Low-Energy Electron Diffraction from Ag(111): Intensity-versus-Energy Curves and Absolute Intensity of the (00) Beam

The intensity of the (00) beam of a (111) surface of Ag has been measured with a Faraday cage as a function of the energy of the incident beam (10 < E < 280 eV), the grazing angle of incidence (46.5° < φ < 83.5°), two azimuths differing by 180°, and the temperature. The I vs E curves, when compared with data for Ag ( 111 ) of other workers who have used different methods of surface preparation, show good agreement in the structure over the whole range of incident angles, indicating that LEED is not strongly sensitive to surface condition. The I vs E curves for the two azimuths are identical, a necessary result of the reciprocity theorem. For comparison with the I vs E structure, a complete 3-beam geometric model is used. This differs from a simple Ewald construction in that it considers also the Bragg conditions between intermediate beams and the final beam. It also requires that there be no difference in the effect of intermediate forward and backward scattered beams. It is shown that the number of possible beams is much too large even at low energies to make positive identification of any structure in the I vs E curves. A comparison with a rigorous multiple-scattering theory yields agreement in the number and position of peaks, but not in heights and widths of peaks. The possibility of comparison of absolute intensities in theory and experiment is investigated and an attempt is made to remove the major differences. Intensity vs temperature measurements are made at closely spaced energies in order to extract the rigid-lattice scattering. Correction of this intensity for surface plasma losses leads finally to maximum scattered intensities of 2% at 100 eV, 10% at 60 eV, and up to 40% at energies below 20 eV.

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niques were prepared using pentane as the solvent. Similar methods were used in preparing calibration samples with the mold release, solder flux, and hydraulic oil samples. All contaminated coupons were gentl y heated in an oven at 50°C for several days to remove both semi-volatile and volatile components. This served to stabi-lize the contaminants, allowing for quantification by weighing. Once the weights became stable, the coupons were cooled and weighed to determine the amount of contaminant present on the surface. When not being weighed or examined, the coupons were kept in a desiccator. 3. RESULTS AND DISCUSSION Grazing-angle incidence reflectance spectroscopy acts to enhance the detection sensitivity for thin layers of residue predominantly through improved coupling of th e electric field intensity of the incident beam with the vibrating dipoles of the surface contaminant layer perpendicular to the metallic surface. Some additional enhancement of the infrared absorption spectrum will also occur due to a length-ening of the effective path length through the absorbing thin film layer [4-6]. If the optical properties of both thin film and substrate are known (or can be de-termined), the reflection-absorption spectrum can be calculated as a function of film thickness and angle of incidence. This capability is particularly useful for in-terpreting experimental data and designing optical instrumentation. Computer codes written at Sandia [7] performed these calculations for a variety of materials. 3.1. FTIR measurements FTIR reflectance data for the full drawing-agent sample set were obtained at NFESC and Sandia using angles of incidence of 75 and 60° for average film thickness ranging from 0.1 to 1 |im, and aluminum substrates with surface finish ranging from 600 to 80 grit. Since the surface finishing operation produced a highly directional roughness, measurements were made both longitudinally and transversely with respect to the polishing grooves. R values were determined at

Surface Contamination and Cleaning ◽

10.1201/9789047403289-5 ◽

2003 ◽

pp. 17-20

Keyword(s):

Thin Film ◽

Absorption Spectrum ◽

Film Thickness ◽

Infrared Absorption Spectrum ◽

Grazing Angle ◽

Incident Beam ◽

Detection Sensitivity ◽

Angle Of Incidence ◽

Solder Flux ◽

Layer 4

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Electron-Channelling Patterns: Principles and Techniques

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100091986 ◽

1976 ◽

Vol 34 ◽

pp. 400-401

Author(s):

David C. Joy

Keyword(s):

