SIMS Profile of AlAs Monolayer in GaAs

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Fig. 11 Secondary ion mass spectroscopy depth profile of an AlAs monolayer doping in GaAs. Comparison between measured points (circles) (Ref 49) and calculations (solid line). Source: Ref 50

The result of chemical reactions at the gas-solid or liquid-solid interface often are specific layer structures, and further reaction behavior depends on their chemical composition. Passive layers on stainless steels (Ref 51) and oxide layers on different alloys and nitride coatings (Ref 52) have frequently been studied. An example of the composition of a passive layer on an Fe-Cr alloy is shown in Fig. 12. Figure 12(a) shows the AES depth profile obtained by using factor analysis and least-squares fitting of the four different standard spectra of metallic and oxidized iron and chromium (Ref 53). Figure 12(b) gives the result of a "convolution" procedure employed in order to calculate the original depth distribution (Fig. 12b) from the measured profile (Fig. 12a). Profile broadening schemes are used to account for the effects of sputtering and information depth influences on the assumed profile in Fig. 12(b) until an optimal fit with the profile in Fig. 12(a) is obtained (Ref 34, 39).

Fig. 12 Depth profile of the chemical composition of a passive layer on an Fe-18at.%Cr alloy. (a) Normalized fractions of the standard components Crmet, Crox, Femet, and Feox in the Auger spectra as a function of the

sputtering time. (b) Concentrations of the alloy elements in metallic and oxidic states after fitting all fractions of the respective components with a sequential-layer sputtering model. Source: Ref 53

High-resolution AES (i.e., scanning Auger microscopy) is another way to obtain the in-depth composition at interfaces by line scanning the focused electron beam (of < 1 pm diameter) across the rim of the crater generated by sputter profiling (Ref 39, 54). An example of such a "crater edge profile" is shown in Fig. 13 for a TiN coating on a high-speed steel interface characterized by the iron Auger intensity (Ref 55). It is clearly seen, by comparison of the traces of the oxygen signal and the titanium signal, that oxygen varies with titanium and not with iron. This means that only titanium oxide, no iron oxide, is contained in the interface.

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