Infrared spectra of ammonia adsorbed on evaporated germanium films

Abstract

The spectra due to various adsorbed species of ammonia have been obtained between 2000 and 1000 cm^–1. A weak band at 1920 cm^–1, which disappears with time or on continued exposure, has been attributed to surface Ge—H bonds resulting from dissociative adsorption. Two mechanisms have been postulated for the removal of adsorbed hydrogen; at low exposures surface recombination of pairs of H atoms is thought to be responsible, while at high exposures the mechanism NH_3(g)+ Ge—H → Ge—NH_2(g) is thought to be more relevant. Bands in the deformation region have been assigned to: adsorbed primary amine (1540 cm^–1), co-ordinatively adsorbed ammonia (1590 cm^–1 and 1320–1250 cm^–1) and physically adsorbed ammonia (1650–1600 cm^–1 and 1150–1000 cm^–1). The reaction: Ge—O—Ge + NH_3(g)→ Ge—OH + Ge—NH₂ has also been inferred from spectra obtained with pre-oxidised germanium.