Atomic composition depth profile

AES Auger electron spectroscopy After the ejection of an electron by absorption of a photon, an atom stays behind as an unstable Ion, which relaxes by filling the hole with an electron from a higher shell. The energy released by this transition Is taken up by another electron, the Auger electron, which leaves the sample with an element-specific kinetic energy. Surface composition, depth profiles... 

The data chain of the collected atoms can be converted to a one-dimensional composition-depth profile. The depth profile shows an average concentration of solute within the aperture, and there is always a possibility that the chemical information from the selected area is a convolution of more than one phase, as indicated diagrammatically in Figure 1.5, which represents the analysis of a FIM specimen containing second phase particles and also an interface across which there is a change of composition. 

Some interesting features can be noticed in these lateral concentration profiles and composition depth profiles. For the Ni-5% Cu alloy, the first few ions detected are Cu ions, even though the composition within the top layer is rather uniform. This can be due to an edge effect, in other words the edges of the (111) layers are much more enriched with Cu atoms than inside the top (111) layer. This can also be simply produced by a preferential field evaporation of Cu atoms from the layer edges. While... 

Table 4.8 ToF atom-probe composition depth profiles in alloy segregation... 

RBS provides a measure of composition-depth profile for elements. It uses a beam of high voltage helium ions to interact with the sample. The sample atoms recoil in a semi-classical collision, such that those ions reflected lose an amount of energy characteristic of the target atom and the amount of material traversed by the reflected ion. However, this method is not good for light elements such as H and He. 

Figure 6a displays a typical composite atomic percent depth profile plot of all the observed elements from a - 1500A thick layer of nearly... 

Equation (22) is particularly useful when a concentration gradient in depth exists. In this case, several spectra at different values of 9 are taken and the analysis is called angle resolved X-ray photoelectron spectroscopy. However, for a maximum efficiency, a flat surface (at an atomic level) is needed to avoid shade effects as shown by Fadley in his early works in the 1970s [44]. An additional problem exists the extraction of concentration profiles, cg(x), from Eq. (22) is an inverse problem the intensity as a function of the analysis angle is the Laplace transform of the composition depth profile of the sample [43] and does not have a unique solution. Several algorithms to solve the inversion problem were developed and tested [46]. They are all very unstable and sensitive to small statistical... 

Tsong TT, Ren DM, Ahmad M (1988) Atomic-layer by atomic-layer compositional depth profiling surface segregation and impurity cosegregation of Pt-Rh and Pt-Ru alloys. Phys Rev B 38(ll) 7428-7435... 

SIMS Secondary Ion mass spectroscopy A beam of low-energy Ions Impinges on a surface, penetrates the sample and loses energy In a series of Inelastic collisions with the target atoms leading to emission of secondary Ions. Surface composition, reaction mechanism, depth profiles... 

Figure 2 Typical ISS apectral data obtained from routine depth profile of cleaned washed steel. Left spectrum represents surface. Right spectrum represents about 50-A depth. Expansiona ahown top left. Relative atomic compositions plotted top right.

Dynamic SIMS, used for obtaining compositional information as a function of depth below the surface. With higher etch rates, the surface is eroded much more quickly than in static SIMS, and depth profiling can be achieved since each successive layer of atoms can be analysed as it is peeled away . 

Figure 5.10. Depth profiles of atomic composition in two-step baked polysilane films prepared under various conditions. [Reproduced with permission from Ref. 24. Copyright 2007 Society for Information Display.]...

The elemental composition, oxidation state, and coordination environment of species on surfaces can be determined by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) techniques. Both techniques have a penetration depth of 5-20 atomic layers. Especially XPS is commonly used in characterization of electrocatalysts. One common example is the identification and quantification of surface functional groups such as nitrogen species found on carbon-based catalysts.26-29 Secondary Ion Mass spectrometry (SIMS) and Ion Scattering Spectroscopy are alternatives which are more surface sensitive. They can provide information about the surface composition as well as the chemical bonding information from molecular clusters and have been used in characterization of cathode electrodes.30,31 They can also be used for depth profiling purposes. The quantification of the information, however, is rather difficult.32... 

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