The influence of coadsorbed sodium atoms on the chemisorption of benzoic acid on Si(100)-2 x 1

The adsorption of benzoic acid on Na-Si(100)-2 x 1 (Theta(Na) = 0.5) at room temperature leads to benzoate in a bidentate coordination. High-resolution electron energy loss spectroscopy spectra show an intense v(s)(OCO) stretching vibration, which is characteristic for benzoate aligned perpendicular to the substrate surface. In contrast, we observe monodentate benzoate species following the exposure of Si(100)-2 x 1 to benzoic acid at room temperature. On both surfaces, the dissociated hydrogen atom bonds to one of the silicon surface atoms. Removal of benzoate from Na-Si(100)-2 x 1 is observed after heating the silicon substrate to 300 degrees C for 1 min. (C) 1999 Elsevier Science B.V. All rights reserved.