Surface science lettersDetermination of the absolute saturation coverage of hydrogen on Ru(001)

We describe here a general methodology for the indirect relative determination of absolute fractional surface coverages. The saturation fractional coverage of hydrogen on Ru(001) has been evaluated in particular. In this case, we used H2CO as a bridge to lead us from the known reference point of the saturation fractional coverage of CO to the unknown reference point of the fractional coverage of hydrogen on Ru(001), which is then used to determine accurately the saturation fractional coverage of hydrogen. We find that θsatH = 1.02±0.05, i.e. the surface stoichiometry is Ru:H = 1:1. The relative nature of the method, which cancels systematic errors, together with the utilization of a glass envelope around the mass spectrometer, which reduces spurious contributions in the thermal desorption spectra, results in high accuracy in the determination of absolute fractional coverages.