First principles study of fatty acid monolayers on au(lll)

Jian Guo Wang, Annabella Selloni

Research output: Contribution to journalArticle

18 Scopus citations

Abstract

First principle density functional theory (DFT) calculations are carried out to study fatty (carboxylic) acid molecules adsorbed on Au(111) via their COOH functional group. Focusing on model systems consisting of monolayers of COOHC 6H 12X molecules with different terminal groups X (X = COOH, SH, and CH 3), we examine various properties including the following: the adsorption structure and the corresponding energetics, the bond dipole and charge transfer at the carboxyl-gold interface and their dependence on the monolayer density, the modification of the Au work function induced by the adsorbed monolayer, the voltage-dependent tunneling current through the monolayer (I - V characteristics) in a molecular junction with a single chemical contact, and the electronic density of states. Our calculations predict that the carboxyl-gold bond dipole is large, ∼1 Debye in the case of dense monolayers, and gives rise to a substantial (∼1.2 eV) electrostatic potential energy drop at the interface. This is at variance with the case of alkanethiol monolayers, for which the S - Au interface bond dipole is very small. This difference between thiol and carboxylic acid monolayers leads to different alignments of the molecular energy levels relative to the Fermi energy of the Au(111) surface, and affects both the computed work function modifications and the I - V characteristics.

Original languageEnglish (US)
Pages (from-to)8895-8900
Number of pages6
JournalJournal of Physical Chemistry C
Volume113
Issue number20
DOIs
StatePublished - May 21 2009

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

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