Acceptor concentration

An important featnre of the photoemission cnrrent is its unusual dependence on the acceptor concentration. It follows from theory and is confirmed by experiments that at low concentrations, the current is proportional to the square root of acceptor concentration At high concentrations, when practically all electrons that... 

Figure 7.15 shows the appearance curves of desipramine and dihydromethysticin [556] in the acceptor wells as a function of time. Because some of the material is lost to the membrane, the curves level off asymptotically at acceptor concentration fractions considerably less the 0.5 value expected in the thin-membrane model (Fig. 7.14). The solid curve for desipramine in Fig. 7.15a is a least-squares fit of the data points to Eq. (7.21), with the parameters Pe 24 x 10-6 cm/s, R 0.13, and xLAG 11 min. The solid curve for dihydromethisticin in Fig. 7.15b is described by the parameters Pe 32 x 10 6 cm/s, R 0.42, and xLAG 35 min.

The membrane saturates with solute early in the transport process. So, for t 20 min, we may assume that CM(oo) ss C,M(t) is reasonably accurate. With this assumption, the acceptor concentration may be expressed in terms of the donor concentration as... 

The primary reaction between good donor solvents, such as Tetralin and octahydrophenanthrene, and acceptors can give rather "ideal" products. For example, at moderate dibenzyl acceptor concentrations (10-20%) dibenzyl is converted only to toluene in these solvents. However, when poor solvents are introduced, secondary reactions become quite important and "non-ideal" products are recovered. The type of secondary... 

Now consider the gradient-pH case, with pHD 3 and pHa 7.4. In Fig. 3.5b, the dashed curve (donor concentration) corresponding to pH 3 decreases more steeply after the retention period than that of the previous iso-pH example. Furthermore, there is not the large initial drop due to the disappearance of the sample into the membrane in the gradient-pH case, retention drops from 56% to 9%. Thus, more of the compound is available for sample concentration determination. The solid curve (acceptor concentration) corresponding to pH 3 also grows more rapidly than in the iso-pH example. The dashed and solid curves cross at 7 h, with C(t)/CD(0) close to the 0.5 value. Note also, that about 70% of the compound ends up in the acceptor well at the end of 16 h - much higher than is possible with the iso-pH method. 

It is very difficult to excite the donor without also exciting some of the acceptor population. This is because the absorption spectra of dyes extend significantly into the blue side of their absorption maxima, so the absorption spectra of the donor and acceptor usually overlap. The donor fluorescence can typically be observed without acceptor fluorescence interference therefore, when measuring FRET efficiency by observing the donor fluorescence, this overlap is not important. However, when observing the acceptor fluorescence the overlap of the donor and acceptor absorption must be taken into account. The total steady-state fluorescence of the acceptor, assuming that [A] = [D (i.e., a equal donor and acceptor concentrations, and 100% labeling) is... 

For a first approximation, k can be simply calculated by dividing by I for a donor-acceptor fusion construct, because both quantities are corrected for overlap and FRET. Note however that this requires [Pg.324]

Linear unmixing will also produce an apparent acceptor concentration ( apparent) that will over-estimate the true abundance of the acceptor (a) ... 

With good acceptors, apparent Fmax values increase with increasing acceptor concentration by a factor of about three at 600 mM maltose concentration.36 They decrease, as do initial reaction rates, with increasing concentrations of such weak... 

For B-doped p-type samples of Si with an acceptor concentration nA of 8.5 x 1019 the 29Si NMR also showed a Knight shift of 33 ppm (both n-type and p-type Knight shifts were reported as unsigned, presumably positive, values see Sect. 3.4.2). Comparison with results for the n-type sample led to the conclusion that there was a nearly equal admixture of s-type wavefunction for the hole wave function near the top of the valence band. 

The decrease in free carriers (holes) after hydrogenation of p-type Si is also evidenced by the decrease in IR absorption at the longer wavelengths, where free-carrier absorption dominates, and by a decrease in the device capacitance of Schottky-barrier diodes, due to the increase in the depletion width (at a given reverse bias) as the effective acceptor concentration decreases. 

Essentially identical profiles seem to be observed for high-resistivity n-and p-type samples deuterated under the same conditions. This is to be expected if the samples are instrinsic in all cases (donor or acceptor concentration < 2 x 1013 cm-3 at 150°C, or < 2 x 1015 cm 3 at 300°C),... 

Fig. 11. Capacitive transient spectra of defect states associated with dislocations in ultra-pure germanium (crystal 281 grown along [100] under 1 atmosphere of H2) The micrographs show the etch pits produced by dislocations on a (100) surface. DLTS peak b has an activation energy of Ev + 20 meV. The net-shallow acceptor concentration is 1010 cm-3.

Fig. 6. Deuterium concentration profiles in LPE grown p-type GaAs Si (p 7x 1018 cm-3) exposed to a rf deuterium plasma for 90 min. at different temperatures (rf power density = 0.2 W/cm2). For these diffusion temperatures, the plateau region is well defined with a deuterium solubility slightly above the silicon acceptor concentration. J. Chevallier era/., Mat. Res. Soc. Symp. Proc. 104, 337 (1988). Materials Research Society. 

Fig. 8. Comparison of the deuterium and active acceptor concentration profiles in a deuterated GalnAs/InP Zn structure showing that the acceptor neutralization exactly extends through the deuterium penetration region (( = 20 min., r=163°C, rf power density = 0.08 W/cm2). J. Chevallier et al., Materials Science Forum, 38-41, 991 (1989). Trans. Tech. Publications.

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