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Thin Silica Films on Si and SIC
Published in Shamil Shaikhutdinov, Introduction to Ultrathin Silica Films Silicatene and Others, 2022
Experimentally, the band structure profile for a SiON film grown on 6H-SiC(0001) has been addressed in elegant way using soft x-ray absorption spectroscopy (XAS) and x-ray emission spectroscopy (XES).71 Since XAS and XES probe electronic transitions from a core level to conduction states and from valence states to the core hole, respectively, element-specific conduction- and valence band partial densities of states could be obtained. The K-edge absorption lines of O (O is→2p) and N (N is →2p), and the O KLL and N KLL Auger transitions were used for analysis. Accordingly, N 2p →1s and O 2p →1s electronic transitions were measured by XES. The obtained XAS and XES data allowed to draw the energy-band profiles across the surface layers. The band gaps were found to be of 6.3 ± 0.6 eV at the silicon nitride layer and 8.3 ± 0.8 eV at the silicon oxide layer as shown in Figure 3.12. The energy-band profile of the SiON layer bears close similarities to the one theoretically predicted and shown in Figure 3.10b for a SiO2 layer. Indeed, further ab initio calculations72 found only small deviation between these two systems.
Solids
Published in Elaine A. Moore, Lesley E. Smart, Solid State Chemistry, 2020
Neil Allan, Elaine A. Moore, Lesley E. Smart
How does this theoretical density of states compare with experiment? Experimentally, the density of states can be determined by X-ray emission spectroscopy, also called X-ray fluorescence (XRF) spectroscopy. When a beam of electrons or high-energy X-rays is incident on a metal, it can remove core electrons. In sodium, for example, the valence electron is 3s, so a 2s or a 2p electron might be removed. The core energy levels are essentially atomic levels, so the electron was removed from a discrete, well-defined energy level. Having a missing electron in a core energy level is an unstable situation, so an electron from an occupied valence level drops down to the vacated energy level, emitting photons as it does so. The photon energy depends on the difference in energies between the valence level from which the electron has come and that of the core level where it ends up. Due to the high energies involved, the emitted photon is usually in the X-ray region of the electromagnetic spectrum. The wavelengths (and hence energies) of all the emitted X-rays are then measured in a special spectrometer. A scan across the emitted X-ray energies corresponds to a scan across the filled levels. The intensity of the radiation emitted depends on the number of valence electrons with that particular energy, that is, the intensity depends on the density of states. Figure 4.2 shows X-ray emission spectra for sodium and aluminium, and we can see that the shape of these curves approximately resembles the occupied part of Figure 4.1, so that the free-electron model appears to describe these bands of energy levels (as we shall see later called conduction bands) reasonably well.
Particle Identification
Published in R. P. Donovan, Particle Control for Semiconductor Manufacturing, 2018
Wayne G. Fisher, Jeffrey M. Davidson
Some techniques less commonly used in environmental studies allow direct determination of the average composition of all particles collected on a filter, or resting on a substrate, without particle dissolution. Techniques that could be extended to analysis of particles in the semiconductor processing environment include proton-induced X-ray emission spectroscopy (PIXE) (Wutjin, 1986), neutron activation analysis (NAA) (Katz, 1977; Fogg and Seeley, 1984), X-ray photoelectron spectroscopy (XPS) (Heinrich, 1980; Bakale and Bryson, 1983), X-ray fluorescence (XRF) (Johnson et al., 1984; Butler, 1979; Fogg and Seeley, 1984; Cullity, 1956), and X-ray diffraction (XRD) (Cullity, 1956).
Recent advances in micro-level experimental investigation in food drying technology
Published in Drying Technology, 2020
Md Imran H. Khan, M. M. Rahman, M. A. Karim
X-ray analysis is proven to be a noninvasive and reliable method for food quality analysis.[36] This method has long been used in the medical field to activate the photosensitisers during treatment of cancer. The high penetrating power of X-rays is harnessed in these treatments. X-ray spectroscopy (X-ray absorption spectroscopy and X-ray emission spectroscopy) involves the transfer of electrons between core and valence orbits. Guo et al. (2002) used X-ray emission spectroscopy to examine the effect of the intermolecular interaction on the local electronic structure of liquid water. Rahman et al.[36] investigated the complex microstructural changes and cell-level water transportation in plant-based food materials during drying. They found that significant changes occurred in moisture content, and cell and pore size distribution with drying time and temperature. The moisture content determined using the X-ray microtomographic images were compared with that determined by the electronic moisture analyzer (EMA) and good agreement was found.[36] X-ray micro-CT imaging method can also be used to investigate the porosity of different material.[45] The researcher used this method to investigate the porosity in fresh apple tissue,[46] and dried apple fruits at different stages of drying.[36] Furthermore, this method was also successfully applied to characterize the multiscale gas transport pathway in fresh apple and pome fruit.[47,48] Microstructural characterization during sludge drying,[49] and different ripening stages of mango was investigated by the X-ray CT.[50] Voda et al.[51] used this technique to determine the impact of freeze-drying on the microstructure of dried carrot. Yang et al.[52] observed the mechanism of cell collapse in three dimensions in eucalyptus urophylla during drying using X-ray CT scanning combined with image processing techniques. They argued that X-ray CT scanning can observe not only all cell deformation but also can measure the extent of cells collapse. Besides, food materials characterization is very important in terms of evaluating better quality attributes, therefore many researcher used X-ray CT to characterize different plant-based food materials, including apple,[53] kiwi,[54] raspberry,[55] mango,[50] beetroot,[56] and banana.[57]