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Cazaux J.,CNRS Laboratory of Engineering and Materials Science
Journal of Electron Spectroscopy and Related Phenomena | Year: 2013

The influence of the refraction effects in quantitative surface analysis is evaluated when Auger electrons or X-ray photoelectrons cross the sample/vacuum surface and other interfaces. Based on elementary quantum mechanical arguments, this evaluation concerns the determination of surface concentrations of homogeneous samples, as well as the determination of thicknesses of over layers or subsurface layers of stratified samples. From various numerical applications, such as the thickness determination of a graphene monolayer in X-ray Photoelectrons Spectroscopy (XPS), it is established that the refraction effects may lead deviations - with respect to the so-called straight-line approximation -, which may reach tenths of a percent for photoelectrons induced by soft X-rays when they are issued from metals and detected at decreasing take-off angles. The consequence in XPS - including Angle-Resolved XPS - and in Auger Electron Spectroscopy (AES) is discussed and some aspects of the discussion may also concern LEED (Low Energy Electron Diffraction) via the fact that the refraction effects results from the difference between the inner and the outer energy of the electrons of interest, a difference equals to the sum of the Fermi energy and the work function and often referred in the LEED literature as inner potential U. PACS79.60.-82.80.Pv73.30.+y29.20.dk68.65.Pq61.05.jh. © 2013 Elsevier B.V. All rights reserved. Source


Canneaux S.,University of Lille1 science and Technologies | Bohr F.,CNRS Laboratory of Engineering and Materials Science | Henon E.,CNRS Institute of Molecular Chemistry - Reims
Journal of Computational Chemistry | Year: 2014

Kinetic and Statistical Thermodynamical Package (KiSThelP) is a cross-platform free open-source program developed to estimate molecular and reaction properties from electronic structure data. To date, three computational chemistry software formats are supported (Gaussian, GAMESS, and NWChem). Some key features are: gas-phase molecular thermodynamic properties (offering hindered rotor treatment), thermal equilibrium constants, transition state theory rate coefficients (transition state theory (TST), variational transition state theory (VTST)) including one-dimensional (1D) tunnelling effects (Wigner, and Eckart) and Rice-Ramsperger-Kassel-Marcus (RRKM) rate constants, for elementary reactions with well-defined barriers. KiSThelP is intended as a working tool both for the general public and also for more expert users. It provides graphical front-end capabilities designed to facilitate calculations and interpreting results. KiSThelP enables to change input data and simulation parameters directly through the graphical user interface and to visually probe how it affects results. Users can access results in the form of graphs and tables. The graphical tool offers customizing of 2D plots, exporting images and data files. These features make this program also well-suited to support and enhance students learning and can serve as a very attractive courseware, taking the teaching content directly from results in molecular and kinetic modelling. © 2013 Wiley Periodicals, Inc. KiSThelP is a cross-platform, open-source program developed to estimate molecular thermodynamic properties, equilibrium constants, transition state theory, and RRKM rate coeffi-cients from electronic structure data. It is a working tool for both the general public and more advanced users. It provides graphical front-end capabilities designed to facilitate calculations and the interpretation of results. This program can serve as an attractive courseware, taking the teaching content directly from results in molecular and kinetic modelling. © 2013 Wiley Periodicals, Inc. Source


Cazaux J.,CNRS Laboratory of Engineering and Materials Science | Kuwano N.,Malaysia Japan International Institute of Technology | Sato K.,Jfe Holdings
Ultramicroscopy | Year: 2013

Due to the influence of refraction effects on the escape probability of the Back-Scattered Electrons (BSE), an expression of the fraction of these BSE is given as a function of the beam energy, E°, and emission angle (with respect to the normal) α. It has been shown that these effects are very sensitive to a local change of the work function in particular for low emerging angles. This sensitivity suggests a new type of contrast in Low Voltage Scanning Electron Microscopy (LVSEM for E°<2. keV): the work function contrast. Involving the change of φ with crystalline orientation, this possibility is supported by a new interpretation of a few published images. Some other correlated contrasts are also suggested. These are topographical contrasts or contrasts due to subsurface particles and cracks. Practical considerations of the detection system and its optimization are indicated. © 2013 Elsevier B.V. Source


Cazaux J.,CNRS Laboratory of Engineering and Materials Science
Journal of Electron Spectroscopy and Related Phenomena | Year: 2014

Some aspects of the time dependence of positive charging of insulating films are evaluated when they are set on conductive substrates and are exposed to X-rays. This evaluation is based on the influence of the electrostatic surface potential due to the positive charges left by the effective secondary electron emission into the vacuum, δx, combined with some work function effects. Valid up to a surface potential of ∼3-5 V, an expression for the nearly exponential decay of δx, time constant τ, is established as a function of the fluence of the irradiation and the geometry and characteristic of the sample and of its environment. The results being a function of the spectral and angular distributions of the emitted SEs, the order of magnitude of the corresponding factors are evaluated numerically for two extreme situations, that of inorganic insulators and that of floating conductors in order to be extended easily to other types of materials. The decay may be preceded by a dwell time, τs, particularly when an external collector is negatively biased. When flood guns are used, the work function effects limit the efficiency of the neutralization effects by the increasing reflection coefficient of the very low energy incident electrons. Finally, the mechanism of the degradation effects of electrons that are issued from the sample holder/sample interface is also developed. This approach may also be adapted other projectiles such as UV photons, ions or electrons. © 2014 Elsevier B.V. Source


Cazaux J.,CNRS Laboratory of Engineering and Materials Science
Journal of Electron Microscopy | Year: 2012

Image formation in scanning electron microscopy (SEM) is a combination of physical processes, electron emissions from the sample, and of a technical process related to the detection of a fraction of these electrons. For the present survey of image contrasts in SEM, simplified considerations in the physics of the secondary electron emission yield, δ, are combined with the effects of a partial collection of the emitted secondary electrons. Although some consideration is initially given to the architecture of modern SEM, the main attention is devoted to the material contrasts with the respective roles of the sub-surface and surface compositions of the sample, as well as with the roles of the field effects in the vacuum gap. The recent trends of energy filtering in normal SEM and the reduction of the incident energy to a few electron volts in very low-energy electron microscopy are also considered. For an understanding by the SEM community, the mathematical expressions are explained with simple physical arguments. © 2012 The Author. Published by Oxford University Press [on behalf of Japanese Society of Microscopy]. All rights reserved. Source

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