Complete Experimental Structure Determination of the p(3 × 2)<i>pg</i> Phase of Glycine on Cu{110}

Abstract

We present a quantitative low-energy electron diffraction (LEED) surface-crystallographic study of the complete adsorption geometry of glycine adsorbed on Cu{110} in the ordered p(3 × 2) phase. The glycine molecules form bonds to the surface through the N atoms of the amino group and the two O atoms of the deprotonated carboxylate group, each with separate Cu atoms such that every Cu atom in the first layer is involved in a bond. Laterally, N atoms are nearest to the atop site (displacement, 0.41 Å). The O atoms are asymmetrically displaced from the atop site by 0.54 and 1.18 Å with two very different O–Cu bond lengths of 1.93 and 2.18 Å. The atom positions of the upper-most Cu layers show small relaxations within 0.07 Å of the bulk-truncated surface geometry. The unit cell of the adsorbate layer consists of two glycine molecules, which are related by a glide-line symmetry operation. This study clearly shows that a significant coverage of adsorbate structures without this glide-line symmetry must be rejected, on the grounds of both the energy dependence of the spot intensities (LEED-IV curves) and systematic absences in the LEED pattern.