Analyzers, electron energy characteristics

If the analyzer is set to accept electrons of an energy characteristic of a particular element, and if the incident X-ray beam is rastered over the surface to be analyzed, a visual display the intensity of which is modulated by the peak intensity will correspond to the distribution of that element over the surface. The result is also an image and this technique is realized with the Quantum 2000. 

If an incident electron beam of sufficient energy for AES is rastered over a surface in a manner similar to that in a scanning electron microscope (SEM), and if the analyzer is set to accept electrons of Auger energies characteristic of a particular element, then an elemental map or image is again obtained, similar to XPS for the Quantum 2000 (Sect. 2.1.2.5). 

This problem asks if red and blue photons can cause potassium metal to lose electrons. We must analyze the energy requirements for ejection of an electron. No electrons will be ejected unless the energy of the photons exceeds some threshold value characteristic of the metal. If the photon energy exceeds this threshold value, electrons will be ejected with kinetic energy given by Equation. An important part of this problem is the conversion of photon frequency to photon energy. 

Electrons excite characteristic transitions in the sample, which can be studied by analyzing the energy loss suffered by the primary electrons. 

The resolution of overlapping spectral peaks depends on their separations, intensities, and widths. Whereas separation and intensity are predominantly functions of the sample, peak width is strongly influenced by the instrument s design. The observed line is a convolution of the natural line, a function characteristic of inelastically scattered electrons that produces a skewed base line, and the instrument function. The instrument function is, in turn, the convolution of the x-ray excitation line shape, the broadening inherent in the electron energy analyzer, and the effect of electrical filtering. This description is summarized in Table I. 

The acronym ESCA refers to the technique of bombarding the surface with X-ray photons, which produce the emission of characteristic electrons measured as a function of electron energy. Because of the low energy of the characteristic electrons, the depth to which the analysis is made is only 20 A. The composition of this thin layer as a function of depth can be determined by sputtering away layers of the surface and analyzing the underlying surfaces. A number of important catalytic properties have been studied by this technique, including oxidation state of the active species, interaction of a metal with an... 

The XPS Measurement. In an XPS spectrometer, the studied material is exposed inside a vacuum chamber to a flux of X-rays (energy 1 keV). The kinetic energy of the photoelectrons ejected from the sample is measured by an appropriate analyzer. This energy is directly related to the binding energy of the electrons inside the sample on a wide scan XPS spectrum, the unscattered electrons result in characteristic peaks their energies serve to identify the elements in the material (atomic composition), to characterize the molecular environment of these atoms (chemical analysis, see inset A of Figure 1), and, by the measurement of the photoelectric lines ratios, to reach some quantitative results. Such type of measurement from the core level peaks can usually be... 

Superficial (surface) compositions are also listed in Table I as determined by XPS with atomic sensitivity factors characteristic of the electron energy analyzer used for these studies. The superficial compositions agree reasonably well with the bulk values for all samples with the exceptions of SAPO-5 and the two Si-VPI-5 samples which show a significant enrichment of Si at the surface. Note that samples which were examined with and without deposited gold (the reference for the binding energy scale) showed little difference in measured compositions with XPS. 

The effort that leads to optimization of the particle morphology is largely one of trial and error, and there is no simple means to describe the distribution of components within individual particulates. Clearly, if the majority of an active component (API) is in the interior of a particle, then the dissolution or release characteristics are likely to differ from particles where the API is predominantly on the surface. The surface distribution of proteins and polymers within spray-dried particles has been studied using electron spectroscopy for chemical analysis that involves analyzing the energy signature of electrons scattered from surfaces while being bombarded by x-rays [11,28-31], Conclusions can then be drawn... 

Electrons energies 0-30 eV above edge Ions — analyzed with mass spectrometer Directional dependence of emitted ions Characteristic X-ray 0.1-15 keV... 

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