bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface Reactivity of Iron Silicide
Authors: Borgmann D. , Rührnschopf K. , Wedler G.
Published: August 2003

The interaction of iron silicide with oxygen has been studied under ultrahigh vacuum conditions by means of X-ray photoelectron spectroscopy (XPS). The XP spectra show unambiguously that oxygen reacts with silicon in the FeSi 2 compound. The O1s XP spectra point to a formation of at least two suboxide species SiO x (x < 2) at room temperature. At higher temperatures increasing sharper signals indicate the transition to one suboxide species.
Adsorption of Al on GaN(110) Surface
Authors: Xie Jianjun , Ping Jiang , Zhang Kaiming , Xie Xide
Published: August 2003

The electronic properties of Al deposited on GaN(110) surface with different adsorption geometries have been studied by using the surface linear muffin tin orbital approach. The layer projected density of states for Al-covered GaN(110) surface is calculated and compared with that of the clean surface. The charge distribution before and after the adsorption of Al are investigated. It is found that the deposited Al atoms prefer to bond with the surface N atoms with some charge transferred from Al to the GaN substrate. Finally, the Al-Ga exchange mechanism is also studied and it is found that the adsorbed Al may replace the second layer Ga atom to form a more stable configuration.
Growth of Epitaxial Co Layers on Sb-Passivated GaAs(110) Substrates
Authors: Teodorescu C. M. , Chrost J. , Ascolani H. , Avila J. , Soria F. , Asensio M. C.
Published: August 2003

The role of Sb in the formation of the Co/GaAs(110) interfaces has been investigated by angular photoelectron diffraction (PD), synchrotron-radiation (SR) core-level photoemission and low-energy electron diffraction. We find that Co forms a metastable bcc phase on GaAs(110), with its principal crystallographic axes parallel to the substrate. From polar-angle-scanned PD, we determine an outward expansion of up to 14% of the lattice constant perpendicular to the surface, for epitaxial Co films grown on nontreated substrates. By Sb passivation of the GaAs(110) surface prior to the Co deposition, the epitaxial quality of the metallic overlayer is improved. The resulting Co phase is found to grow in a perfect bcc (110) orientation with a minor disruption of the substrate underneath and a reduced intralayer spacing outward expansion of less than 1%.
Growth of the Organic Molecular Semiconductor PTCDA on Se-Passivated GaAs(100): An STM Study
Authors: Kendrick C. , Kahn A.
Published: August 2003

We investigate the monolayer and multilayer growth of the organic molecular semiconductor (OMS) 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) on the Se-passivated GaAs(100) (2 × 1) surface using STM. Deposition of ~2 ML PTCDA at room temperature results in the formation of clusters, implying good chemical passivation of the substrate. However, we also find a significant number of molecules pinned at high energy defect sites, some of which induce molecular ordering. At higher PTCDA coverage we find that the film invariably orients to the substrate revealing a critical, though weak, molecule-substrate interaction. We present the first molecularly resolved STM images obtained from a thick PTCDA film (~ 60 Å) and show unit cell dimensions and orientation in excellent greement with our previous LEED study.
X-Ray Investigation of the Degradation of Zn-Doped GaInAsP/InP Heterointerface
Authors: Aleksandrov P. A. , Belova N. E. , Nazarov S. A. , Nefedov A. A. , Fanchenko S. S. , Chaplanov V. A. , Yu. Schumilov D.
Published: August 2003

We report the results of crystal truncation rod study for the following heterostructure: GaInAsP layer grown on Zn-doped InP substrate. Two series of experiments have been performed within 4.5 years. The profiles of coherent (200) polarizability and lattice mismatch have been derived by fitting experimental diffraction intensity data. The comparison of these profiles for two series has shown essential enlargement of the distorted interface region with time. The obtained degradation length value 0.15 μm is consistent with the estimations for the degradation spatial scale due to Zn-induced interdiffusion of In ions through the interface.
Photoemission Study of Quantum Well States in Thin ErAs Films on GaAs(100)
Authors: Wigren C. , Ilver L. , Kanski J. , Nilsson P. O. , Karlsson U. O.
Published: August 2003

Quantum well states in very thin epitaxial ErAs layers on GaAs(100) have been found in angle-resolved photoelectron spectra. From the dispersive properties of the quantum well states effective masses are obtained representing electron motion parallel to the surface layers and orthogonal to the layers.
Structure of TiO2 Rutile (110) (1 × 1) from Ion Scattering Measurements
Authors: Hird B. , Armstrong R. A. , Seel J. A.
Published: August 2003

9.22 keV oxygen ion scattering has been used to examine the (110) surface structure of TiO 2 rutile. Peaks in the spectrum of the emitted ions at 45° and at 77° are found at the energies expected for O +– Ti and O +– O collisions by surface atoms. Surface preoparation to optimize the 1 × 1 structure involved annealing a previously sputtered surface to 600°C, first in 10-6 Torr of O 2, and then in UHV. Azimuthal and elevation angular variations of the yields for low incidence angles show shadowing effects. Preliminary analysis seems to be consistent with the (1 × 1) model of a complete surface layer, with rows of oxygen atoms above on the titanium bridge sites. The data suggests that our sample preparation produces incomplete rows of above-surface oxygen atoms, or frequent steps.
Al2O3 α Surface Structure Characterization by RHEED
Authors: Gillet M. , Bruna J. C.
Published: August 2003

