Angular resolved UV photoemission from ordered layers of carbon monoxide on a nickel(100) surface

Angular resolved UPS measurements have been performed on the (√2 × √2)R45° and compressed structures of the adsorption system CO/Ni(100). Due to the operation of dipole selection rules the dependence of normal exit photoemission on angle of photon incidence is found to be a sensitive probe of initial state symmetry. The polar angular dependence of emission from the 4σ orbital follows closely that predicted by Davenport, provided that a correction for refraction and total photoelectron current conservation is applied. Such polar angular dependences show band shifts indicative of dispersion effects, which become more marked at higher CO coverages. An azimuthal angular dependence of emission was not observed despite the presence of ordered adlayers.     

Angular resolved photoemission from PbS (100) for 16.85 eV and 21.22 eV excitation energy

Angular resolved photoelectron spectra are presented for the narrow-gap semiconductor PbS. Two different photon energies and two different azimuthal orientations of the (100) surface are employed. The experimental results provide a further test for the validity of the one-dimensional density of states approach in the case of the lead chalcogenides. The experimental binding energies of 10 three-dimensional critical points are compared with the prediction of two independent band structure calculations.     

Angle resolved photoemission study of surface states on the Pt(997) vicinal surface

One-dimensional atomic chains can be synthesized on stepped surfaces and the electronic structure of the high vicinal surface plays an essential role in determining the physical properties of atomic chains grown on top of it. We have applied surface analysis techniques to study the surface of a Pt(997) single crystal. The STM image of the surface showed that the surface was uniform with a well defined distance between the terraces. Angle resolved photoemission spectroscopy (ARPES) was used to characterize the electronic states of the Pt(997) surface, and confinement of electrons with wave vector perpendicular to the step direction was observed.     

Angular resolved photoemission from palladium single crystals

Photoelectron spectra emitted normal to Pd(001), (011) and (111) faces are presented for He I (21.2 eV) and for Ne I (16.8 eV) radiation. The spectra are different from each other, and in each case the Ne I spectra show a distinct narrowing compared to the He I spectra. Most of the features in all these spectra can be accounted for in terms of initial states only, if different cross-sections are assumed for bands derived from particular d orbitals. This analysis is consistent only for d orbitals related to surface rather than bulk co-ordinates. Spectral features which do not fit this analysis are found to be very sensitive to surface adsorption. An example of the variation in emission away from the surface normal is given.     

Angle resolved UV photoemission spectra from a Bi(0001) surface

Angle resolved photoemission spectra taken from a Bi(0001) surface for hv = 16.9 and 21.2 eV exhibit (1) broad features which appear to be associated with one dimensional density of states, rather than band like features, and (2) a weak dependence upon the direction of incident light These effects can be explained by a large number of nondegenerate final state bands available for optical emission and by a uniform mixing of atomic orbitals in the initial states.     

Observation of p- and d-like surface states on CuCl(100) by angle-resolved photoemission

In the course of a systematic ultraviolet photoemission study of the electronic band structure of CuCl, we have identified two occupied surface states on CuCl(100), situated at 0.25 and 3.0 eV below valence band maximum in normal emission spectra. They essentially show pure p- and d-like orbital symmetry, respectively. We interpret them as a chlorine p_x,y-like occupied antibonding resonance and a copper Γ₁₂-derived state split off from the bulk orbitals by the surface potential. We also present critical point energies along Γ-X and Γ-L.     

Angular resolved L3VV Auger emission spectra from Cu(100)

The angular intensity distribution of electron induced L₃VV Auger electron emission from a Cu(100) crystal has been measured. Angular positions of relative maxima in the distribution are aligned with prominent crystallographic directions suggesting strong diffraction effects.     

Angle-resolved photoemission from surface states

The role of the evanescent part of the unoccupied complex band structure in photoemission from surface states is revealed. The frequency dependence of the emission intensity from two surface states on the (100) and (111) surfaces of Al in the photon energy range from 40 to 110 eV is explained within an ab initio one-step theory of photoemission. A novel embedding method to determine surface states is presented. A high sensitivity of surface states spectra to details of the surface potential barrier is predicted, which offers a way to efficiently monitor surface properties.     

