Imaging of sub-surface nano particles by tapping-mode atomic force microscopy

Time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), and tapping mode atomic force microscopy (TM-AFM) were used to study the surface of a poly(N-vinyl-2-pyrrolidone) thin film containing nano silica particles. ToF-SIMS results illustrate that the topmost layer of the thin film consists of PVP and a small amount of poly(dimethyl siloxane) (PDMS). Nano silica particles are localized underneath this layer. XPS results suggest that the concentration of the silica particles increases as the sampling depth increases from 5.3 to 7.2 nm. TM-AFM phase imaging is shown to be capable of detecting the presence of these sub-surface nano silica particles.