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IBM Journal of Research and Development

Issue 3 • Date May 1978

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Displaying Results 1 - 15 of 15
  • Preface

    Page(s): 212
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (189 KB)  

    It has been recognized for many years that the understanding and exploitation of solid state phenomena depend largely on the ability to accurately describe the microscopic structures of surfaces and interfaces, and to define correlations between those structures and physical and chemical phenomena of interest. Only during the last decade have experimental and theoretical tools been developed that make it possible to investigate surface structure and related surface phenomena in the required detail. View full abstract»

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  • Model Study in Chemisorption: Molecular Orbital Cluster Theory for Atomic Hydrogen on Be(0001)

    Page(s): 213 - 234
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1063 KB)  

    The interaction between atomic hydrogen and the (0001) surface of Be has been studied by using clusters of Be atoms to simulate the substrate. The largest cluster used contains 22 Be atoms, 14 in the first layer and 8 in a second layer. An H atom is added to the Be clusters at four high symmetry adsorption sites. Ab initio molecular orbital Hartree-Fock wave functions have been obtained and the interaction energy of H with the Be cluster is studied as a function of vertical distance from the surface. Thorough studies of various aspects of the computations and of the appropriate interpretation of the cluster results are reported. Our results show that three of the sites considered have similar binding energies, De ≈ 50 kcal/mol (≈2.1 × 105 J/mol), and (vertical) equilibrium distances from the surface, re ≈ 0.1 nm. For the fourth site, H directly over a Be atom, De is ≈30 kcal/mol (1.3 × 105 J/mol), and re is ≈0.14 nm. We expect that the dissociative adsorption of H2 on Be(0001) will be exothermic. A model calculation for diffusion of H into the bulk indicates that this process is energetically unfavorable for an ideal (0001) surface. The vibrational energies for the motion of H normal to the surface are found to be substantially different for sites with different surface coordinations. The nature of the covalent bond formed between H and Be(0001) is analyzed. View full abstract»

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  • Core-Level Photoemission and LEED Studies of Adsorption at Fe Surfaces: Comparison Between CO and O2

    Page(s): 235 - 249
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (737 KB)  

    Carbon monoxide and oxygen interactions with αFe(100) and polycrystalline surfaces have been studied by x-ray photoemission (XPS or ESCA) and low energy electron diffraction (LEED) at temperatures between 123 K and 473 K. For CO, the XPS results demonstrate the existence of four electronically distinct CO adsorption states; one is dissociative and three are molecular. The binding energy analyses are consistent with one of the latter molecular adsorption states, formed on the polycrystalline surface, having a stretched CO bond compared with the equivalent state on the Fe(100) surface. For oxygen, only dissociative chemisorption is observed, even at 123 K. Assuming monolayer coverage at saturation allows calibration of the coverage for all other situations of CO and O2 adsorption. It is demonstrated that at coverages of just greater than a monolayer (293 K adsorption), Fe oxide species are already present and that FeIII dominates. Studies at grazing angles, designed to enhance the surface sensitivity of the core-level measurements, fail to reveal recognizable FeII or FeIII species much below monolayer coverage even though LEED studies indicate that an FeO-like geometric structure has developed at coverages much lower than this. View full abstract»

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  • Reaction of Atomic Hydrogen with Si(111) Surfaces: Formation of Monohydride and Trihydride Phases

    Page(s): 250 - 259
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (636 KB)  

    By using a realistic tight-binding or LCAO (linear combination of atomic orbitals) model, detailed calculations of surface states, local densities of states, and theoretically simulated photoemission spectra have been carried out for two qualitatively distinct structural models for chemisorption of atomic hydrogen on Si(111)1×1 surfaces. In the low-coverage model, called the monohydride phase or Si(111):H, it is assumed that a single hydrogen atom sits on top of each surface Si atom, thus saturating all dangling bonds. In the high-coverage model, designated as the trihydride phase or Si(111):SiH3, SiH3 radicals are bonded to the surface Si atoms. Due to the radically different atomic structures, the theoretical spectra of the two phases show striking differences. A comparison of the theoretical spectra with the ultraviolet photoemission spectra taken during hydrogen chemisorption on the quenched Si(111)1×1 surface clearly shows that at low coverages the monohydride is formed, while at high coverages the trihydride phase is formed. Formation of the monohydride phase is expected on simple chemical and structural considerations, and it has been observed on other Si surfaces. However, formation of the trihydride phase is unique to Si(111)1×1 and as such, it has important implications regarding the structure and stability of clean Si(111)1×1. View full abstract»

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  • Chemisorption of Ethane on W(111)

