Adsorbate-driven morphological changes on Cu(111) nano-pits

Abstract

Adsorbate-driven morphological changes of pitted-Cu(111) surfaces have been investigated following the adsorption and desorption of CO and H. The morphology of the pitted-Cu(111) surfaces, prepared by Ar(+) sputtering, exposed a few atomic layers deep nested hexagonal pits of diameters from 8 to 38 nm with steep step bundles. The roughness of pitted-Cu(111) surfaces can be healed by heating to 450-500 K in vacuum. Adsorption of CO on the pitted-Cu(111) surface leads to two infrared peaks at 2089-2090 and 2101-2105 cm(-1) for CO adsorbed on under-coordinated sites in addition to the peak at 2071 cm(-1) for CO adsorbed on atop sites of the close-packed Cu(111) surface. CO adsorbed on under-coordinated sites is thermally more stable than that of atop Cu(111) sites. Annealing of the CO-covered surface from 100 to 300 K leads to minor changes of the surface morphology. In contrast, annealing of a H covered surface to 300 K creates a smooth Cu(111) surface as deduced from infrared data of adsorbed CO and scanning tunnelling microscopy (STM) imaging. The observation of significant adsorbate-driven morphological changes with H is attributed to its stronger modification of the Cu(111) surface by the formation of a sub-surface hydride with a hexagonal structure, which relaxes into the healed Cu(111) surface upon hydrogen desorption. These morphological changes occur ∼150 K below the temperature required for healing of the pitted-Cu(111) surface by annealing in vacuum. In contrast, the adsorption of CO, which only interacts with the top-most Cu layer and desorbs by 200 K, does not significantly change the morphology of the pitted-Cu(111) surface.

Polarization-Dependent Infrared Spectroscopy of Adsorbed Carbon Monoxide To Probe the Surface of a Pd/Cu(111) Single-Atom Alloy

“…Comparison of the intensity of this peak to the intensity of the peak for 0.33 ML CO on Cu(111) at low temperature, where on-top sites are saturated (largest signal for on-top site), implies that only 0.0015 ML of CO can adsorb on the Cu(111) surface at room temperature and this pressure. Mudiyanselage et al have also observed a 2070 cm –1 peak on Cu(111) at 300 K in the presence of gas phase CO, which was similarly weak for similar CO pressures . The weakness of the CO peak for the Pd-free surface thus indicates that the large peak observed in Figure b for the Pd/Cu(111) surface under an ambient CO pressure of 1 × 10 –2 Torr is due to CO adsorbed directly on the Pd atoms in the Cu(111) surface.…”

Formation of a Ti–Cu(111) single atom alloy: Structure and CO binding

“…Cu surfaces above about 300 K during exposure to elevated CO pressures (~0.1 Torr) due to COinduced surface restructuring. [45][46][47] In UHV, however, the coverages of such low-coordination sites on pure Cu surfaces becomes negligible after heating to 500 K, 46 which is well below the 700 K annealing temperature employed in our experiments prior to Ti deposition. On the basis of these comparisons, the present results suggest that the binding properties of CO on Cu-covered Ti containing islands are similar to those of low-coordination Cu sites on pure Cu surfaces.…”

“…Prior studies of sputter-damaged Cu surfaces demonstrate that bands near 2090 and 2100 cm -1 arise from CO adsorbed on Cu sites with 7-to 8-fold vs. 6-fold coordination, respectively, where the latter coordinative environment is analogous to kink/corner sites or Cu 1 adatoms. [45][46] Similar low-coordination sites also form on…”

Water–gas shift catalysis over transition metals supported on molybdenum carbide

“…For Au 2.5-3 nm particle size on Mo 2 C, coordinatively unsaturated sites may chemisorb CO leading to higher WGS rates. We note that since it is known small clusters of Cu also generate coordinatively unsaturated Cu atoms that can chemisorb CO [21] , the lack of such uptake, as indicated by the constant apparent CO reaction As shown in Figure 2, for promoted Mo 2 C, the CO surface coverage is higher leading to a higher WGS rate. In addition, there is an increase in the apparent H 2 O order from ~0 to more than 0.6.…”