1,721,080 research outputs found
AES and core level photoemission in the study of a -C and a-C:H
No full textThe state of the art in the use of two probes of the occupied electron states, namely C KVVAuger emission and C 1s photoemission, in the study of a-C and a-C:H is reviewed, with particular attention to the issue of deriving the sp2 fraction. The local character of the two probes justifies decomposition of the relative spectra into an sp2 and an sp3 component. While however decomposition of the C 1s spectrum relies upon a theoretical basis and allows accounting for disorder effects in the amorphous state, no theory is available to support C KVV spectrum decomposition which has therefore to rely upon a purely empirical basis. In addition, the introduction of disorder related effects is not straightforward for this spectrum. A real validation of the sp2 fraction measurement is lacking for both techniques, though there are indications that both allow qualitative or even semi-quantitative (C 1s spectrum) understanding of the electronic structure of amorphous carbon systems. Beside the sp2 fraction evaluation, other pieces of information, concerning the spatial organization of the sp2 sites, are possibly extracted from these spectr
On the use of elastic peak electron spectroscopy (EPES) tomeasure the H content of hydrogenated amorphous carbon films
No full textQuasi-elastic scattering of 1–2 keV electrons is consideredwith respect to measuring theHcontent in hydrogenated amorphous carbon (a-C :H)materials. Interest in the technique lies in the fact that H cannot be typically detected by electron spectroscopic means (AES or XPS for instance). The feasibility of the approach is demonstrated and a quantification procedure is proposed. At the same time however, limitations of the technique (electron stimulated H desorption, low intensity of the H related signal and its spectral interference with the π-plasmon peak) are discussed
Measuring the energy of the graphite pi + sigma plasmon peak
No full textWe examine the graphite plasmon loss structure in reflection electron energy loss spectroscopy (REELS) and XPS with respect to the issue of measuring the energy, Ep, of the pi + sigma plasmon peak. The two spectra differ in shape because they are based on different physical processes. In fact, a static core hole – leading to intrinsic (in addition to extrinsic) losses – exists only for XPS. We show that no single energy can be measured on the two spectra for the pi + sigma peak. Possible procedures to deal with the matter are considered
The spatial extent of surface effects on electron inelastic scattering
No full textWe calculate the thickness of the surface scattering layer, defined as the region where electron inelastic scattering is affected by the surface, using the semi-classical treatment of electron energy loss provided by the Chen–Kwei theory. To this end, we consider the depth-dependent, surface-related contributions to the inverse inelastic mean free path, namely, the excitation of surface plasmons and the reduction in bulk plasmon excitation (Begrenzung effect). We find that surface effects extend further after electrons cross the surface than before they cross it. The ‘pre-surface thickness’ is given by the ratio of the electron velocity to the plasma frequency, the characteristic decay length for surface effects. All thickness estimates increase linearly with the electron velocity and decrease as (cosα)x with the angle α between the electron trajectory and the surface normal
Reflection electron energy loss spectroscopy: role of the Bethe–Born factor
No full textThe article deals with two issues concerning reflection electron energy loss spectroscopy (REELS), namely, which angular cutoff
should be used to properly define the phase space of energy loss into plasmon excitations and how approximate evaluations of
the surface component of the momentum transfer can affect the surface excitation parameter. With regard to the first point, we
demonstrate the crucial role of plasmon energy dispersion in determining the angular range for inelastic scattering. As for the
second point, we show that an exact evaluation of the surface component of the momentum transfer is needed if the surface
excitation parameter has to be determined in a reliable way over the entire range of angles of surface crossing
Analisi della forma di riga Auger in transizioni del tipo core-valenza-valenza (CVV): la transizione L2,3VV del silicio
No full textElectron irradiation of silicon dioxide: a non-destructive measurement of the in-depth induced compositional changes
No full textJoint experimental and computational study of silicon dioxide electron energy loss spectra
No full textExperimental reflection electron energy loss spectra from silicon dioxide are excited by electrons with energy ranging from 90 eV to 2 keV. A Monte Carlo simulation, shortly described, is utilized to calculate the same spectra. The comparison between simulated and experimental spectra shows substantial agreement, particularly at high exciting energies. Differences at low exciting energies are mainly ascribed to surface effects
Metastability of the Si(111)/Cu interface: A spatially resolved Auger line-shape spectroscopy investigation
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