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Mar 1972

Volume 9, Issue 2, pp. 561-1044


Theory of Chemisorption

J. R. Schrieffer

J. Vac. Sci. Technol. 9, 561 (1972); http://dx.doi.org/10.1116/1.1317718 (8 pages) | Cited 18 times

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The basic concepts in the theory of chemisorption of atoms on metals will be reviewed. The sharp atomic levels of the free atom are broadened into virtual levels by electron tunneling between the atom and the solid. For rapid tunneling, correlation effects on the adatom are weak and a self-consistent field molecular orbital approach is appropriate. The adatom density of states can vary from a Lorentzian level to states split above and below the valence band of the solid, corresponding to the bonding and antibonding orbitals of a surface complex formed between the adatom and its surroundings. The Anderson model treats only Coulomb interactions on the adatom, while the CNDO method of quantum chemistry has been recently employed to include Coulomb interactions in the solid. For strong intra-atomic Coulomb interaction on the adatom, correlation effects are important and the localized magnetic moment on the adatom as predicted by the unrestricted Hartree–Fock approximation is quenched. Correlations have been treated by extended valence bond methods, multiple scattering theory, and configuration mixing techniques. Semiquantitative agreement with experiment is obtained in a number of systems.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Influence of Surface Crystallography on Nitrogen Adsorption on Tungsten

D. L. Adams and L. H. Germer

J. Vac. Sci. Technol. 9, 569 (1972); http://dx.doi.org/10.1116/1.1317719 (1 page)

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Abstract Unavailable
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
73.30.+y Surface double layers, Schottky barriers, and work functions

Theory of Work-Function Changes Induced by Alkali Adsorption

N. D. Lang

J. Vac. Sci. Technol. 9, 569 (1972); http://dx.doi.org/10.1116/1.1317720 (1 page)

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Abstract Unavailable
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.20.Hb Impurity and defect levels; energy states of adsorbed species

LEED and Work Function Study of Cs and O Adsorption on W(112)

C. A. Papageorgopoulos and J. M. Chen

J. Vac. Sci. Technol. 9, 570 (1972); http://dx.doi.org/10.1116/1.1317721 (5 pages) | Cited 7 times

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Adsorption of Cs and O on W(112) has been studied with systematic variations of the composition and the sequence of deposition of the adsorbates. The results suggest that Cs and O form a W-O-Cs double layer, regardless of the sequence of deposition. The differences in structure of Cs on clean W and O∕W are compared. It is found that Cs and O affect the structures of each other. The change in work function of the surface at various Cs and O coverages are reported. Throughout the coverage range of the present study, there is no apparent evidence of cesium oxide formation.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
73.30.+y Surface double layers, Schottky barriers, and work functions
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Self-Consistent Screening of Charges Embedded in a Metal Surface

S. C. Ying, J. R. Smith, and W. Kohn

J. Vac. Sci. Technol. 9, 575 (1972); http://dx.doi.org/10.1116/1.1317722 (4 pages) | Cited 11 times

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This paper first develops a general theory of the screening change induced in an inhomogeneous electron gas by a small perturbing charge. This theory is applied to the screening of a point charge embedded in a metal surface. The first stage of this program which is reported here, uses the jellium model for the unperturbed metal surface and treats both the unperturbed and perturbed systems in the Thomas–Fermi approximation. Self-consistency, which is maintained in the present paper, leads to results which differ significantly from earlier results obtained with infinite barriers, which are by their nature not self-consistent.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species

Appearance Potential Study of the Band Structure of Transition Metals on Transition Metal Surfaces

J. E. Houston and Robert L. Park

J. Vac. Sci. Technol. 9, 579 (1972); http://dx.doi.org/10.1116/1.1317723 (5 pages) | Cited 16 times

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Soft x-ray appearance potential spectra have been obtained for dilute coverages of transition metals on transition metal surfaces. The appearance potential spectrum of a given core level is the differential excitation probability as a function of sample potential. For transition metals this produces a strong positive threshold peak whose width is related to the unfilled portion of the d band. The titanium-nickel system is of particular interest since, in their pure form, titanium and nickel have nearly empty and nearly filled 3d bands respectively. In preliminary studies of this system, we find the 2math peak of nickel in dilute concentration on a titanium surface to be identical to the titanium 2math peak obtained from dilute coverages of titanium on a nickel surface. The width of these peaks is intermediate between the clean Ti and Ni values. This result, which suggests a common band model for an alloy of stoichiometry near that of TiNi, is contrasted with recent experimental and theoretical studies of dilute transition metal alloys.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Field Emission Energy Distributions of Hydrogen and Deuterium on the (100) and (110) Planes of Tungsten

E. W. Plummer and A. E. Bell

J. Vac. Sci. Technol. 9, 583 (1972); http://dx.doi.org/10.1116/1.1317724 (8 pages) | Cited 22 times

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Total energy distributions of field emitted electrons from the tungsten (110) and (100) planes as a function of coverage by hydrogen and deuterium have been recorded utilizing a spherical deflection energy analyzer. The elastic tunneling resonance spectrum gives a plot of the “local density of states” in the adsorbate. The inelastic tunneling spectrum reveals those discrete excitation energies available in the adsorbate–substrate complex. These spectroscopic data have been used to infer the chemical nature of the binding states which have been observed in the flash desorption spectrum of hydrogen from tungsten.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Energy Distribution in Field Emission from Adsorbate Covered Surfaces

D. Penn, R. Gomer, and M. H. Cohen

J. Vac. Sci. Technol. 9, 590 (1972); http://dx.doi.org/10.1116/1.1317725 (1 page)

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Abstract Unavailable
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79.70.+q Field emission, ionization, evaporation, and desorption
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Tunneling from Cambridge Surface States

J. W. Gadzuk

J. Vac. Sci. Technol. 9, 591 (1972); http://dx.doi.org/10.1116/1.1317726 (6 pages) | Cited 8 times

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Solids with electron band structures given by a simple analytic function of wavenumber (E∼k2 for free electron bands; E∼k for tightbinding bands) possess localized electron states at their surfaces which are easily treated within the complex k vector formalism developed especially by Heine and collaborators. These surface states, which will be called Cambridge surface states, can occur not only in energy gaps caused by Bragg reflections at Brillouin zone faces but also in spin-orbit split gaps and hybridization gaps within the zone. In this work a theory of tunneling and field emission of electrons from such surface states is developed. The field emission energy distribution from d-band metal surface states is calculated using Harrison’s d-band pseudopotential theory, and the results are favorably compared with experimental data. Since the existence conditions for Cambridge surface states depend crucially upon the boundary conditions at the surface, the act of measurement via a tunneling process can sufficiently alter the boundary conditions that “surface states” are either created or destroyed by “looking” at them. In particular the strong coupling ion neutralization tunneling experiments of Hagstrum are very susceptible to this effect.
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73.20.At Surface states, band structure, electron density of states
73.40.Gk Tunneling

Electron Stimulated Desorption of Excited Neutrals: CO on W

Ivor G. Newsham, James V. Hogue, and Donald R. Sandstrom

J. Vac. Sci. Technol. 9, 596 (1972); http://dx.doi.org/10.1116/1.1317727 (4 pages) | Cited 4 times

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A time-of-flight technique is used to study the release of excited neutrals and ions by electron-stimulated desorption ESD for the system CO on W. The method ensures the detection of the excited neutral particles without interference from photons produced by the electron beam. Use of a channel electron multiplier allows the counting of individual particle arrivals, insuring high sensitivity and allowing the use of low electron current densities. Energy distributions are obtained from the flight-time distributions for both kinds of particles, using a (100) single-crystal sample. The release of excited neutrals for this system in the temperature range 130 to 270 K is demonstrated.
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79.20.La Photon- and electron-stimulated desorption

Simultaneous SIMS, ElD, and Flash-Filament Investigations of the Interaction of Gases with a Tungsten Surface

A. Benninghoven, E. Loebach, and N. Treitz

J. Vac. Sci. Technol. 9, 600 (1972); http://dx.doi.org/10.1116/1.1317728 (3 pages) | Cited 8 times

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A UHV system, containing a heatable (up to >2600 °K) W ribbon target, a Finkelstein ion source (Ar+, 2 keV) with magnetic mass separator, an electron source (300 eV), a quadrupole secondary ion mass filter with a counting channel electron multiplier and a quadrupole gas analyzer, is used for the study of the adsorption and desorption of H2, O2, and CO on W by simultaneous, i.e., fast interchanging “static” SIMS [secondary (ion induced) ion mass spectroscopy] and EID [electron induced (ion) desorption] and by flash-filament measurements. Different binding states can be distinguished. The emission cross sections of the adsorbate-specific ions by ion bombardment depend far less upon the gas exposure (and therefore upon the coverage) than those corresponding to electron bombardment.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
79.20.La Photon- and electron-stimulated desorption

