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  • 1
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A general expression for the energy and angular distribution of Auger/photoelectrons emitted from a specimen with an arbitrary depth profile is presented. The central quantities in this expression are the so-called partial escape distributions, which describe the probability that a signal electron generated in a certain depth interval escapes from the surface with a direction in a certain angular interval after experiencing a certain number of inelastic scattering processes. The partial escape distributions accounting for elastic scattering are calculated in the transport approximation. Comparison of analytical calculations with Monte Carlo data based on the more relastic Mott crosssection for elastic scattering yields excellent agreement. As an illustration of the general approach, the energy/angular spectrum of a sample with a model depth profile has been evaluated using analytical calculations and Monte Carlo data. The results obtained show that the proposed formalism properly accounts for elastic and inelastic processes and correctly predicts the shape of the energy distribution in the vicinity of the peak. It is, moreover, shown that the true intrinsic spectrum and depth profile may be reconstructed simultaneously from the measured energy/angular distribution of emitted electrons.
    Additional Material: 6 Ill.
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  • 2
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Reflection electron energy loss spectroscopy (REELS) spectra for Al, Ni, Pt and Au were measured in the energy range 300-1500 eV for different scattering geometries. The energy dependence of the loss spectra was found to depend strongly on the shape and the magnitude of the elastic scattering cross-section. This effect is extremely pronounced in the angle-resolved spectra, but also persists in the angle-integrated case. It was moreover observed that the relative intensities of the surface excitations in REELS spectra exhibit a similar dependence on the elastic scattering properties. These experimental observations are in good agreement with MC calculations accounting for elastic scattering through the differential Mott cross-section and demonstrate that quantitative information regarding the inelastic scattering probability can only be extracted from REELS spectra if the exact shape of the elastic scattering cross-section is accounted for and a quantitative description of surface excitations is available.
    Additional Material: 5 Ill.
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  • 3
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 23 (1995), S. 823-832 
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Different methods of calculating efficiently the angular distribution of photoelectrons escaping from uniform amorphous and polycrystalline targets are analysed in detail. Comparison has been made between the analytical results and Monte Carlo simulation data. The analytical approach is based on the solution of the kinetic equation in the transport approximation. The Monte Carlo codes comprise the conventional forward simulation algorithm and the reverse trajectory method. The reverse trajectory method employs the reciprocity theorem and allows same statistically significant results to be obtained with less computational effort. The angular distributions of photoelectrons leaving Al, Si, Cu, Ag, Ta and Au samples have been calculated as a function of polar and azimuthal angles for electron energies relevant in quantitative XPS analysis. It has been found that both Monte Carlo methods provide equivalent results. The discrepancies between the transport approximation and the Monte Carlo data do not exceed, as a rule, 5%. The largest deviations of the analytical results from those found by Monte Carlo codes are observed in the vicinity of the emission directions, where the photoelectric differential cross-section has its minima, and are about 15%. The agreement between the results obtained by different approaches, corresponding to the magic angle geometry, is within 2% for all cases studied.
    Additional Material: 7 Ill.
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  • 5
    ISSN: 0142-2421
    Keywords: auger spectrometry ; carbicle ; titanium calibration ; electron scattering ; background correction ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Auger sputter depth profiling was performed on a specially prepared TiC sample with carbon concentration varying with depth. This resulted in a series of Auger spectra corresponding to TixC1-x, with x varying between 0.1 and 0.95. Although the carbon concentration gradient is not known a priori, there exists a method to associate any of these spectra with a given stoichiometry, utilizing the smooth relationship between the C and Ti signal for a large range of stoichiometries and imposing the constraint of atomic fractions adding up to unity. In this way the stoichiometry of each spectrum has been determined, leading to a large series of standard spectra, that allow the stoichiometry of any unknown TixC1-x specimen to be calibrated on the basis of its Auger spectrum. Sensitivity factors and calibration curves established in this way are given for peak areas, while it was found that it is impossible to establish meaningful calibration curves for Auger peak-to-peak heights owing to chemical effects in the spectra. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 5 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 23 (1995), S. 696-704 
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The influence of surface roughness on total as well as angle-dependent signal electron intensities has been studied by means of an effective and simple theoretical model. It was found that the influence of surface roughness may be accounted for in the usual formalism for AES/XPS by using an effective depth distribution function (DDF). Comparison of the model with experimental results and Monte Carlo calculations are very satisfactory and indicate that the model developed here should provide useful guidance for quantifying the influence of surface roughness in XPS/AES. For an emission angle of ∼ 35°, the depth distribution function assumes an exponential form with an effective attenuation length varying only by a few per cent as the relative surface area, which characterizes the roughness, is varied over a large range. This result implies that the influence of surface roughness on a given intensity ratio is very small for this geometry and may usually be neglected. This statement not only pertains to a layered sample but applies to a specimen with an arbitrary depth profile. Generally, the effective DDF is dominated by the influence of surface roughness, while the effects of elastic scattering are less pronounced. In this case, the combined influence of surface roughness and elastic scattering is simpler to describe than the influence of elastic scattering on the signal electron emission process from an ideally flat sample.
    Additional Material: 7 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 23 (1995), S. 737-752 
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: An approach is developed to separate the spectral contributions of electrons that have experienced a certain number of inelastic collisions and together constitute the observable lineshape in AES/XPS. The only assumption concerning the emission process that is made in this general approach is that energy losses and deflections occur separately. This means that the method can account for elastic scattering with arbitrary sophistication, while it can also be applied to spectra from samples exhibiting surface roughness or specimens with an arbitrary depth profile and even single crystals where diffraction effects dominate the peak intensities. If the details of the emission process are properly understood, such a so-called partial intensity analysis may serve to assess the structural characteristics of an unknown specimen. Conversely, if the sample structure is known, it can be employed to assess experimentally the details of the emission process (elastic scattering, roughness, diffraction). At any rate, a partial intensity analysis allows proper background correction of the spectral lineshape to be performed if this is the ultimate aim of analysis. This again holds true without regard to the emission process and is possible without any kind of fitting or ad hoc assumptions. On a very similar basis, a method is derived to gain accurate information about the inelastic transport characteristics from reflection experiments in the case when the other quantities governing the particle transfer are known. The results are general in that the starting point of the method, i.e. the yield equation, in principle also describes the fundamentals of other techniques employing particle-solid interaction.
    Additional Material: 13 Ill.
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  • 8
    ISSN: 0142-2421
    Keywords: electron transport ; background correction ; partial intensities ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A recently developed procedure to eliminate the inelastic tail below the characteristic peaks in AES/XPS spectra is analysed theoretically and tested using experimental Auger spectra from four homogeneous solids (Au, Pt, Ta and Ni). To this end, the parameter in this procedure accounting for the details of the emission process was determined for the cylindrical mirror analyser (CMA) geometry. It is shown that application of this procedure to the raw data consistently removes the inelastic tail accompanying each characteristic peak, while at the same time the background of secondaries (and, in the case of electron-excited AES, the contribution of backscattered primaries) can be strongly suppressed, rendering the task of peak area determination trivial. The proposed procedure is shown to be applicable over a wide energy range, significantly exceeding the quasi-elastic regime. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 4 Ill.
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