Crystal Structure ◽

Electron Flux ◽

Lattice Structure ◽

Incident Beam ◽

Bloch Wave ◽

Crystalline Solid ◽

Angle Of Incidence ◽

Electron Channelling ◽

Regular Arrangement ◽

Backscattered Signals

In a crystalline solid the regular arrangement of the lattice structure influences the interaction of the incident beam with the specimen, leading to changes in both the transmitted and backscattered signals when the angle of incidence of the beam to the specimen is changed. For the simplest case the electron flux inside the specimen can be visualized as the sum of two, standing wave distributions of electrons (Fig. 1). Bloch wave 1 is concentrated mainly between the atom rows and so only interacts weakly with them. It is therefore transmitted well and backscattered weakly. Bloch wave 2 is concentrated on the line of atom centers and is therefore transmitted poorly and backscattered strongly. The ratio of the excitation of wave 1 to wave 2 varies with the angle between the incident beam and the crystal structure.

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Algorithms for determining the phase of RHEED oscillations

Journal of Applied Crystallography ◽

10.1107/s1600576715020415 ◽

2015 ◽

Vol 48 (6) ◽

pp. 1927-1934 ◽

Cited By ~ 5

Author(s):

Zbigniew Mitura ◽

Sergei L. Dudarev

Keyword(s):

Experimental Data ◽

Direct Method ◽

Incident Beam ◽

Diffraction Theory ◽

High Energy ◽

Angle Of Incidence ◽

High Energy Electron ◽

Dynamical Diffraction ◽

Glancing Angle ◽

Low Symmetry

Oscillations of reflection high-energy electron diffraction (RHEED) intensities are computed using dynamical diffraction theory. The phase of the oscillations is determined using two different approaches. In the first, direct, approach, the phase is determined by identifying the time needed to reach the second oscillation minimum. In the second approach, the phase is found using harmonic analysis. The two approaches are tested by applying them to oscillations simulated using dynamical diffraction theory. The phase of RHEED oscillations observed experimentally is also analysed. Experimental data on the variation of the phase as a function of the glancing angle of incidence, derived using the direct method, are compared with the values computed using both the direct and harmonic methods. For incident-beam azimuths corresponding to low-symmetry directions, both approaches produce similar results.

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Influence of Surface Condition on the Bonding Strength of Thermal Sprayed Coatings

Thermal Spray 1997: Proceedings from the United Thermal Spray Conference ◽

10.31399/asm.cp.itsc1997p0763 ◽

1997 ◽

Author(s):

V.Yu. Ulianitsky ◽

J.A. Nikolaev ◽

T.P. Gavrilenko ◽

M.C. Kim ◽

J.W. Hong

Keyword(s):

Bonding Strength ◽

Substrate Surface ◽

Surface Condition ◽

Surface Preparation ◽

Spray Coating ◽

Thermal Spray Coating ◽

Substrate Material ◽

Detonation Spraying ◽

Wide Scale ◽

Detonation Gun

Abstract The role of surface roughness in coating adhesion mechanism is studying for detonation spraying. Roughness was produced by conventional grit blasting, D-gun blasting and was formed as a result of spraying of high-adhesive thin layer of detonation coating. Cermet and alloy powders were sprayed by detonation gun Ob. The coating bonding strength measurements show the WC+25Co adhesion to be above 200 MPa independently of a substrate surface preparation. Contrary, NiCrSiB coatings are very sensitive to surface conditions their adhesion varies from 180 MPa to zero. As-sprayed alloy particles fail in adherence because of insufficient energy to fuse substrate material at a flat surface. Only developed (wide scale) roughness may be fused partially by these particles for their bonding to the substrate. Otherwise, high heated cermet particles do not need special surface preparation (except cleaning) for fusion of substrate material to provide high bonding with it. The wide scale and ball shape roughness, which is similar to the self-reproduced coating roughness, provides the best conditions for the coating bonding and it is recommended as the purpose of surface treatment before thermal spray coating.