The morphology of α Al 2 O 3 surfaces annealed in vacuum has been investigated by reflection high energy electron diffraction (RHEED). We have studied two kinds of faces: (0001) and [Formula: see text]. The two faces behave differently. At high temperature the (0001) surface is unstable with only small facets and give evidence for variations of stoichiometry and structure with formation of an Al layer. The [Formula: see text] surfaces give large facets and the diffraction patterns are consistent with (2 × 1) surface structure.
Ab initio Total Energy Studies of the α-Cr2O3 (0001) and $(01\bar{1}2)$ Surfaces
Authors: Rehbein C. , Michel F. , Harrison N. M. , Wander A.
Published: August 2003

The surface structure of the basal plane and of the thermodynamically most stable facet of the α phase of Cr 2 O 3 has been studied using periodic ab initio Hartree–Fock theory. The Cr-terminated (0001) surface, which is nonpolar but charged, is found to be stable. However, a large scale relaxation of the surface layer away from the ideal bulk-terminated structure has been found. The outermost layer of Cr 3+ ions moves inward toward the second layer of O 2- ions by nearly 50% of their original interlayer spacing. The [Formula: see text] surface, which is oxygen-terminated, is also nonpolar, and stable. Again an appreciable relaxation, with the top layer moving outward compared with the ideal bulk structure, is found. The driving force behind both effects is presumed to be mainly electrostatic.
In Situ Grazing Incidence X-ray Scattering Study of the Epitaxial Growth of Ag on MgO(001)
Authors: Robach O. , Renaud G. , Barbier A. , Guénard P.
Published: August 2003

The growth of Ag on MgO(001) was investigated from sub monolayer up to 600 Å coverage. A new method for the preparation of very flat, clean and stoichiometric MgO(001) surfaces is described. The growth is found to be intrinsic, with negligible influence of surface defects. Twins appear at the very first stages of deposition while stacking faults form during the coalescence. A detailed mechanism is proposed for the elastic and plastic misfit relaxation processes. The introduction of a new dislocation within an island is, whatever its size, preceded by a strong deformation of its edges. Plastic relaxation is shown to be a continuous process that starts well before coalescence and the appearance of an interfacial dislocation network.
Oxidation Behavior of a Fe/MnO Ultrathin Film Studied by XPS
Authors: Di Castro V. , Ciampi S. , Sestili L.
Published: August 2003

The oxidation of a 9-Å-thick iron layer on MnO at room temperature has been investigated by X-ray photoelectron spectroscopy. By exposure to O 2, iron is oxidized first to Fe(II) and then to Fe(III). During the oxide formation a fast oxygen adsorption and initial oxidation to Fe(II) is followed by a slower oxygen incorporation and Fe(III) formation. After exposure to 1500 L O 2 Fe 3 O 4 seems to be formed at the surface, while the iron layer is not completely oxidized.
MoS2 Microtubes: An Electron Microscopy Study
Authors: Remškar M. , Škraba Z. , Cléton F. , Sanjinés R. , Lévy F.
Published: August 2003

Recently it was found that instability of thin weakly bonded MoS 2 sheets against folding can lead to a growth of hollowed microtubes with several mm lengths, 1–20 μm diameter and less than 0.1 μm wall thickness.1 Bent sheets can directly roll up into the tube or they can produce in their microfolds a turbulent gas flow of transported molecules which promotes a tubelike growth mode. These uncommon stable features of inorganic crystals reveal a great similarity to much smaller carbon fullerences and especially to inorganic ( MoS 2, WS 2) nested fullereness-nanotubes.2 Scanning electron microscopic studies of cylindrical microtubes and twisted microribbons are combined with high resolution electron microscopic observations of stacking faults.
O-Ru(0001) Surface Bond and Band Formation
Authors: Sun Chang Q.
Published: August 2003

Incorporating the bond-to-band and the potential barrier model [J. Phys. Chem. Solids58, 903 (1997); J. Phys.: Cond. Matt.27, 5823 (1997)] into the existing database reveals that the O-Ru(0001) triphase results from the formation of O -1, hybridized O -2 and the addition of a virtual bond, respectively. Oxygen is located at the center of a tetrahedron, forming a Ru 4 O cluster. Initially (<1/4 ML), the Ru 4 O ( O -1+ Ru ++ 3Ru dipole) forms, retaining C 3v symmetry. Then (1/2 ML), the Ru 4 O develops into a Ru 2 O ( O -2+ 2Ru + + 2Ru dipoles) by forming another bond with a surface Ru atom; as a result, a dipole-ion pairing row forms. Finally (1.0 ML), a virtual bond [2Ru(dipoles)+] forms by redistributing the dipole electrons; this process not only reduces the dipole moment but also narrows the antibond subband. The first layer spacing depends upon bond geometry and the second layer spacing contracts due to charge redistribution.
Nonlocal Screening of the Photon Fields in Surface Photoemission from Simple Metals
Authors: Barberán Nuria , Bausells Joan , Ardiles Erika
Published: August 2003

A hydrodynamical model calculation that includes retardation, nonlocal effects within the constitutive equation as well as damping through a constant parameter, has been used to interpret the surface photoemission results for simple metals. Special attention has been paid to the effects that multipole surface modes have in the spectrum. The photon field is screened by the electron gas modeling the vacuum–metal interface with a low density overlayer. A constant initial state for the electron at the Fermi level is assumed. We conclude that the main structure of the photoemission spectrum, a peak at ω0<ωp, is not produced by the generation of multipole modes, and instead these modes produce a secondary structure between ω0 and ωp whose number and position depend on the electronic profile.
The Feasibility of Determining Vacancy Migration Energy by Atomic Force Microscopy Data
Authors: Blagov E. V. , Klimchitskaya G. L. , Mostepanenko V. M.
Published: August 2003

