Structure Of Solid Surfaces Research Articles

Core excitations and secondary electron spectra of Cu(100)

Electronic transitions near the 2s, 2p, 3s and 3p edges of Cu(100) are investigated with electron energy loss spectroscopy and compared with real-space multiple-scattering calculations that take into account the momentum transfer q in the electron scattering process. The interplay between q and the different angular momentum channels involved in the transitions show that while for the 2p-edge with a large energy loss (and with a large q) dipole transitions dominate the spectrum, the non-dipole channels are very strong for the 3s-edge even with small q. The methods are extended to scattering states up to 300 eV above the Fermi level in order to identify structures in the secondary electron emission spectra. The strength of electron energy loss spectra in reflecting the electronic structure of solid surfaces is emphasized along with the necessity of a complete theoretical analysis before the dipole approximation may be applied.

Ion scattering studies of modified metal surfaces

The technique of ion backscattering and channeling provides valuable information about the structure of solid surfaces, both clean and as modified by adsorbed atoms. Analysis of the backscattering data is based on the concepts of shadowing and blocking. Because the theory of Rutherford scattering is well understood, it is possible, using comparisons between experiment and computer simulations for model structures, to extract information about the geometry and dynamics of atoms on solid surfaces. Studies of the structure of clean W(110) and Nb(110) surfaces, and the modification of these surfaces with H adsorption/absorption will be presented. Ion scattering also provides structural information about solid-solid interfaces. Results for Pd deposited on A1(111), and for Ni on W(110) will be discussed.

Comments on diffusion of desorbing adsorbate

A simple mesoscopic model for combined diffusion and desorption at realistic solid surface structures, i.e. graphite surface and fcc(111) or hcp(0001) metal surfaces based on the master equation approach is proposed. The differences in the coupling between diffusion and desorption caused by the presence of inequivalent adsorption sites and related appearance of a new time scale is discussed. The analysis of available experimental data suggests that far from equilibrium measurements, for example scattering measurements of the adsorbate dynamic structure factor S( q , ω), combined with laser induced thermal desorption can access those time scales.

Comments on diffusion of desorbing adsorbate

A simple mesoscopic model for combined diffusion and desorption at realistic solid surface structures, i.e. graphite surface and fcc(111) or hcp(0001) metal surfaces based on the master equation approach is proposed. The differences in the coupling between diffusion and desorption caused by the presence of inequivalent adsorption sites and related appearance of a new time scale is discussed. The analysis of available experimental data suggests that far from equilibrium measurements, for example scattering measurements of the adsorbate dynamic structure factor S( q,ω) , combined with laser induced thermal desorption can access those time scales.

Scanning tunneling microscopy and the atomic structure of solid surfaces

Scanning tunneling microscopy and the atomic structure of solid surfaces

Estimation of pore and surface structures of solids by dye adsorption: the preadsorption method and fractal analysis

Determination de la structure et la dimension des pores des fibres de charbons actifs par adsorption de differents colorants (orange II, Rouge acide 88, Bleu de methylene, Violet cristal, Bleu de phtalocyanine, Rouge acide 27 et vert de naphtol)

Mono-Atomic Tips and Scanning Tunneling Microscopy

The power of the Scanning Tunneling Microscope (STM) to resolve the detailed structure of solid surfaces is based on the strong distance dependence of the tunnel current, while the tip is scanned over the surface to be investigated.In the first part of the paper, the basic principles of operation of the STM are to be reviewed, and examples of the information that can be obtained today are presented. From this, it will be evident that knowledge of the atomic arrangement of the tip is important in order to separate tunnel-current changes related to the tip from those owing to the structure of interest, namely, the sample surface.

An X-Ray Diffraction Attachment tor Thin Filam Analysis of High Sensitivity

ABSTRACTA Seemann-Bohlin X-ray diffration attachment has been developed recently. In addition, two new intensity factors are introduced to existing intensity formula of Seemann-Bohlin diffractometer. Its characteristic is that the glancing angle is rather small and that no crystal monochromator is put in the incident path. Compared with the conventional diffractometer, it is superior in many aspects: (1). Very high sensitivity in identifying the structures of solid surfaces and thin films, with the intensities being 7–20 times those of the conventional method. For example, in analysing a gold film of 70 Å thick by 1KW X-ray, a fairly good pattern was obtained up to 2θ=120° with the scanning speed of 4°(2θ)/min. (2). All diffraction peaks obtained give the information of the surface layer in nearly the same depth. It thus enables one to study the variation of the composition, the lattice constants, and the structures with depth. (3). It can also be used for thick polycrys-talline samples, and the intensities are 3–20 times those of the conventional diffractometer. This method can be used for various ordinary diffractometers.

Inverse photoemission

Inverse photoemission (or ultraviolet bremsstrahlung spectroscopy) is an emerging new technique for the study of the electronic structure of solid surfaces. It has the important characteristic of being able to probe states between the Fermi level and vacuum level. Here we survey current experimental practice and future prospects, including discussion of band-pass and low-pass photon filters, grating spectrographs, and electron sources. Examples of recent work are presented, drawing on studies of band mapping, energy-loss satellites, surface states, adsorbates, and spin polarization effects. Emphasis is on k-resolved inverse photoemission spectroscopy (KRIPES).

