Adsorption configurations and thermal chemistry of acetylene on the Ge(100) surface

Abstract

The adsorptionstructures and thermal desorption behavior of C 2 H 2 on Ge(100) were studied in ultrahigh vacuum by scanning tunneling microscopy(STM) and temperature programmed desorption(TPD). The STM investigation revealed that, at low coverage, C 2 H 2 initially adsorbs onto the Ge(100) surface with two types of configurations: (i) a di-σ configuration on top of a single Ge–Ge dimer (on-top) and (ii) a tetra-σ configuration parallel to the dimer axes, bridging two neighboring Ge dimers (p -bridge). TPD measurements show that chemisorbed C 2 H 2 desorbs from Ge(100) nondissociatively with two different desorption features, denoted as α (520 K) and β (560 K). In addition, it was found that the desorption of C 2 H 2 follows first order kinetics for both states and that the desorption energies of the α (520 K) and β (560 K) states are 1.3 and 1.4 eV, respectively. STM studies of the adsorption of C 2 H 2 at various Gesurface temperatures indicate that the α and β features correspond to the on-top and p -bridge configurations, respectively.