STM and DFT studies of CO2 adsorption on O-Cu(100) surface (original) (raw)
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The Journal of Chemical Physics, 2011
Adsorption of CO 2 on the rutile(110) surface was investigated using dispersion-corrected density functional theory and scanning tunneling microscopy (STM). On the oxidized surface the CO 2 molecules are found to bind most strongly at the five-fold coordinated Ti sites adopting tilted or flat configurations. The presence of bridging oxygen defects introduces two new adsorption structures, the most stable of which involves CO 2 molecules bound in tilted configurations at the defect sites. Inclusion of dispersion corrections in the density functional theory calculations leads to large increases in the calculated adsorption energies bringing these quantities into good agreement with experimental data. The STM measurements confirm two of the calculated adsorption configurations.
The CO-induced restructuring of Co(11−20) has been investigated with temperature-programmed desorption (TPD), low-energy electron diffraction, scanning tunneling microscopy (STM), and density functional theory. CO induces a (3 × 1) surface reconstruction at room temperature, involving the anisotropic migration of Co atoms as uncovered by STM. The TPD investigations of the unreconstructed and reconstructed surface through exposure to CO at 100 K and room temperature, respectively, showed a slightly lower desorption peak temperature for the unreconstructed surface. Based on the STM observations, two theoretical model surfaces with (3 × 1) periodicity were investigated and compared to the unreconstructed surface, one with a missing and one with an added, [0001]-directed, zigzag row of Co atoms. The calculated adsorption energies infer that the added row structure is the energetically preferred surface under CO exposure. The most favorable adsorption energies were found for 4 CO coordinated to the added (topmost) row of the model surface, with the largest difference to the unreconstructed surface. Calculations of transition states yielded a significant energy barrier for removing Co from the topmost, unreconstructed layer of the hcp packing. The initial restructuring occurred preferentially through a carbonyl-type species where the migrating Co atom was bonded to two CO molecules.
CuO Surfaces and CO 2 Activation: A Dispersion-Corrected DFT+U Study
We have used computational methodology based on the density functional theory to describe both copper(I) and copper(II) oxides, followed by the investigation of a number of different low index CuO surfaces. Different magnetic orderings of all the surfaces were studied, and reconstructions of the polar surfaces are proposed. A detailed discussion on stabilities, electronic structure, and magnetic properties is presented. CuO(111) and CuO(111) were found to have the lowest surface energies, and their planes dominate in the calculated Wulff morphology of the CuO crystal. We next investigated the adsorption of CO 2 on the three most exposed CuO surfaces, viz., (111), (111), and (011), by exploring various adsorption sites and configurations. We show that the CO 2 molecule is activated on the CuO surfaces, with an adsorption energy of −93 kJ/mol on the (011) surface, showing exothermic adsorption, while (111) and (111) surfaces show comparatively weak adsorption. The activation of the CO 2 molecule is characterized by large structural transformations and significant charge transfer, i.e., forming a negatively charged bent CO 2 −δ species with elongated C−O bonds, which is further confirmed by vibrational analyses showing considerable red shift in the frequencies as a result of the activation.
Adsorption and diffusion dynamics of atomic and molecular oxygen on reconstructed Cu(100)
Physical Review B, 2007
Adsorption dynamics of O 2 on Cu͑100͒ and on reconstructed Cu͑100͒-͑2 ͱ 2 ϫ ͱ 2͒R45°-O at 300 and 553 K have been investigated by employing a supersonic molecular-beam surface-scattering technique. Experimental results suggest that an activated direct adsorption channel is operative on the clean Cu͑100͒, whereas the adsorption of O 2 on the reconstructed Cu͑100͒ is mediated either by a precursor state or by steering effects. First-principles molecular-dynamics simulations and potential-energy surface calculations show that the nature of the adsorption dynamics of O 2 is different between the clean and reconstructed Cu͑100͒ surfaces. The O 2 molecule is likely to diffuse away from the reconstructed area or to completely desorb from the surface, while in the case of the clean Cu͑100͒ surface, the adsorption occurs through a direct dissociative trajectory. We also find that in the case of the reconstructed surface, the steering occurs higher over the surface and that the recoil effect does not modify the surface as much as in the case of the clean surface. Moreover, the mobility of O and Cu adatoms on the reconstructed Cu surface is significantly lower than that on the clean surface both in the direction of the missing rows and in the direction perpendicular to them.
Selective molecular adsorption in sub-nanometer cages of a Cu2O surface oxide
Physical Chemistry Chemical Physics, 2013
In this study the identity of diverse adsorption sites on a 5-7 Cu 2 O/Cu(111) surface oxide structure has been identified. The 5-7 membered rings formed by a topological defect on stoichiometric Cu 2 O present different electronic structures from the originating hexagonal rings, as shown by combined bias dependent scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The adsorption of CO as a probe molecule on the 5-7 structure, studied using infrared reflection-absorption spectroscopy (IRRAS), shows the existence of special adsorption sites. By combining experimental and theoretical results, it is determined that CO molecules can be selectively confined inside the 7-membered oxide rings with internal dimensions of B0.85 nm, leading to a marked different adsorbate-substrate interaction than in either clean Cu(111) or Cu 2 O. The implication of these newly discovered sites on the chemistry of copper for catalytic reactions is discussed. a 1.134 Å for gas-phase CO bond length. b Cu (CUS) denotes the coordinateunsaturated-site of Cu on the Cu 2 O(111) surface.
