Analyzer transmission function

Quantification is simple if the atoms are homogeneously distributed with depth since the intensity of each XPS peak is then directly related to the abundance of that particular element at the specimen surface. The peak intensity will usually be reported as a peak area and this will be normalized using atomic sensitivity factors (the intensity of the photoelectron transition of interest, I, is related to the concentration of that element within the XPS analysis volume, and the sensitivity factor, S, in the following way F= concentrationxS). Such atomic sensitivity factors are a function of the basic physical parameters, such as the relative photoelectron cross-sections of the different elements, electron attenuation lengths, and instrumental parameters, such as analyzer transmission functions, of the XPS experiment. The ratio of normalized peak area to the sum of normalized peak areas for the major peaks of all elements detected in the spectrum provides an analysis as an atomic fraction (or when multiplied by 100, atomic %). 

J = Electron flux, electron/cm -s T(Ej) = analyzer transmission function a = analysis area, cm ... 

The relation between intensity ratios and concentration ratios may be directly evaluated from (7, L, T, and A, which is often called the first-principles t tproach. Ratios of X are computed as explained in the section Inelastic Electron Mean Free Path, and T ratios can be evaluated using (23) or with respect to a reference spectrometer as stated in the section Analyzer Transmission Function. The instruments softwares include an evaluation of T for data treatment this should be considered with a critical mind. 

In practice, it is much more convenient to measure the ratio of the elastic-peak intensity for the material of interest to the elastic-peak intensity for a selected standard material, Is(AQ), for the same electron energy and experimental conditions. Both I( AS2) and Is(AS2) can be measured in arbitrary units, and it is not necessary to determine the primary-electron intensity or the analyzer transmission function. We then have... 

Ejected electron analyzers can be calibrated at lower energies (<25 eV) using UV photoelectron spectroscopy and comparison with quantitative photoelectron spectra. The intensity ratios provide a relative transmission function (7 ) directly. Quantitative (relative) photoelectron spectra have been reported by Hotop and Niehaus79 at an ejection angle of 90°, and these results have been used by Yee et al.66 to calibrate a 127° analyzer for which the correction curve has already been shown in Fig. 3. More recently Gardner and Samson80 reported quantitative (relative) photoelectron spectra that can be used as a standard for analyzer... 

Fig. 26. Inelastic background of an X-ray-excited Cu spectrum. The dots represent the spectrum as recorded, corrected for the transmission function of the analyzer. The dashed line represents the inelastic background, calculated with appropriate A, B,K(Eq, T), and f x). The resulting atomic Cu reference spectrum is depicted by the solid line [113]. Reprinted with permission from M. Schleberger, D. Fujita, and S. Tougaard, J. Electr. Spectr. 82,173 (1996), 1996, Elsevier Science.

We took EAE spectra from several materials at different excitation energies, ranging from 500 to 4 keV. All spectra were corrected for the transmission function of the analyzer. For further experimental details see Reference [113]. The EAE spectra need to be corrected for the background due to backscattered primaries and due to the secondary electron cascade [114]... 

FTIR is another surface-sensitive spectroscopic tool to analyze biomedical polymers since sample preparation is very simple for this technique. FTIR spectra should be recorded in reflection mode instead of transmission mode in order to analyze the functional groups present on polymer surfaces. ATR-FTIR has been apphed to study in vitro mineralization of porous starch scaffolds cultured in bone marrow stromal cells harvested from Wistar rats. Mineral deposition in in vitro cultures is usually followed by von Kossa stain or Alizarin red stain or by calcium uptake. These methods provide erroneous results because the scaffold matrix itself can take up some calcium from the medium. ATR-FTIR is devoid of the limitation and provides reliable information on the mineralization process. In the... 

FIGURE 5. Typical AES spectrum of an oxidized aluminum surface, (a) d A ( )/d spectrum, (b) EN(E) spectrum. The factor of E is due to the transmission function of the analyzer. The common means of measuring peak intensity, peak-to-peak height (p-p), and peak-to-background height (p-b) are indicated. 

The intensity/energy response function (lERF) of a spectrometer is the product of the area from which photoelectrons are collected, of the transmission function (T), and of the detector efficiency D). With a microfocused X-ray beam, such as in SSX 100/206 spectrometer, the area of collection is defined by the X-ray spot size and is smaller than the acceptance area of the analyzer. The relative intensity of the peaks is sensitive to the position of the sample on the vertical axis. When a broad X-ray source is used, the lERF includes also the variation of the area of collection as the latter may depend on the energy of the photoelectrons detected (cf. the section on Basic Equations). 

The analysis of model biochemical compounds [glucose derivatives, poly(amino acids), etc.] with the SSX 100/206 spectrometer at a pass energy of 50 eV has shown that two systematic errors may compensate each other. The presence of organic contamination at the sample surface reduced the apparent 0/C ratio, because the contamination overlayer contained less oxygen than most of the analyzed standards. On the other hand, the assumption of a constant transmission function exagerated (by about 10%), the computed 0/C concentration ratio. The two errors compensated each other and the apparent 0/C concentrations ratios were in excellent agreement with the values expected from stoichiometry. 

Median radius of the analyzer Radius of analyzer internal hemisphere Radius of analyzer external hemisphere Factor accounting for surface roughness Irradiated area surface area Transmission function Average transmission function Electrical potential of the analyzer internal hemisphere Electrical potential of the analyzer external hemisphere Slit width displacement of energy levels upon the formation of a doubly ionized atom... 

To fulfill Eq. 15, the transmission function of the NSE spectrometer has to be limited to a certmn wavelength range. This is mainly done by the velocity selector in the incoming beam and by the limited wavelength acceptance of the analyzer for processes causing a broadening of the wavelength distribution in the scattered beam. For more detailed information see the article by Mezei in Ref. (8). 

In the case of static SIMS, a reduced volume is examined. To offset the parallel loss in detection limits/sensitivities associated with the analysis of smaller volumes, the secondary ion transmission functions of Time-of-Flight SIMS instruments (these are best snited to Static SIMS applications) can approach 100%, with all ions simnltaneously recorded. As a result, surface detection limits for Iron on a Silicon snbstrate is in the low 10 atoms/cm range, whereas that for Boron on Silicon is in the mid 10 atoms/cm range (note the different units used). These detection limits can extend fnrther for the more electropositive/electronegative elements when analyzed under appropriate conditions. 

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