A computation is performed of the constant force lines and profiles of the lateral force component when scanning the atomic force microscope tip in contact mode above a close-packed surface, containing a vacancy type defect with allowance for the displacements of the surface atoms. Three different scanning regimes are investigated which may exist for the different values of the scanning force: without modification of the surface, with a single jump of the defect in opposition to the scanning direction, and with a "dragging" of a vacancy behind a tip. It is shown that by the lines of constant force one may conclude what regime is actually realized, and that by the profiles of the lateral force component one may estimate quantitatively the value of the vacancy migration energy.
REM Studies of Adsorption-Induced Phase Transitions and Faceting in the Si(111)-Au System
Authors: Aoki Koyu , Minoda Hiroki , Tanishiro Yasumasa , Yagi Katsumichi
Published: August 2003

Initial stages of Au adsorption processes on Si(111)-(7 × 7) surfaces at ~780°C, a temperature range where the surface structure undergoes successive phase transitions [(7 × 7)–("1 × 1")–(5×2)–("1 × 1")], were observed in situ by reflection electron microscopy. All of the phase transitions are heterogeneous on the surface and start at surface atomic steps. During Au adsorption on Si(111)-(7 × 7), and subsequently on Si(111)-("1 × 1") surface with wide terraces, steps advance toward the step-down direction. At a Au coverage of ~0.3 ML, the 5 × 2 structure nucleates at step edges, and the nuclei expand both to the lower side terraces and to the higher side terraces. At this stage, an effect of current for heating the specimen was noted. From measurements of such movements of the steps and the domain boundaries, the density of Si atoms in the "1 × 1" phase is estimated to be 1.3–1.7 ML at a Au coverage of ~0.3 ML. Au adsorption on Si(111) surfaces with narrow terraces causes bunching of the steps. After nucleation of the 5 × 2 structure, the bunched [Formula: see text] steps become straight along the [Formula: see text] direction, and are transformed into the (335) facet planes at a Au coverage of 0.50 ML. It was found that the (335) facet planes are stabilized by adsorbed Au atoms. Destruction of the (335) facet is noted at a Au coverage of 0.73 ML.
Formation and Chemical Selectivity of Partially Ga-Terminated Si(111) Surfaces
Authors: Ichikawa Masakazu , Fujita Ken , Kusumi Yukihiro
Published: August 2003

Nanoscale stripes of the Si(111)-(7 × 7) structure with atomic accuracy can be formed on the [Formula: see text]-terminated Si(111) surface, by selective thermal desorption of Ga atoms from step edges, when the surface is tilted toward the [Formula: see text] direction. The nanoscale stripes of the 7 × 7 structure can also be formed in expected areas by selective thermal desorption of Ga atoms induced by STM stimulation. A Ga-terminated area is found to be chemically less active for adsorption of oxygen, disilane and antimony molecules which selectively react in the 7 × 7 area. By using the chemical selectivity and the nanoscale 7 × 7 stripe for formation method, a stripe pattern with the antimony-adsorbed 7 × 7 areas and [Formula: see text] areas is produced as a demonstration of nanostructure formation.
Epitaxial Insulating Films
Authors: Henzler M. , Zielasek V. , Erdös D. , Wollschläger J.
Published: August 2003

The study of insulating films is possible also with electrons, as soon as the charging up of the surface and the electron damage are avoided. Thin epitaxial films do not charge up, as long as the thickness is less than about 5 nm. Therefore the epitaxy of several insulating films could be studied using the spot profile analysis of low energy electron diffraction (SPA-LEED). The results show special features of growth, which are described as elastic bending of the growing films. For this phenomenon defects of the substrate or special growth conditions may be decisive. The features may be enhanced due to the strong binding within the ionic film compared to the weaker bonding to the substrate. Point defects are generated in NaCl films by electron bombardment with an energy over about 30 V. Since these defects have an electronic transition (color centers), they are easily quantitatively measured with electron energy loss spectroscopy. Therefore their effect on the background intensity of the elastic scattering has been studied quantitatively for the first time.
Theoretical Analysis of RHEED Intensities for Growing Surfaces
Authors: Mitura Z. , Dudarev S. L. , Whelan M. J.
Published: August 2003

Calculations of specular beam rocking curves are carried out for growing surfaces. The one-dimensional model of the scattering potential is assumed. A contribution from a partially covered layer to the whole crystal scattering potential is taken to be proportional to the coverage of the layer. Surprisingly, for higher glancing angles, results of one-dimensional dynamical calculations show a similarity to those predicted by the kinematical column approximation. An analysis of why this happens has been carried out.
Interface Structure and Preferred Orientation of Ag/Si(111) Revealed by X-Ray Diffraction
Authors: Akimoto Koichi , Lijadi Melania , Ito Shingo , Ichimiya Ayahiko
Published: August 2003

We studied buried interface structures of [Formula: see text] and Ag/Si(111)-(7 × 7) samples using grazing incidence X-ray diffraction with synchrotron radiation. We also measured the crystal orientation of the Ag overlayers of the samples. Of the numerous [Formula: see text] structures, only boron-induced [Formula: see text] structure has been detected in buried interfaces. We studied the buried interface superstructure of Ag(26 nm thick)/[Formula: see text], and detected a [Formula: see text] fractional order reflection peak. This means that the [Formula: see text] structure remained at the interface. Our results for the crystal orientation of the Ag overlayers of [Formula: see text] showed that Ag{110}, Ag{100} and Ag{111} planes were grown on the surface. By measuring several samples prepared at various substrate temperatures, (290–370 K), we found a strong correlation between the appearance of interface [Formula: see text] structure and the growth of the Ag{110} plane. In contrast, our results for the crystal orientation of the Ag overlayers of Ag(26 nm thick)/Si(111)-(7 × 7) showed that only the Ag{111} plane was grown on the surface.
Atomistic Visualization of Mechanical Interaction in Gold Crystalline Boundaries by Time-Resolved High Resolution Transmission Electron Microscopy
Authors: Kizuka Tokushi
Published: August 2003

The atomic processes in mechanical interaction were visualized by time-resolved high resolution transmission electron microscopy at a spatial resolution of 0.2 nm and a time resolution of 1/60 s.

