HYDROGEN ADSORPTION ON SULFUR AND NITROGEN COVERED RU(001) SURFACES

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.