Depth profiles interpreting

Though a powerfiil technique, Neutron Reflectivity has a number of drawbacks. Two are experimental the necessity to go to a neutron source and, because of the extreme grazing angles, a requirement that the sample be optically flat over at least a 5-cm diameter. Two drawbacks are concerned with data interpretation the reflec-tivity-versus-angle data does not directly give a a depth profile this must be obtained by calculation for an assumed model where layer thickness and interface width are parameters (cf., XRF and VASE determination of film thicknesses. Chapters 6 and 7). The second problem is that roughness at an interface produces the same effect on specular reflection as true interdiffiision. 

If the spectra of the k relevant components are known, the abstract matrices can be transformed into interpretable spectra and concentration matrices, respectively, and as a final result, one obtains the required component depth profile. If one or more of the spectra of the k relevant components are not known, a quantified component depth profile cannot be constructed. 

Chemical effects are quite commonly observed in Auger spectra, but are difficult to interpret compared with those in XPS, because additional core levels are involved in the Auger process. Some examples of the changes to be seen in the KLL spectrum of carbon in different chemical environments are given in Fig. 2.24 [2.130]. Such spectra are typical components of data matrices (see Sect. 2.1.4.2) derived from AES depth profiles (see below). 

In summary, such simple classification schemes for drug-likeness can, in a very fast and robust manner, help to enrich compound selections with drug-like molecules. These filters are very general and cannot be interpreted any further. Thus, they are seen rather as a complement to the more in-depth profiling of leads and drugs by using molecular properties and identifying trends in compound series. 

Depth Profiling. The quantitative interpretation of AES data requires a knowledge of the distribution of the grain boundary segregants both laterally on the... 

Figure 16. Depth profiles from three ODP Sites, showing Li isotopic composition variations in pore waters (open symbols) and associated sediments (filled symbols), (a) Site 918, Irminger Basin, north Atlantic (Zhang et al. 1998) (b) Site 1038, Escanaba Trough, northeastern Pacific (James et al. 1999) (c) site 1039, Middle American Trench off of Costa Rica (Chan and Kastner 2000). The average composition of seawater is noted on each profile with dashed line (note different scales). Whereas sediments have relatively monotonous compositions, pore waters have compositions reflecting different origins and processes in each site. Interpretations of the data are summarized in the text under, Marine pore fluid-mineral processes. ...

Interpretation of Analytical Results—Tritium. The locations of transects in the Sedan ejecta field at which samples were collected are shown in Figure 1. The distribution of tritium with depth at five sites on Sedan crater lip is shown on Figure 2. Except for the 9A area, the various sectors of the crater lip have very similar tritium depth profiles. The 9A area is a unique sector of the crater lip. A large mass of earth lifted by the detonation fell back to the crater in the 9A area earlier than the rest of the crater ejecta. Part of this material slumped into the crater, and the rest remained on the crater lip forming a prominence on the crater profile. Missile ejecta is thinner on this high point, and open-field radiation levels are lower. Tritium concentrations in the ejecta or slumped material at 9A are lower than in the rest of the crater lip mass. 

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. 

Ultrahigh sensitivity in qualitative elemental and molecular compound analysis, isotope analysis, rapid depth profiling of composition, but no chemical information. Spectra interpretation and quantitation difficult. 

SIMS has become one of the most important tools for the characterization of experimental products because of its minimal sample requirements, high spatial resolution, excellent sensitivity, and unsurpassed ability for depth-profile measurements. Most of the experimental work can be split into two different areas. The first consists of studies examining diffusion rates of different elements in minerals or melts under a variety of pressure, temperature, and fluid conditions, typically by using an isotopically enriched tracer. These analyses are done either by cutting a surface parallel to the diffusion direction and taking a traverse of spot analyses (for conditions in which profiles in the tens to hundreds of micrometers are expected) or by depth-profiling in from the mineral surface to depths of as much as 5-10 micrometers. In the latter mode, depth resolution on the tens of nanometer scale is possible (see Chapter 4). The second area is focused on determining partition coefficients for trace elements between different minerals and fluids/melts at specific temperatures, pressures, and fluid conditions, to provide the data needed to interpret trace element contents measured in natural minerals. This type of analysis typically involves spot analysis of mineral run products. 

Samples can be collected from a depth profile by carefully lowering a cylindrical sampling bottle (commercially available). It should be gradually lowered to deeper sections so that each bottle collects undisturbed water. The depths of perforated sections, and other details of the well construction, must be known for proper interpretation of the data obtained in each profile. 

The interpretation of pore-water concentration versus depth profiles of O2 and NO in oxic sediments is based on a one-dimensional, steady-state model in which the production or consumption of a solute in a sedimentary layer is balanced by transport into or out of the layer by solute diffusion and burial advection. In mathematical form. 

Rae, J.E. Allen, J.R.L. (1993) The significance of organic matter degradation in the interpretation of historical pollution trends in depth profiles of estuarine sediment. Estuaries 16, 678-82. 

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