Atomic concentration

For a detailed discussion on the analytical teclmiques exploiting the amplitude contrast of melastic images in ESI and image-EELS, see chapter B1.6 of this encyclopedia. One more recent but also very important aspect is the quantitative measurement of atomic concentrations in the sample. The work of Somlyo and colleagues [56]. Leapman and coworkers and Door and Gangler [59] introduce techniques to convert measured... 

Triphenylphosphine oxide [791-28-6], C gH OP, and triphenyl phosphate [115-86-6], C gH O P, as model phosphoms flame retardants were shown by mass spectroscopy to break down in a flame to give small molecular species such as PO, HPO2, and P2 (33—35). The rate-controlling hydrogen atom concentration in the flame was shown spectroscopically to be reduced when these phosphoms species were present, indicating the existence of a vapor-phase mechanism. 

To obtain the peak atomic concentration resulting from this peak number of implanted ions requires knowing N, the atomic density of the substrate. The general relation for the concentration of the implanted species at the peak of the distribution is given by equation 13 ... 

Mineral and Chemical Composition. X-ray diffraction is used to determine the mineral composition of an Mg(OH)2 sample. Induced coupled plasma (icp) spectrophotometry is used to measure the atomic concentrations present in a sample. X-ray fluorescence analysis is another comparative instmmental method of determining chemical composition. 

The mechanism of the synthesis reaction remains unclear. Both a molecular mechanism and an atomic mechanism have been proposed. Strong support has been gathered for the atomic mechanism through measurements of adsorbed nitrogen atom concentrations on the surface of model working catalysts where dissociative N2 chemisorption is the rate-determining step (17). The likely mechanism, where (ad) indicates surface-adsorbed species, is as follows ... 

Trace elements added to copper exert a significant influence on electrical conductivity. Effects on conductivity vary because of inherent differences ia effective atomic size and valency. The decrease ia conductivity produced by those elements appearing commonly ia copper, at a fixed atomic concentration, rank as follows Zn (least detrimental), Ag, Mg, Al, Ni, Si, Sn, P, Fe (most). Table 12 summarizes these effects. In the absence of chemical or physical interactions, the increase in electrical resistivity is linear with amounts of each element, and the effect of multiatom additions is additive. 

An alternative, but to some extent complementaty approach to the structure of grain boundaries notes that as the tilt angle between the crystals forming the grain boundary increases, planes of lower atomic concentrations, the high index planes, such as (221), (331) and (115) in the face-centred strucmre, become parallel to the grain boundary. There is therefore a decrease in the number of metal-metal bonds at the boundary as the tilt angle increases. 

The approximate calculation of the surface energies of metals as a function of crystal structure described earlier uses the enthalpy of sublimation, s, and the co-ordination number to calculate the energy as a function of the atomic concentration on the surface. The atomic areas of the principal configurations are as follows ... 

As in RBS analysis, ERS can provide information on the atomic concentration of hydrogen as a function of depth (measured in atoms/cm ). This is derived from the height Aobs°f ERS spectrum (counts per channel), at energies corresponding to particular depths within the sample (see Figure 3c). For a sample consisting of H and another material X, with composition the spectrum height... 

Several features of ISS quantitative analysis should be noted. First of all, the relative sensitivities for the elements increase monotonically with mass. Essentially none of the other surface spectroscopies exhibit this simplicity. Because of this simple relationship, it is possible to mathematically manipulate the entire ISS spectrum such that the signal intensity is a direct quantitative representation of the surface. This is illustrated in Figure 5, which shows a depth profile of clean electrical connector pins. Atomic concentration can be read roughly as atomic percent direcdy from the approximate scale at the left. 

Thus, as for XP S, the average surface concentration Na can, in principle, be calculated by measurement of the Auger current, according to Eq. (2.13). Again, as in XPS, relative sensitivity factors are generally used. The Auger current for the same transition XYZ in a standard of pure A is measured under the same experimental conditions as in the analysis of A in M, whereupon the ratio of the atomic concentrations is... 

Among the alkali metals, Li, Na, K, Rb, and Cs and their alloys have been used as exohedral dopants for Cgo [25, 26], with one electron typically transferred per alkali metal dopant. Although the metal atom diffusion rates appear to be considerably lower, some success has also been achieved with the intercalation of alkaline earth dopants, such as Ca, Sr, and Ba [27, 28, 29], where two electrons per metal atom M are transferred to the Cgo molecules for low concentrations of metal atoms, and less than two electrons per alkaline earth ion for high metal atom concentrations. Since the alkaline earth ions are smaller than the corresponding alkali metals in the same row of the periodic table, the crystal structures formed with alkaline earth doping are often different from those for the alkali metal dopants. Except for the alkali metal and alkaline earth intercalation compounds, few intercalation compounds have been investigated for their physical properties. 

