First-principles study of thiols adsorption and self-assembly on GaAs surface

This work has been performed at University of Sherbrooke (Canada) as a part of the Epitaxial Quantum Dot Biosensor project under supervision of Professor Jan J. Dubowski

Thiol on GaAs molecular structure

Self-assembled monolayers (SAMs) of organosulfur compounds on solid surfaces attract a lot of interest both from fundamental perspective and due to their potential applications among which are development of precursors for the growth of II-VI materials, creation of transition layers for ohmic contacts and Schottky diodes, surface passivation, nanolithography, electrochemical applications and biosensing.

Theoretical modeling of the semiconductor-thiol interface can provide valuable information about the bonding nature in such material system and, ultimately, it would help to design and optimize a semiconductor-thiol interface addressing specific application. In contrast to alkanethiols on gold which are considered a prototype example of SAMs, theoretical studies of thiols on GaAs appear to be missing in the literature. The adsorption of a thiol is strongly influenced by the surface chemical reactivity, lattice constant, crystallographic orientation, etc. Therefore a little information available from the well-studied SAMs of thiols on noble metals can be applied to GaAs.

We investigate the properties of thiols adsorbed on GaAs surface as a link for further immobilization of bio-molecules aiming for the semiconductor-based bio-detector. The calculations are performed using a density functional theory (DFT) in a periodic supercell approach, based on pseudopotentials and numerical localized atomic orbitals as basis sets, as implemented in the SIESTA code. Different exchange-correlation functionals are tested. Among the properties under study are molecular dynamics of adsorption process, equilibrium geometries of chemisorbed species, nature of chemical bonding of thiol to GaAs surface, binding energies, geometries of optimal packing and formation of self-assembled monolayers (SAM), effect of different thiol terminations (end-groups), head-groups and thiol chain length, adsorption on various surface orientations and reconstructions, adsorption on doped and oxidized GaAs surfaces.

Gallery

Publications

  • O. Voznyy, J. J. Dubowski,
    Structure of thiol self-assembled monolayers commensurate with GaAs (001) surface,
    Langmuir, 24, 2008, p.13299.
  • O. Voznyy, J. J. Dubowski,
    Adsorption kinetics of hydrogen sulfide and thiols on GaAs (001) surfaces in a vacuum,
    J. Phys. Chem. C, 112 (10), 2008, p.3726-3733.
  • O. Voznyy, J. J. Dubowski,
    Structure, Bonding Nature, and Binding Energy of Alkanethiolate on As-Rich GaAs (001) Surface: A Density Functional Theory Study
    J. Phys. Chem. B, 110 (47), 2006, p.23619-23622
  • Conferences