The adsorption of hydrogen on a ruthenium (101̄0) surface

Publisher Website
Google Scholar
Abstract
Video-LEED, HREELS, TDS, and Δφ measurements were used to investigate the adsorptive, structural, and vibrational properties of the Ru(101̄0)/H system between 100 and 500 K. At all temperatures investigated hydrogen adsorbs dissociatively with very high initial sticking probability (s0≈1.0) with apparent precursor mechanism. The saturation coverage at 100 K is extraordinarily high (Θmax =2≂1.728×1015 H atoms cm−2), up to this coverage four H binding states α, β1, β2, and β3 can be distinguished having desorption energies between 56 KJ/mol (α) and 80 KJ/mol (β3). The H binding states are intimately correlated with the four observable ordered H phases: At Θ=1 a c(8×2) or ‘‘1×2’’ structure with weak split spots appears which transforms at higher coverages into a clear 1×2 phase with likewise weak spots and with maximum intensity at Θ=1.2. It follows a c(2×2)-3H phase (I maximum at Θ=1.5) with rather more intense ‘extra’ spots which fade away with increasing coverage until at Θ=2.0 a (1×1)-2H pattern is reached. The (positive) H-induced work function change Δφ runs through two maxima and saturates at ∼250 mV. The vibrational loss spectra which were measured in two perpendicular azimuths exhibit a variety of bands which can be correlated with the ordered H phases and point to H species bound in two different kinds of threefold coordinated sites. Our data suggest several structural similarities with the neighboring system in the periodic table, Rh(110)/H, but also interesting differences.