XPS Depth Profiling

The normal application of XPS will give information on the atomic composition over the entire sampling depth. It is useful to be able to explore whether surface segregation may be occurring and for this to be achieved it is appropriate to use the escape depth as a tool for the analysis of different depths. 

Different X-ray energies. As indicated in Table 9.5, the escape depth is a function of the photoelectron energy. This is illustrated by a study of surface 

XPS sampling depths as a function of core kinetic energy and take off angle. 

Sputtering. For analysis of thicker films destructive methods have to be used. For inorganic materials bombarding the surface with a heavy ion, such as argon, allows the slow removal of the surface and exposure of sublayers. In the case of organic and other covalently bonded materials this approach is not very helpful since the species that are created may not be representative of the original material. 

---

The diffusion coefficients for Rb, Cs and Sr in obsidian can be calculated from the aqueous rate data in Table 1 as well as from the XPS depth profiles. A simple single-component diffusion model (9j characterizes onedimensional transport into a semi-infinite solid where the diffusion coefficient (cm2-s 1) is defined by ... 

Figure 6. Comparison of XPS depth profiles for Cs in obsidian at various temperatures (broken lines) with predicted penetration depths based on profiles calculated by Equation 4 (solid lines).

Elemental analyses found such films to be Zn rich (with respect to Se) [139,142], The films were oxygen rich, and it is probable that, as was often found with ZnS, the films are a mixture of ZnSe and Zn(OH)2, together with a little ZnO in some cases [140], An XPS depth profile study found the surface of the films to be more stoichiometric (although still Zn rich) than near the substrate [143],... 

There are several methods available to probe the actual interphase to demonstrate the existence of interpenetrating networks directly. Among these techniques are depth profiling by SIMS (secondary ion mass spectrometry) or SNMS (sputtered neutral mass spectrometry), and the use of X-ray photoelectron spectroscopy (XPS) depth profiling or Auger electron spectroscopy (AES) depth profiling. 

Fig. 12.60. 3D-XPS depth profile of passive film formed on Al for pH 8.4, at V= 0.4 V for 1 hr distribution of two different O species (as indicated) before the breakdown occurred. (Reprinted from J. O M. Bockris and L. Minevski, J. Electroanal. Chem. 349 388, copyright 1993, with permission from Elsevier Science.)...

Figure 4.10 C/Si ratios of plasma polymer films of TMS prepared in a flow system reactor (Tfs) and in a closed system reactor (Tcs), as generated by XPS depth profiling.

Figure 31.1 Cu 2p 3/2 photoelectron spectra from XPS depth profile runs on [2A] surfaces, a) native surface, b) alkaline cleaned surfaces, and c) alkaline cleaned and deoxidized surface the arrow shows the direction of sputtering time into the alloy.

Figure 31.6 XPS depth-profile summary graphs of (a) Cu 2p and (b) O Is peak area as a function of sputtering time.

Figure 33.8 XPS depth profile of plasma polymer of TMS deposited on (a) (Ar-hH2) plasma treated pure iron, (b) O2 plasma treated pure iron.

Figure 7.23 XPS Depth profile of a titanium surface coated with calcium phosphate which contains Ca, P, and O. C in the profile is from surface contamination.

Nevertheless few results have been obtained concerning their epitaxial growth. Electrodeposition of epitaxial CdSe quantum dots on gold single crystals has been reported [218, 219]. In the same way epitaxial layers of CdTe [220] and CdSe [221] have been electrodeposited on (111) InP. Using cyclic voltammetry K. Rajeshwar [222] has electrosynthesized CdSe/ZnSe superlattices (non epitaxial). XPS depth profiles have clearly demonstrated the modulation in the Cd and Zn content. 

The reaction thickness was found to be about 50 nm by XPS depth profiling analyses. A potential window of 3 V could be achieved for Mn oxide electrode in the [BMP][DCA] IL. Similar results were found for the [EMIM][DCA] IL electrolyte, and the penetration depth of [DCA] into Mn oxide was found to be about three times deeper than that of [BFJ . This contributed to a much higher specific capacitance of the Mn oxide electrode in [EMIM][DCA] (72 F g- ) compared with that obtained in... 

Cumpson, P.J., 1999. Angle-resolved XPS depth-profiling strategies. Appl. Surf. Sci. 144—145, 16-20. 

The resistance of Pdg3Ag2Aui5 and Pd74Agi4Aui2 to bulk sulfide formation was more recently reported by Braun [21]. After exposure to 1000 ppm H2S/H2 for 30 h, neither ternary developed a bulk sulfide surface S (confined to 40 run) was detected only by XPS depth profile. At 400 °C, both alloys exhibited clean-H2 permeability similar to that of pure Pd. Upon exposure to 100 ppm H2S at 400 °C, both lost 70% of their pure H2 permeability, but recovered most of that when the H2S was removed [55]. Recovery is consistent with the absence of a bulk sulfide scale. Performance in H2S was in the range that might be expected for PdAu with Au from 4% to 26%. 

Figure 3.11 XPS depth profile for the 500° C annealed sample. The in-depth distributions of oxygen, silicon, aluminium and erbium are reported.

---