Adsorbate-induced Reconstruction Research Articles

Structural determination of an adsorbate-induced surface reconstruction:p4g(2×2)Nversusc(2×2)Oon Ni(100)

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Adsorbate-induced reconstruction in the Ni(110)-H system.

The adsorbate-induced reconstruction of the room-temperature Ni(110)-H surface has been resolved by scanning tunneling microscopy. The structure, known as ``streaky'' (1\ifmmode\times\else\texttimes\fi{}2) from LEED observations, is found to be primarily a (5\ifmmode\times\else\texttimes\fi{}2) Ni reconstruction with small domain size along the 〈001〉. Top-layer Ni atoms are paired long the 〈001〉 by a 0.5-A\r{} lateral displacement to form tetramers and every fifth 〈001〉 row is missing. The barrier height, measured simultaneously with a constant-current topograph, is found to be higher along the 〈001〉 missing rows.

Phase transformations of the H/W(110) and H/Mo(110) surfaces

We present results of combined theoretical and experimental studies of the surface phases produced by hydrogen adsorption on tungsten (110) and molybdenum (110) planes. We have formulated a theoretical model which has the following ingredients: (1) a possible adsorbate-induced lateral shift reconstruction of the substrate surface; (2) two-body and three-body interactions among hydrogen atoms; and (3) a coupling of the overlayer ordering to the substrate reconstruction. This model gives good agreement with the observed phase diagram for H/W(110) which shows a (2×1) phase at low coverages and a (2×2) phase, as well as substrate reconstruction, at high coverages. In the case of H/Mo(110), for which no reconstruction is observed, the lack of a (2×1) phase suggests the presence of a strong three-body interaction among the adatoms.

Effect of the adsorbate-induced surface reconstruction on thermal desorption spectra: H 2/Pt(100)

The high temperature ( T⪆300K) thermal desorption spectra for hydrogen from Pt(100) are characterized by a shift of the peak maximum to higher temperatures with increasing initial coverage and by narrow peak widths. These features are explained by the adsorbate-induced surface reconstruction.

Effect of the adsorbate-induced surface reconstruction on thermal desorption spectra: H 2/Pt(100)

The high temperature ( T ≳ 300 K) thermal desorption spectra for hydrogen from Pt(100) are characterized by a shift of the peak maximum to higher temperatures with increasing initial coverage and by narrow peak widths. These features are explained by the adsorbate-induced surface reconstruction.

Structure determination of an adsorbate-induced multilayer reconstruction: (1 x 2)-H/Ni(110).

The reconstructed (1\ifmmode\times\else\texttimes\fi{}2) structure formed by saturation of a Ni(110) surface with adsorbed H atoms at T&lt;180 K was investigated by LEED. Excellent agreement between experimental and calculated I-V spectra for eleven nonequivalent beams was obtained for a model in which parallel rows of Ni atoms in the topmost layer are laterally shifted by 0.3 A\r{} (``row pairing'') and which exhibits periodic vertical displacements (``buckling'') of the atoms in the second layer.

X-ray absorption near-edge structure of adsorbate-induced reconstruction: (2x1)O on Cu(110)

Abstract We present O K-edge near-edge absorption spectra for (2 sx 1)O on Cu(110) and accompanying multiple-scattering calculations for models with an unreconstructed substrate and with missing-row and saw-tooth adsorbate-induced reconstructions. The calculated NEXAFS has been analysed to assess the importance of multiple scattering as a function of the azimuthal angle of the electric field vector, and to identify the dominant structure-sensitive multiple-scattering paths. We find strong support for an oxygen-induced reconstruction of the Cu(110) substrate, though an unequivocal resolution between the missing-row and saw-tooth models must await further measurements.

X-ray absorption near-edge structure of adsorbate-induced reconstruction: (2 × 1)O on Cu(110)

We present O K-edge near-edge absorption spectra for (2 sx 1)O on Cu(110) and accompanying multiple-scattering calculations for models with an unreconstructed substrate and with missing-row and saw-tooth adsorbate-induced reconstructions. The calculated NEXAFS has been analysed to assess the importance of multiple scattering as a function of the azimuthal angle of the electric field vector, and to identify the dominant structure-sensitive multiple-scattering paths. We find strong support for an oxygen-induced reconstruction of the Cu(110) substrate, though an unequivocal resolution between the missing-row and saw-tooth models must await further measurements.

Summary Abstract: Growth kinetics of an adsorbate-induced surface reconstruction

Summary Abstract: Growth kinetics of an adsorbate-induced surface reconstruction

Surface science aspects of interfacial electrochemistry

One of the most important tasks in physical electrochemistry today is the determination, on a microscopic level, of the structure and the properties of the solid–electrolyte interface. To obtain such information, two somewhat different approaches are currently employed. The first one deals with in situ spectroscopy, i.e., with spectroscopic techniques which are applicable in the presence of the electrolyte. The second route involves electrode emersion and the study of the surface properties outside the electrochemical cell, e.g., under UHV conditions. In the following, selected examples for the study of electrode surfaces are given, which are believed to be of topical interest to a general surface science audience. Those include surface states at the metal–electrolyte interface, adsorbate-induced surface reconstruction and restructuring, and the study of metal deposits in the submonolayer range.

Adsorbate-induced reconstruction of the Ni(100) surface.

Adsorbate-induced reconstruction of the Ni(100) surface.

