J C Le Bosse’s research while affiliated with National Institute of Applied Science and other places

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Publications (34)


Mirror electron microscopy applied to the determination of the total electron reflection coefficient at a metallic surface
  • Article

January 2001

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9 Reads

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19 Citations

M Babout

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J C Le Bosse

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J Lopez

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[...]

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C Guittard

It is shown that the intensity of the electronic current backscattered from the surface is the convolution product of the total reflection coefficient by the energy distribution of the incident beam. A deconvolution method has been used to obtain this coefficient and this method is based on a rigorous inversion of the convolution integral operator. Numerical tests show that this method is not very sensitive to the experimental random noise. Results are given for W(100), Cu(100), and O/Cu(100) surfaces, and these are correlated with earlier measurements.


Interaction energy between two atoms chemisorbed at a transition metal surface

November 2000

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5 Reads

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9 Citations

Journal of Physics C Solid State Physics

A detailed investigation of the interaction energy between two identical monovalent atoms chemisorbed at a transition metal surface is presented in terms of a tight-binding model. The direct interaction between the adatoms is explicitly included in the model. Information on the diadatom chemisorption process is obtained from an algebraical investigation of the limiting cases corresponding to weak and strong adatom-metal couplings. The intermediate coupling domain is studied through a computation carried out in the case of the (100) surface of an s-band simple cubic crystal with or without steps.


Energy of interaction between two atoms chemisorbed at FCC and BCC transition metal surfaces

November 2000

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6 Reads

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2 Citations

Journal of Physics C Solid State Physics

The energy of interaction between two identical atoms chemisorbed on the (100) surface of a BCC or FCC transition metal is numerically investigated using a Green function technique based on the use of the Kalkstein and Soven Green functions for the substrate. These results are compared with previous results (1980) concerning the (100) face of an s band simple cubic crystal and with algebraic predictions. The authors find a good agreement; more precisely the overall qualitative features are the same for the three lattice structures. From this it follows that simple models can be used in chemisorption theory, allowing one thereby to categorise and improve one's understanding of experimental results.


Comments on the sensitivity of the indirect interaction behaviour with the range of the adsorbate-substrate hopping integrals

November 2000

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3 Reads

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2 Citations

Journal of Physics C Solid State Physics

The authors investigate the sensitivity of the indirect interaction behaviour with the range of the adsorbate-substrate hopping integrals. They show that this sensitivity is quite large. It means that the common approximation which consists of restricting the adsorbate-substrate interactions to nearest neighbours is often incorrect. They show also that there is a general tendency to obtain a repulsive indirect interaction when electrons can go from an adatom to the other 'via' only one surface atom through direct electronic resonances. All these results are illustrated by a computation carried out in the case of the (100) surface of a single s band simple cubic crystal. As a consequence of their results, it can be emphasised that a careful computation of the adsorbate-substrate hopping integrals is necessary to obtain reliable results in the computation of the indirect interaction energy between adatoms.


Threshold effects in LEED: Resonance or interference effects?

November 2000

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12 Reads

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9 Citations

Journal of Physics C Solid State Physics

Much work has been done on threshold effects in LEED assuming their resonance origin. The authors use here a perturbation expansion to separate the contributions of interference and resonance effects in LEED profiles. They show, on five typical examples, that oscillations near thresholds have a clear interference origin. It appears that it is difficult to find situations for which resonance conditions are actually satisfied. This fact has important consequences on the information that one can extract from analysis of threshold effects.


A general picture of threshold effects in LEED

November 2000

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12 Reads

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8 Citations

Journal of Physics C Solid State Physics

The authors reinvestigate the interpretation of fine structures associated with beam emergence threshold in LEED. This work is based upon a new expansion of the total amplitude matrix of the crystal in a power series of the off-diagonal part of the bulk amplitude matrix. They clearly show that the pure resonance picture is incorrect, even in the favourable case where the fine structures fall inside a forbidden gap. Their alternative picture is that the dominant mechanism is an interference between the waves directly reflected at the barrier or at the bulk, and the waves associated with processes including on metal-metal reflection at the barrier. This interpretation, which proved to be adequate in their previous study of Al(001) and Ni(001), holds equally well for the fine structure measured by Adnot and Carette (1977) on W(001) in the presence of a band-gap. As a consequence the authors discuss why McRae's method (1967) to extract structural information from a 2D surface band structure cannot be used.