The Journal of Chemical Physics, 2003
The potential energy surface ͑PES͒ describing the diffusion and vibration of CO molecules adsorbed on a Cu͑100͒ surface has been calculated using density functional theory within two different generalized gradient approximations ͑GGAs͒, employing a slab representation of the surface. One goal of the study was to investigate the origin of the discrepancy between a recently published PES ͓J. Chem. Phys. 114, 1053 ͑2001͔͒ and inferences that had been made from various experiments. A further aim was to create a PES that could provide a better basis for modeling and understanding of the diffusive and vibrational motion in the CO/Cu͑100͒ system. We found that the calculated PES has a global minimum on-top of the substrate atoms in line with the experimentally determined adsorption site. Diffusion is preferred across the bridge site, a saddle point, with a diffusion barrier of 95Ϯ30 meV and 125Ϯ30 meV for the two GGAs. Vibrational frequencies deduced from the PES agree with experimental results to within 10 meV.
CO adsorption on – a STM study
Surface Science, 1998
Scanning tunneling microscopy (STM) studies of CO adsorption on Co(101 :2) at room temperature are reported. Upon adsorption of CO, added rows are found to nucleate at, and grow out from, the step edges of the Co(101 :2) surface. The added row structure exhibits (1×2) periodicity in well-ordered regions. The added rows are parallel to the [1010]-directed close-packed rows of the Co(101 :2) surface. Co atoms are released from the step edges to form this (1×2) structure, which never evolves to cover the whole surface. The (3×1) structure, which is of the pure overlayer type, forms upon further CO dosing to coexist with the (1×2) structure.
Photoelectron diffraction determination of the local adsorption geometry of CO on Cu(2 1 0)
Surface Science, 2001
Using C 1s and O 1s scanned-energy mode photoelectron diraction, the local adsorption site and orientation of CO adsorbed on Cu(2 1 0) has been determined. The results show that the molecule adsorbs in an essential on-top site through the C atom with C±Cu and C±O bondlengths generally consistent with previous studies on low index Cu surfaces. The molecule has a signi®cant tilt 18 AE 6° of the C±O axis away from the surface normal, with components both perpendicular and parallel to the [0 0 1] steps on this surface.
Theory of Tip-Dependent Imaging of Adsorbates in the STM: CO on Cu(111
The processes of local electron injection or extraction in the scanning tunneling microscopy (STM) and spectroscopy (STS) lead to the creation of short-lived excited states localized at the electrode surfaces. The dynamic relaxation of the transient negative or positive ion resonances, due to both local and long-range interactions, is the clue to the understanding of numerous phenomena in STM/STS ranging from the "anomalously" large tip height corrugation amplitudes on clean metal surfaces to the observation of quantum mirages and features in the STS, which are not observed with the help of other surface spectroscopies. Quantum nanodynamics theory (QND) has been applied to calculate the interaction potential of a single CO molecule with the Cu(111) surface, with a transient negative ion resonance formed when an electron is injected from the tip, and the tunneling conductance on the clean and CO covered Cu(111) surface using a clean metal tip Al/Al(111) and a Pt(111) tip with an adsorbed CO molecule at the apex. Within QND and three-dimensional scattering theory, regarding the tunneling as an excited-state problem, we provide the explanation of the tip-dependent STM image of a single CO molecule on Cu(111). The appearance of the CO molecule as an indentation, using a clean metal tip and as a protrusion with a tip terminated by a CO molecule, is understood as a result of tunneling through two competing channels. Tunneling via adsorbate-induced ion resonances enhances the tunneling conductance. In contrast, tunneling via metal ion resonances only leads to attenuation of the conductance in the presence of the adsorbate. The current in the vicinity of the adsorbed CO molecule is reduced when a clean metal tip is used; i.e., CO appears dark in the STM image, because metal ion resonances on Cu(111) derive from the surface states with image state components coupling to plasmons and are therefore very diffuse. With a CO-terminated tip, the major current channel is, for symmetry reasons, from the 2π-derived orbital of the tip CO molecule, via the diffuse 2π-derived orbital of the CO molecule on the sample, hence adsorbed CO appears bright.
Electrochemistry Communications, 2018
It was recently demonstrated that the sequential or seriatim application of electrochemical scanning tunneling microscopy (ECSTM) and differential electrochemical mass spectrometry (DEMS) enables the correlation, under actual reaction conditions, of a specific structure on a Cu electrode surface with the generation of a particular CO-reduction product. As an extension of the operando hyphenated-technique approach, we paired ECSTM with electrochemical polarization-modulation IR reflection-absorption spectroscopy (ECPMIRS) to identify a delineating potential that affected the coverage, the molecular orientation, and the adlattice structure of CO adsorbed on Cu(100) in 0.1 M KOH under CO 2-reduction conditions. The results may have significant ramifications on the theory-based reaction mechanism for the formation of C 2 compounds, as well as insights into the mode of coordination between CO and zerovalent Cu.