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

Paper SS2-MoA8
Reaction of Amino Acids on the Ge(100) Surface

Monday, November 13, 2006, 4:20 pm, Room 2004

Session: Functionalization of Semiconductor Surfaces
Presenter: S.J. Jung, Korea Advanced Institute of Science and Technology (KAIST)
Authors: S.J. Jung, Korea Advanced Institute of Science and Technology (KAIST)
J.S. Kachian, Stanford University
S. Kim, Korea Advanced Institute of Science and Technology (KAIST)
S.F. Bent, Stanford University
Correspondent: Click to Email
The adsorption of amino acids on the Ge(100) surface was investigated with multiple internal reflection Fourier transform infrared (MIR-FTIR) spectroscopy, scanning tunneling microscopy (STM) and density functional theory. All amino acids consist of a carboxylic acid (-COOH) and an amino (-NH@sub 2@) functional group attached to the same tetrahedral @alpha@-carbon atom. Amino acids are distinguished by the different R-groups attached to the @alpha@-carbon. The simplest amino acid is glycine, with an H as the R-group. Our MIR-FTIR results indicate that for glycine, the principal surface product is formed by OH dissociation of the carboxylic acid group. This result is consistent with calculations, which indicate that the OH dissociation product is the most thermodynamically stable. More than one surface product is evident in the spectra, however, with the results suggesting products containing nitrogen dative bonds. Based on the understanding of glycine, the effect of the side chain can be probed in more complex amino acids. Histidine (C@sub 6@H@sub 9@N@sub 3@O@sub 2@), a basic amino acid, has an imidazole group as the R-group. STM results reveal the ordering of histidine molecules on the Ge(100) surface. At saturation coverage, the STM images show globally ordered arrays consisting of dumbbell shape features that are independent of the direction of the underlying dimer rows of the Ge (100) surface. We will present the adsorption structures and discuss the role of adsorbate-adsorbate intermolecular interactions based on the experimental results and ab initio calculations of glycine. The studies of glycine and histidine allow us to understand the competitive tendencies of the amine and carboxylic acid functional groups in amino acids and also identify the reactivity of the moieties present in the side chain. These results provide a basis for future studies of amino acid polymers, i.e. proteins, which can be used in biocompatible materials of the future.