Hydrogen adsorption on nitrogen- and sulfur-modified Ru(001) surfaces
was investigated using X-ray and ultra-violet photoelectron spectrosco
pies (XPS and WS), low-energy electron diffraction (LEED) and thermal
desorption spectroscopy (TDS). On a S-covered Ru(001), two thermal des
orption peaks of hydrogen at 135 and 265 K were clearly observed at su
lfur coverages > 0.1, at which p(2 X 2)-S islands start to form. The i
ntensities of these two peaks increase with theta(S) up to 0.21, and t
hen decrease rapidly at higher sulfur coverages. At theta(S) = 0.33, c
orresponding to a complete (root 3 X root 3)R30 degrees LEED pattern,
hydrogen adsorption was fully suppressed. Compared with hydrogen desor
ption from H2S decomposition on Ru(001), it was concluded that the hyd
rogen desorption peak at 135 K is correlated with the formation of p(2
X 2)-S unit cells. Our experiments further demonstrate that preadsorb
ed N-atoms also inhibit the adsorption of hydrogen with each N-adatom
blocking four hydrogen adsorption sites.