Angular resolved photoemission and the band structure of solids

Current models used to described angular resolved photoemission data are discussed. Emphasis is placed on the energies of structure in the spectrum and its relationship to the bulk band structure. Taking the lead salts (PbS, PbSe, PbTe) as an example a detailed comparison between measured and calculated spectra is given using time reversed LEED functions to describe the final state. On the basis of this comparison criteria are discussed that allow the application of simpler models for the interpretation of angular resolved photoemission. Such models include the direct, k-conserving model and the model of complete neglect of k conservation as well as the use of free electron like final states.     

Time-resolved two-color interferometric photoemission of image-potential states on Cu(100)

We describe an interferometric time-resolved photoemission technique that makes it possible to simultaneously observe the decay of optical induced polarizations and populations at surfaces in a two-color excitation scheme. In this scheme initially unoccupied electronic surface states are coherently excited by the interaction of laser pulses with frequency ω_a and the two-photon polarization which is induced by laser pulses with frequency ω_a/2. Interference is observed by changing the delay between both laser pulses using an actively stabilized two-color Mach–Zehnder interferometer. We demonstrate this technique for excitation of the n=1 image-potential state on a Cu(100) surface. PACS 78.47.+p; 79.60.Bm; 73.20.-r; 82.53.Kp; 42.50.Md     

Resonant photoemission from SmS(100)

A strong, sharp resonance enhancement of 4f photoemission has been observed on SmS(100) surfaces for photon energies in the region of the 4d-4f transitions at about 126 eV. The discrete final state reached via the excitation hν+4d¹⁰4f⁶→4d⁹4f⁷ autoionizes primarely via a super Coster-Kronig transition of the type 4d⁹4f⁷→4d¹⁰4f⁵ + unbound electron. Other decay channels, e.g, Sm 5p emission, as well as a surface induced binding energy shift in the Sm³⁺ final state are identified and discussed.     

Angular resolved Auger emission from clean and sulfur covered Ni(110) surface

The angular dependence of the nickel M₂₃VV and of the sulfur L₂₃VV Auger transitions are studied in detail, on clean and sulfur covered Ni(110) surfaces. New experimental data are presented for the anisotropy of both transitions as a function of polar and azimuthai angles of emission. Our model, which incorporates at the same time the multiple scattering effects in the final state wave function and the intrinsic anisotropy of the Auger emitter, is found to give a satisfactory account of the observed auger anisotropy. We find a large sensitivity to the position of the sulfur adsorbed atoms. The best agreement is obtained for the hollow site. slightly less than 0.9 Å above the top nickel layer. This conclusion is consistent with previous LEED and MEIS studies, but does not agree with the long bridge site obtained from quantum chemistry calculations. Moreover the sulfur emitter on this particular Ni(110) face appears to have an intrinsic anisotropy.     

Angular momentum projection from non-axial intrinsic states in Si

States of definite angular momentum projected from seven Hartree-Fock solution of ²⁸Si are used as a basis in which to diagonalize the Hamiltonian. It is found that each of these HF solutions contributes appreciably to the low energy spectrum.     

Bichromatic two-photon photoemission spectroscopy of image potential states on Ag(100)

Bichromatic two-photon photoemission spectroscopy (Bi2PPES) leads to an increased signal-to-noise ratio compared to conventional two-photon photoemission spectroscopy and therefore allows the observation of the first four image potential states as well as a lineshape analysis with improved accuracy on Ag(100). The n=2 image state with a measured linewidth of 37 meV FWHM is the narrowest unoccupied structure measured on any solid surface so far. The intrinsic linewidths of the first two image states were determined as 21±4 meV and 5±5 meV, respectively, in reasonable agreement with theoretical calculations. Disordered adsorption of oxygen on Ag(100) leads to a linewidth broadening of the first and — to a lesser extent — of the second image potential state. A quantitative analysis of the broadening suggests that the underlying mechanism is lifetime shortening due to scattering of the image state electrons by the adsorbate atoms.     

On interpretation of intrinsic surface states on Si(111) surface

Extended Hückel theory is applied to the Si9111) ideal and relaxed surfaces. In addition to the results obtained by selfconsistent pseudopotential calculations of Schlütter et al., new surface states gave been found. The results are essentially independent of surface relaxation.     

Electron states on the (100) surface of copper

The scattering-theoretical method has been used to determine the electron states on the (100) surface of copper. The bulk energy bands were obtained from an empirical tight-binding calculation. The effective masses were calculated from the surface state dispersion relations.