Energy levels, x-ray

In HRTEM, very thin samples can be treated as weak-phase objects (WPOs) whereby the image intensity can be correlated with the projected electrostatic potential of crystals, leading to atomic structural information. Furthermore, the detection of electron-stimulated XRE in the electron microscope (energy dispersive X-ray spectroscopy, or EDX, discussed in the following sections) permits simultaneous determination of chemical compositions of catalysts to the sub-nanometer level. Both the surface and bulk structures of catalysts can be investigated. 

X-ray tube—A metal anode is bombarded with high-energy electrons causing inner-shell electrons to be ejected and replaced by higher shell electrons. The loss in energy of these electrons as they drop to the lower levels is on the order of the energy of x-rays, and x-rays are emitted. 

The core-level x-ray photoemission spectrum of the Mn 2p core level for (Ga,Mn)As with x = 0.074 was measured and was analyzed by a configuration interaction (Cl) cluster-model assuming a Mn2+ and Mn3+ ground state (Okabayashi et al. 1998). For the d5 configuration, the p-d exchange energy (which is conventionally referred to as Nop for DMS) should be negative and NoP —1.2 eV is obtained for /t-(d5) centers with an optimized parameter set. 

The specific surface areas were determined by means of nitrogen adsorption and the metallic surface areas by using adsorption of 3-methylthiophen in liquid phase (ref. 9). The bulk composition of each sample was determined by chemical analysis and expressed by the atomic ratios Al/Ni and M/Ni. The catalysts were observed by transmission electron microscopy (JE0L 200 CX-TEM) and analysed either globally or at point level with a lateral resolution of 1.5 nm by means of a STEM (VG - HB 501) connected to an energy - dispersive X-ray analyser (EDAX). 

A Tracor Northern quantitative energy-dispersive X-ray analysis system with solid-state detectors was used for the electron microprobe measurements. The method is based on electron microbeam point analyses on a maceral level (18, 19) The emitted characteristic X-ray fluorescence radiation is used to quantify sulfur. Other elements of interest, such as iron and calcium, are monitored simultaneously to ensure that only the organic sulfur component is characterized. The measured... 

Comparison between the core-level X-ray absorption spectroscopy (XAS), emission (XES), and X-ray photoemission spectroscopies (XPS) usually shows that the spectral edges rarely coincide with each other and with the Fermi level. It is common practice, however, to place F at the emission threshold which corresponds to a fully relaxed ion core (16). For defining the structure of the edge, an energy resolution of at least 1-2 eV is required in the range of 5-20-keV X-ray photons. This can be achieved with Bonse-Hart channel-cut silicon monochromator crystals. 

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