Surface extended x-ray-absorption fine structure of low-Z adsorbates studied with fluorescence detection

Comparison of x-ray-fluorescence-yield and electron-yield surface extended x-ray-absorption fine-structure spectra above the S K edge for c(2×2)S on Ni(100) reveals an order-of-magnitude higher sensitivity for the former technique. Thiophene (C4H4S) chemisorption on Ni(100) is studied with S coverages down to 0.08 monolayer. The molecule dissociates at temperatures as low as 100 K by interaction with fourfold hollow Ni sites. Blocking of these sites by oxygen leaves the molecule intact. © 1985 The American Physical Society.