Simple model for an adsorbate-induced surface phase transition

A qualitative model is proposed for the description of an adsorbate-induced surface reconstruction in terms of the theory of first-order phase transitions.

The coverage-dependent ordering of chemisorbed hydrogen on the (110) surface of nickel

The dissociative adsorption of hydrogen on Ni(110) at low temperatures has been studied in great detail with He diffraction. With increasing hydrogen exposure, a c(2 × 6), a c(2 × 4), two different c(2 × 6) and a (2 × 1) phase corresponding to coverages of θ = 1 3 , 1 2 , 2 3 , 5 6 and 1 monolayers (ML) have been identified. The corrugation functions of all phases have been determined by intensity analyses of He-diffraction spectra using the hard-wall approximation. The analyses were performed in a model-free manner using symmetry-compatible Fourier representations of the corrugations, and the results were underpinned by additional calculations with the adatoms modeled as Gaussian hills. The best-fit corrugations of all phases up to 1 ML deliver direct pictures of the adatom configurations, and allow an absolute coverage determination on purely crystallographic grounds in good agreement with the relative coverages determined by flash-desorption measurements. The most important structural elements are long H-zig-zag chains along the close-packed Ni rows with the hydrogen atom sites near threefold coordination. The rather long-ranged lateral interaction between the hydrogen chains favors alternation of zig-zag with zig-zag elements in all submonolayer phases. The c(2 × 6) phase with θ = 5 6 ML constitutes an interesting intermediate as 1 6 ML H-adatoms are obviously forced into twofold coordinated sites to form a distorted close-packed hexagonal pattern of H atoms. Thus, the phase jump of 2.5 Å of all zig-zag chains necessary to form the (2 × 1) where all close-packed Ni rows are covered with parallel zig-zag chains seems to become feasible via a compression of the c(2 × 6) with θ = 5 6 ML . Further hydrogen can subsequently be accommodated via an adsorbate-induced reconstruction of the Ni substrate. Improved diffraction experiments provide the full two-dimensional corrugation function for the final (1 × 2) structure which corresponds to a saturation coverage of ≅ 1.5 ML whereby probably 1 2 ML hydrogen is adsorbed on the second Ni layer.

Adsorbate-Induced Soft-Phonon Reconstruction of the Ni(100) Surface

A systematic study of the lattice dynamics of several (2\ifmmode\times\else\texttimes\fi{}2) overlayers on Ni(100) leads to the conclusion that the reconstruction of the nickel surface with a carbon overlayer is of the softphonon type. The reconstruction is driven by the freezing of the ${S}_{1}$ nickel surface phonon.

Surface ferromagnetism and chemisorption: Polarized electron diffraction calculations on Fe(110) p(2 × 2)- S

Intensity and exchange-induced scattering asymmetry versus energy profiles have been calculated for spin-polarized low-energy electron diffraction (SPLEED) from ferromagnetic Fe(110) p(2 × 2)- S. The strong sensitivity of our asymmetry results to the magnetization of the topmost substrate layer suggests SPLEED as a powerful probe of the effect of chemisorption and adsorbate-induced substrate reconstruction on surface ferromagnetism.

Surface ferromagnetism and chemisorption: Polarized electron diffraction calculations on Fe(110)p(2×2)-S

Intensity and exchange-induced scattering asymmetry versus energy profiles have been calculated for spin-polarized low-energy electron diffraction (SPLEED) from ferromagnetic Fe(110)p(2×2)-S. The strong sensitivity of our asymmetry results to the magnetization of the topmost substrate layer suggests SPLEED as a powerful probe of the effect of chemisoption and adsorbate-induced substrate reconstruction on surface ferromagnetism.

Two-dimensional phases in chemisorption systems

A discussion is given of two-dimensional phase transitions observed in chemisorption systems. The general problems encountered in experimental studies of these phenomena are reviewed. This is followed by a survey of the available data, after which some specific chemisorption systems are discussed: H/Fe(110) as an example of a lattice gas system; H/W(100) as an example of adsorbate-induced reconstruction; O/Ni(111) and H/W(110) as examples of critical-exponents studies.

Chemisorption and phase changes on W(100) and Mo(100)

The surface ’’phases’’ observed by LEED and other techniques in adsorption studies are usually ascribed to pairwise interactions between the adsorbate and the substrate, and between the adsorbed species themselves. However, in the case of chemisorbed hydrogen — and probably other overlayers — on W(100) and Mo(100) the phase changes appear to involve an adsorbate-induced reconstruction of the substrate. The structures are similar to those observed on the clean substrates at low temperture and they are characterized by a periodic lattice distortion whose wave vector depends on the adsorbate density and the temperature. Presumably the driving mechanism involves a lowering of the surface electronic energy and the periodicity may therefore reflect the geometry of the two-dimensional Fermi surface.

Hydrogen on Tungsten(100): Adsorbate-Induced Surface Reconstruction

Hydrogen on Tungsten(100): Adsorbate-Induced Surface Reconstruction

Similar surface structures for CO and N2adsorbed on W(210)

LEED observations of intensity-voltage spectra for (2*1) structures formed by both CO and N2 adsorption on W(210) show remarkable similarities between the two sets of spectra and significant differences from corresponding spectra from the clean surface. Possible structural models to account for these results are considered, with emphasis on the possible relevance to recent suggestions of adsorption-induced reconstruction of tungsten surfaces.