Electron Energy Loss Spectra of a Ni(110) Surface as a Function of Surface Impurity

F. Steinrisser and E. N. Sickafus

J. Vac. Sci. Technol. 9, 603 (1972); http://dx.doi.org/10.1116/1.1317729 (1 page) | Cited 3 times

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Abstract Unavailable
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79.20.Kz Other electron-impact emission phenomena

Direct Comparison of Auger Electron Spectroscopy with Appearance Potential Spectroscopy

R. G. Musket

J. Vac. Sci. Technol. 9, 603 (1972); http://dx.doi.org/10.1116/1.1317730 (5 pages) | Cited 3 times

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Direct comparison of Auger electron spectroscopy (AES) with appearance potential spectroscopy (APS) has been accomplished. In situ determination of the respective spectra for various surface conditions of an Fe-Cr-Ni alloy has shown that the relative sensitivities of the two techniques are strongly dependent upon the surface condition and that for a given element one technique may indicate an increase with a change in surface condition while the other technique may indicate a decrease. To a first approximation, such effects may be explained in terms of the respective electronic transitions. The results suggest that AES should be employed for elemental and, in some cases, chemical analyses and APS should be reserved for the study of the chemical binding of atoms in surfaces.
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82.80.-d Chemical analysis and related physical methods of analysis
68.35.Dv Composition, segregation; defects and impurities

A Quantitative Study of Auger Electron Signals of Phosphorus on Silicon Using a Quartz Crystal Microbalance

L. L. Levenson, L. E. Davis, C. E. Bryson, J. J. Melles, and W. H. Kou

J. Vac. Sci. Technol. 9, 608 (1972); http://dx.doi.org/10.1116/1.1317731 (4 pages)

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The Auger electron intensities of phosphorus on the (111) face of silicon have been measured as a function of coverage. Measurements of phosphorus coverage were obtained by using a quartz crystal microbalance during phosphorus (P2) evaporation from gallium phosphide crystals. A mass spectrometer was used to determine sticking coefficients on both the microbalance and sample.
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79.20.Fv Electron impact: Auger emission
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Scattering of Low Energy Ions (He+ and Ar+) as a Surface Analysis Technique

D. J. Ball, T. M. Buck, C. G. Caldwell, D. MacNair, and G. H. Wheatley

J. Vac. Sci. Technol. 9, 611 (1972); http://dx.doi.org/10.1116/1.1317732 (1 page) | Cited 2 times

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Abstract Unavailable
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61.05.Np Atom, molecule, and ion scattering (for structure determination only)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Backscattering of Hydrogen and Rare Gas Ions from Metal Surfaces

W. Eckstein and H. Verbeek

J. Vac. Sci. Technol. 9, 612 (1972); http://dx.doi.org/10.1116/1.1317733 (4 pages) | Cited 2 times

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Energy and angular distributions of H1+, Ne+, and Ar+ backscattered from polycrystalline Nb and W targets were measured. The bombarding energy used was 15 keV. The pressure in the target region during bombardment was kept below 2×10−9 Torr. As an energy spectrometer we used an electrostatic spherical condenser. Surface impurities were detected by observing the binary scattering peaks of Ne+. The shape of the energy spectra of backscattered protons depends strongly on the surface cleanness and on the crystalline structure of the target.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Ion Bombardment Induced Surface Damage in Tungsten and Molybdenum Single Crystals

J. J. Bellina and H. E. Farnsworth

J. Vac. Sci. Technol. 9, 616 (1972); http://dx.doi.org/10.1116/1.1317734 (4 pages) | Cited 2 times

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The clean, annealed W(110) and Mo(110) surfaces were bombarded by 1013-1015 noble-gas ions having kinetic energies between 100 and 1000 eV. The degradation of intense peaks in the major beams was observed with a rapid-scan, Faraday collector system. The dependence of the rate of degradation on ion mass and energy and target mass was determined to depend on the energy transferred in two-body, linear, hard-sphere collision. Comparison with sputtering yields and thermal desorption of embedded ions indicated when knock-on lattice distortion rather than direct sputtering or ion embedding probably caused the intensity degradation.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.80.Jh Ion radiation effects
61.82.Bg Metals and alloys

Investigation of Surface Topography of Oxygen on Nickel Single Crystals by Helium Ion Backscattering

W. Heiland and E. Taglauer

J. Vac. Sci. Technol. 9, 620 (1972); http://dx.doi.org/10.1116/1.1317735 (4 pages) | Cited 16 times

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In an experiment which combines low energy noble gas ion backscattering with LEED the sorption of oxygen on the (110) face of a nickel single crystal is investigated. The energy of the backscattered He+ ions is governed by binary collisions whereas the intensity of the spectrum is given by the cross sections, the concentration of surface atoms, the neutralization probabilities and the geometry. The spectra obtained by varying the angle of incidence relative to the surface and the crystal orientation, can be explained by the assumption that in the case of the (2×1) structure every second place in the top [110] rows of Ni is occupied by an oxygen atom. From a shadow effect observed at small angles of incidence it can be estimated that the adsorbed oxygen protrudes beyond the plane of the Ni atoms by about 0.4–0.8 Å.
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61.05.Np Atom, molecule, and ion scattering (for structure determination only)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Multiple Scattering of Low Energy Noble Gas Ions from a Nickel Single Crystal Surface

E. Taglauer and W. Heiland

J. Vac. Sci. Technol. 9, 623 (1972); http://dx.doi.org/10.1116/1.1317736 (1 page)

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Abstract Unavailable
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61.05.Np Atom, molecule, and ion scattering (for structure determination only)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Entrapment of Helium at Vacancies in a (100) Tungsten Crystal

E. V. Kornelsen

J. Vac. Sci. Technol. 9, 624 (1972); http://dx.doi.org/10.1116/1.1317737 (1 page)

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Abstract Unavailable
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61.72.S- Impurities in crystals

Auger Electron Spectroscopy Studies of Sputter Deposition and Sputter Removal of Mo from Various Metal Surfaces

M. L. Tarng and G. K. Wehner

J. Vac. Sci. Technol. 9, 625 (1972); http://dx.doi.org/10.1116/1.1317738 (1 page) | Cited 1 time

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Abstract Unavailable
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81.70.Jb Chemical composition analysis, chemical depth and dopant profiling
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.20.-m Impact phenomena (including electron spectra and sputtering)

Elastic and Inelastic Low-Energy Electron Diffraction (LEED) from Solids

G. E. Laramore

J. Vac. Sci. Technol. 9, 625 (1972); http://dx.doi.org/10.1116/1.1317739 (9 pages) | Cited 1 time

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A brief survey of some of the recent literature on elastic and inelastic low-energy electron diffraction (LEED) from solids is given, Our present knowledge of the electron-solid force law is discussed. The state of the art of theoretical model calculations of LEED intensity profiles is described and compared with the current status of experimental measurements. Prescriptions for obtaining surface crystallographic information directly from the experimental LEED profiles are described. The use of inelastic LEED as a spectroscopic probe of the electronic excitations of the surface region of solids is also mentioned.
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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
79.20.Kz Other electron-impact emission phenomena

Comparison of Experimental and Theoretical LEED Spectra for Al

R. Baudoing, L. deBersuder, C. Gaubert, V. Hoffstein, J. Lauzier, and H. Taub

J. Vac. Sci. Technol. 9, 634 (1972); http://dx.doi.org/10.1116/1.1317740 (5 pages) | Cited 3 times

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We present a comparison between the experimental and theoretical LEED rotation diagrams obtained from the (001) surface of Al. The experiment was performed at E=20 eV over a large range of polar angles with the help of a new LEED goniometer which permits us to vary the polar angle between 0° and 90° and the azimuthal angle between 0° and 360° without opening the system. Realizing that rotation diagrams (which exhibit most directly dynamical effects) constitute perhaps the most crucial test of any dynamical theory of LEED, we have performed calculations using the following formalisms: multiple scattering theory of McRae–Kambe, band structure-matching, one-dimensional multiple scattering model, and inelastic collision model. The results of these calculations (performed for the same incidence conditions) are compared and their relationship with experiment is discussed.
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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Low Energy Electron Diffraction Spectra from {001} Surfaces of Face Centered Cubic Metals: Theory and Experiment