As discussed earlier, the XPS technique is quantitative. If A, is the area under the peak in the spectrum that is characteristic of element i, then the atomic concentration of element i on the surface of the sample is given by the expression ... 

Fig. 37. Atomic concentrations for various elements at the six locations shown in Fig. 36. Reproduced by permission of John Wiley and Sons from Ref. [41 ].

Figure 2. Calculated length of the Fenni wavevector along the line, kp, for AgPd, CuPt and CnPd random alloys versns the noble metal atomic concentration, c. Dashed lines are drawn as a gnide for the eyes. The solid line indicates the value, V2/2, at which kp is exactly commensurate with LIq or LI2 orderings.

To eliminate the O atom concentration from this expression, we consider the net rate of formation of O atoms and use the steady-state approximation to set that net rate equal to zero ... 

Kinetic studies of the cryophotoclustering process are now in progress. Preliminary results indicate that, under certain conditions, the rates of formation of diatomic and triatomic silver may usefully be approximated by simple, second-order kinetics 149). A simple analysis predicts that the slope of a log[Ag ]/[Ag] versus log ) plot, where Ag and Ag represent absorbances, and t represents the irradiation time, should have a value close to 1.0 for n = 2, and 2.0 for n =3 149). A typical plot is shown in Fig. 17. The observed slopes, 0.9/1.0 and 2.1/2.2, support the Agj and Agj assignments for the run indicated in Fig. 18, and correlate exactly with earlier assignments based on Ag-atom concentration experiments. 

A possible layered precursor to the layered nanoproduct conversion mechanism is thus proposed. The silver clusters formed at the initial heating stage by the partial decomposition of AgSR serve as nuclei at further reaction stages, and their distribution naturally inherits the layered pattern of the precursor. The following growth is mainly controlled by the atom concentration and atom diffusion path, which are both constrained by the crystal structure of the precursor [9]. 

The Fe-B nanocomposite was synthesized by the so-called pillaring technique using layered bentonite clay as the starting material. The detailed procedures were described in our previous study [4]. X-ray diffraction (XRD) analysis revealed that the Fe-B nanocomposite mainly consists of Fc203 (hematite) and Si02 (quartz). The bulk Fe concentration of the Fe-B nanocomposite measured by a JOEL X-ray Reflective Fluorescence spectrometer (Model JSX 3201Z) is 31.8%. The Fe surface atomic concentration of Fe-B nanocomposite determined by an X-ray photoelectron spectrometer (Model PHI5600) is 12.25 (at%). The BET specific surface area is 280 m /g. The particle size determined by a transmission electron microscope (JOEL 2010) is from 20 to 200 nm. 

One way to relate the concentration of an intermediate to other concentrations is by assuming that earlier reversible steps have equal forward and reverse rates. The proposed mechanism begins with the decomposition of Bf2 molecules into Br atoms, most of which recombine rapidly to give Br2 molecules. At first, Br2 molecules decompose faster than Br atoms recombine, but the Br atom concentration quickly becomes large enough for recombination to occur at the same rate as decomposition. When the two rates are equal, so are their rate Rate of decomposition = Rate of recombination expressions Rr2] =. 1 [Br] ... 

FIG. 3. Absolute atomic concentrations in units of 10 al./cm. determined by ERD. RBS, and optical reflection and transmission spectroscopy, of (a) hydrogen, (b) carbon, and (c) silicon as a function of the carbon fraction. v. Results are presented for the series ASTI (filled circles), AST2 (filled triangles), ATLl (open circles), and ATL2 (open triangles). (From R. A. C. M. M. van Swaaij. Ph.D. Thesis, Universiteit Utrecht. Utrecht, the Netherlands, 1994. with permission.)... 

In Figure 3b and c the absolute atomic concentrations of carbon and silicon, respectively, are shown as a function of the carbon fraction. As expected, the carbon concentration increases upon alloying. In contrast, the silicon content decreases rapidly, which implies that the material becomes less dense. As it was reported that the Si—Si bond length does not change upon carbon alloying [116], it thus... 

Fig. 5.3. Distribution of helium mnetastable atoms concentration along cylinder at different pressures of He[39] ( / - 1.310 2 Torr 2- 2.510-2 3- 710-2 Torr)...

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