Surface Imperfections and Heterogeneous Catalysis

The existence of the relationship between surface lattice imperfections and heterogeneous catalysis was proposed by H.S. Taylor in 1925. Since then, much work has been done to support this relationship. Various approaches have been used such as by applying catalytic activity versus annealing temperature curves of cold-worked, electron- or ion- bombarded metals. However, the results are rather qualitative. More recently, techniques such as AES, LEED, and EELS have been used to characterize the electronic, atomic, and defect structures of solid surfaces on an atomic scale. These were successfully applied first by G.A. Somorjai's group and then by other investigators. Many interesting and quantitative relationships were obtained between step or kink concentration and adsorptive or catalytic activities on well-defined surfaces. This article reviews the qualitative and quantitative results.

Multiphoton resonance ionization of sputtered neutrals: a novel approach to materials characterization

Ionization of neutral atoms sputtered from ion bombarded solids by multiphoton resonance ionization has been demonstrated for the first time. The ionization efficiency is several orders of magnitude greater than other post-ionization methods. This approach should find applications in the characterization of the chemistry and structure of solid surfaces and in the trace analysis of a wide variety of materials.

Solid surfaces under laser irradiation

The electronic structure of solid surfaces under laser irradiation is studied. Intense laser fields are shown to shift and/or split energy levels coupled by laser photons. This is related to various optical couplings between electronic states. The effects of strong electromagnetic fields on chemisorbed species are considered, together with the photoinduced static electric field. This may produce a change in the substrate-adatom system, which could lead to an enhancement of desorption processes.

Extended fine structure analysis using electron beams

Appearance potential spectroscopy has found use primarily as a core level probe of the electronic structure of solid surfaces. The observation of extended fine structure above appearance potential edges, analogous to that observed above X-ray adsorption edges, gives promise that atomic spacings in the surface region may also be determined. Most previous studies of appearance potentials have depended on observing changes in the soft X-ray yield. Poor detection efficiencies and low flourescence yields have limited the usefulness of this approach. Using the secondary electron yield, however, we have recently succeeded in observing fine structure extending more than 400 eV above appearance potential edges. We are currently employing this approach to study the structure of SiO 2 films on Si substrates. Initial attempts at Fourier inversion and problems due to diffraction of the incident electron beam and multiple scattering effects will be discussed.

菊池パターンによる表面構造の研究

It has been considered that the surface atoms (ions) of the (100) face of a NaCl-type alkali halide are rumpled. In this review, it is described that the surface structure of solids can be estimated by the Kikuchi patterns of LEED in surface state resonance and of RHEED. The surface ions in MgO (001) lie in a plane in the as-cleaved face and are rumpled in the annealed face, in which the angle between the Mg-O bond direction and the (001) face is 3°

Structure of solid surfaces

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStructure of solid surfacesLarry L. Kesmodel and Gabor A. SomorjaiCite this: Acc. Chem. Res. 1976, 9, 11, 392–398Publication Date (Print):November 1, 1976Publication History Published online1 May 2002Published inissue 1 November 1976https://doi.org/10.1021/ar50107a002RIGHTS & PERMISSIONSArticle Views166Altmetric-Citations13LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1015 KB) Get e-Alerts Get e-Alerts

The electronic structure of solid surfaces

We present a short review of the current status of electronic structure calculations for ordered solid surfaces. For the $s\ensuremath{-}p$ bonded metal surfaces, emphasis is centered entirely on self-consistent field (SCF) calculations employing a local density approximation for exchange and correlation. For semiconductor surfaces both SCF and empirical tight-binding methods are discussed, while for transition metal surfaces, where no SCF calculations have been carried out, a number of different schemes for solving Schr\"odinger's equation at a surface are reviewed that use plausible but not self-consistent forms for the surface potential. Finally, calculations for chemisorbed systems are briefly covered, with emphasis on ordered monolayers on semiconductor and transition metal surfaces.

