Surface Electronic Structure Of Cu Research Articles

Enhance the activity of multi-carbon products for Cu via P doping towards CO2 reduction

Electronic structure engineering is a powerful method to tailor the behavior of adsorbed intermediates on the surface of catalysts, thus regulating catalytic activity towards CO2 electroreduction. Herein, we prepared a series of P-doped Cu catalysts for CO2 electroreduction into multi-carbon (C2+) products by regulating the surface electronic structure of Cu. The introduction of P could stabilize the surface Cu δ + species, enhancing the activity for C2+ products via adjusting the adsorbed strength of the CO intermediates (*CO). When the molar ratio of P to Cu was 8.3%, the catalyst exhibited a Faradaic efficiency of 64% for C2+ products, which was 1.9 times as high as that (33%) for Cu catalysts at the applied current density of 210 mA cm−2. Notably, at the applied current density of 300 mA cm−2, the P-doped Cu catalyst with the molar ratio of P to Cu of 8.3% exhibited the highest partial current density for C2+ products of 176 mA cm−2, whereas the partial current density for C2+ products over the Cu catalyst was only 84 mA cm−2. Mechanistic studies revealed that modulating the molar ratios of P to Cu regulated the adsorbed strength of *CO. A moderate adsorbed strength of *CO induced by appropriate P doping was responsible for the facilitated C–C coupling process.

Spin-polarized multi-photon photoemission and surface electronic structure of Cu(001)

We have investigated the influence of controlled modifications of the surface electronic structure of Cu(001) on the spin polarization of photoelectrons emitted via multi-photon excitation. Using ultrashort, circularly polarized laser pulses with ∼3 eV photon energy, spin-polarized electrons can be selectively excited from the spin–orbit (SO) coupled d-bands of Cu into the unoccupied n=1 image potential (IP) state on the Cu(001) surface. Upon lowering the IP state energy level by submonolayer Cs deposition, we show that the IP energy can be tuned into two-photon resonance with initial state d-bands of different double group symmetry, leading to a sign reversal of the spin polarization that is observed at the IP state level. Similarly, exploiting the parallel-momentum IP state dispersion, the resonant tuning of the IP state energy level to different branches of the SO split d-bands is demonstrated. Our results highlight the role of resonant and off-resonant excitation pathways in determining the spin polarization in the excited states. The additional information contained in spin-resolved multi-photon photoemission experiments can be exploited to obtain insights into the mechanism of population of excited states.

2光子光電子顕微鏡の開発とCu(111)表面電子状態のイメージング

2光子光電子顕微鏡の開発とCu(111)表面電子状態のイメージング

Relationship between strain and the surface electronic structure of Cu(111) films on Ru(0001): Theory and experiment

The relationship between strain and surface electronic structure of Cu(111) films grown on Ru(0001) is studied by a combination of tunneling spectroscopy and ab initio theoretical calculations. Experimentally, the relaxation of the 5.5% in-plane lattice mismatch between Ru(0001) and Cu(111) changes layer-by-layer the lateral lattice parameter of the Cu film, while the surface state, that is above the Fermi level for the pseudomorphic monolayer of Cu, shifts down in energy with increasing thickness until it becomes the occupied surface state of Cu(111). The effects due to strain in the Cu films are distinguished from those due to the proximity to the Ru substrate by detailed comparisons with theoretically expanded Cu(111) and Cu/Ru(0001) surfaces. Our ab initio calculations indicate that the observed energy shift must be essentially assigned to the decreasing tensile stress of the deposited film.

Rare Gases on Noble-Metal Surfaces: An Angle-Resolved Photoemission Study with High Energy Resolution

In this paper, we present a systematic angle-resolved photoemission (ARUPS) study on prototypical adsorbate systems consisting of a rare-gas monolayer (Ar, Kr, Xe) on a noble-metal (111) surface (Cu, Ag, Au). Although the coupling between substrate and physisorbed overlayer is weak, there is a significant influence on the Shockley-type surface state that is still observable on the well-ordered monolayer systems. The results show that there is an immediate correspondence between the surface-state binding energy and the nobleness of the rare-gas adsorbates, reflecting the short-range repulsive forces between adsorbate and substrate. In the case of Au(111), one can observe an increase of the spin−orbit splitting of the Shockley state with decreasing nobleness. In addition, we discuss the influence of the × Xe superlattice on the surface electronic structure of Cu(111).

The effect of sputtering-induced disorder on the surface dielectric tensor of Cu(110)

The effect of low-energy sputtering on the surface electronic structure of Cu(110) was studied under room temperature conditions by means of reflection-anisotropy spectroscopy (RAS) at photon energies between 1.6 and 6 eV. Sputtering times varied from 0 to 60 min, and the energy of the Ar + ions was 500 eV. Spectral changes that depended on fluence in a reproducible manner were observed. We argue that vacancies in the top layer are responsible for some of the strongest changes, at least for short sputtering times. The spectra could be reproduced by local-field calculations where the screened dipole–dipole interaction coefficients between the top layer and the underlying ones were reduced by a factor proportional to the vacancy concentration. Both components of the surface dielectric tensor are calculated. The behaviour of the RAS signal for longer sputtering times is discussed.

Two-photon photoemission spectroscopy at clean and oxidized Cu(110) and Cu(100) surfaces

Two-photon photoemission spectra of Cu(110) and Cu(100) are measured using ∼ 3.2 eV excitation laser with ∼ 20 fs pulse width. The spectra are measured as a function of laser polarization, excitation energy, bias voltage, and oxygen coverage. They are discussed in terms of the bulk and surface electronic structure of Cu and hot electron relaxation dynamics, and compared to previous nanosecond laser studies. In addition, three-photon photoemission through the n = 1 image potential state on Cu(100) is observed.

A high-resolution angle-resolved photoemission study of relativistic effects on the surface electronic structure of Cu(001)

A high-resolution angle-resolved photoemission study of relativistic effects on the surface electronic structure of Cu(001)

A high-resolution angle-resolved photoemission study of relativistic effects on the surface electronic structure of Cu(001)

A high-resolution angle-resolved photoemission study has located a second Cu(001) M surface state, having a binding energy of 2.11 eV, 65 meV below the d-band maximum. The dispersion of this state has been measured along the ∑ and Y surface Brillouin zone lines. Comparison with a projection of a relativistic band structure indicates that this state lies in an absolute spin-orbit gap along ∑ and the first quarter of the Y line from M . Beyond this point along Y it lies in an absolute d-d hybridisation gap. In addition, the dispersion of the well-known Y 2 Tamm surface state has been measured along Y for the first time.

Relativistic effects on the surface electronic structure of Cu(001): Observation of a spin-orbit-gap surface state.

A second Cu(001) M\ifmmode\bar\else\textasciimacron\fi{} surface state located near the d-band maximum has been characterized using angle-resolved photoemission. High energy resolution, provided by a new dispersive spectrometer, was necessary to identify and characterize the surface state. At M\ifmmode\bar\else\textasciimacron\fi{} the state, which has odd parity with respect to the (100) mirror plane, lies 65 meV below the d-band maximum, at 2.113 eV binding energy. Comparison with the surface projection of a recently calculated relativistic bulk band structure, indicates that this state lies in an absolute spin-orbit gap. The gap extends along one third of \ensuremath{\Sigma}\ifmmode\bar\else\textasciimacron\fi{} in the surface Brillouin zone.