Nuclear-reaction analysis of H at the Pb/Si(111) interface: Monolayer depth distinction and interface structure

Hydrogen atoms buried at the interface between Pb layers and the Si(111) surface were investigated by resonant nuclear reaction analysis (NRA) using ${}^{1}\mathrm{H}{(}^{15}\mathrm{N},\ensuremath{\alpha}\ensuremath{\gamma}{)}^{12}\mathrm{C}$ in grazing incidence geometry. Pb atoms were deposited on the H-terminated Si(111) surface at 110 K, and the H depth was clearly distinguished with a depth scale of one monolayer. The NRA spectrum revealed a monotonous shift to higher energy with increasing Pb coverage indicating H remains at the interface between Pb and the Si substrate. The dependence of the spectral shift on the Pb coverage was found to have an offset corresponding to a depth of about 0.1 nm. This offset suggests a model for the Pb/H/Si(111) interface structure implying that the initial Pb layer resides in the preadsorbed H layer.