AVS 53rd International Symposium
    Surface Science Monday Sessions
       Session SS2-MoA

Paper SS2-MoA2
Adsorption of Ethanethiol, Ethanol, and Mercaptoethanol on Ge(100)-2x1

Monday, November 13, 2006, 2:20 pm, Room 2004

Session: Functionalization of Semiconductor Surfaces
Presenter: J.S. Kachian, Stanford University
Authors: J.S. Kachian, Stanford University
S.F. Bent, Stanford University
Correspondent: Click to Email
The adsorption of ethanethiol, ethanol and mercaptoethanol on Ge(100)-2x1 at 310 K was investigated to gain a fundamental understanding of bonding in these systems for use in practical applications surrounding semiconductor passivation. Vibrational spectra of the products of these three reactions obtained via multiple internal reflection Fourier transform infrared (MIR-FTIR) spectroscopy in ultrahigh vacuum suggest that the products are formed via dissociation of the X-H bond, where X represents the electronegative atom(s)-O and/or S--in the adsorbate. It is believed that these reactions are preceded by a dative-bonded state in which the electronegative atom of the adsorbate donates a lone pair of electrons to the down atom of a germanium dimer. Density functional theory was used to investigate this pathway, and potential energy surfaces and frequency spectra obtained by calculation support the postulated mechanism. The results will be discussed in the context of relative reactivity of S versus O groups. Further, these results can be applied towards the analysis of larger molecules, which contain reactive centers in addition to that of a thiol or alcohol group. Of particular interest is the thiol-containing amino acid cysteine. This molecule, which introduces competition between thiol, amino and carboxyl moieties, is largely responsible for the formation of disulfide bonds in proteins, thus leading to stable three-dimensional protein structure. Understanding the reactivity of the thiol moiety in the context of a biologically relevant molecule brings the concept of nanoscale biosensors one step closer to reality.