    Page(s): 260 - 264
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    Ethane is chemisorbed on W(111) with a sticking probability of ≈0.003. The carbon Auger spectrum at saturation co verage exhibits a two-peak structure similar to that for graphite, while the LEED (low energy electron diffraction) pattern is almost identical to that obtained for an atomically clean surface. Heating the surface to ≈773 K causes desorption of hydrogen and changes th e carbon Auger spectrum to a three-peak structure similar to that for tungsten carbide. After annealing, the LEED pattern is affected in different ways depending on the precise conditions, but it may in certain circumstances almost disappear. Exposure to ethylene produces a similar sequence of events. A large kinetic isotope effect is observed with the ratio of the sticking probabilities [S(C2H6)/S(C2D6), W(111), T = 300 K] being ≈3. A similar ratio is measured for tungsten at T = 2500 K. These data suggest that chemisorption is dissociative in nature, probably involving the reaction C2H6 → C2H5* + H → subsequent steps. Heating of the surface completely dissociates the adsorbed gas, leaving adsorbed carbon and gas phase hydrogen. In analogy with previous work on methane, we believe the large isotope effect suggests that the initial dissociation reaction is dominated by the tunneling of a hydrogen atom through a potential barrier. The implications of this conclusion for other saturated molecules will be discussed. View full abstract»

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  • Molecular Geometries of Acetylene and Ethylene Chemisorbed On Cu, Ni, Pd, and Pt Surfaces

    Page(s): 265 - 276
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (731 KB)  

    Ultraviolet photoemission measurements of the valence orbital electronic structure of acetylene and ethylene chemisorbed on Cu(100) or Cu(111), Ni(111), Pd(111), and Pt(111) are presented. We compare the measured energy levels of these chemisorbed species to those of the free molecule and use a similar comparison of the relative changes in ground state energy levels of distorted free molecules calculated with a SCF-LCAO (Self Consistent Field—Linear Combination of Atomic Orbitals) method to determine the molecular geometries of these chemisorbed species. The limitations and accuracies of such an approach are discussed. From the determined geometries we identify two trends in the structure of these chemisorbed molecules on these surfaces: first, increasingly greater molecular distortions occur with increasing atomic number of the substrate atom, and secondly, greater molecular distortions occur for ethylene than for acetylene on the same metal. These trends are consistent with a π-d bonding interaction and can be accounted for by the electronic structure of the substrate and of the molecule, respectively. With the exception of ethylene on Pd or Pt, we determine molecular geometries characteristic of small rehybridization. The molecular geometry of ethylene on Pd or Pt is generally characteristic of rehybridization to an sp3 configuration. View full abstract»

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  • Sputter Profiling Through Ni/Fe Interfaces by Auger Electron Spectroscopy

    Page(s): 277 - 284
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (490 KB)  

    Sputter characteristics of nickel-iron systems in the form of layer interfaces and bulk alloy films have been studied by Auger electron spectroscopy. The sputter rates for pure nickel and iron and their alloys have been determined and are independent (within 10%) of the grain size and film composition. The various factors that contribute to the broadening of depth profiles have been examined. The initial broadening of 4.5 nm at zero overlayer thickness is mainly attributed to the effects of electron escape depth and compositional mixing due to ion bombardment. For thin films, the depth-dependent broadening induced by sputter damage has an approximately exponential dependence on the overlayer thickness. For thick films, this broadening is estimated to be about 10% of the sputter distance. The effect of ion-induced surface compositional mixing as a function of incident Ar+ ion energy has been studied by taking advantage of the different sampling depths of low and high energy Auger electrons. View full abstract»

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  • Characterization of Electron Traps in Aluminum-Implanted SiO2

    Page(s): 285 - 288
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (355 KB)  

    Johnson, Johnson, and Lampert have studied the effect of Al implantation on the trapping behavior of SiO2. The large fluence that they used (1 × 1014 Al/cm2) and the low annealing temperatures (up to 600°C) resulted in a trapping efficiency of 1 and made it impossible to characterize the traps. In the present study a lower fluence and higher annealing temperatures to reduce the trapping efficiency are used to permit characterization of the traps. The predominant trap cross sections are 1.26 × 10−16 and 1.40 × 10−17 cm2. In a companion paper by DiMaria, Young, Hunter, and Serrano the location of the trapped charge is discussed. View full abstract»

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  • Location of Trapped Charge in Aluminum-Implanted SiO2

    Page(s): 289 - 293
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    The position of the centroid of electrons trapped on sites resulting from aluminum implantation into SiO2 is measured by using the photo I–V technique for energies from 15–40 keV, oxide thicknesses from 49–140 nm, and post-implant annealing temperatures from 600–1050°C in N2 for 30 min. The centroid of the trapped electrons is found to be identical to that of the implanted aluminum from SIMS measurements, regardless of annealing temperature from 600 to 1050°C, and located closer (by less than 9 nm) to the Al-SiO2 interface than predicted from the Lindhard-Scharff-Schøtt (LSS) calculations of Gibbons, Johnson, and Mylroie. Comparison of centroids determined from photo I–V and SIMS measurements as a function of SiO2 thickness also implies that the distributions of the ions and negative trapped charge are the same. The trapping behavior of these sites is discussed in the accompanying paper by Young et al. View full abstract»

