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

Part of Epitaxial Quantum Dot Biosensor project.

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,
  Submitted to Langmuir
• 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

• Upcoming!
  O.Voznyy, J.J.Dubowski,
  Reconstructions of the Au(111) and GaAs(001) surfaces driven by the thiol-thiol interactions,
  Canadian Association of Physicists (CAP) Congress 2008, Session Materials: Semiconductors, Quebec, Canada, June 10.
• O.Voznyy, J.J.Dubowski,
  Structure and adsorption mechanisms of thiol self-assembled monolayers on GaAs (001) surfaces,
  APS March Meeting, Focus Session L20: Self-Assembled Organic Overlayers, New Orleans, LA, USA.
• O.Voznyy, J.J.Dubowski,
  Effect of Surface Reconstruction on Adsorption Kinetics and Quality of Self-Assembled Monolayers of Thiols on GaAs (001),
  MRS 2007 Fall Meeting, Boston, MA, USA.
• O. Voznyy, J. J. Dubowski,
  Thiols Self-Assembled Monolayers on GaAs (001): Better Order on Imperfect Surfaces,
  13th Canadian Semiconductor Technology Conference (CSTC 2007), Montreal, Canada.
• G. Marshall, O.Voznyy, X. Ding, D. Lepage, J.J.Dubowski,
  GaAs-molecular interface for quantum semiconductor bio-sensor,
  RQMP annual meeting, Montreal, May 14, 2007.
• O. Voznyy, J. J. Dubowski,
  Kinetics of thiols adsorption on different GaAs (001) surface reconstructions and evidences of binding to As-overlayer
  E-MRS 2007 Spring Meeting, Symposium O, Strasbourg, France.
• O.Voznyy, J.J.Dubowski,
  First-principles Study of Adsorption Energetics of Alkanethiols on GaAs(001),
  (poster),
  MRS 2006 Fall Meeting, Symposium D, 0950-D04-44, Boston, MA, USA.
• O.Voznyy, J.J.Dubowski,
  Adsorption and Self-Assembly of Alkanethiols on GaAs (001) Surface,
  IEEE Lasers & Electro-Optics Society Annual Meeting, Montreal, October 29, 2006.
• O.Voznyy, J.J.Dubowski,
  Ab-initio study of self-assembled monolayers of thiols on (001) GaAs,
  Photonics North, Nanophotonics and Photon-based Atomic Level Manipulation, Quebec City, Quebec, Canada, June 7, 2006.
• O.Voznyy, J.J.Dubowski,
  Ab-initio modeling of GaAs-thiol interface,
  RQMP annual meeting, Montreal, May 26, 2006.