Nanometer-sized tips of gold were approached, contacted, bonded, deformed and fractured inside a 200 kV electron microscope using a piezo-driving specimen holder. The crystallographic boundary formed after the contact. A few layers near the surfaces and bonding boundaries were responsible for the approach, contact and bonding processes. Atomic scale mechanical tests, such as the friction test, compressing, tensile and shear deformation tests, were proposed. A new type of mechanical processing at one-atomic-layer resolution was demonstrated. Atomic scale contact or noncontact type surface scanning similar to that in atomic force microscopy was also performed with the gold tips.
A Reflection High Energy Electron Diffraction–Reflectance Anisotropy Spectroscopy Study of Silicon Growth Dynamics During Gas Source Molecular Beam Epitaxy from Silanes
Authors: Joyce B. A. , Zhang J. , Taylor A. G. , Lees A. K.
Published: August 2003

Molecular beam epitaxy (MBE) provides an ideal experimental vehicle for the in situ study of thin film growth dynamics. By using a combination of reflection high energy electron diffraction (RHEED) and reflectance anisotropy (difference) spectroscopy [RA(D)S], it is possible to separate morphological (long range order) and local electronic structure effects, which we demonstrate with the growth of silicon films from disilane ( Si 2 H 6) on Si(001) (2 × 1)+(1 × 2) reconstructed surfaces.

The rate-limiting step in Si growth from both monosilane ( SiH 4) and disilane is the desorption of molecular hydrogen and we have found using RAS that, over a significant range of temperature and coverage, hydrogen desorption follows zeroth order kinetics as the result of a step-mediated process. Finally, we show how this influences the growth rate on substrates of differing degrees of vicinality.
Strain Relief via Island Ramification in Submonolayer Hereroepitaxy
Authors: Müller Bert , Nedelmann Lorenz P. , Fischer Bjørn , Brune Harald , Barth Johannes V. , Kern Klaus , Erdös Daniel , Wollschläger Joachim
Published: August 2003

The mechanisms of strain relief in sub monolayer heteroepitaxy of Cu/Ni(100) are studied using variable temperature scanning tunneling microscopy and high resolution low energy electron diffraction. It is demonstrated that pseudomorphic copper islands, as they grow in size, undergo a spontaneous shape transition. Below a critical island size of about 500 atoms the islands have a compact shape, while above this size they become ramified. The shape transition of the coherently strained islands, predicted theoretically by Tersoff and Tromp, is driven by the size-dependent outward relaxation of the step edge atoms due to the positive lattice mismatch. The ramified island shape, which reflects the energy minimum of binding and strain energy, is characterized by only one parameter: the arm width of the monolayer-high copper islands w =22±1) atoms.
Prefactor and Step Edge Barrier Determination for Initerlayer Diffusion in Homoepitaxial Systems: Ag/Ag(111)
Authors: Roos K. R. , Tringides M. C.
Published: August 2003

Interlayer diffusion is controlled by the probability that an atom will hop from a higher to a lower level. This probability depends on the additional step edge barrier ΔEs which an atom experiences at a step because of the lower coordination as it moves over the barrier, and possibly on the different prefactors νs, νt for an atom at the step versus one at a terrace position. It is important to develop experimental methods that separate out the two contributions. We have reanalyzed the STM-based method,1 which measures the fraction of islands with second layer occupation at different deposition temperatures, to show how the two contributions can be identified. In addition, we have developed a diffraction-based method that measures the step density of nucleated islands as they compete for atom capture with the steps at the perimeter of the terraces. RHEED experiments on Ag/Ag(111) result in ΔEs=0.15±0.03 eV and νs/νt=2.3×102±0.2, in good agreement with the results, ΔEs=0.13±0.03 eV and νs/νt=103±0.3, deduced from the data of Ref. 1.
Wandering and Bunching Instabilities of Steps Described By Nonlinear Evolution Equations
Authors: Uwaha Makio , Sato Masahide
Published: August 2003

We study wandering and bunching instabilities of steps in a surface diffusion field with a direct electric field applied perpendicular to the steps. The drift of adatoms induced by the electric field modifies the surface diffusion length in the upper terrace and that in the lower terrace. This asymmetry causes wandering instability of an isolated step when the drift is opposite to the step motion. Near the critical point the time evolution of a step obeys the Kuramoto–Sivashinsky equation, which gives rise to spatiotemporal chaos. The asymmetry also causes bunching instability of an array of repulsive straight steps. The instability near the critical point is an amplification of density large wavelength. The step density after the instability obeys the Benney equation, which shows a stable array of solitons corresponding to the formation of stable bunches.
Epitaxial Free Energy and Stability under Epitaxial Strain
Authors: Marcus P. M.
Published: August 2003

