Photofield emission spectroscopy of surface electronic states of tungsten

doi:10.1016/0039-6028(86)90769-7

Surface Science

Volume 172, Issue 2, 1 July 1986, Pages 477-495

https://doi.org/10.1016/0039-6028(86)90769-7 Get rights and content

Abstract

A novel photofield emission spectrometer has been used to observe departures from free electron behaviour in the total energy distributions of photofield emission from the (100), (110), (111), (211), and (510) facets of a tungsten field emitter. Measurements with p-polarized light at grazing incidence at seven photon energies in the visible and near ultraviolet show departures from free electron behaviour having the same form as those observed in field emission distributions, but shifted to higher energy by one photon energy. The shapes and polarization dependence of the distributions are precisely those expected for surface photoexcitation from electron states near the surface to vacuum tunnelling final states. These observations provide strong evidence that the surface photoeffect is the dominant mechanism of excitation by p-polarized light in photofield emission from tungsten.

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REPRINT OF: Surface electronic structure of Ti-covered W(111) by photofield emission
2011, Ultramicroscopy
Photofield emission (PFE) measurements are employed to examine modifications of the surface electronic structure of the tungsten (1 1 1) facet upon deposition of thin films (1–3 monolayers) of titanium. With the help of DFT simulations, the observed PFE features are interpreted as adsorbate-induced resonance states with energies just below the Fermi level, localized predominantly at the exposed surface atoms. Comparison between the computed surface DOS distributions and the measured PFE spectra is also used to verify various possible arrangements of the Ti adatoms, supporting the DFT-favored model of Ti growth in registry with the W(1 1 1) substrate until a full physical overlayer of the adsorbate is completed.
Surface electronic structure of Ti-covered W(111) by photofield emission
2010, Ultramicroscopy
Photofield emission (PFE) measurements are employed to examine modifications of the surface electronic structure of the tungsten (1 1 1) facet upon deposition of thin films (1–3 monolayers) of titanium. With the help of DFT simulations, the observed PFE features are interpreted as adsorbate-induced resonance states with energies just below the Fermi level, localized predominantly at the exposed surface atoms. Comparison between the computed surface DOS distributions and the measured PFE spectra is also used to verify various possible arrangements of the Ti adatoms, supporting the DFT-favored model of Ti growth in registry with the W(1 1 1) substrate until a full physical overlayer of the adsorbate is completed.
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We present theoretical and experimental study of the structural and electronic properties of the Ti/W(1 1 1) adsorption system. Atomic arrangements of the considered surfaces and their electronic structures have been obtained from first-principles pseudopotential calculations based on the density functional theory in a plane-wave-basis implementation. The corresponding experimental data have been provided by photofield emission spectroscopy. Investigations of the clean and Ti-covered W(1 1 1) surfaces indicate substantial structural relaxations deep into the substrate, and a noticeable modification of the surface electronic properties of the system induced already by a thin film of titanium. Configuration with adatoms positioned in substrate-lattice-continuation (i.e., deep-hollow) sites is found to be energetically most favorable. A good agreement between the measured photofield emission spectra and the computed local-density-of-states distributions confirms our theoretical predictions for a clean W(1 1 1) substrate as well as Ti coverages of 0.25 and 1 ML.
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We present results of theoretical and experimental studies of the structural and electronic properties of Ta(1 1 2) and W(1 1 2) surfaces. Atomic geometries of these surfaces and their electronic structures have been obtained from the first-principles pseudo-potential calculations based on the density functional theory and the use of the plane wave basis set. In the experimental part of our studies we have performed measurements of the photofield emission spectroscopy. The calculated density-of-states distributions are compared and discussed with energy distributions of electrons extracted from photofield emission characteristics. The photofield emission spectra measured for the surface regions of considered systems present very dense structures of features, while the corresponding dependences obtained for the bulk have much more smooth shape. Experimental results correspond very well with calculated density-of-states distributions.
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Photofield emission spectroscopy of surface electronic states of tungsten

Abstract

Surface Sci.

Surface Sci.

Phys. Rev.

Progr. Surface Sci.

Phys. Rev.

Phys. Rev. Letters

Surface Sci.

Surface Sci.

Phys. Rev.

Surface Sci.

J. Vacuum Sci. Technol.

Phys. Rev. Letters

Phys. Rev. Letters

Phys. Rev. Letters

Phys. Rev.