively, use of the soft GCIB etching conditions resulted in exclusive emission of pure Au cluster cations with nearly no Au-Si cluster cation formation. Depth profile analyses of the Bi₃⁺ SIMS combined with soft GCIB etching can be useful for studying the chemical environments of atoms at the surface without altering the original interface structure during etching.