First-principles ground-state total-energy calculations show that tetragonal crystals generally have two structures at which the energy is a minimum, which are appropriately called tetragonal phases in equilibrium. The calculations also show that a small isotropic two-dimensional (epitaxial) strain in the basal plane of a tetragonal phase produces a first-order phase transition to another tetragonal phase, By defining and calculating a special free energy for the states produced by epitaxial strain, the stability limits of each phase and the occurrence of a first-order phase transition between them are clearly demonstrated. Epitaxially strained states and the epitaxial free energy are calculated for vanadium. The epitaxial free energy as a function of the epitaxial stress for these strained states is shown to be similar to free-energy curves calculated for other first-order phase transitions which have analytic descriptions.
Atomic Paths in Scanning of the AFM Tip above the Close-Packed Surface in Repulsive Mode
Authors: Blagov E. V. , Klimchitskaya G. L. , Mostepanenko V. M.
Published: August 2003

The paths are calculated for the surface and tip apex atoms when scanning the AFM tip above the close-packed lattice in contact mode. The interaction of the sample and the tip atoms is considered in elastic approximation. The dependence of the atomic paths on the type of the tip and its orientation is investigated. It is shown that the vertical characteristic sizes of the atomic paths are several times larger than the vertical resolution of the atomic force microscope.
The Structure of Fe on Al(001)
Authors: Hochstrasser M. , Atrei A. , Bolliger B. , Eismann R. , Erbudak M. , Pescia D.
Published: August 2003

The structure of Fe deposited on Al(001) at room temperature has been investigated during growth. It is found that even less than 1 monolayer (ML) of Fe destroys the atomic order at the surface due to the interdiffusion of Fe and Al. After deposition of 3±0.5 ML, short-range order at the surface is restored due to islands which locally have the body-centered cubic structure and are aligned in registry with the Al matrix. These islands coalesce during further Fe deposition, and produce poor long-range order at an Fe dose of 5±0.5 ML. At this coverage, magnetic ordering is found perpendicular to the surface. The in-plane component of the surface magnetization is detected above 8±0.5 ML.
Dynamics of Zero-Mass Gibbs Interfaces
Authors: Wang Liqiu
Published: August 2003

Conservation laws and the second law of thermodynamics are used to study the dynamics of zero-mass Gibbs interfaces, which can be used to approximate the behavior of the real interfacial region. The work is characterized by the introduction of quantities representing the net action of two bulk phases on the interface and by the use of the second law of thermodynamics to provide the required constitutive equations.
On the Nature of the ${\rm O}\mbox{-}{\rm C\lc{o}}(10\bar{1}0)$ Triphase Ordering
Authors: Sun Chang Q.
Published: August 2003

It is shown that the model for oxygen chemisorption improves our understanding of the [Formula: see text] surface reaction. The disordered p (2×1)-O precursor is identified as molecule adsorption in which the paired O -1 rests on top of the surface along the close-packed direction. Meanwhile, O -1 polarizes its rest neighbors, leading to the protruding domain boundaries. At higher coverage, c (2×4)-4O and then p (2×1)-2O develop due to O -2 hybridization. O -2 is located at a threefold hollow site and forms a tetrahedron with two Co atoms at the surface and one atom in the second layer. The lack of one atom of bonding is compensated for by an electron cloud of dipoles; namely, a virtual bond forms. The virtual bonding lowers the STM protrusions and narrows the antibonding band.
Direct Methods for Surfaces
Authors: Marks L. D. , Bengu E. , Collazo-Davila C. , Grozea D. , Landree E. , Leslie C. , Sinkler W.
Published: August 2003

This paper reviews recent progress in the application of Direct Methods to solve surface structures using surface X-ray or transmission electron diffraction data. The basic ideas of (crystallographic) Direct Methods are presented, as well as the additional problems posed by trying to apply them to surfaces and how they connect to the mathematical theory of projections. Surface crystallography notation is presented, which differs from the widely used LEED notation in that it emphasizes the surface symmetry. This is followed by a description of methods for structure completion and refinement, followed by applications to some experimental systems, both those where the structure was previously known (calibration tests) and a few where it was not, concluding with problems and limitations.
Low Energy Electron Diffraction Analysis of Ultrathin Ag Films on W(110)
Authors: Poon H. C. , Tong S. Y. , Chung W. F. , Altman M. S.
Published: August 2003

We have measured low energy electron diffraction data for clean W(110), ultrathin and thick Ag films on W(110). The data are analyzed by full dynamical multiple scattering calculations to determine the structure of the Ag-film/W(110) system. The multiple scattering calculation takes into account the incommensurate scattering between the non-pseudomorphic Ag films and the W(110) substrate. We have examined the effect of dynamical inputs used in the calculation. We find that for normally incident electrons, the surface barrier at the vacuum-film interface and the inelastic damping modify mainly relative intensities of the diffraction peaks while the energy-dependent inner potential at low energies influences peak positions. After the dynamical inputs are independently determined, we use the data below 25 eV where the electron's mean free path is long, to determine the layer spacing at the Ag film – W substrate interface. A major trend we find is that the layer spacing at the interface decreases as the Ag film's thickness increases.
Quantitative Analysis of the Evolution of Surface Growth Morphology in LEEM
Authors: Hannon J. B. , Kellogg G. L. , Bartelt M. C. , Bartelt N. C.
Published: August 2003

We describe Monte Carlo simulations and diffusion equation analysis which are useful in deriving kinetic parameters from low energy electron microscopy experiments. An analysis of the etching of the Si(001) surface with molecular oxygen is made, illustrating the power of these techniques.
LEEM Studies of Phase Separations and Surface Depletion of Co and Ni on Si(111)
Authors: Phaneuf R. J. , Bennett P. A.
Published: August 2003

