EVIDENCE FOR A NEW SURFACE-STATE OF HYDROGEN ON NI(111)

Hydrogen and deuterium were ion implanted into Ni(111) and characterized by thermal desorption spectroscopy. In addition to the thermally populated β1 and β2 features and a peak at 250 K from bulk implantation, we have observed the existence of another peak below the β1 peak (at 306 K for heating rate of 5 K/s), This feature can, under particular conditions, be weakly populated using standard adsorption of H2, but is considerably enhanced by implantation. Using sequential implantation and adsorption of isotopically labelled di-hydrogen, we show that the new state is associated with the surface and not the bulk. Furthermore, its intensity is correlated with the presence of a subsurface hydrogenic species that desorbs with the high temperature part of the β2 state. © 1990.