Thermal desorption study of Ba and hydrogen coadsorption on Ni(110) surface

In this work, we study the coadsorption of barium (Ba) and hydrogen (H) on Ni(100) surfaces using mainly thermal desorption spectroscopy (TDS) in correlation with Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and work function (WF) measurements. Two different processes have been used for the coadsorption experiments: (1) Ba deposition on hydrogenated Ni(110) and (2) H adsorption on Ba-covered Ni(110). In both cases, H gives two different TD energy states, β1 and β2. The first state is the same with that of H adsorption on clean Ni(110), pointing to a direct H–Ni bonding, while the second, which is attributed to a H–Ba interaction, shifts to higher temperature as Ba-coverage increases up to ΘBa=0.9 ML. This shift indicates a gradually developing attractive H–Ba interaction leading to BaH2 formation. The formation of BaH2 does not depend on the sequence of Ba and H deposition. For ΘBa≥0.3 ML, H adsorption on Ba/Ni(110) does not induce any WF change, as H2 does on alkali-covered surfaces. This means that the Ba/Ni(110) surface might be a stable negative H ion source.