Low energy electron microscopy images of Si(111) surfaces during sub monolayer deposition of Co or Ni at temperatures near 700°C reveal a phase separation into a disordered "ring cluster" phase and the ordered 7 × 7 reconstruction. For Co/Si(111) we find that temperature-driven phase separations at a fixed dose are reversible and occur at a fixed surface coverage. The shape of the phase boundary reveals a repulsive interaction between Co-containing ring clusters in the disordered phase. For Ni/Si(111), dissolution into the bulk prevents reversible separations between surface phases. At coverages close to 1/7 ML an ordered close-packed [Formula: see text] ring cluster phase forms for Co/Si(111), but not for Ni/Si(111). The [Formula: see text] phase disappears irreversibly on heating, due to the nucleation and growth of stable silicide islands.
A Free Electron Laser–Photoemission Electron Microscope System (FEL–PEEM)
Authors: Ade H. , Yang W. , English S. L. , Hartman J. , Davis R. F. , Nemanich R. J. , Litvinenko V. N. , Pinayev I. V. , Wu Y. , Madey J. M. J.
Published: August 2003

We report first results from our effort to couple a high resolution photoemission electron microscope (PEEM) to the OK-4 ultraviolet free electron laser at Duke University (OK-4/Duke UV FEL). The OK-4/Duke UV FEL is a high intensity source of tunable monochromatic photons in the 3–10 eV energy range. This tunability is unique and allows us to operate near the photoemission threshold of any samples and thus maximize sample contrast while keeping chromatic berrations in the PEEM minimal. We have recorded first images from a variety of samples using spontaneous radiation from the OK-4/ Duke UV FEL in the photon energy range of 4.0–6.5 eV. Due to different photothreshold emission from different sample areas, emission from these areas could be turned on (or off) selectively. We have also observed relative intensity reversal with changes in photon energy which are interpreted as density-of-state contrast. Usable image quality has been achieved, even though the output power of the FEL in spontaneous emission mode was several orders of magnitude lower than the anticipated full laser power. The PEEM has achieved a spatial resolution of 12 nm.
Growth Curves, Measurement and Three-Dimensional Reconstruction in the Histopathology of Temporal Bones
Authors: Chrobok Viktor , Meloun Milan , Šimáková Eva , Antoš Karel , Ježek Bruno
Published: August 2003

The paper consists of three parts, in which the opportunities for measurement in histopathology of the temporal bone are shown. Measurement of size and distance (1D measurement) is used for determining the growth curves during the fetal period. Measurement of area (2D measurement) shows a difference in volume of mesenchymal tissue in the middle ear cavity between the groups with and without kidney pathology during the prenatal period. A computer 3D reconstruction of malformations of the middle and inner ears can be applied in understanding the pathology of the hearing organ. The first part concerns the application of measurements of size and distance to a set of 121 temporal bones from 71 fetuses. For evaluation, the following parameters were collected from the histological samples: the height and width of the stapes, the height of the vestibule, the length of the macula sacculi, the length of the macula utriculi, and the height and width of the cochlea. Regression analysis was applied to the data set to determine the relationship of the growth curves of particular structures. The data for growth curves from 36 aborted, presumably normal fetuses, are used. So the growth curves show the normal development of these structures. The Mitscherlich model was found to be the most satisfying for the growth curve in the fetal period. The amount of mesenchymal tissue in the middle ear (2D measurement) was determined after computer digitalization (Lucia) of the samples’ area of the middle ear cavity. Statistical tests confirmed a larger amount of this tissue in the group of samples obtained from fetuses with pathological kidney findings (agenesis of kidneys, Potter’s sequence), in comparison with a group of spontaneously aborted fetuses without kidney damage.The 3D computer reconstruction of the temporal bone, the third topic, was created using our own Medicus software written for the project. In a sample of bone without pathology, reconstruction enabled assessment of basic anatomical structures and two temporal bones show malformation of the stapes (VATER syndrome) and the cochlea (trisomy 21).
Kommt es bei Bellscher Fazialisparese zu einer Beeinflussung der Funktion der Tuba Eustachii?
Authors: Gudziol V. , Mewes T. , Stetter S. , Mann W.J.
Published: August 2003

Fragestellung: Es wird angenommen, dass sich die Funktion der Tuba auditiva infolge einer Schädigung der parasympathischen Schleimhautversorgung ändert. Methodik: Deshalb wurde an 20 Patienten mit peripherer idiopathischer Fazialisparese mit Hilfe einer Druckkammer und dem Dual-Impedanz-Verfahren nach Münker der Tubenöffnungsdruck, Tubenverschlussdruck und der positive sowie negative Residualdruck bestimmt. Ergebnisse: Es zeigte sich, dass sich die Werte der gesunden Seite nicht signifikant von der kranken Seite unterscheiden. Schlussfolgerung: Es wird angenommen, dass Sekretfilmänderungen im dem Ostium pharyngeum nahen Tubenabschnitt keinen wesentlichen Einfluss auf das Tubenöffnungs- bzw. Verschlussverhalten haben.
Implications of Ultrasonographic Measurements of Internal Jugular Veins in the Placement of Central Venous Catheters in ENT Cancer Patients
Authors: Prim M.P. , De Diego J.I. , Moreno P. , Garcia J. , Gavilán J.
Published: August 2003

