SXPS and XANES Studies of Interface Reactions of Organic Molecules on Sulfide Semiconductors

Abstract

The interaction of the organic heterocycle 2-mercaptobenzothiazole (MBT) with CdS(10ī10) surfaces was investigated using SXPS and NK XANES spectra excited with synchrotron radiation. The molecules were found to be chemisorbed after deprotonation at the nitrogen atom. Angular dependent NK XANES measurements of the adsorbate complex indicated an upright and tilted orientation of the MBT molecular planes of the adsorbed MBT molecules in the [ī12ī10] direction of the crystal. In consequence of an interface reaction step an overlayer of the disulfide bis-(2-benzothiazolyl)disulfide (BBTD) was detected. This second reaction step was found to be induced by photoelectrical generation of electron—hole pairs in the semiconductor. A proposed reaction model includes the transport of the charge carriers to the semiconductor surface and subsequent charge transfer across the interface. The model was verified by adsorption experiments on differently doped semiconductor crystals which resulted in distinct differences in adsorbate composition.