The unexpected formation of Au-Si by the resonance neutralization of Ar during the low energy bombardment of Au nanoparticles on c-Si

Nanoscale Au layers, with irregular porosities, have been formed by the low energy Ar⁺ bombardment of Au nanoparticles that were sputter-deposited onto native oxide-covered Si surfaces. High-resolution field emission scanning electron microcopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) have been used to characterize the formation and evolution of the nanoporous layer. Under Ar⁺ bombardment, the Au nanoparticles that were initially deposited were observed to flatten and spread across the native oxide surface, without diffusing, finally coalescing at their edges to form a nanoporous film having irregular pore dimensions. XPS showed that this evolution was accompanied by the loss of Au as a result of sputtering. The formation of such porous films necessitates strong interfacial bonding to avoid the lateral diffusion of the Au nanoparticles, and their ultimate coalescence into larger nanoparticles.We demonstrated that Ar⁺ beam bombardment invariably caused the formation of Au^δ+-Si^δ− bonding, rather than the expected Au^δ−-Si^δ+ bonding, and we explain this to be due to the resonance neutralization of the Ar⁺ beam on impacting the Au layer. We also reveal that the presumed formation of AuSi_x is not quantifiable by XPS, due to the superposition of the chemical shift of the Au nanoparticles with that of the quantum size effect, during Au loss on sputtering.