Objective: To assess the possible differences between right and left internal jugular veins in head and neck cancer patients, in order to choose one of them for cannulation. Patients and Methods: A prospective study was designed including 102 internal jugular veins of 51 head and neck cancer patients evaluated by means of duplex Doppler ultrasonography. Patency, presence of thrombosis, characteristics of the vein wall, compressibility, area of vein both at rest and during Valsalva maneuver, expiratory flow speed, Valsalva flow speed, and jugular flow on each side were registered in all veins. Results: Thrombosis with impaired compressibility was found in 0.9% of the veins. All parameters were higher on the right side, but only expiratory flow speed (p = 0.049), area during Valsalva (p = 0.047), and jugular flow (p = 0.047) showed a significant difference. Conclusion: In head and neck cancer patients, the area parameters of the right internal jugular vein suggest more favorable anatomical conditions for the placement of central venous catheters than the left one.
Bilateral Facial Nerve Paralysis Secondary to Acute Myelogenous Leukemia
Authors: Gungor Atila , Cincik Hakan , Poyrazoglu Ethem , Sali Murat , Candan Hasan
Published: August 2003

Bilateral facial paralysis is a rare condition. We present a case of acute myeloblastic leukemia manifesting itself in bilateral hearing loss and bilateral facial paralysis. We suspected systemic disease because of the abnormal blood cell count of the case. The diagnosis of leukemia was made with histological examination of a bone marrow aspirate. Computed tomography and gadolinium-enhanced magnetic resonance imaging scans revealed bilateral infiltration of the mastoid bones, middle ears and facial nerves. One should always remember that bilateral facial paralysis may be the first sign of a life-threatening illness. If infiltration is observed in the air-filled cells of the mastoid bone, before emergency surgery is planned, the possibility of leukemic infiltration should be considered.
Primary Nasal Tuberculosis
Authors: Balatsouras Dimitrios G. , Korres Stavros , Ferekidis Eleftherios
Published: August 2003

Despite the worldwide increase in tuberculosis lately, primary nasal tuberculosis remains a rare manifestation of the disease, presenting sometimes a confusing diagnostic problem. In this paper, we report the case of a middle-aged female patient, who presented with a lesion of the left nasal cavity and symptoms indicative of malignancy. From the results of the biopsy, a tuberculous nasal granuloma was suspected, and tissue cultures confirmed the diagnosis. Further investigation did not prove any other primary tuberculous lesion, and treatment with standard antituberculosis drugs resulted in complete remission of the disease.
Paraffinoma – A Complication Caused by Nasal Packing following Sinus Surgery
Authors: Foghsgaard S. , Barfoed C. , Hamilton Therkildsen M.
Published: August 2003

A 55-year-old woman developed a swelling in the upper and lower lids of the right eye 7 weeks after endonasal sinus surgery with nasal packing. Histological examination showed a lipogranulomatous reaction of foreign body type caused by paraffin. We recommend avoidance of ointments containing paraffin in nasal packing after sinus surgery.
Congenital Submandibular Salivary Gland Fistula
Authors: Durgun Vedat , Kapan Metin , Kapan Selin , Onur Ender
Published: August 2003

In this study, we present a patient with a congenital cervical submandibular gland fistula who was admitted to the hospital for nodular thyroid hyperplasia. After bilateral subtotal thyroidectomy, the fistula tract and the submandibular salivary gland on the right side of the neck and the obliterated sinus on the left side of the neck were excised. The pathological examination led to the diagnosis of adenomatous hyperplasia of the thyroid gland with focal lymphocytic thyroiditis and mixed-type main salivary gland (submandibular gland) with cystic dilatation in one duct. Congenital salivary gland fistulae are rare and may be associated with abnormalities of the branchial apparatus or arise from aberrant or accessory salivary tissue. Excision of the fistula and the remaining submandibular gland is considered the treatment of choice in congenital fistulae, but traumatic fistulae generally resolve with conservative treatment within 3 weeks.
Mutism after Posterior Fossa Tumour Resection in Children: Incomplete Recovery on Long-Term Follow-Up
Authors: Steinbok Paul , Cochrane D. Douglas , Perrin Richard , Price Angela
Published: August 2003

Introduction: Mutism after posterior fossa tumour resection is generally said to be transient. Our experience suggested that speech did not usually normalise, and that mutism was associated with neurologic deficits that did not recover fully. Methods: Children with mutism after posterior fossa tumour resection, and alive more than 2 years post-operatively, were reviewed retrospectively. Charts were reviewed and parents contacted to ascertain details about mutism, associated neurologic deficits, and the most recent speech and neurologic status. Results: There were 7 children, with follow-up ranging from 2.5 to 13.1 years (mean 6.8 years). Tumours were midline, with 4 astrocytomas and 3 medulloblastomas. Mutism was noted immediately after post-operative extubation in all patients. Speech reappeared 1–15 weeks post-operatively, except for 1 patient, who remained mute at 2.5 years. Speech returned to normal in only 1 patient. Mutism was always accompanied by new or worsened cerebellar ataxia, which resolved incompletely in the long term. Sixth nerve palsies occurred in 3 and recovered incompletely. Seventh nerve paresis occurred in 2 and recovered completely. Conclusion: Mutism after posterior fossa tumour resection is associated with other neurologic deficits, particularly ataxia. Whereas speech usually returns, contrary to general opinion, speech rarely normalises. Other associated deficits rarely resolve completely. These findings have significant implications for counselling of family and patients.
Direct Repair of the Pars interarticularis for Spondylolysis and Spondylolisthesis
Authors: Lundin David A. , Wiseman Diana , Ellenbogen Richard G. , Shaffrey Christopher I.
Published: August 2003

