CO adsorption on a Cu(211) surface: First-principle calculation and STM study

Abstract

Chemisorption of CO on the stepped Cu(211) surface is studied within ab-initio density functional theory (DFT) and scanning tunneling microscopy (STM) imaging as well as manipulation experiments. Theoretically we focus on the experimentally observed ordered (2×1) and (3×1) COphases at coverages Θ = monolayer (ML). To obtain also information for isolated CO molecules found randomly distributed at low coverages, we also performed calculations for a hypothetical (3×1) phase with Θ = 1 3 ML. The adsorption geometry, the stretching frequencies, the work functions and adsorption energies of the CO molecules in the different phases are presented and compared to experimental data. Initially and up to a coverage of 1 2 ML CO adsorbs upright on the on-top sites at step edge atoms. Determining the most favorable adsorption geometry for the 2 3 ML ordered phase turned out to be nontrivial, both from the experimental and the theoretical point of view. Experimentally, both top-bridge and top-top configurations were reported, whereby only the top-top arrangement was firmly established. The calculated adsorption energies and the stretching frequencies favor the top-bridge configuration. The possible existence of both configurations at 2 3 ML is critically discussed on the basis of the presently accessible experimental and theoretical data. In addition, we present observations of STM manipulation experiments and corresponding theoretical results, which show that CO adsorbed on-top of a single Cu-adatom, which is manipulated to a location close to the lower step edge, is more strongly bound than CO on-top of a step edge atom.

Oxidation of CO Catalyzed by a Cu Cluster: Influence of an Electric Field

“…To provide a comparison, available experimental [52][53][54] and other theoretical results [49][50][51][68][69] are also listed therein. Our calculated E ad = À0.48 eV for the (2 2) CO/Cu(111) system agrees very well with available experiment results of E ad = À0.46 to À0.52 eV, [52][53][54] which confirms the validity of our accuracy settings and calculation method.…”

“…[49][50] In the case of (2 1) Cu(211) surface, our calculated E ad = À0.69 eV is close to À0.61 eV obtained from the thermal desorption spectroscopy, [54] and other theoretical data from RPBE functional. [68] Therefore, the stepped surface has stronger adsorption ability than that of the flat surface.…”

Comparative study of CO adsorption on flat, stepped, and kinked Au surfaces using density functional theory

“…The electron-ion interaction for C, O, and Au is described by ultra-soft pseudo-potentials supplied with VASP. A 450 eV plane-wave energy cut-off was used for all calculations and is found to be sufficient for these systems as reported by other studies [13,23]. In all calculations, the generalized gradient correction of Perdew and Wang [24] (PW91) was used which is found to give more accurate results than those based on the local density approximation (LDA) [12,25,26].…”

“…For Au(111), a p(2×2) structure was used along with other coverages ranging from 0.33 ML (1 CO per unit cell) to 1 ML(3 CO molecules per unit cell). CO molecules were adsorbed on several sites to find the preferred adsorption site in such a way that CO molecule sits perpendicular to the surface with carbon atom close to the surface as reported in number of experiments [7,22,23]. A Monkhorst-Pack k-point mesh of 4×4×1 was used for (100) and 5×5×1 was used for (111).…”

Low Barrier Carbon Induced CO Dissociation on Stepped Cu

“…The initial Cu surface has 2% of graphitic carbon relative to the total amount adsorbed molecular CO. CO coverage on Cu(211) after exposure to 3L of CO at 110 K is approximated to be between 1/6 and 1/2 ML. The estimation is derived from Refs [11][12][13], where CO adsorbs in (2x1) at on-top site of Cu atoms at the step edges. The adsorption of molecular CO results in a structurally rich C 1s spectrum (b), where peak Cu-CO (blue) represents the main peak for adsorbed molecular CO and S1 (green) and S2 (orange) are the shake-up structures, as explained by Tillborg et al [14].…”