Thermally Activated Reactions of Nitrobenzene at the Ge(100)-2 × 1 Surface

Abstract

The adsorption of nitro compounds on the germanium surface serves as a model system for understanding the formation of interfacial germanium oxynitride. We have studied the adsorption and thermal reactions of nitrobenzene on the Ge(100)-2 × 1 surface under ultrahigh vacuum conditions. A combination of infrared spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed desorption experiments together with density functional theory calculations was used to elucidate possible product structures and their associated reaction mechanisms. Our study suggests that nitrobenzene initially forms a 1,3-dipolar cycloaddition product with a Ge(100) surface dimer as the major species. Minor side products are also formed at 300 K. Upon heating, some of the adsorbates molecularly desorb, while a fraction of the adsorbates undergo oxygen atom insertion into the surface, transforming them into triplet nitrene products. The energetics and pathways of nitrobenzene on the Ge surface are discussed in comparison with those seen on the closely related Si(100)-2 × 1 surface, with some differences arising from the smaller adsorption energy of organic adsorbates on Ge.