D. W. Jepsen, P. M. Marcus, and F. Jona

J. Vac. Sci. Technol. 9, 638 (1972); http://dx.doi.org/10.1116/1.1317741 (1 page)

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Abstract Unavailable
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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Absolute Intensity Energy LEED Spectra for Clean Ni(001) Surfaces

J. E. Demuth, S. Y. Tong, and T. N. Rhodin

J. Vac. Sci. Technol. 9, 639 (1972); http://dx.doi.org/10.1116/1.1317742 (4 pages)

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The uncertainties in LEED intensity spectra for Ni(001) due to current measurement techniques, normalization procedures, beam deflections, and the preparation of a clean surface are investigated and discussed. Encouraging agreement is obtained between experimental spectra obtained from a clean, flat surface and theoretical spectra computed from a realistic multiple scattering model for Ni(001).
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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Specular Electron Reflectivities from Disordered Overlayers; Substrate-Overlayer Optical Distances

S. Andersson and B. Kasemo

J. Vac. Sci. Technol. 9, 643 (1972); http://dx.doi.org/10.1116/1.1317743 (2 pages)

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Specular electron reflectivities from disordered overlayers of Na and K on Ni(001) are presented. At very low energies the observed intensity variations over the range of a total energy gap are explained in terms of incoherent scattering from the disordered overlayer. The intensity variations are reproduced in a simple model calculation. The extraction of structural information from these observations is discussed.
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61.05.jd Theories of electron diffraction and scattering

Averaged Low-Energy Electron Diffraction Intensities from Ni(111)

Max G. Lagally, Tran C. Ngoc, and Maurice B. Webb

J. Vac. Sci. Technol. 9, 645 (1972); http://dx.doi.org/10.1116/1.1317744 (5 pages) | Cited 4 times

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Conventionally, crystal structures are determined by comparing diffracted intensities with kinematic intensities calculated for proposed models. Intensities in low-energy electron diffraction are complicated by multiple scattering and are calculable only in dynamic theories. Here it is demonstrated for both specular and nonspecular beams from Ni(111) that the kinematic intensity can be recovered from LEED data by averaging at constant momentum transfer, thus making the much simpler conventional analysis applicable to surfaces.
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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Medium Energy Electron Diffraction

A. R. Moon and J. M. Cowley

J. Vac. Sci. Technol. 9, 649 (1972); http://dx.doi.org/10.1116/1.1317745 (3 pages) | Cited 2 times

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In recent years low energy electron diffraction (LEED—electron energy range 10–500 eV), and to a lesser extent reflection high energy electron diffraction (RHEED—energy range 40–100 keV), have played an important role in the investigation of surfaces of solids. Both techniques are however beset with many experimental and theoretical difficulties. Diffraction techniques in the medium energy range (MEED—energy range 1–10 keV) should have theoretical and experimental advantages over both LEED and RHEED. These advantages are discussed and a review is made of the available theoretical methods suitable for this energy range.
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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

The Band Structure of Graphite Studied by Secondary Electron Emission

R. F. Willis and B. Fitton

J. Vac. Sci. Technol. 9, 651 (1972); http://dx.doi.org/10.1116/1.1317746 (6 pages) | Cited 6 times

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Well-defined maxima have been observed in the secondary electron emission spectrum of graphite excited by low-energy electrons, the energies of which show good agreement with emission from final states located at critical points in the conduction band of a recent band structure calculation. Variation of the intensity of the maxima with angle of incidence of the primary beam, and the observation of interband transition thresholds, indicates that excitation occurs via direct transitions obeying optical selection rules. Transitions to higher excited states in the third Brillouin zone, of relevance to LEED intensity theories, have also been observed.
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71.20.Ps Other inorganic compounds
79.20.Hx Electron impact: secondary emission

Gas-Metal Interaction at Low Pressure—Thermodynamic and Structural Aspects

J. Oudar

J. Vac. Sci. Technol. 9, 657 (1972); http://dx.doi.org/10.1116/1.1317747 (7 pages) | Cited 3 times

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The chemical adsorption of a gas on a metallic surface can take place with or without nucleation. In this review we will especially refer to results concerning the adsorption of oxygen and sulfur on different metals where nucleation phenomena may be explained by the formation of two-dimensional surface compounds involving reconstruction of the metallic substrate.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

Carbon Monoxide Oxidation on a Pt(110) Single Crystal Surface

H. P. Bonzel and R. Ku

J. Vac. Sci. Technol. 9, 663 (1972); http://dx.doi.org/10.1116/1.1317748 (5 pages) | Cited 18 times

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The catalytic reaction between CO and O2 on a Pt (110) surface is investigated by residual gas analysis for different partial pressures of CO and O2 and various temperatures. The surface cleanliness of the Pt crystal is monitored by Auger electron spectroscopy. The results of the reaction study are generally in agreement with previous studies for polycrystalline Pt catalysts. The temperature dependence of the formation rate of CO2 exhibits a maximum whose position depends on the composition of the gas phase. At T=215°C two different rate laws are valid. For PO2>PCO the rate of CO2 formation is proportional to PO21.1PCO−0.6, while for PO2>PCO it is proportional to PO20.25PCO0.75. These observations support the idea that the reaction obeys an Eley-Rideal mechanism in the pressure and temperature range investigated, and the results are evaluated accordingly. The influence of segregated Si on the CO oxidation reaction is investigated and found to be small.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Decomposition of CO2 on (100)W

L. R. Clavenna and L. D. Schmidt

J. Vac. Sci. Technol. 9, 668 (1972); http://dx.doi.org/10.1116/1.1317749 (1 page) | Cited 1 time

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Abstract Unavailable
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Reactive Scattering of N2O Molecular Beams from Clean and Carbon-Covered (100) Platinum Single-Crystal Surfaces

L. A. West and G. A. Somorjai

J. Vac. Sci. Technol. 9, 668 (1972); http://dx.doi.org/10.1116/1.1317750 (5 pages)

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Thermal energy molecular beams of N2O have been scattered from a platinum (100) surface maintained in the temperature range 900–1500 K in an ultrahigh vacuum chamber. The angular distribution of the scattered beams was monitored with a quadrupole mass spectrometer, the target surface structure by low energy electron diffraction, and the composition by Auger spectroscopy. The effect of surface temperature and surface structure on the surface decomposition of N2O has been studied. At 1200 K, using a clean surface, the angular distribution of one of the reaction products, NO, follows the cosine law, but deviations from this behavior seem to occur if the surface is covered by a layer of carbon. At still higher temperatures N2O reacts with the carbon layer on the surface and removes it by the oxidation reaction N2O+C→CO+N2. The mechanisms of reactive scattering based on the experimental observations are discussed.
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34.50.Lf Chemical reactions

The Adsorption of Methane by Tungsten (100) and Tungsten (111)

John T. Yates and Theodore E. Madey

J. Vac. Sci. Technol. 9, 672 (1972); http://dx.doi.org/10.1116/1.1317751 (1 page) | Cited 1 time

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Abstract Unavailable
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.30.+y Surface double layers, Schottky barriers, and work functions

Adsorption and Flash Decomposition of Ethylene on Tungsten Single-Crystal Faces

B. D. Barford and R. R. Rye

J. Vac. Sci. Technol. 9, 673 (1972); http://dx.doi.org/10.1116/1.1317752 (5 pages) | Cited 5 times

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The interaction of ethylene with the (100), (110), (111), and (211) faces of tungsten was studied by means of thermal desorption spectroscopy. Ethylene decomposition yields a single broad hydrogen peak at ∼300 K on W(111), two poorly resolved hydrogen peaks at ∼300 and ∼400 K on W(211), hydrogen peaks at ∼300 and ∼450 K with an area ratio of 1:2 on W(110), and a single decomposition peak at ∼275 K on W(100). Assuming di-σ-bonded ethylene, these results are consistently interpreted in terms of the limitations on ethylene adsorption imposed by the structure of the surface; and the stability of adsorbed ethylene is interpreted from consideration of the structure of the resulting ethylene-surface complex. The absence of two equal peaks on all except the (211) face eliminates the possibility of a two-step decomposition suggested by previous work.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

LEED and Mass Spectrometry Studies of Benzene and Cyclohexane Adsorption on Nickel Single Crystal Faces

