Elemental concentration profiles

Great progress has been made, however, in our later study using in situ SXS [Stamenkovic et ak, 2007a], where, by simultaneously fitting the intensity ratio between two different sets of crystal truncation rod (CTR) data that constrain the fit to the full CTR data [Robinson, 1986 Warren, 1990], it was possible to reveal the elemental concentration profile at the surface (Fig. 8.13c). Based on the in situ SXS results depicted in Fig. 8.13a, the topmost surface layer is confirmed to be 100 at%... 

Figure 5.66 Elemental concentration profiles in a thermometric couple. (A) Ideal case elemental concentration is constant from interface to nucleus of crystal. (B) Nonideal case slow diffusivity generates concentration gradients from interface to nucleus of crystal.

Isotopic ratio profiles versus elemental concentration profiles... 

Even in the absence of uphill diffusion, a trace element concentration profile often does not match that for a constant diffusivity by using the effective binary diffusion treatment. Hence, the effective binary diffusivity depends on the chemical composition, which is expected. 

In the trivial case of Kj=l, the trace element concentration profile is uniform (the same as the initial concentration). 

In contrast to SIMS, in SNMS - where the evaporation and ionization processes are decoupled -the matrix effects are significantly lower, because the composition of sputtered and post-ionized neutrals corresponds more closely to the composition in the solid sample (compared to the sputtered secondary ions in SIMS), which means the RSCs of elements vary by about one order of magnitude. Consequently, a semi-quantitative analysis by SNMS can also be carried out if no suitable matrix matched CRM is available. This is relevant for thin film analysis, especially for the determination of elemental concentration profiles in depth, for studying the stoichiometric composition of thin films and interdiffusion effects. 

Warner, R. R., Myers, M. C. and Taylor, D. A. (1988). Electron probe analysis of human skin Element concentration profiles. J. Invest. Dermatol. 90 78. 

Figure 7. Element concentration profiles in sample treated at 1500 C...

Millard and Hedges (1999) produced a mathematical model based on the rate of diffusion of uranyl ions through water saturated bone and adsorption coefficients between uranyl and bone. This model was designed to calculate the amount of time taken to develop an observed elemental concentration profile within a single bone, and can be used to estimate the amount of time needed for a particular bone to reach equilibrium. In the case of fossil bones, where equilibrium is clearly not reached despite millions of years of potential exchange, such a model predicts the amount of time that the bone remained as an open system, able to incorporate trace elements via diffusion. Further incorporation of metals is halted by the closure of bone porosity, presumably after growth of authigenic apatite. 

The relationships between particle flux, trace element flux and trace element concentration in sediment are more complicated in deep lakes. In a deep lake, there may be a significant proportion of dissolved element held in the water column. If the water column dissolved element inventory approaches the magnitude of the annual flux for that element, then a steady state model is invalid. Instead, the dynamic model outlined in Figure 7 must be used to allow for the time delay in the response of the sediment to changes in trace element supply rate. The disadvantage of this, compared with the steady state sitnation, is that an observed trace element concentration profile does not lead back to a nniqne trace element supply history. However, a trace element snpply history does lead to a definite trace element concentration profile, so it is possible to see if any particular supply history is compatible with the observed concentration data. A practical example of this from Lake Baikal is shown in Boyle et al. (1998), where the exceptional water depth makes this effect particularly strong. 

The insensitivity of the sediment record of deep lakes to changes in trace element supply, does not mean that the trace element concentration profile in the sediment cannot show sharp changes. A change in the particle deposition rate will cause an instantaneous change in sediment composition through dilution. However, for deep lakes, particularly for low Kd values, this dilution effect is reduced by the high water column trace element inventory (Fig, 8b). This means that in deep lakes it is important not to infer external trace element supply simply using sediment trace element accumulation rates. 

If palaeolimnological methods are to be reliably applied to element concentration profiles, then two, often unstated, assumptions must hold true. 

There are problems for palaeolimnological interpretation of element concentration profiles if diffusion from the water column to the sediment is greater than sedimentation and if elements migrate within the sediment after burial. Diffusion between the water column and the sediment is potentially a huge problem. Diffusive loss or gain to the upper surface of the sediment would matter little, as the effect would be similar to sedimentation. If,... 

Elemental concentration profiles Graphical presentation depicting variations in elemental concentration along a given line of the sample. 