Spondylolysis and spondylolisthesis can be associated with significant low back pain, especially in physically active adolescents. Non-operative management is usually successful in improving symptoms, but surgical intervention is occasionally required for those that fail reduction of activity and bracing. In a subpopulation of these patients, direct repair of the pars interarticularis defect can be an effective modality of treatment. The advantage of direct pars repair over intertransverse fusion with or without segmental instrumentation is the preservation of the anatomic integrity and motion of the affected segment. We describe our experience in 5 patients (aged 15–18 years) managed by direct pars interarticularis repair after failing multimodality non-operative treatment. The length of stay averaged 3.2 days (range 3–4 days). All 5 patients were able to return to full activity with either no (60%) or minor (40%) symptoms. No immediate or delayed complications were noted. Patients were followed a minimum of 30 months (range 30–78 months). All 5 patients demonstrated evidence of bony fusion by radiographic criteria. This demonstrates that direct pars repair is a safe and effective modality to treat select groups of patients with spondylolysis and low-grade spondylolisthesis.
Parietal Foramina Are Not Synonymous with Giant Parietal Foramina
Authors: Tubbs R. Shane , Smyth Matthew D. , Oakes W. Jerry
Published: August 2003

Introduction: Enlarged parietal foramina have historically been described as merely the normal parietal foramina (which usually transmit emissary veins connecting the occipital veins to the superior sagittal sinus) in which the diameter exceeds approximately 5.0 mm. Methods: We have observed well over 500 cadaveric wet and dry specimens for simultaneous bilateral enlarged and normal parietal foramina. Results: We have found two bony adult calvaria, which demonstrate both enlarged parietal ‘foramina’ and the normally appreciated parietal foramina. Conclusions: Although a rare occurrence, enlarged parietal foramina occur in conjunction with the normally sized and positioned parietal foramina. This dismisses earlier hypotheses that enlarged parietal foramina are merely parietal foramina that are increased in their diameter.
Spasticity in a Child with Myelomeningocele Treated with Continuous Intrathecal Baclofen
Authors: Bergenheim A. Tommy , Wendelius Margareta , Shahidi Saeed , Larsson Eva
Published: August 2003

Patients with myelomeningocele may often suffer from severe spasticity. Surgical treatment of the underlying pathology such as hydromyelia and tethered cord may be successful, but failures are not uncommon. Those cases may offer a surgical challenge since further therapeutic options are limited. We present the case of a 7-year-old boy with myelomeningocele and related conditions suffering from severe spasticity and pain in his lower limbs. Surgical efforts with untethering and posterior fossa decompression failed to improve the symptoms. A test with 25 µg intrathecally delivered baclofen showed a total relief of spasticity and pain so that a pump for continuous baclofen delivery was implanted. During 32 months of follow-up, his spasticity has been under excellent control on 55–157 µg baclofen per day. Continuous delivery of intrathecal baclofen may be a surgical option to consider in patients with myelomeningocele and severe spasticity.
Presacral Neurenteric Cyst in an Infant
Authors: Satyarthee G.D. , Mahapatra A.K.
Published: August 2003

Intraspinal neurenteric cysts are rare congenital cystic lesions, formed due to displacement of elements forming the alimentary canal. We report an 11-month-old infant presenting with a soft, fluctuant and transilluminant swelling posterior to the anus since birth; the size of the swelling varied with alterations in intraspinal pressure subsequent to crying, coughing, or sneezing. MRI showed a multiloculated lesion anterior to the sacrum and coccyx. Near total excision was carried out without any worsening in the neurological status.
HLA Typing and Parkinson’s Disease
Authors: Lampe J.B. , Gossrau G. , Herting B. , Kempe A. , Sommer U. , Füssel M. , Weber M. , Koch R. , Reichmann H.
Published: August 2003

Idiopathic Parkinson’s disease (IPD) is a neurodegenerative disorder of unknown aetiology. Several antigens have been associated with IPD using serological methods. We systematically analysed HLA class I and II alleles in 45 German Caucasian IPD patients using sequence-specific oligonucleotides and sequence-specific primer technology. Applying Bonferroni adjusted p values, we demonstrate a statistically significant increase of the DQB1*06 allele (p = 0.002) in IPD which may indicate an association between IPD and the immune system. Alternatively, HLA alleles might be in linkage disequilibrium with genes located next to the HLA locus.
Alcohol Misuse: A Risk Factor for Putaminal Damage by Ischemic Brain Infarct?
Authors: Leppävuori A. , Vataja R. , Pohjasvaara T. , Kaste M. , Mäntylä R. , Erkinjuntti T.
Published: August 2003

The relationship between alcohol consumption and the risk of ischemic stroke has been widely studied, whereas the effect of alcohol use on stroke features is not well established. This study compared the clinical and stroke features of ischemic stroke in two groups of patients with ischemic stroke: those with a history of alcohol misuse and those with a history of more social drinking. DSM-IV criteria were used to diagnose alcohol use disorder (dependency or abuse) in 275 of 486 consecutive patients aged 55–85 years, 3–4 months after ischemic stroke. Magnetic resonance imaging of the head was performed 3 months after stroke. Alcohol use disorder was diagnosed in 37/275 (13.5%) of ischemic stroke patients. These patients had more frequently (70.3 vs. 34.5%; OR 4.5; 95% CI 2.2–9.1; p < 0.000) an infarct affecting the putamen compared with patients who indulged in more social drinking. Another predisposed area was the superior anterior cerebral artery area. The stroke due to large- artery atherosclerosis was more common in patients with alcohol use disorder. The misuse of alcohol seemed to be associated with cerebral infarct localization in the putamen and superior anterior cerebral artery area. Prospective studies are needed to verify our preliminary finding.