G. Dalmai-Imelik and J. C. Bertolini

J. Vac. Sci. Technol. 9, 677 (1972); http://dx.doi.org/10.1116/1.1317753 (5 pages) | Cited 1 time

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Benzene adsorption at 25 °C on nickel single crystal (111) and (110) faces gives oriented LEED patterns. Mass spectrometry analysis of gases desorbed by heating shows that a part of benzene is adsorbed reversibly, whereas another part is completely cracked as hydrogen, and carbon is left on the surface. Self-hydrogenation can be observed and followed on the (110) face. Cyclohexane adsorption at 25 °C gives a (1×2) LEED pattern at low coverage on (110) face. No oriented structure is observed on the (111) face. In contrast to benzene adsorption we only observe hydrogen in the gas phase by thermal desorption. Benzene and cyclohexane adsorption at higher temperatures give LEED patterns that we assume to be due to carbide formation on the surface. These results are discussed and compared with those of ethylene and ethane adsorption.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Phase Transitions in Two-Dimensional Absorbed Layers on Copper Investigated by LEED and Auger Spectroscopy

J. L. Domange

J. Vac. Sci. Technol. 9, 682 (1972); http://dx.doi.org/10.1116/1.1317754 (3 pages) | Cited 1 time

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The equilibrium between one adsorbed phase of sulfur ions (loosely packed) and a reconstructed two-dimensional copper sulfide phase, is studied in ultrahigh vacuum on low index faces of copper. The nucleation from the loosely packed phase of nuclei of the two-dimensional sulfide is characterized under conditions for which sulfur dissolution or evaporation is negligible. The domain of the temperature-coverage diagram for which adsorbed sulfur is present at equilibrium in the two phases is determined. The data lead to an interpretation of adsorption isotherms at low temperature and point to the existence of a critical temperature above which the evolution of surface structure towards saturation proceeds without discontinuity.
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68.35.Rh Phase transitions and critical phenomena
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Surface Phonons and Magnos

T. Wolfram, R. E. DeWames, and E. A. Kraut

J. Vac. Sci. Technol. 9, 685 (1972); http://dx.doi.org/10.1116/1.1317755 (11 pages)

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A brief introductory survey of surface phonons and magnons is presented. Long-wavelength surface modes include optical modes in ionic crystals, magnetostatic waves in magnetic insulators, and elastic surface waves. The effects of retardation on the optical modes lead to surface polaritons. Calculations based on discrete atomic models show that additional surface modes occur in the ionic crystals due to abrupt changes in the short-range forces at the surface and that the electrodynamic modes are pseudosurface states when they exist in the bulk band. Experiments relating to these modes are reviewed briefly. Magnetostatic modes are the magnetic analog of the electrodynamic optical modes in ionic crystals. When the exchange interaction is considered the magnetostatic surface modes are converted into pseudosurface states called dipole-exchange surface modes which lie within the bulk spin-wave band. Elastic surface waves in isotropic, anisotropic, piezoelectric, and layered media are discussed briefly. Various types of elastic waves include generalized Rayleigh, pseudosurface, electroacoustic, Love, Lamb, Sezawa, and Stoneley waves. Short-wavelength surface waves include acoustic and optical phonons and acoustic and optical magnons in ferro-and antiferromagnets. Surface magnons are discussed and experiments and theory relating to surface spin dynamics are reviewed. Surface phonon characteristics are described and relevant experiments are mentioned.
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68.35.Ja Surface and interface dynamics and vibrations
75.30.Ds Spin waves

Surface Debye–Waller Factors and Thermal Expansion Coefficients for Mo(100) and Cr(100)

D. Tabor and J. M. Wilson

J. Vac. Sci. Technol. 9, 695 (1972); http://dx.doi.org/10.1116/1.1317756 (4 pages) | Cited 2 times

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Using LEED we have measured Debye-Waller factors for Mo(100) and Cr(100) surfaces near normal incidence. The derived effective Debye temperature as a function of electron beam energy shows fluctuations which are 18–25% higher on peaks near the Bragg voltage than on those measured near half-order Bragg voltages. The results suggest that the origin of these fluctuations is multiple diffraction. The thermal expansion coefficient has also been estimated. Measurements of energy shifts of the (00) intensity peaks with temperature give values between two and three times the average bulk value over the same temperature range. These results are consistent with large vibrational amplitudes when discussed in terms of the Grüneisen relation and a simple inter-atomic potential.
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68.35.Ja Surface and interface dynamics and vibrations
65.40.De Thermal expansion; thermomechanical effects
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Theory of the Inelastic Scattering of Low-Energy Electrons from Crystal Surfaces by One-Phonon Processes

V. Roundy and D. L. Mills

J. Vac. Sci. Technol. 9, 699 (1972); http://dx.doi.org/10.1116/1.1317757 (6 pages)

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In this paper, we present a theoretical discussion of the form of the differential cross section per unit solid angle, per unit energy shift for the inelastic scattering by one-phonon processes of low-energy electrons from the surface of a semi-infinite crystal. A number of general features of the cross section are discussed, with particular attention to a comparison with the results obtained from the kinematical theory of the scattering process. We have also carried out a series of numerical studies of the dependence of the shape of the energy loss spectrum on momentum transfer for an electron incident on the (100) surface of an fcc crystal. For a general value of the momentum transfer, the energy loss spectrum consists of one or more lines that arise from the scattering off surface modes, and a band that has its origin in scattering produced by bulk modes. The shape of the latter feature, as well as the position of the surface mode peaks, is found to be quite sensitive to the values of the atomic force constants appropriate to the surface layer. It is suggested that the experimental study of the shape of the loss spectrum will provide a powerful means of probing the frequency spectrum of the atomic vibrations near the surface.
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61.05.jd Theories of electron diffraction and scattering
79.20.Ap Theory of impact phenomena; numerical simulation

Surface Phonons and Gas Surface Interactions

G. Armand, P. Masri, and L. Dobrzysnski

J. Vac. Sci. Technol. 9, 705 (1972); http://dx.doi.org/10.1116/1.1317758 (8 pages) | Cited 2 times

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Modifications to the band frequencies of a crystal occur with gas adsorption on the surface. If the adsorbed species are small mass or if they are strongly bonded, theoretical calculations predict the appearance of new frequencies which lie above the band frequencies of the crystal (surface phonons) and of a modification of the Rayleigh waves. Results of calculations with different models of monoatomic crystals and one adsorbed layer are presented. Two main consequences are discussed: the entropy variation due to adsorption, which yields a modification of the pre-exponential factor of the desorption rate equation; the amount of energy exchange between a colliding particle and a crystal, which decreases as the surface phonon-frequencies increases. Experimentally the existence of surface phonons correlated to adsorption can be supported by data from energy loss of low energy electrons and by infrared absorption measurements. Indirect support is also provided by experimental results dealing with the pre-exponential factor of desorption rates, and with reflection of light atom beams at a crystal surface.
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68.35.Ja Surface and interface dynamics and vibrations
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Low Energy Electron Spectroscopy—a Tool for Studies of Surface Vibrations

Harald Ibach

J. Vac. Sci. Technol. 9, 713 (1972); http://dx.doi.org/10.1116/1.1317759 (7 pages) | Cited 11 times

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Surface vibrations are investigated with a high resolution electron spectrometer (ΔE≈10 meV). For sufficiently low electron energies the electrons are scattered mainly by the extended electric dipole field associated with certain types of surface vibrations. The excitation of Fuchs-Kliewer surface modes in infrared-active materials is illustrated in zinc oxide. On the cleaved (111) silicon surface a surface phonon of ℏω=56 meV is found. Furthermore, the localized modes of oxygen adsorbed on a (111) silicon surface are discussed. The sensitivity of electron spectroscopy is several orders of magnitude higher than light spectroscopy.
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79.20.-m Impact phenomena (including electron spectra and sputtering)
68.35.Ja Surface and interface dynamics and vibrations

Surface Phonons in Realistic Models of Ionic Crystals

F. W. de Wette, T. S. Chen, and G. P. Alldredge

J. Vac. Sci. Technol. 9, 720 (1972); http://dx.doi.org/10.1116/1.1317760 (1 page)

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68.35.Ja Surface and interface dynamics and vibrations

LEED Thermal Scattering Studies of Xe (111) Surfaces

A. Ignatjevs, T. N. Rhodin, S. Y. Tong, B. I. Lundqvist, and J. B. Pendry

J. Vac. Sci. Technol. 9, 720 (1972); http://dx.doi.org/10.1116/1.1317761 (1 page)

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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