Controlling the thickness of the P, N, and depletion layers, as well as the dopant element concentration profile through the depletion layer, the photosensitivity (S) and the quantum efficiency (QE) are controlled. The photosensitivity represents the... 

Fig. 10 Panel a-c Distribution of TMs (Mn, Co, and Ni, respectively) over a single selected slice (one voxel thickness) through the 3D volume of the Ix-cyled electrode. Panel d Overlay of all TMs over the same slice. Panel e Elemental concentration profile over the line (5 pm in length) indicated in panel d. Reprinted with permission from reference [60]. Copyright 2014 American...

Fig. 7. (a) Impurity elements are rejected into the Hquid between the dendritic solidification fronts, (b) Corresponding impurity concentration profiles. Cq, weld metal composition k, impurity partitioning coefficient in the Hquid maximum impurity soHd solubiHty eutectic composition at grain... 

Interdiffusion of bilayered thin films also can be measured with XRD. The diffraction pattern initially consists of two peaks from the pure layers and after annealing, the diffracted intensity between these peaks grows because of interdiffusion of the layers. An analysis of this intensity yields the concentration profile, which enables a calculation of diffusion coefficients, and diffusion coefficients cm /s are readily measured. With the use of multilayered specimens, extremely small diffusion coefficients (-10 cm /s) can be measured with XRD. Alternative methods of measuring concentration profiles and diffusion coefficients include depth profiling (which suffers from artifacts), RBS (which can not resolve adjacent elements in the periodic table), and radiotracer methods (which are difficult). For XRD (except for multilayered specimens), there must be a unique relationship between composition and the d-spacings in the initial films and any solid solutions or compounds that form this permits calculation of the compo-... 

The detected yield is a function of the concentration of the element being profiled, the resonance cross section, the detector efficiency, and dE/dx. To be specific. 

Because of the complex nature of the discharge conditions, GD-OES is a comparative analytical method and standard reference materials must be used to establish a unique relationship between the measured line intensities and the elemental concentration. In quantitative bulk analysis, which has been developed to very high standards, calibration is performed with a set of calibration samples of composition similar to the unknown samples. Normally, a major element is used as reference and the internal standard method is applied. This approach is not generally applicable in depth-profile analysis, because the different layers encountered in a depth profile of ten comprise widely different types of material which means that a common reference element is not available. 

TOF-SIMS can be applied to identify a variety of molecular fragments, originating from various molecular surface contaminations. It also can be used to determine metal trace concentrations at the surface. The use of an additional high current sputter ion source allows the fast erosion of the sample. By continuously probing the surface composition at the actual crater bottom by the analytical primary ion beam, multi element depth profiles in well defined surface areas can be determined. TOF-SIMS has become an indispensable analytical technique in modem microelectronics, in particular for elemental and molecular surface mapping and for multielement shallow depth profiling. 

An extrapolation of the concentration profile over the last half of element N is used to calculate the outlet concentration Cout> giving... 

Since the nuclear and electronic scattering cross sections for alpha particles are well known, the relative concentrations of the elements and their depth profiles can be easily obtained. The relative element concentrations are determined by the relative scattering intensities. The depth profile is obtained from the energy spread of the scattered particles, which lose energy before and after the nuclear collision, by inelastic scattering with electrons. The knowledge of the elements areal density and of the film thickness allows the determination of film density. 

Applications Table 8.58 shows the main fields of application of inorganic mass spectrometry. Mass-spectrometric techniques find wide application in inorganic analysis, and are being used for the determination of elemental concentrations and of isotopic abundances for speciation and surface characterisation for imaging and depth profiling. Solid-state mass spectrometry is usable as a quantitative method only after calibration by standard samples. 

Under conditions of p-PIXE, the beam can be scanned across the surface of the specimen and thus provide concentration data as a function of position. Since spectra have to be accumulated at many points on the specimen with this technique, the analysis duration may be hours rather than minutes. Concentration values at different points or concentration profiles for selected elements can be determined by... 

CPAA may be employed to determine trace element concentrations in bulk solid material, but its importance in our present context is that it permits the characterization of a thin surface layer, i.e. the mass of the analyte element per surface unit, with a good detection limit and outstanding accuracy. For example the composition of a surface layer (or foil) of known thickness can be determined, or, conversely, the thickness of a surface layer of known concentration. Depth profiling or scanning is not possible, and a disadvantage of the method is that heating occurs during irradiation. It is also not possible to discriminate between different oxidation states of the analyte element or between different compounds. 

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