Evidence for heterogeneous oxidation on the surface of a plasma SiC nanopowder based on synchrotron-excited XPS

The surface chemistry of a plasma SiC nanopowder was characterized by X-ray photoelectron spectroscopy using a tunable synchrotron X-ray source. The sample surface was representative of SiC nanopowder surfaces in interaction with ambient air, with no significant influence from carbonaceous deposits. By choosing an incident photon energy in the range 200-1200 eV, the escape depth of photoelectrons was altered from 0.5 to 3 nm based on the C 1s, Si 2p and O 1s core-level transitions. The spectral series gave evidence for surface enrichment of silica and sp2-bonded elemental carbon. Several models of surface enrichment were tested against the spectral intensities as a function of escape depth. This analysis led to sp2-carbon islands and two types of oxidation depths. While on the larger part of the surface, the silica is only a near-monolayer in thickness, there are surface regions that are oxidized to a depth of >= 3 nm. These heavily oxidized regions are attributed to defected open channel pores on the outer surface of nanoparticle agglomerates, based on the previous electron tomography results.

Automated summary

The surface chemistry of a plasma SiC nanopowder was characterized using X-ray photoelectron spectroscopy. The results showed surface enrichment of silica and sp2-bonded elemental carbon, with varying oxidation depths.