Magnons in Thin Films

J. C. Levy and J. L. Motchane

J. Vac. Sci. Technol. 9, 721 (1972); http://dx.doi.org/10.1116/1.1317762 (5 pages) | Cited 10 times

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In Heisenberg ferromagnetic thin films with {100} surfaces, the spin waves are analyzed in an exact treatment. The bulk and surface modes are separated and discussed. When the number N of parallel layers is finite, space quantization and phase shifts due to the surface perturbation are precised. Magnon specific heat, ferromagnetic resonance and the contribution to the fluctuation of the surface magnetization from the bulk and surface modes are studied in a microscopical way for very thin films. Anomalous variations of specific heat at very low temperature are found to exist. The ferromagnetic resonance is demonstrated to give a detailed study of the surface perturbation. Bulk and surface contributions occur in catalytic effects such as ortho-para conversion.
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75.30.Ds Spin waves
75.70.Ak Magnetic properties of monolayers and thin films

Excitation of Collective Modes in Electron–Solid and Ion–Solid Scattering

A. A. Lucas and M. Šunjić

J. Vac. Sci. Technol. 9, 725 (1972); http://dx.doi.org/10.1116/1.1317763 (7 pages) | Cited 5 times

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Charged particles approaching or leaving a solid surface scatter inelastically on the long-range Coulomb field of real or virtual surface collective excitations of the solid. A quantum theory of this scattering process, applicable to the case of “fast” particles, is presented. Two particular examples are discussed: (i) electron spectroscopy of surface plasmons in metals; (ii) observation of surface “plasmons” in transition metals excited by field emitted ions in field ion microscopy.
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79.20.Ap Theory of impact phenomena; numerical simulation
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Elastic and Inelastic Low-Energy Electron Diffraction (ELEED, ILEED) from an Al(100) Surface

J. M. Burkstrand and F. M. Propst

J. Vac. Sci. Technol. 9, 731 (1972); http://dx.doi.org/10.1116/1.1317764 (7 pages) | Cited 3 times

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Elastic and inelastic low-energy electron diffraction (ELEED, ILEED) observations have been made on a clean surface of Al (100). Measurements on the (10) and (11) elastic diffraction beams were made using normally incident electrons in the energy range 30≤E≤170 eV. Peaks in the energy loss distribution are seen near 5.5, 10, 15, 26, and 31 eV, the dominant peaks near 10 and 15 eV corresponding to surface and bulk plasmon excitations, respectively. Two types of structure are observed in the inelastic angular profiles: one closely correlated with the structure in the elastic angular profile and the second being substructure corresponding to different ILEED conditions. Intensity profiles (as a function of incident energy) for the (10) and (11) elastic and inelastic diffraction beams have been measured. These profiles also show primary and secondary structure. The experimental results agree with the theoretical predictions of Duke et al.
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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Inelastic Diffraction of Low-Energy Electrons from Aluminum: Surface Plasmon Dispersion Relation

C. B. Duke and A. Bagchi

J. Vac. Sci. Technol. 9, 738 (1972); http://dx.doi.org/10.1116/1.1317765 (5 pages) | Cited 2 times

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A two-step diffraction model is used to calculate the inelastic scattering of low-energy 50≲E≲150 eV electrons from Al (100) and Al (111). Analysis of experimental data for the specular beam of electrons scattered from Al (111) permits the approximate determination of the surface-plasmon dispersion relation; ℏω(P∥)=10.1−0.7P∥+10P∥2eV; and damping Γ(P∥)=1.4+0.7P∥eV for P∥ measured in reciprocal Angstroms. Analysis of data for both faces using several diffracted beams permits the identification of the dynamical origin of most of the prominent structures evident in the inelastic cross sections. The dispersion relation of the bulk plasmons is taken insofar as possible from high-energy-electron-transmission data. However, analysis of the low-energy (reflection) data leads to a lower threshold plasmon energy ℏωb≃14.2 eV, than that extracted from most high-energy (E∼20 keV) experiments (ℏωb≃15 eV). This discrepancy may result from the use in the reflection experiments of single-crystals rather than polycrystalline films.
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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Variation of Characteristic Energy Losses in the Curie Temperature Region of Ni(111)

B. Heimann and J. Hölzl

J. Vac. Sci. Technol. 9, 742 (1972); http://dx.doi.org/10.1116/1.1317766 (1 page)

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Abstract Unavailable
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79.20.Kz Other electron-impact emission phenomena
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Plasmon Angular Profiles in Low Energy Electron Diffraction from Single Crystals

R. J. Stein and R. M. Stern

J. Vac. Sci. Technol. 9, 743 (1972); http://dx.doi.org/10.1116/1.1317767 (4 pages) | Cited 4 times

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Measurement of surface and bulk plasma peaks in the secondary electron distribution from Ni(100) and W(110) provides confirmation of two-step inelastic diffraction. Angular profiles are made in the neighborhood of selected prominent elastic diffraction maxima. Momentum conservation parallel to the surface leads to the prediction of a doublet structure in the angular distribution of diffracted electrons having lost the surface plasmon energy. This structure is observed. The observed structure in the bulk plasmon loss angular profile is more complex and is indicative of other conservation laws.
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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

The Role of Surface Plasmons in Van Der Waals Attraction between Solids

E. Gerlach

J. Vac. Sci. Technol. 9, 747 (1972); http://dx.doi.org/10.1116/1.1317768 (2 pages)

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As has been shown by Casimir, Van der Waals attraction between solids, separated by a gap, can be obtained from the ground state energy of all electromagnetic modes of the system. In the present paper it is shown that, in a slightly generalized sense, the retarded Van der Waals attraction corresponds to the ground state energy of the interacting surface plasmons on either side of the gap. This concept establishes an interesting connection between the large field of surface plasmon physics and numerous technical applications in the field of adhesion between solids.
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68.35.Gy Mechanical properties; surface strains
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Inner Shell Ionization of Surface Atoms by Electron Impact

Robert L. Gerlach and A. R. DuCharme

J. Vac. Sci. Technol. 9, 748 (1972); http://dx.doi.org/10.1116/1.1317769 (1 page)

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Abstract Unavailable
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79.20.Kz Other electron-impact emission phenomena

Auger Spectroscopy Study on the Surface Composition of Copper–Nickel Alloys after Annealing and Sputtering

Katsuya Nakayama, Masatoshi Ono, and Hazime Shimizu

J. Vac. Sci. Technol. 9, 749 (1972); http://dx.doi.org/10.1116/1.1317770 (3 pages) | Cited 11 times

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The changes in surface composition of Cu–Ni alloys after various treatments have been observed by means of Auger electron spectroscopy. A retarding field analyzer consisting of four spherical grids was used. Samples of six different compositions were examined to obtain the calibration curve between the chemical composition and the peak-to-peak height of the derivative Auger peak. The sample surfaces were only polished with emery papers and rinsed in water and acetone. The apparatus was ion pumped to the mid 10−9-Torr range without baking so as not to affect the samples by heating. It was found that the Ni content on the sample surfaces for 80% Ni alloy decreases during the annealing process above 100 °C; and sputtering with argon ions of about 500 eV causes the nickel to become enriched in the surface layers. A slight increase of the nickel was observed on the surface of 38% Ni alloy after initial heating.
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68.35.Dv Composition, segregation; defects and impurities
81.70.Jb Chemical composition analysis, chemical depth and dopant profiling
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Surface Quantization and Surface Transport in Semiconductor Inversion and Accumulation Layers

Frank Stern

J. Vac. Sci. Technol. 9, 752 (1972); http://dx.doi.org/10.1116/1.1317771 (2 pages) | Cited 4 times

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Recent experimental and theoretical work on the properties of inversion layers and accumulation layers near semiconductor-insulator interfaces is summarized, with emphasis on quantization effects associated with strong normal electric fields.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.At Surface states, band structure, electron density of states

Two-Dimensional Impurity States in an n-Type Inversion Layer of Silicon

Nobuo Kotera, Yoshifumi Katayama, Isao Yoshida, and Kiichi F. Komatsubara

J. Vac. Sci. Technol. 9, 754 (1972); http://dx.doi.org/10.1116/1.1317772 (4 pages)

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Shallow impurity states associated with the electric subband in the n-type surface inversion layers have clearly been observed on the Si (100) surface. Measurements of the conductivity and the transconductance have been made at temperatures from 4.2 to 300 K, especially at low gate voltages near the threshold for the surface inversion, whose values are given in terms of effective mobility as well as field effect mobility. When the surface carrier density is less than 5×1010 cm−2, the surface conductance varies as exp(−ϵa∕kT) and the activation energy ϵa has been determined to be 1.2 meV. In this case, the peak of the transconductance, the differential conductance with respect to the gate voltage, disappears at 12 K, which agrees with the activation energy. When the surface carrier density is more than 1×1011 cm−2, the effective mobility is independent of temperature below 20 K and the electron statistics might be degenerate.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.25.+i Surface conductivity and carrier phenomena
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Parametric Approach to Calculating the Effect of a Magnetic Field on the Energy of Surface Bound States