The Structure of Surfaces

The past several years have seen a virtually explosive development of structural surface science. The techniques of low-energy electron diffraction and electron spectroscopy have found a multitude of applications in investigations of various surface and interfacial phenomena. Studies of the atomic structure of clean solid surfaces of low Miller index by low-energy electron diffraction, LEED, are being expanded to higher Miller index or stepped surfaces, as well as to studies of the structure of adsorbed gases. There are recent LEED studies of catalysts and of electrode surfaces that were examined before and after surface reactions. Among the various techniques of electron spectroscopy, Auger electron spectro­ scopy is the most widely applied to studies of surfaces. The composition of the surface can be determined with a sensitivity of about 1% of a monolayer (about 1013 atoms/cmZ), all elements being detectable this way except hydrogen and helium (1). Auger electron spectroscopy (AES) has also been used to determine the valency of surface atoms, i.e. the oxidation state of the same element in various compounds (2). More recently, other techniques such as ultraviolet photoelectron spectroscopy (3), electron loss spectroscopy (4, 5), and X-ray photoelectron spectroscopy (6) have all been utilized in surface studies to determine surface composition and valency. These techniques are based on one-electron processes and, therefore, the experi­ mental data may be analyzed more easily than in the case of AES, which involves a two-electron process. In this chapter, we review the recent advances made in surface crystallography and in studies of surface structure of solids and of adsorbed layers. This field is developing so rapidly that by the time this review is published, most of the information reported here from the various areas of structural surface science will need updating. We first consider those surfaces for which there have been attempts at obtaining an exact structural analysis from LEED measurements. These are unreconstructed metal surfaces and simple layers of chemisorbed atoms. We go on to review the present state of understanding of more complex surfaces of metals, semiconductors, and insulators where a complete structural analysis is not yet possible.

Abstract: Electronic structure of Si and Ge surfaces—clean and with chemisorbed layers

Practical techniques have been developed for performing self−consistent calculations of the electronic structure of solid surfaces. The method exploits the fact that the disturbance produced by the surface is significant only in the first few atomic layers, and that beyond this the potential may be assumed to be identical to that of the bulk solid. The charge density in the surface region is calculated by numerically solving Schroedinger’s equation for the surface region tails of the bulk wavefunctions and for bound surface states. The self−consistent surface region potential is constructed using a fitted model potential for the ion cores, the exact Hartree potential, and a local approximation for the exchange and correlation potential. The calculations outlined above have been carried out for the Si(lll) surface. An inward relaxation of the surface atom plane of 0.34 Å is suggested by empirical chemical considerations, and the consequences of this and several other amounts of relaxation were explored. In all cases, a band of surface states was found within the absolute energy gap whose charge has a clear ’’dangling bond’’ character. Its shape was dependent on relaxation, going from sp3 to pz with increasing relaxation. A major qualitative difference found in going from 0.17 to 0.34 Å was the appearance of two additional bands of surface states below the valence bands and in internal gaps. These states are clearly identified with the strengthened bonds between the first and second layers, and contribute structure to the surface density of states, which has recently been verified in spectroscopic measurements. The calculated workfunction and surface Fermi level pinning are in excellent agreement with experiment. Similar calculations have been carried out for Ge(lll). The main difference from the Si results is a change in the nature of the energy vs parallel momentum relation for the dangling bond surface state. A second energy minimum appears which has a charge distribution that is not dangling bond−like, and that could participate in chemisorption bonds to second layer Ge atoms. The theoretical methods employed are also suitable for treating ordered adsorbed overlayers. H chemisorbed on Si(lll) has been studied, and a single fully occupied band of surface states has been found to lie in internal energy gaps of the valence band, 4−7 eV below the valence band maximum. The charge density contributed by this band is concentrated in the Si−H bond. Spectroscopic structure associated with this band of surface states has been seen experimentally. Another chemisorption system studied was Al substitutionally adsorbed on Si(lll), one of several structures which has been observed for this system. Since Al in this position has its valence requirements satisfied, a filled−band (saturated bond) picture might have been anticipated. Instead, three partially occupied bands of surface states have been found, indicating a metallic surface. This is especially remarkable considering that the Al atoms are 3.84 Å apart, compared to 2.86 Å in Al metal. A consequence of this result is the possibility that adsorbed metal films only a few layers thick may provide an adequate model of semiconductor metal interfaces which is suitable for study on an atomic scale by our methods.

Approximate calculation of the electronic structure of solid surfaces and interfaces between material media

In this paper an approximation to the method of local orbitals is proposed for studies of solid surfaces and the interface between materials. This approximation yields a nonlocal one-particle operator of the Hartree-Fock form for the electronic structure. This operator is diagonalized in a linear-combination-of-atomic-orbitals-type method using a basis of approximate local orbitals. In this paper the question of correlation is ignored. Solutions are obtained for several simple prototype systems, solid He, solid Ne, ${\mathrm{H}}_{2}$ on solid Ne, H on solid He, and the catalytically active $\mathrm{O}_{}^{\ensuremath{-}\ensuremath{-}}{}_{3}{}^{}$ center of a fine particle of MgO.

Determination of the Structure of Solid Surfaces by Low-Energy Electron Diffraction

Major advances occurring during the past two years in the development of the theory of low-energy electron diffraction (LEED) are surveyed. The quantitative nature of mathematical models of LEED from periodic systems is indicated by reference to analyses of observed LEED intensities from low-index faces of aluminum, nickel and copper. Extensions of these models to describe elastic LEED from partially disordered adsorbed overlayers are noted. Applications of model calculations to ascertain the atomic geometry of adsorbed overlayers are described. Analyses of observed LEED intensities for c (2×2) overlayers of oxygen and sulphur on the (100) faces of nickel and copper serve as examples of such applications. The analysis of inelastic LEED intensities to determine the dispersion relation of surface plasmons is illustrated for Al (111).