Potassium adsorption on hydrogen-covered Ru(0001) studied by metastable quenching spectroscopy, thermal desorption, and electron-stimulated desorption

Abstract

Metastable quenching spectroscopy, thermal desorption spectroscopy, and electron stimulated desorption spectroscopy were used to study how potassium adsorption affects hydrogen binding to the Ru(0001) surface. Potassium causes the appearance of Penning ionization peaks from H/Ru surface states, which are found to be more prominent with Ne ∗ than with He ∗. This intensity difference is explained qualitatively by a model in which the competition between metastable quenching by resonance ionization or by Penning ionization is examined in terms of surface work function, the metastable atom ionization potential, and the image-charge potential. Potassium adsorption on Ru(0001) precovered with hydrogen leads to the appearance of a narrow high temperature peak in the H 2 thermal desorption spectrum. At that temperature H 2 desorbs simultaneously with the last of the adsorbed potassium left on the surface. This peak is increased and broadened if the Ru surface is sputtered prior to H 2 and K coadsorption. The presence of potassium increases the ESD H + yield by a factor of up to 30 times that without potassium, with the yield peaking at the potassium coverage giving the minmum work function, and sharply decreasing as the potassium coverage is increased further. This effect is discussed in terms of a model proposed by Lanzillotto, Dresser, Alvey and Yates for similar results on the H/K/Ni(111) system.