Adsorption of Acetic Acid on Ge(100) Surface
The adsorption structure of acetic acid on Ge(100) at room temperature has been studied with scanning tunneling microscopy (STM) and ab initio pseudopotential calculations. The conversion of acetic acid to acetate on Ge(100) surface occurs by dissociation of the O-H bond and by the formation of the Ge-O bond. The abstracted hydrogen saturates the dangling bond of the other Ge dimer atom or is diffused to neighbor dimer. Our STM results illustrate the different adsorption configurations: (i) by using only one oxygen (unidentate form) or both oxygen atoms (bidentate form). Bidentate structures are divided into two types: in the end-bridge structure two Ge-O bonds bridge the ends of two adjacent dimers in a dime row which is oriented parallel to the dimer row, and in the on top structure two Ge-O bond bridge on the single dimer which is oriented perpendicular to the dimer row. Acetic acid exposed surfaces were annealed to investigate the annealing effect. When the binding energies of possible products were computed on the Ge(100) surface, the on top structure are more stable than other geometries. However on top bidentate products are observed only after annealing. It can be seen thermodynamically preferred over the bidentate product.
Adsorption of Benzoic Acid on Ge(100) Surface
The adsorption of benzoic acid molecule onto the Ge(100) surface was investigated using scanning tunneling microscopy (STM) at room temperature. The bright protrusions are observed in the filled - state STM image $(V_s = - 2.0 V)$ and contributed to adsorbed benzoate molecules onto the Ge dimer. We measured the voltage dependent STM images to investigate the detailed geometry. At low coverage, adsorbates show round shaped-bright protrusions which are two types of adsorption structures. Benzoic acid molecule binds to a Ge-Ge dimer via Ge-O linkage through the dissociation of O-H bond on Ge(100). In case of A feature, benzoate forms a unidentate...