G. A. Baraff and Joel A. Appelbaum

J. Vac. Sci. Technol. 9, 758 (1972); http://dx.doi.org/10.1116/1.1317773 (1 page)

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73.20.At Surface states, band structure, electron density of states

Band Structure Investigation on p-Type Silicon Inversion Layers by Piezoresistance and Mobility Measurements

G. Dorda, H. Friedrich, and E. Preuss

J. Vac. Sci. Technol. 9, 759 (1972); http://dx.doi.org/10.1116/1.1317774 (3 pages) | Cited 4 times

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Piezoresistance and mobility measurements have been performed between 310 and 77 °K with p-type inversion layers on (100), (110), and (111) silicon. An explanation of the dependences on the gate voltage (perpendicular electric field) can be given by the interaction of the quantized heavy (HHB) and light hole bands (LHB) at the surface. The interface stress caused by the insulating layer removes the valence band degeneracy, which results in ellipsoidal energy surfaces. By use of this model the energy positions of the subbands have been calculated. The state of degeneracy is found at higher gate fields. These theoretical results make it possible to interpret as well anomalies in piezoresistance as the initial rise and orientation anisotropies of the mobility. The ratio of heavy and light holes taking part in the transport have been deduced as a function of the gate voltage. The influence of the band-band scattering between LHB and HHB will be discussed. Analogous effects are expected for surfaces of AIII–BV semiconductor compounds.
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73.20.At Surface states, band structure, electron density of states
73.50.Dn Low-field transport and mobility; piezoresistance

Semiconductor Inversion Layers and Phonons in Half-Space

Shinji Kawaji, Hiroshi Ezawa, and Koichi Nakamura

J. Vac. Sci. Technol. 9, 762 (1972); http://dx.doi.org/10.1116/1.1317775 (7 pages) | Cited 6 times

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Electron-surfon interaction is used to calculate the mobility μ of electrons in the lowest subband in N-channel Si MOS-FET on the (111), (110) and (100) surfaces and at around room temperature. The surfons are the quanta of elastic waves in isotropic elastic continuum (which is to represent Si) occupying a half-space and having a stress-free plane boundary. In the approximations of high temperature surfon distribution and of elastic scattering, the result is (i) that the dependence of μ upon temperature and surface electron concentration can be fairly well reproduced but (ii) that the magnitude of μ has turned out to be about 10 times as high as the experimental values so far as bulk values are used for the deformation potential constants and for the effective masses of electrons. The correction due to the presence of SiO2 layer on Si is estimated to be small. It can be argued that correction due to intervalley scattering and electron population in the upper subbands are in the direction of improving the fit to the experiments. Still, the magnitude of μ remains unexplained unless the values of the deformation potential constants and effective masses of electrons differ in the surface region from the corresponding bulk values.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Effects of Surface Orientation on Transport Properties of Electrons and Holes on Oxidized Silicon Surfaces

Y. Takeishi, T. Satô, H. Maeda, and K. Hirabayashi

J. Vac. Sci. Technol. 9, 769 (1972); http://dx.doi.org/10.1116/1.1317776 (1 page) | Cited 1 time

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73.25.+i Surface conductivity and carrier phenomena

Correlation of Electronic, LEED, and Auger Studies of ZnO Surfaces

J. D. Levine, A. Willis, W. R. Bottoms, and Peter Mark

J. Vac. Sci. Technol. 9, 770 (1972); http://dx.doi.org/10.1116/1.1317777 (1 page) | Cited 1 time

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Abstract Unavailable
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73.20.At Surface states, band structure, electron density of states
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
79.20.Fv Electron impact: Auger emission

A Quantitative Study of Nucleation and Growth of Copper I—Oxide on Copper Single Crystals

M. Jardinier-Offergeld and F. Bouillon

J. Vac. Sci. Technol. 9, 770 (1972); http://dx.doi.org/10.1116/1.1317778 (10 pages) | Cited 4 times

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A microgravimetric study shows that the rate of oxidation of the (100) face of copper is convenient for the observation of the different steps of the process: induction, nucleation, and growth of the oxide particles. The rate of those steps and the number of nuclei depend upon crystallographic orientation of the metal, temperature of reaction, and pressure of oxygen. Sticking probabilities and activation energies of the different steps have been determined. Our results show under which conditions Rhead's theoretical scheme founded on surface diffusion remains valid.
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81.65.Mq Oxidation

Study of Adsorption and Nucleation of Cadmium on Tungsten and Germanium by a Molecular Beam Technique

R. J. H. Voorhoeve, R. S. Wagner, and J. N. Carides

J. Vac. Sci. Technol. 9, 780 (1972); http://dx.doi.org/10.1116/1.1317779 (4 pages) | Cited 1 time

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Polycrystalline tungsten, and several germanium single crystal faces, such as (111), (110), (211), etc., were bombarded with a calibrated cadmium beam of thermal energy. Various adsorption states were revealed by continuously monitoring cadmium evaporated from the substrate. Multilayer adsorption was found to precede growth of bulk cadmium for both types of substrate. The extent of this adsorption is 3–4 monolayers on tungsten and 2 monolayers on germanium (111). The heat of adsorption varies from 27 to 51 kcal∕mole for tungsten, and is 25–32 kcal∕mole for germanium. The nucleation of bulk cadmium has been studied with the same technique. Monitoring the evaporated cadmium during deposition allowed determination of the critical adatom coverage at which nucleation of bulk cadmium occurred. The nucleation kinetics shows critical behavior on germanium substrates but not on clean tungsten.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
64.60.Q- Nucleation

Leed Auger Study of Growth of Al on Nb (110)

A. G. Jackson and M. P. Hooker

J. Vac. Sci. Technol. 9, 784 (1972); http://dx.doi.org/10.1116/1.1317780 (1 page) | Cited 1 time

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Abstract Unavailable
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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
79.20.Fv Electron impact: Auger emission

Field Ion Microscopy of Vapor-Deposited Platinum on Tungsten

N. V. Durai Raghavan and R. J. Bayuzick

J. Vac. Sci. Technol. 9, 784 (1972); http://dx.doi.org/10.1116/1.1317781 (4 pages)

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Platinum was vapor-deposited on tungsten under high vacuum conditions. The resultant thin films were then examined in the field ion microscope at 78 °K. The platinum deposits were obtained under three different conditions. Deposits on substrate held at 78 °K gave several localized but crystalline deposits which were 10–100 Å in diameter and approximately 25 Å thick. A short anneal of the substrate at 1100 °K, after deposition was performed at 78 °K, resulted in evidence for the existence of a pseudomorphic deposit of platinum on tungsten, less than 10 Å in thickness. Deposition at 1100 °K followed by annealing at 1100 °K resulted in appreciable bulk diffusion and the field ion images obtained were typical of those from alloys.
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68.55.-a Thin film structure and morphology
68.37.Vj Field emission and field-ion microscopy
68.60.Dv Thermal stability; thermal effects

Oxygen Reactions on Platinum and Rhenium

A. Cassuto, A. Peutenero, and B. Weber

J. Vac. Sci. Technol. 9, 788 (1972); http://dx.doi.org/10.1116/1.1317782 (1 page)

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Abstract Unavailable
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Measurement of the Growth of Oxide Layers on Metals by Low-Energy Electron Spectroscopy: Aluminum

Yoshitada Murata and Shunsuke Ohtani

J. Vac. Sci. Technol. 9, 789 (1972); http://dx.doi.org/10.1116/1.1317783 (3 pages) | Cited 5 times

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The energy-loss spectra of 350-eV electrons reflected from aluminum were observed during the oxidation of a freshly evaporated film. The loss spectra due to surface plasma showed characteristic variations in the process of oxidation. The thickness of the oxide layer was measured by using the dispersion relation of surface plasmons. This method was shown to be useful for studying thin oxide layers (<20 Å). Oxide films grew on aluminum in different ways when the pressures were 1×10−7 and 1×10−8 Torr, where most of the residual gas was hydrogen and water. In the former case, the oxide layer in the initial stage was islandlike, whereas in the latter case it was uniform. Oxide films grew abruptly about 20 min after evaporation of the aluminum, as was confirmed by an analysis of the residual gas. The rate of growth of uniform oxide layers was consistent with a logarithmic law.
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81.65.Mq Oxidation
79.20.Kz Other electron-impact emission phenomena
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Chemical Shifts in the Auger Spectrum of Yttrium on Oxygen Adsorption

