Depth profiling modelling

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. 

The depth profiles in Fig. 3.26 show that the typical flat channeling implantation profile is generated with low doses only. Increasing the dose superimposes the normal implantation profile shape. Undertaking such experiments with homogeneous wafers enables the production of calibrating models for semiconductor production. 

The Auger depth profile obtained from a plasma polymerized acetylene film that was reacted with the same model rubber compound referred to earlier for 65 min is shown in Fig. 39 [45]. The sulfur profile is especially interesting, demonstrating a peak very near the surface, another peak just below the surface, and a third peak near the interface between the primer film and the substrate. Interestingly, the peak at the surface seems to be related to a peak in the zinc concentration while the peak just below the surface seems to be related to a peak in the cobalt concentration. These observations probably indicate the formation of zinc and cobalt complexes that are responsible for the insertion of polysulfidic pendant groups into the model rubber compound and the plasma polymer. Since zinc is located on the surface while cobalt is somewhat below the surface, it is likely that the cobalt complexes were formed first and zinc complexes were mostly formed in the later stages of the reaction, after the cobalt had been consumed. 

The electron interaction between nanosized gold particles and iron oxide support is only one factor which determines the properties of the gold/oxide system. For instance, in the Au/FeO,c/Si02/Si(l 0 0) model sample the depth profile (after successive Ar ion bombardment at a... 

Solution of equation (10) which involves sedimentation in the presence of mixing and that of equation (11) which contains the sedimentation term only, are exponential in nature. The major conclusion which arises from this is that the logarithmic nature of the activity-depth profiles by itself is not a guarantee for undisturbed particle by particle sediment accumulation, as has often been assumed. The effects of mixing and sedimentation on the radionuclide distribution in the sediment column have to be resolved to obtain pertinent information on the sediment accumulation rates. (It is pertinent to mention here that recently Guinasso and Schink [65] have developed a detailed mathematical model to calculate the depth profiles of a non-radioactive transient tracer pulse deposited on the sediment surface. Their model is yet to be applied in detail for radionuclides. )... 

Simple steady-state models can only predict mean concentrations. Seasonal variations and concentration depth profiles in the water column of lakes give further insight into the mechanisms governing the removal of metal ions. Data on depth concentration profiles of trace metals in lakes are however still scarce (Sigg, 1985 Sigg et al., 1983 Murray, 1987). In a similar way as in the oceans, it might be expected to observe in lakes different types of profiles for different elements, depending on the predominant removal mechanism (Murray, 1987 Whitfield and Turner, 1987). 

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 ... 

Most models of the permeation of drugs through skin consider only steady-state conditions the drug amount in the donor is infinite and the concentration of accumulated drug in the acceptor is comparatively small and therefore negligible. Under these conditions the concentration-depth profile for a homogeneous membrane at time t is given by... 

Depth profiles of (a) salinity (%o), (b) dissolved oxygen (ml /L), and (c) percent saturation of dissolved oxygen in the Southeastern Atlantic Ocean (9°30 W 11°20 S). Samples were collected in March 1994. Dotted lines represent the curves generated by the one-dimensional advection-diffusion model (see text for details). The values of Dz, Vz, and J are the ones that best fit the data. Data are from Java Ocean Atlas (http /odf.ucsd.edu/joa). Values of percent saturation of oxygen less than 100 reflect the effects of aerobic respiration. Values greater than 100 indicate a net input, such as from photosynthesis. (See companion website for color version.)... 

Photoacoustic imaging method is useful for the analysis of localization of various components in two-dimension and photoacoustic method has one more advantage that it can be applied to the non-destructive depth-profiling. Thus, in future, 3-dimensional analysis should be possible by this method. For the development of this possibility, the model experiments were performed. 

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 5. Depth profiles of soil temperature for a site at 4100 m in southern Tibet (see text) calculated using MAT from nearby Lhasa (3660 m) of 8°C and a local air-T lapse rate of 6 °C/km, a) showing modeled seasonal fluctuations in soil temperature at various depths, and (b) seasonal deviations from predicted 818Osc values at MAT.

This paper discusses SIMS as a multi-dimensional technique for the analysis of inorganic and organic materials. The paper is divided into two parts inorganic and organic (or molecular) SIMS. The inorganic SIMS part focuses on the methods of quantitative analysis and depth profiling applications. In particular, SIMS matrix effects are defined and the physical models and empirical methods used to quantify SIMS results are reviewed. 

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