On the extraction of surface barrier potentials from threshold effects in LEED: Saturation on Cu(001) revisited
  • Article
  • Full-text available

November 2000

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29 Reads

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1 Citation

Journal of Physics C Solid State Physics

The authors give a critical discussion of the extraction of the surface barrier potentials from LEED threshold effects as introduced by Dietz, McRae and Campbell (1980) for Cu(001). They show that their approximation, together with experimental and theoretical procedure, introduce an effective phase for the total-internal-reflection coefficient at the barrier from which the correct barrier shape cannot be extracted. Without the trick of a discontinuous barrier shape, the authors' correct analysis gives a better description than the empirical analysis. There remains, however, some discrepancy and the extraction of the Cu(001) barrier shape still needs both more experimental data and more theoretical studies for which the authors have specified the LEED framework.

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Determination of the W(001) and W(110) surface potential barriers

November 2000

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11 Reads

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2 Citations

Journal of Physics C Solid State Physics

Very low-energy electron diffraction fine structure profiles measured on W(001) and W(110) are presented. These data are analysed using a new surface potential barrier and by taking into account a possible variation of the inner potential inside the atomic top layer. From a thorough comparison of several measured and calculated spectra it is found that a good overall fit of fine structure data can be obtained on both surfaces using a unique one-dimensional barrier model. Optimal values of the model parameters (the top layer inner potential Vs and the centre of mass of the screening charge z0) are however quite different on the two surfaces. On W(001), Vs is nearly 4 eV less attractive than the bulk inner potential. On W(110), this value is only about 0.4 eV. Also, z0 is about 0.5 AA farther from the centre of the topmost layer on W(001) than on W(110). These results are explained by the difference in the atomic density on these two tungsten surfaces. This work shows that, especially for loosely packed surfaces, possible variation of the ion-core potentials near the surface has not to be overlooked in low-energy scattering on surfaces.


VLEED analysis of W(110) data in the range 0-30 eV

November 2000

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10 Reads

Journal of Physics C Solid State Physics

New very long-energy-electron reflection data on W(110) are presented. Spectra measured at several angles of incidence in the 0-30 eV range are compared with calculated profiles. These are obtained using a surface barrier model in which possible variation of the inner potential at the top layer is taken into account. An accurate barrier shape is required to reproduce fine structure oscillations in the vicinity of beam emergencies. However, best overall adjustment to experimental data is obtained when saturation of the inner potential at the surface is introduced. The analysis suggests that the absolute value of the inner potential in the topmost layer is reduced by the order of 1 eV on W(110).


Effect of the variation of the inner potential of the crystal surface in VLEED

November 2000

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19 Reads

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1 Citation

Journal of Physics C Solid State Physics

In very low-energy electron diffraction (VLEED), the fine structures appearing below the emergence thresholds in I00(E) are usually used to test surface barrier models. The authors reinvestigate this problem, in particular for the case of a loosely packed surface. Two surface barrier models are tested in the case of a very-low-energy intensity profile (E <or approximately=5 eV) obtained on the W(001) surface for theta =45 degrees along the (10) azimuth: the modified image barrier introduced by Jennings and Read (1974) and a new saturated image barrier. Neither of these models yields a good fit of experimental data as long as one assumes that the barrier joins the bulk inner potential at the top layer edge continuously or with a potential step. Without challenging the validity of the muffin-tin approximation inside the first layer, it can be suspected that the top-layer potential is less attractive than any bulk-layer one. it is found that for both barrier models, shifting the top-layer inner potential upwards leads to a significant improvement of the fit. It is also found that the modified image barrier tends to exhibit a non-physical region of constant potential potential near the top layer and as a consequence the saturated image barrier appears to be more reliable. Finally this work illustrates the fact, that, especially for loosely packed surfaces, the surface barrier concept must not be restricted to the vacuum region but has to be extended inside the crystal region where the bulk potential is modified by the presence of the surface.


Citations (12)


... For other details see [5,8,9]. As usually the averages in (3) are performed over a grand canonical ensemble and a Hamiltonian H of adsorbate-substrate and adsorbate-adsorbate interactions is following: ...

Reference:

Monte Carlo Simulation of Partially Ordered Atomic Layers Adsorbed on the Monocristalline Surfaces
Two-Site Correlations in a Surface Layer Adsorbed on the Crystal
  • Citing Article
  • November 1991

Acta Physica Polonica Series a

... Therefore, the expression obtained for W QQ (R) needs no additional terms of the electrostatic origin. On the other hand, indirect terms of a different nature [18][19][20][86][87][88][89][90][91][92], which can contribute to the overall interaction between two adsorbed entities, are not taken into consideration by functions Eqs. (4) and (5). ...

The dipole-dipole interaction between two adatoms viewed as a surface plasmon mediated interaction
  • Citing Article
  • August 1981

Surface Science

... From the reflection property of light, for the rough surface incident light scatter in many directions, as each ray of light meets the surface at a different orientation [26], each ray of light follows the law of reflection having a different normal line at the point of incidence. This is true for regularly machined surface (Fig. 1). ...