J. M. Baker and J. L. McNatt

J. Vac. Sci. Technol. 9, 792 (1972); http://dx.doi.org/10.1116/1.1317784 (5 pages) | Cited 2 times

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Adsorption of monolayer amounts of oxygen on yttrium films and molybdenum foil was studied with Auger electron spectroscopy. Exposure of yttrium to 0.3–15×10−6 Torr sec of oxygen resulted in the growth of new Auger peaks shifted by about −4 eV from the yttrium metal peaks involving the 4p, 4d, and valence levels. For molybdenum these levels were unaffected by oxygen adsorption. A background correction technique was applied in order to remove the effects of secondary electron emission from the data. The growth of the shifted peaks is followed in the spectra and the results are discussed in terms of the electronic structure of the metal and its oxide.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.20.Fv Electron impact: Auger emission

Effects of Oxygen on Silver Surface Structure

G. Rovida, F. Pratesi, M. Maglietta, and E. Ferroni

J. Vac. Sci. Technol. 9, 796 (1972); http://dx.doi.org/10.1116/1.1317785 (4 pages) | Cited 10 times

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The chemisorption of oxygen on the (100), (110), and (111) faces of silver single crystals was studied with LEED, secondary electron spectroscopy, and other auxiliary techniques. The effect of exposures to oxygen at pressures up to 1 Torr and temperatures up to 500 °C was investigated using a crystal isolation valve. The chemisorbed oxygen causes mainly a strong faceting of the (100) and (110) faces, and a 4×4 superstructure on the (111) face. The effect of the internally diffused oxygen on the surface behavior was also investigated.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)

The Surface Potential of Oxygen on Iron, Cobalt, and Manganese

G. K. Hall and C. H. B. Mee

J. Vac. Sci. Technol. 9, 799 (1972); http://dx.doi.org/10.1116/1.1317786 (1 page)

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Abstract Unavailable
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Retardation of Plutonium Oxidation by a PuO Surface Film

D. T. Larson and D. L. Cash

J. Vac. Sci. Technol. 9, 800 (1972); http://dx.doi.org/10.1116/1.1317787 (4 pages)

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An anomalous rate minimum exists at about 400 °C for the oxidation of plutonium, i.e., there is a decrease in the oxidation rate as the temperature is increased toward the rate minimum. In situ X-ray diffraction studies have shown that in the temperature region of the rate minimum, there is an increased rate in the formation of PuO. The influence of a PuO surface film on the oxidation of plutonium was investigated with an ellipsometer to determine if a PuO film affects the oxidation rate. Measurements showed that the PuO surface film does retard oxidation at 80 °C. It is further postulated that the anomalous rate minimum for plutonium oxidation near 400 °C results from the increased rate of formation of the protective PuO surface film.
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81.65.Mq Oxidation

Atomic and Molecular Scattering from Crystallographically Well-Defined Surfaces

Robert P. Merrill

J. Vac. Sci. Technol. 9, 803 (1972); http://dx.doi.org/10.1116/1.1317788 (1 page)

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61.05.Np Atom, molecule, and ion scattering (for structure determination only)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Quantum Theory of Desorption of Adatoms from Solid Surfaces

Bernard Bendow and See-Chen Ying

J. Vac. Sci. Technol. 9, 804 (1972); http://dx.doi.org/10.1116/1.1317789 (4 pages) | Cited 2 times

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We present a three-dimensional multiphonon theory of the desorption rate, for an atom adsorbed in a localized state on the surface of a solid, due to interactions with lattice vibrations. The central quantity in the theory is the time and position-dependent displacement-displacement correlation function of the lattice. The temperature dependent lifetime, and the angular and energy distributions, of desorbed adatoms are considered for model systems. Detailed numerical calculations are presented, employing a Debye model for the substrate lattice, and a Morse-like potential for the interaction between the adatom and each substrate atom.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Properties of 0.01-eV Helium Atoms Scattered Inelastically from Silver (111)

R. B. Subbarao and David R. Miller

J. Vac. Sci. Technol. 9, 808 (1972); http://dx.doi.org/10.1116/1.1317790 (4 pages) | Cited 6 times

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Out-of-plane density distribution and in-plane velocity distribution measurements for low-energy (0.01-eV) helium scattering inelastically from 550 K silver (111) are presented. The data suggest that surface phonon interactions have a negligible effect on the observed scattering.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.05.Np Atom, molecule, and ion scattering (for structure determination only)

Quantum-Mechanical Theory of the One-Phonon Inelastic Scattering of Gas Atoms in Three Dimensions by a Simplified Continuum Model of a Solid

Frank O. Goodman

J. Vac. Sci. Technol. 9, 812 (1972); http://dx.doi.org/10.1116/1.1317791 (2 pages) | Cited 1 time

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A quantum-mechanical treatment of the one-phonon inelastic scattering of gas atoms in three dimensions by a solid surface is presented. Three major approximations made in the calculations are (i) the first order distorted wave Born approximation is used to calculate the relevant transition probabilities, (ii) atoms near the surface of the solid are treated, from the point of view of their dynamics, as though they were in the bulk, and (iii) the gas-surface interaction is represented by an infinite-step potential with zero well-depth, thus eliminating the possibility of bound states of gas atoms at the surface. The theory is a generalization of the one-dimensional theory reviewed by F. O. Goodman to three dimensions. For the system He-Ag, comparisons are made with experimental scattering distributions and speed measurements of the type reported by R. B. Subbarao and D. R. Miller. Using independently-measured values of the various theoretical parameters, satisfying agreement between theory and experiment is obtained.
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79.20.Ap Theory of impact phenomena; numerical simulation

One-Phonon Transitions Observed in the Scattering of He Atoms from a LiF(001) Surface

S. S. Fisher and J. R. Bledsoe

J. Vac. Sci. Technol. 9, 814 (1972); http://dx.doi.org/10.1116/1.1317792 (5 pages) | Cited 7 times

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For the scattering of a nearly monoenergetic beam of thermal-energy He atoms from a cleaved (001)LiF crystal surface, speed distributions of the reflected atoms are measured at suitably spaced scattering angles (θr) within the plane of incidence. From the measurements, elastic and one-phonon inelastic scattering processes are identified. Elastically scattered atoms distribute themselves in a set of sharp diffraction peaks. One-phonon inelastically scattered atoms are dispersed about each diffraction peak. The most probable velocities of the inelastically scattered atoms exhibit a characteristic sawtooth variation with θr which, to first approximation, corresponds to conservation of the component of atom momentum tangent to the surface.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Scattering of Atoms and Molecules from Tungsten: Effect of Surface Composition and Crystal Orientation

R. E. Stickney, D. V. Tendulkar, and S. Yamamoto

J. Vac. Sci. Technol. 9, 819 (1972); http://dx.doi.org/10.1116/1.1317793 (6 pages) | Cited 3 times

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Molecular beam techniques have been used to study the scattering of various gases (He, Ar, N2, CO, and D2) from W(112) and W(110) crystals. The crystal temperature is varied from 300 to 2400 °K, and the partial pressure of oxygen is varied from an undetectable level to 1×10−7 Torr to alter the amount (coverage) of oxygen adsorbed on the surface. The results illustrate the strong dependence of the scattering process on surface composition and crystal orientation. The dependence is particularly strong in the case of He, where diffraction is observed at one extreme and essentially diffuse scattering is observed at the other extreme. The results for CO and N2 appear to be consistent with existing data on their sticking probabilities for W(112) and W(110).
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.05.Np Atom, molecule, and ion scattering (for structure determination only)

Interaction of Atomic and Molecular Hydrogen Beams with Surfaces at Very Low Temperatures

G. Marenco, A. Schutte, G. Scoles, and F. Tommasini

J. Vac. Sci. Technol. 9, 824 (1972); http://dx.doi.org/10.1116/1.1317794 (4 pages) | Cited 9 times

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The transfer of energy from beams of atomic and molecular hydrogen to various surfaces (H2O, Ne, Ar) at liquid helium temperatures and UHV conditions has been investigated by means of a microcalorimetric technique. Evidence is given of the recombination of atomic hydrogen on H2O and Ar surfaces. Seeding the surfaces with up to one monolayer of H2 is found to increase the energy transfer by an order of magnitude.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
34.50.Lf Chemical reactions