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  • Electronic Properties of (100) Surfaces of GaSb and InAs and Their Alloys with GaAs

    Page(s): 304 - 314
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    Smooth, monocrystalline (100) surfaces of the alloys In1−xGaxAs and GaSb1−y Asy were prepared by molecular beam epitaxy. Both As-stabilized c(2 × 8) and metal-stabilized c(8 × 2) surface reconstructions were observed for In1−xGaxAs over the entire alloy range. GaSb1−yAsy exhibited a c(2 × 6) or (2 × 3) structure for y ≲ 0.2, and, after a transition region, the anion-stabilized c(2 × 8) or the Ga-stabilized c(8 × 2) structures for y ≳ 0.5. Electron energy loss spectroscopy revealed the simultaneous presence of two empty, dangling-bond derived surface states in both alloy systems. For In1−xGaxAs the In-derived empty surface state lies ≈0.4–0.5 eV below that of Ga and moves from above the conduction band edge into the band gap for x ≳ 0.6. The overlap between the Ga-and In-derived empty surface states causes the quenching of the Ga(3d) surface exciton. For GaSb1−yAsy the Sb dangling bonds generate an empty, localized surface state which lies 0.2–0.3 eV above the empty, Ga-derived surface state. Both levels lie above the conduction band edge throughout the alloy range. View full abstract»

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  • Oriented Epitaxial Films of (NMP) (TCNQ)

    Page(s): 315 - 320
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (513 KB)  

    An important step in the characterization of organic conductors is the ability to correlate the solid state electrical properties of these materials with their composition and crystal structure. In many cases it has not been possible to grow single crystals of suitable size or purity for such investigations. The use of epitaxial films represents an alternative approach. In addition, such films may be potentially useful as larger area conductive surfaces. This paper describes the preparation of relatively large-area, oriented epitaxial films of the organic conductor N-methylphenazinium- 7,7,8,8-tetracyanoquinodimethanide (NMP) (TCNQ) by means of vacuum evaporation. Factors that appear to affect the degree of orientation, the film areas, and the chemical composition include the source temperature, the kind of evaporation (rapid or slow), the degree of lattice matching between the substrate and the organic material, and the substrate surface charge potential. View full abstract»

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  • Recent Papers by IBM Authors

    Page(s): 321 - 325
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (457 KB)  

    Reprints of the papers listed here may usually be obtained by writing directly to the authors. The authors' IBM divisions are identified as follows: CHQ is Corporate Headquarters; DPD, Data Processing Division; FED, Field Engineering Division; FSD, Federal Systems Division; GPD, General Products Division; GSD, General Systems Division; GTD, General Technology Division: OPD, Office Products Division; RES, Research Division; SCD, System Communications Division: and SPD, System Products Division. Journals are listed alphabetically by title; papers are listed sequentially for each journal. View full abstract»

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  • Recent IBM Patents

    Page(s): 326 - 327
    Save to Project icon | PDF file iconPDF (206 KB)  
    Freely Available from IEEE
  • Authors

    Page(s): 328 - 330
    Save to Project icon | PDF file iconPDF (284 KB)  
    Freely Available from IEEE
  • X-Ray Photoelectron Spectroscopy of SiO2-Si Interfacial Regions: Ultrathin Oxide Films

    Page(s): 294 - 303
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (589 KB)  

    The composition and width of the interfacial region formed between thin thermally-grown oxide films and single-crystal Si substrates were nondestructively characterized by means of x-ray photoelectron spectroscopy. Data obtained from variations in core-level binding energies, from variations in photoelectron line intensities, and from variations in photoelectron linewidths indicate the presence of a nonstoichiometric oxide-Si transition region. The composition and width of this region are dependent upon substrate orientation, but are invariant with change in other oxidation processing parameters. Transition regions formed on 〈100〉 oriented substrates are narrower and more completely oxidized than those formed on 〈111〉 oriented substrates. Although both Si-Si bonds and SiO-Si groups are present in this nonstoichiometric region, they do not appear to be a mixture of Si and SiO2. Instead, a continuous distribution of Si tetrahedra, Si-(O)x(Si)4−x, are formed, in which x changes from 0 to 4 as one proceeds from the substrate to the stoichiometric SiO2 film. View full abstract»

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Aims & Scope

The IBM Journal of Research and Development is a peer-reviewed technical journal, published bimonthly, which features the work of authors in the science, technology and engineering of information systems.

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Editor-in-Chief
Clifford A. Pickover
IBM T. J. Watson Research Center