Depth profiling line shape

As an example of the use of AES to obtain chemical, as well as elemental, information, the depth profiling of a nitrided silicon dioxide layer on a silicon substrate is shown in Figure 6. Using the linearized secondary electron cascade background subtraction technique and peak fitting of chemical line shape standards, the chemistry in the depth profile of the nitrided silicon dioxide layer was determined and is shown in Figure 6. This profile includes information on the percentage of the Si atoms that are bound in each of the chemistries present as a function of the depth in the film. 

Therefore, the fractional column density (and the total column density N according to Eq. (20)) can only be obtained from the optical depth if Tex is known. If a gaussian line shape is assumed, integration of the observed line profile yields... 

It is not to be expected that the straight-line Equation 21 would apply to the thermocline layers of other lakes. Both N and K were calculated from temperature profiles the shape of which depends in a complex manner on the climate of the area, thermal regime, depth, and volume of the lake. It seems, however, that by arguments presented earlier in this section, an inverse relationship between the stability frequency and eddy diffusion coefficient would, in general, hold in the pycnocline layers of lakes. If such a relationship is established, it would be possible to obtain estimates of K from the values of the stability frequency N, which are much easier to compute. 

FIGURE 10. Sputter depth profile of an oxidized aluminum sample, (a) Peak-to-peak heights of the O and Al KLL transitions (Figure 9) as a function of sputter time, (b) Composition as determined by Eq. (5) using the peak-to-peak heights of (a), (c) Composition as determined by Eq. (5) but fitting the spectra to sums of the aluminum oxide and metal line shapes. Note the apparent decrease in the Al concentration and the increase in the O concentration at the interface of (b). 

Second, progress has been made in the theoretical approach to the analysis of DCEMS measurements. The underlying theory of resonance excitation (-> excitation matrix) in the sample by y-quanta including secondary absorption and emission processes, electron transport (- transport tensor), and detection response (—> response function) have been included in a least-squares fit routine [ 103. 105). Adjustable parameters in this fitting are. on the one hand, the hyperfine interaction and line shape variables, and, on the other hand, the variables that give a parametric representation of the depth profiles. The response parameters are also included to allow energy calibration of the experimental apparatus. 

From the results so far it can be concluded that the thickness of the damage layer produced by 2 keV Ar+ is measurable more or less accurately according to the surface specificity of the operational conditions. In addition, it has been found there were no significant changes in the line shapes of any of the spectra following 2 keV Ar bombardment, when recorded at < > = 90 . It therefore seems correct to combine XPS (and XAES) analysis at normal emission with 2 keV Ar+ in order to depth-profile an Si02/Si sample. 

Thus the shape of the line profile directly reflects the density distribution of the ejecta. It is, however, important to check whether the lines are really optically thin, since even the forbidden can have depths of the order of unity or larger. For [O I] X 6300 we have 1=2 (n(0 I)/109 cm-3) tyr 1.1 Mc (Vc/ 103 km/s)- 3 tyr 2-... 

For optical depth t 1 the observed interstellar molecular lines usually have a gaussian shape. This is to be expected, since collisional broadening, which causes the Lorentzian line profile, should be negligible and become important only at gas densities 1012 — 1014 cm- 3. If thermal motions of the molecules were the only source of line broadening the line half power width (i.e. the width between half power points) would be given by... 

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