D.A. Duncan;T.J. Lerotholi;W. Unterberger;D. Kreikemeyer;D.P. Woodruff;
While there is growing interest in investigations of biologically-related molecules on surfaces, motivated in part by issues concerned with biocompatibility and biochemical sensors, there are very few such studies that involve quantitative determination of the local adsorption geometries. The technique of scanned-energy mode photoelectron diffraction (PhD) is particularly well-suited to this problem because it allows one to determine the local adsorption site of constituent atoms in an element-and chemical-state-specific fashion. Here we report the results of two new studies, namely of the nucleobase molecule uracil (a six-membered ring comprising CH.CH.CO.NH.CO.NH) on Cu(110), and the simplest amino acid, glycine (NH2CH2COOH), on Cu(111). For uracil the results, as might be expected, are closely similar to those reported previously for thymine  (in which one of the CH species in the uracil ring is replaced by C-CH3). Specifically, adsorption leads to two N 1s peaks in the XPS, consistent with deprotonation of one of the two NH species in the ring, and a single O 1s peak indicating equivalence of the two O atoms. Analysis of the O 1s and N 1s PhD spectra shows that the adsorption geometry is essentially the same as for thymine. Specifically, the molecular plane is essentially perpendicular to the surface, and the molecule bonds to the surface through the two O atoms and the deprotonated N atom that lies between them. All three of these bonding atoms occupy near-atop sites on the Cu(110) surface.
surface structure; copper; uracil; glycine
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