Auger sputter depth profiles

Fig. 3.29 Auger sputter depth profile of a layered Zr02/SiC>2/Si model catalyst. While the sample is continuously bombarded with argon ions which remove the outer layers of the sample, the Auger signals of Zr, O, Si and C are measured as a function of time. The depth profile is a plot of Auger peak intensities against sputter time. The profile indicates that the outer layer of the model...

Figure 10. Factor analysis applied to the Auger sputter depth profile of a WjN film deposited on W (a) usual AES depth profile (b) factor analysis of the W peak structure (c) factor analysis of the N peak structure.

Fig. 12. Auger electron spectroscopy (AES) sputter-depth profile of CAA-treated titanium after various exposure.s in vacuum (a) as anodized, (b) 450°C for 1 h, and (c) 7(X)°C for 1 h. The sputter etch rate is 1.5 nm/min. The line indicates the original interface. The arrow denotes oxygen diffused into the substrate. Adapted from Ref. [51].

The two instruments most suited to the sputter depth profiling of individual particles are the Auger and ion microprobes. The characterization of automobile exhaust particles produced in the combustion of leaded gasoline will be used to illustrate this point. 

Auger electron maps for Cr and SI Indicated that the smallest Sl/Cr ratio occurred at the pointed end of Area A. These Auger electron maps are shown In Figure 17. AES survey spectra obtained from Area B were equivalent to spectra obtained from unstressed resistors. Sputter depth profiles were obtained from both areas and they Indicated that the resistor film In Area A was only 70% as thick as the film In Area B. Sputter depth profiles obtained from an unstressed resistor were equivalent to those from Area B. The conclusion reached was that Si was diffusing away from a portion of the resistor when high currents were passed through the film. 

The composition of wet thermal oxide on SiC has been established to be close to stoichiometric Si02 from Auger electron spectroscopy sputter depth profiles and from the refractive index of the oxide determined by ellipsometry [4,12,14,19,21,24-27]. Dry oxide on 3C-SiC has been found to contain much more silicon than stoichiometric Si02 [27]. The carbon content of the SiC thermal oxide layer, away from the interface, determined by Auger spectroscopy, has been reported as at below detection limits for wet oxide on 6H-SiC [25] at below detection limits [24,26] and also at 2% for dry oxide on 3C-SiC [27] and at 14% for wet oxide on 3C-SiC [27]. The oxide on SiC grown below 1200°C is amorphous, but above 1200°C the oxide grown is increasingly crystalline [15,18,20,22-24,28]. 

One characteristic of CAA oxides is that they contain significant amounts of fluorine. Sputter depth-profiles obtained by Auger electron spectroscopy(53,5s,65) show a buildup of fluorine in the barrier layer. Although adsorbed fluorine is considered detrimental to aluminum adhesive bonds (as discussed earlier in Section 2.4),( 2) CAA titanium oxides exhibit remarkable bond durability, probably because the fluorine is incorporated into the oxide rather than adsorbed onto it. 

Baunack S, Subba Rao RV, Wolff U, Characterization of oxide layers on amorphous Mg-based alloys by Auger electron spectroscopy with sputter depth profiling . Analytical and Bioanalytical Chemistry, 2003 375 896-901. 

Table 2 shows that AES sputter depth profiles provide quantitative infonnation on elemental composition as a function of depth but are not nomially u.sed to extract chemical information. Until recently, due to the better energy resolution of the electron analyzer and to easier interpretation of spectra, chemical analysis was performed mainly by XPS. However, since the Auger transitions recorded in AES... 

AES analysis is done in one of four modes of analysis. The simplest, most direct, and most often used mode of operation of an Auger spectrometer is the point analysis mode, in which the primary electron beam is positioned on the area of interest on the sample and an Auger survey spectrum is taken. The next most often used mode of analysis is the depth profiling mode. The additional feature in this mode is that an ion beam is directed onto the same area that is being Auger analyzed. The ion beam sputters material off the surface so that the analysis measures the variation, in depth, of the composition of the new surfaces, which are being continu-... 

Roughness from sputtering causes loss of depth resolution in depth profiling for Auger Electron Spectroscopy (AES), X-Ray Photoelectron Spectroscopy (XPS), and SIMS. 

A variation on depth profiling that can be performed by modern scanning Auger instruments (see Sect. 2.2.6) is to program the incident electron beam to jump from one pre-selected position on a surface to each of many others in turn, with multiplexing at each position. This is called multiple point analysis. Sets of elemental maps acquired after each sputtering step or each period of continuous sputtering can be related to each other in a computer frame-store system to derive a three-dimensional analysis of a selected micro volume. 

Figure 6.10 Depth profile of Auger Electron Spectroscopy (AES) sputtering of marmatite surface in the presence of cupric ion and ethyl xanthate...

A new method of interpreting Auger electron spectroscopy (AES) sputter profiles of transition metal carbides and nitrides is proposed. It is shown that the chemical information hidden in the shape of the peaks, and usually neglected in depth profiles, can be successfully extracted by factor analysis (FA). The various carbide and nitride phases of model samples were separated by application of FA to the spectra recorded during AES depth profiles. The different chemical states of carbon, nitrogen and metal were clearly identified. 

Figure 26.3 Factor analysis of the W2N/W sample, (a) Usual AES depth profile the insert shows the shape of the derivative C KLL Auger peak at the film-substrate interface, (b) FA of the tungsten signal left, the pure components spectra right, the concentrations profile the sputtering time per cycle was 30 s.

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