Surface EXAFS via differential electron yield

Abstract

Surface-sensitive analysis via extended X-ray absorption fine-structure (EXAFS) spectroscopy is demonstrated using a thickness-defined SiO2 (12.4 nm)/Si sample. The proposed method exploits the differential electron yield (DEY) method wherein Auger electrons escaping from a sample surface are detected by an electron analyzer. The DEY method removes local intensity changes in the EXAFS spectra caused by photoelectrons crossing the Auger peak during X-ray energy sweeps, enabling EXAFS analysis through Fourier transformation of wide-energy-range spectral oscillations. The Si K-edge DEY X-ray absorption near-edge structure (XANES) spectrum appears to comprise high amounts of SiO2 and low Si content, suggesting an analysis depth, as expressed using the inelastic mean free path of electrons in general electron spectroscopy, of approximately 4.2 nm. The first nearest neighbor (Si—O) distance derived from the Fourier transform of the Si K-edge DEY-EXAFS oscillation is 1.63 Å. This value is within the reported values of bulk SiO2, showing that DEY can be used to detect a surface layer of 12.4 nm thickness with an analysis depth of approximately 4.2 nm and enable `surface EXAFS' analysis using Fourier transformation.