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Diffraction by crystals

Outline of Crystallography for Biologists ◽

10.1093/oso/9780198510512.003.0009 ◽

2002 ◽

Author(s):

David Blow

Keyword(s):

Fourier Transform ◽

Three Dimensional ◽

Incident Beam ◽

Two Dimensions ◽

Three Dimensions ◽

Dimensional Structure ◽

Angle Of Incidence ◽

X Ray ◽

Max Von Laue ◽

The Fourier Transform

In Chapter 4 many two-dimensional examples were shown, in which a diffraction pattern represents the Fourier transform of the scattering object. When a diffracting object is three-dimensional, a new effect arises. In diffraction by a repetitive object, rays are scattered in many directions. Each unit of the lattice scatters, but a diffracted beam arises only if the scattered rays from each unit are all in phase. Otherwise the scattering from one unit is cancelled out by another. In two dimensions, there is always a direction where the scattered rays are in phase for any order of diffraction (just as shown for a one-dimensional scatterer in Fig. 4.1). In three dimensions, it is only possible for all the points of a lattice to scatter in phase if the crystal is correctly oriented in the incident beam. The amplitudes and phases of all the scattered beams from a three-dimensional crystal still provide the Fourier transform of the three-dimensional structure. But when a crystal is at a particular angular orientation to the X-ray beam, the scattering of a monochromatic beam provides only a tiny sample of the total Fourier transform of its structure. In the next section, we are going to find what is needed to allow a diffracted beam to be generated. We shall follow a treatment invented by Lawrence Bragg in 1913. Max von Laue, who discovered X-ray diffraction in 1912, used a different scheme of analysis; and Paul Ewald introduced a new way of looking at it in 1921. These three methods are referred to as the Laue equations, Bragg’s law and the Ewald construction, and they give identical results. All three are described in many crystallographic text books. Bragg’s method is straightforward, understandable, and suffices for present needs. I had heard J.J. Thomson lecture about…X-rays as very short pulses of radiation. I worked out that such pulses…should be reflected at any angle of incidence by the sheets of atoms in the crystal as if these sheets were mirrors.…It remained to explain why certain of the atomic mirrors in the zinc blende [ZnS] crystal reflected more powerfully than others.

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HOLOGRAPHIC INVERSION OF DIFFUSE ELECTRON DIFFRACTION INTENSITIES FOR THE Ni(001)/K STRUCTURE

Surface Review and Letters ◽

10.1142/s0218625x94000321 ◽

1994 ◽

Vol 01 (02n03) ◽

pp. 319-334 ◽

Cited By ~ 28

Author(s):

K. HEINZ ◽

H. WEDLER

Keyword(s):

Electron Diffraction ◽

Lattice Gas ◽

Three Dimensional ◽

Incident Beam ◽

Real Space ◽

Reference Wave ◽

Angle Of Incidence ◽

Intensity Pattern ◽

Diffuse Intensity ◽

Adsorption Structure

At low temperatures many adsorbates arrange in lattice gas disorder on crystalline substrates. In a low energy electron diffraction (LEED) experiment this leads to diffuse intensities super-imposed on the sharp spots caused by the substrate. For the disordered adsorption system Ni(001)/K, we present two-dimensional intensity distributions as function of the electron energy and angle of incidence. They can be measured very fast (20 s per frame) and reliably using an automatic video based data acquisition technique. We show that diffuse intensity spectra DI(E) taken as function of energy for fixed surface parallel electron momentum transfer carry the information about the local adsorption structure. This is equivalent to conventional I(E) spectra taken for sharp spots. In the light of recent proposals it is shown that the diffuse single energy intensity pattern is not a hologram of the local structure because e.g. the reference wave is ill defined. However, the diffraction processes disturbing the pure reference wave cancel when the intensities of different energies are suitably averaged. It is demonstrated that the holographic reconstruction of real space information from such scanned energy data leads to reliable and well resolved atomic images. Full widths at half-maximum of such atomic images are not greater than 1 Å. Substrate atoms behind the reference atom in direction of the incident beam are imaged best. So, image reconstructions for different beam directions produce a full and high quality three-dimensional image of the local adsorption structure.

