Depth profiling cluster

New developments which have still to be checked for their usability in data evaluation of depth profiles are artificial neural networks [2.16, 2.21-2.25], fuzzy clustering [2.26, 2.27] and genetic algorithms [2.28]. 

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... 

PHI TRIFT IV ToF-SIMS (Physical Electronics, USA) employs three electrostatic analyzers in the ion path to filter the background and metastable secondary ions. Using liquid metal cluster ion guns (such as Aut ion beam for sputtering of sample surface) increased sensitivity compared to a Ga+ primary ion beam are obtained (www.phi.com). The application of dual primary ion guns is useful for an effective dual beam depth profiling on multi-layered samples. 

The profiles of the unleached glass surface showed essentially no change in intensity of the sodium and potassium ions as a function of depth. However, Si and B ion intensities were found to be consistently lower at the outer surface than within the bulk of the glass. Depth profiles for both ions have a similar shape. This effect is believed to result from surface hydration which alters the yield of ions from the borosilicate network. Unhydrated glass surfaces, introduced into the spectrometer immediately fter fracturing, showed little or no depression of either Si or B signals, and hydrate clusters, such as Si(0H)+ were much reduced in intensity. 

Figure 5.8c shows a confocal depth profile of the same urothelial cell, taken along the red dashed line in Figure 5.8b. This profile indicates that the cell is much thicker (ca. 8 pm) than a squamous cell, which explains its much higher IR absorbance. The Raman mean cluster spectra observed for the different regions are...

Figure 19. Distribution of H- He ages across a sewage plume (shaded) for an unconfined aquifer in Cape Cod, Massachusetts. Depth profiles in piezometer clusters along the plume are shown. The inset shows the increase of H- He ages along a single flowline through the core of the plume where sewage (boron, detergents) concentrations have maximum values (adapted from Dunkle Shapiro et al. 1999).

For completeness, it should be noted that other cluster ion beams, including C24H12+ and Cgo [370], giant glycerol [371], Ir4(CO)7+ [372], Au4oo [373], and Aruoo [374] also have potential for molecular depth profiling and some of them have already proved their ability in... 

Angle of Incidence Controlling the depth at which the cluster energy is deposited is paramount for successful depth profiling. One way to achieve that... 

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