Ras Investigation Of Benzene Adsorption On Vicinal Single-Domain Si(001)-(2 X 1) Surfaces

Optical spectroscopies such as reflectance anisotropy spectroscopy (RAS) and surface differential reflectivity spectroscopy (SDRS) have been extensively employed to characterize the surfaces and interfaces of semiconductors [1-5]. RAS measures the difference of the reflectance between two principal axis in the plane of surface while SDRS gives the change of the reflectivity during adsorption. Clean silicon surfaces (001) have been studied in experimental [3,6,7] and theoretical investigations [8-11] within these techniques, but few studies only report on optical properties of adsorbates on Si(001) [12-17]. In early works [12,13], the atomic hydrogen and the molecular oxygen have been employed to inform on the origin of the different structures observed on the clean spectrum of silicon. The authors demonstrated that one of the structures is directly related to the dangling bonds of silicon. Only qualitative pieces of information have been obtained on the assignment of the structures. Here, we want to demonstrate that the RAS technique is suitable to inform quantitatively as well as qualitatively onto the occupation of dimers. To this end, we will compare the RA spectrum obtained on an hydrogenized Si(001)-2 x 1 surface to the RA spectrum recorded on the surface saturated with benzene molecules. Indeed, when atomic hydrogen is adsorbed onto the silicon surface at about 300 degrees C, the dimers remain intact and almost all the dangling bonds are filled with one hydrogen atom. When the clean silicon surface is exposed to benzene molecules, only one dimer out of two is occupied [18]. The comparison of these two model systems will allow us to evidence a quantification of the RA signal related to the dangling bonds. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.