Chemisorption Surface Titration and Surface Reconstruction of Alloys

W. M. H. Sachtler

J. Vac. Sci. Technol. 9, 828 (1972); http://dx.doi.org/10.1116/1.1317795 (2 pages) | Cited 3 times

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Field ion microscopy revealed that chemisorption of CO and N2 on W induces surface reconstruction even at 78 K. Photoelectron emission from Ru films shows that CO wipes out memory of presintering: films of different initial work function yield equal final work function. Several alloy films equilibrated below 300 °C possess concentration gradients between surface and interior. By chemisorbing H2 or CO on CuNi, AgPd or AuPt the atoms of the VIIIb elements are counted. For RuPt the characteristic work function increase due to CO permits an estimation of the Ru content of the surface. CO adsorption on AuPt and AgPd causes drastic surface reconstruction, the surfaces becoming enriched with the element forming the stronger bonds with CO.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.30.+y Surface double layers, Schottky barriers, and work functions

Adsorption Studies with Cu∕Ni Alloys

G. Ertl and J. Küppers

J. Vac. Sci. Technol. 9, 829 (1972); http://dx.doi.org/10.1116/1.1317796 (7 pages)

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The adsorption of oxygen and carbon monoxide at clean (110) faces of Cu∕Ni alloys with 16, 45, 60, and 77% Ni content has been studied by means of LEED, Auger electron spectroscopy, work function measurements, and flash desorption. The results are compared with the behavior of the elementary metals. After proper preparation no phase segregation within the alloys could be detected and the surface and bulk compositions were shown to be identical by Auger spectroscopy. The adsorption of oxygen causes at first the appearance of a 2×1 structure on all surfaces, as is the case with Cu (110) and Ni (110). The corresponding change of the work function increases continuously with increasing Ni content. Further oxygen exposure leads to the formation of a c6×2 structure as on Cu (110) on a 16% Ni crystal, and to disordered adsorption at room temperature with the other samples. However, the 77% Ni surface develops a 2×2 structure after annealing. CO forms different ordered structures (1×2, 2×1 and c2×2 with the alloys. The adsorption energy of CO on the 45, 60, and 77% Ni samples is similar to that on Ni (110); the binding is somewhat weaker on the 16% Ni surface. Detailed measurements with the 60% Ni surface showed that the heat of adsorption is constant over a wide range of coverages. The results are discussed qualitatively from the point of view of the electronic structure of Cu∕Ni alloys and the theory of chemisorption.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.30.+y Surface double layers, Schottky barriers, and work functions

Application of Various Methods for the Determination of Adsorption Lifetime and Desorption Energy of Oxygen on Tungsten

H.-W. Wassmuth, H. Werner, and A. K. Mazumdar

J. Vac. Sci. Technol. 9, 835 (1972); http://dx.doi.org/10.1116/1.1317797 (5 pages) | Cited 1 time

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The adsorption lifetime τ and the desorption energy Q of oxygen atoms on a polycrystalline tungsten surface have been determined as functions of the coverage θ by using a uhv mass spectrometer. A method based on contact potential and sticking probability measurements (T=1200–2500 K), a combined study of steady state and transient state desorption processes (T=2000–2600 K), and three different types of flash desorption measurements under single flight detection conditions (T=1900–2600 K) were employed. Satisfactory agreement of the results obtained from the different methods was observed. A compensation effect, depending on the coverage θ, was found between the pre-exponential factor of τ and the desorption energy Q which varies between 6.3 eV at θ=0 to 3.4 eV at θ=1. A further experiment employing a pulsed molecular beam method is in progress.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

LEED∕Auger Spectroscopy Study of the Adsorption of Alkali Metals on Mo(110)

S. Thomas and T. W. Haas

J. Vac. Sci. Technol. 9, 840 (1972); http://dx.doi.org/10.1116/1.1317798 (4 pages) | Cited 2 times

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LEED and Auger electron spectroscopy have been used to study the adsorption of Na, K, Rb, and Cs on a Mo(110) surface. Alkali ions were deposited (at room temperature; pressure <1×10−10 Torr) from zeolite ion sources which enabled the absolute coverage to be measured. Peak-peak heights of Cs-47, K-251, Rb-56 and 75 eV Auger peaks and of Mo Auger lines were monitored as a function of coverage. Quantitative estimates of Na adsorption could not be made using AES owing to the low Auger yield of Na. LEED patterns showed a hexagonal close packed arrangment of the alkalis on Mo(110).
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Madelung Potential in Surface Reconstruction

John W. May and C. E. Carroll

J. Vac. Sci. Technol. 9, 843 (1972); http://dx.doi.org/10.1116/1.1317799 (4 pages)

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A reconstructed surface layer on a metal may resemble a two-dimensional ionic crystal. We test this ionic model by estimating the Madelung potential at the sites of foreign anions in mixed layers on nickel. For oxygen on Ni(100), the Madelung potential shifts the electronic energy levels of the ions, and these shifts are consistent with recent experimental data obtained by ion neutralization spectroscopy and photoemission. For sulfur and selenium on Ni(100), reconstruction to form mixed layers is consistent with the data only if the S and Se ions are considerably distorted.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Field Ion Microscopic Study on Promoted Evaporation of Platinum by Adsorbed Hydrogen

Osamu Nishikawa

J. Vac. Sci. Technol. 9, 847 (1972); http://dx.doi.org/10.1116/1.1317800 (4 pages)

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The previously reported observed number of hydrogen-promoted field-evaporated platinum atoms at 21 K exhibited a maximum for the adsorption period of several milliseconds and a decreased constant number for a longer adsorption period. The effects of temperature and residual tip voltage during an adsorption period are described. An unexpected finding is a maximum number of evaporated atoms at a residual tip voltage of 20%∼30% of the helium best image voltage and a decreased number at 40%∼60%. The coincidence between the hydrogen image voltage, the tip voltage at which H3+ occurs, and the residual tip voltage at which the number of evaporated atoms decreases, is mentioned.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
68.37.Vj Field emission and field-ion microscopy

Adsorption of Oxygen on the (100) Plane of Tungsten

M. Bacal, J. L. Desplat, and T. Alleau

J. Vac. Sci. Technol. 9, 851 (1972); http://dx.doi.org/10.1116/1.1317801 (6 pages) | Cited 1 time

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The effect of oxygen adsorption on the (100) tungsten surface has been investigated in a thermionic electron emission microscope and by means of contact potential measurements (Kelvin method). Surface contamination was closely controlled. The measurements indicate that the work function versus oxygen pressure curves agree with those of Batzies. The oxygen desorption energy decreases with increasing oxygen coverage. The initial sticking coefficient S0, slope (dΔϕ∕dn)0 and dipole moment μD deduced from the experimental results are S0=0.17, d(Δϕ∕dn)0=4.3×10−15 eV at−1 cm2, μD=2.2 D.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
73.30.+y Surface double layers, Schottky barriers, and work functions

Adsorption and Absorption of Hydrogen by Niobium

L. Johnson, M. J. Dresser, and E. E. Donaldson

J. Vac. Sci. Technol. 9, 857 (1972); http://dx.doi.org/10.1116/1.1317802 (4 pages) | Cited 1 time

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Adsorption of hydrogen on a clean niobium surface and the absorption of hydrogen into the bulk were investigated. The sticking probability of hydrogen on a clean niobium surface was found to be about 0.13. Evidence for a precursor surface adsorption state and subsequent diffusion into the bulk was found; the sticking probability is independent of temperature when the surface is clean but becomes temperature dependent at higher coverage. The solubility studies indicate ideal interstitial solution obeying Sievert’s law at concentrations of dissolved hydrogen below 0.1 at.% but show deviation from this ideal solution above 0.5 at.%. The heat of solution was found to vary from −16 to −10 kcal∕mol. The resistivity of niobium depends on hydrogen concentration and also on temperature and time. The deviations from ideal solution agree with a hydrogen cluster model.
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68.08.-p Liquid-solid interfaces
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
64.75.-g Phase equilibria

Photoemission and Surfaces

T. E. Fischer

J. Vac. Sci. Technol. 9, 860 (1972); http://dx.doi.org/10.1116/1.1317803 (8 pages) | Cited 1 time

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Photoelectric emission is examined for its usefulness to the investigation of surfaces. Emphasis is placed on various experimental techniques and the information they yield. Energy distributions of photoelectrons are used for the determination of energy parameters of semiconductor surfaces and their variations with temperature, illumination and adsorption, and for the observation of surface states on clean surfaces and of energy levels associated with adsorbates. Modulation of photoemission by applied fields (Schottky effect) or by illumination (photomodulation) yields information on the photoemissive process and on the nature of the energy barrier of surfaces. The vectorial photoeffect, i.e., the polarization dependence of photoemission at oblique incidence, holds considerable promise for the observation of optical transitions at surfaces.
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