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Wechselwirkung kondensierter Molekularstrahlen mit festen Oberflächen

Zeitschrift für Naturforschung A ◽

10.1515/zna-1968-0214 ◽

1968 ◽

Vol 23 (2) ◽

pp. 274-279 ◽

Cited By ~ 15

Author(s):

E. W. Becker ◽

R. Klingelhöfer ◽

H. Mayer

Keyword(s):

Steel Surface ◽

Tangential Velocity ◽

Incident Beam ◽

Stainless Steel Surface ◽

Angle Of Incidence ◽

Mean Velocity ◽

Tangential Velocity Component ◽

Polished Stainless Steel ◽

The Mean ◽

Angle Of Reflection

The reflection of a beam of nitrogen clusters from a polished stainless steel surface is investigated. The scattered flux shows a strong maximum at an angle of reflection almost 90°, independent of angle of incidence. The mean velocity of the reflected beam is about equal to the tangential velocity component of the incident beam. Measurements with increased background pressure demonstrate that the reflected beam still consists essentially of clusters.

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APPLICABILITY OF A NEW SURFACE PREPARATION METHOD FOR STEEL STRUCTURE USING LASER

Proceedings of International Structural Engineering and Construction ◽

10.14455/isec.res.2016.143 ◽

2016 ◽

Vol 3 (2) ◽

Author(s):

Hiroshi Ogami ◽

Katashi Fujii ◽

Yukio Manabe ◽

Kohei Ota ◽

Asuo Yonekura

Keyword(s):

Preparation Method ◽

Surface Condition ◽

Surface Preparation ◽

Steel Structure ◽

Steel Structures ◽

Laser Cleaning ◽

Coating Film ◽

Test Results ◽

Corrosion Prevention ◽

Accelerated Corrosion

Surface preparation is very important in re-painting of steel structures so as to extend the effective term of corrosion prevention. Though grinding or blasting have been widely used to remove rust and old coating film on steel surface, both these methods have difficulty in completion of rust-removal and cause some problems such as dust scattering, noise, etc. In order to solve these problems, this paper presents the laser cleaning method which instantaneously sublimes/evaporates the rust on the surface of steel structure. The authors investigate the effects and the applicability of laser cleaning using the specimens made by accelerated corrosion method. The test results confirmed that the laser cleaning can remove the rust almost much as using sand blast, and the salt on the surface of steel can also be evaporated as good as the rust. Moreover, this method seems can be applied on wet surface condition because the moisture and water on the surface of steel can also be evaporated.

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The reflection and diffraction of X-rays

Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character ◽

10.1098/rspa.1931.0147 ◽

1931 ◽

Vol 133 (821) ◽

pp. 274-291 ◽

Cited By ~ 4

Keyword(s):

Critical Angle ◽

Close Agreement ◽

Wave Length ◽

Length Distribution ◽

Incident Beam ◽

Electromagnetic Theory ◽

Spherical Mirror ◽

Angle Of Incidence ◽

X Rays ◽

Carbon Target

The agreement between the theories of the reflection of X-rays by solids and observations is discussed. Generally the observations so far obtained are not in close agreement with each other or with theory. The writers find that X-rays of wave-lengths 13·3 Å. (Cu Lα) and 44·7 Å. (C Kα) are reflected by glass, quartz and stainless steel at angles considerably greater than the calculated critical angles. The radiation from carbon has been focussed by a spherical mirror for an angle of incidence of 45°. The ratio of the intensity of the reflected to the incident beam, when X-rays from a carbon target are incident on a glass mirror, has been determined approximately by a photographic method and is found to agree with the Fresnel electromagnetic theory provided a higher absorption of the X-rays occurs than has been previously supposed. This evidence of reflection for angles of incidence greater than the critical angle, which is 6° for glass at a wave-length of λ = 44·7 Å., is confirmed by observations with a glass diffraction grating with which the λ = 44·7 Å. line has been observed for angles of incidence on a plane grating up to 19°. A new plane ruled grating spectrometer is described by means of which the C Kα line has been obtained with short exposures in all orders from the 18th negative to the 13th positive. Microphotometer curves of the wave-length distribution of the energy in the grating spectrum of carbon radiation are given, and these indicate that it consists almost entirely of the Kα line, λ = 44·7 Å. Using Rowland’s method of coincidences the wave-length λ C kα is found to be 44·7 5 Å. relative to λ Cu Lα = 13·32 Å.

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