Characterisation of surface roughness by laser light scattering: Specularly scattered intensity measurement
  • Citing Article
  • August 1997

Wear

... This function is described by the ISO standards and many research items [49]. In many primary studies, the ACF was proposed for the analysis of roughness isotropy [50] or anisotropy [51], description and realizations of homogeneous and isotropic two-dimensional Gaussian random processes [52], isotropic exponential and transformed exponential multiscale correlations [53], measurements of the variance of surface height obtained in several scattering geometries and also for stylus measurements [54], statistical computations of the root mean square (RMS) height, skewness (Ssk), and kurtosis (Sku) of the roughness height distribution [55], direction parallel and perpendicular to grooves, classification of data (signal) to the individual groups [56], identification of the periodicity and randomness [57], angular distribution characterization [58], the relationship between the height of a one-dimensionally rough surface and the intensity distribution of the light scattered by surface [59], vertical and lateral information about surface roughness [60], statistical irregularities of the waveguide substrate [61], characterization of the random component of the surface profile [62], determination of the domination in the frequency spectrum [63], and, frequently, characterization of the roughness measurement of the machined surfaces [64]. ...

Characterisation of surface roughness by laser light scattering: Diffusely scattered intensity measurement
  • Citing Article
  • February 1999

Wear

... Roughness measurement of thin film Surface roughness plays an important role in the fabrication of electrochromic devices. A variety of methods such as stylus profilometry [164], atomic force microscopy [165], scanning electron microscopy [165], scaterometer [166], and interferometry methods [167]. Stylus profilometry, atomic force microscopy, and interferometry, though useful in thickness measurement, still have few disadvantages. ...

Functional significance of different techniques for surface morphology measurements
  • Citing Article
  • February 1995

International Journal of Machine Tools and Manufacture

... Theoretical papers devoted to the problem can be grouped according to: (i) the number of layers in the system (two, three, or the infinite number); or (ii) which interaction is considered. The latter means either the test-charge (in rare cases, test-dipole) electrostatic self-energy arising due to the existence of interface(s) between the media with different dielectric permittivities, which is usually called the image force energy [25][26][27][28][29][30][31][32][33], or the interaction energy between the charges (or dipoles) located in the same layer or in different layers [6,8,[34][35][36][37][38][39][40][41][42][43]. ...

Interaction energy between two identical atoms chemisorbed on a normal metal
  • Citing Article
  • March 1978

Surface Science

... The evaluation of the site occupancy pair correlation function is obtained from the statistical mechanics treatment of chemisorbed layers in terms of lattice gas model. On the basis of the experimental results described in Section 2 the site occupancy pair correlation functions of CO adsorbed on Pt(111) were determined [9] by a Monte Carlo simulation at constant coverage and temperature. The model involves adsorption energy and repulsive pair interaction potentials up to third neighbours, depending only on distance. ...

Determination of site-occupancy pair correlation functions of CO adsorbed on Pt(111) adapted for DLEED intensity calculations
  • Citing Article
  • July 1997

Surface Science

... Theoretically, under certain conditions this electron can be reflected back and forth a large number of times, forming a quasi-bound state [272] and traveling along the surface like in a waveguidesuch implied states were named "electronic surface resonances" [272]. This effect was widely discussed in the 1970s in relation to fine structure of very low energy electron diffraction (VLEED) spectra observed experimentally (so-called "threshold" or "preemergent beam" effects) [272][273][274]. However, later it was noted that despite the rather strict conditions under which such resonances can exist, VLEED fine structures are very commonly observed. ...

Threshold effects in LEED: Resonance or interference effects?
  • Citing Article
  • November 2000

Journal of Physics C Solid State Physics

... The interference produces the energy-dependent intensity modulations that explain well the experimentally observed "threshold effects" [273,275]. Similar mechanism should also produce fine structures in ARPES spectra, however until recently they were very rarely observed and recognized. In this work we investigate the unusual features present in ARPES spectra and provide arguments that they are analogous to the threshold effects observed in VLEED. ...

A general picture of threshold effects in LEED
  • Citing Article
  • November 2000

Journal of Physics C Solid State Physics

... Compton [1] reported that the scattered X-rays contain both a coherent and an incoherent portion of discrete electrons. Bosse et al. [2] studied the theoretical description of coherent and incoherent multiple scattering of electrons at a single-crystal surface partially covered with a disordered overlayer. Langer [3] studied the peculiarities of the phenomena of modification of wavelength in incoherent scattering. ...

Theory of coherent and incoherent back-scattering of electrons at a disordered surface and its relationship with short-range order and local geometry in absorbed overlayers
  • Citing Article
  • November 2000

Journal of Physics C Solid State Physics