Selective doping

TCPP was doped selectively into the P4VP-cylinder domains of the PS-fo-P4VP (162 400 87 400) films prepared from the chloroform solution. Figure 12.3c and i show an AFM image of a film doped with TCPP and the height profile of the line indicated in the image, respectively. On the surface ofthe TCPP-doped films, there... 

To date, the majority of enzyme-based potentiometric sensors do not involve detection with an ionophore-doped selective membrane and fall outside of the scope of this chapter. The same is also true for most Severinghaus-type gas sensors, where a gas-permeable membrane covers an inner solution in which the gaseous analyte is determined with an ISE. Most Severinghaus-type electrodes use a pH-sensitive glass electrode to monitor the pH of this inner filling solution. However, ammonia has been detected indirectly with an ammonium-selective ionophore-based ISEs upon protonation in that inner solution, and the use of other ionophore-based ISEs for the more selective detection both in enzyme-based and Severinghaus-type ISEs is readily conceivable. 

In order to obtain appreciable conductivities, semiconductors must be doped witli small amounts of selected impurities. It is possible to switch tire doping type from n to p type, or vice versa, eitlier during tire growtli of a crystal or by tire selective introduction of impurities after tire growtli. The boundary region between tire p type and n type regions is... 

Laser Photochemistry. Photochemical appHcations of lasers generally employ tunable lasers which can be tuned to a specific absorption resonance of an atom or molecule (see Photochemical technology). Examples include the tunable dye laser in the ultraviolet, visible, and near-infrared portions of the spectmm the titanium-doped sapphire, Tfsapphire, laser in the visible and near infrared optical parametric oscillators in the visible and infrared and Line-tunable carbon dioxide lasers, which can be tuned with a wavelength-selective element to any of a large number of closely spaced lines in the infrared near 10 ]lni. 

The oxidative dehydration of isobutyric acid [79-31-2] to methacrylic acid is most often carried out over iron—phosphoms or molybdenum—phosphoms based catalysts similar to those used in the oxidation of methacrolein to methacrylic acid. Conversions in excess of 95% and selectivity to methacrylic acid of 75—85% have been attained, resulting in single-pass yields of nearly 80%. The use of cesium-, copper-, and vanadium-doped catalysts are reported to be beneficial (96), as is the use of cesium in conjunction with quinoline (97). Generally the iron—phosphoms catalysts require temperatures in the vicinity of 400°C, in contrast to the molybdenum-based catalysts that exhibit comparable reactivity at 300°C (98). 

Another interesting applications area for fullerenes is based on materials that can be fabricated using fullerene-doped polymers. Polyvinylcarbazole (PVK) and other selected polymers, such as poly(paraphcnylene-vinylene) (PPV) and phenylmethylpolysilane (PMPS), doped with a mixture of Cgo and C70 have been reported to exhibit exceptionally good photoconductive properties [206, 207, 208] which may lead to the development of future polymeric photoconductive materials. Small concentrations of fullerenes (e.g., by weight) lead to charge transfer of the photo-excited electrons in the polymer to the fullerenes, thereby promoting the conduction of mobile holes in the polymer [209]. Fullerene-doped polymers also have significant potential for use in applications, such as photo-diodes, photo-voltaic devices and as photo-refractive materials. 

The high sensitivity and selectivity of the EPR response enables diamagnetic systems to be doped with very low concentrations of paramagnetic ions, the fate of which can be followed during the progress of a reaction. The criteria [347] for the use of such tracer ions are that they should give a distinct EPR spectrum, occupy a single coordination site and have the same valency as, and a similar diffusion coefficient to, the host matrix ion. Kinetic data are usually obtained by comparison with standard materials. 

Doping of solid reactant involves the introduction of a controlled amount of an impurity into solid solution in the host lattice. Such impurities can be selected to cause the generation or destruction of those electronic or structural defects which participate in the rate process of interest. Thus, the influence of the additive on kinetic behaviour can provide evidence concerning the mechanism of reaction [46,47]. Even if the... 

Before constructing an electrode for microwave electrochemical studies, the question of microwave penetration in relation to the geometry of the sample has to be evaluated carefully. Typically only moderately doped semiconductors can be well investigated by microwave electrochemical techniques. On the other hand, if the microwaves are interacting with thin layers of materials or liquids also highly doped or even metallic films can be used, provided an appropriate geometry is selected to allow interaction of the microwaves with a thin oxide-, Helmholtz-, or space-charge layer of the materials. 

It is known32 reported that the solid electrolyte itself, i.e. Y203-doped-Zr02, is a reasonably selective catalyst for CH4 conversion to C2 hydrocarbons, i.e., ethane and ethylene32 and this should be taken into account in studies employing stabilized Zr02 cells. At the same time it was found54 that the use of Ag catalyst films leads to C2 selectivities above 0.6 for low methane conversions. 

Recently, microspheres (5-40 pm diameter) of these Ion-doped glasses have been prepared and evaluated (65). Ions can be selected to produce either sharp (Tb, Sm , Eu ) or broad (Mn , UO2, Cu, ... 

DOPED PA MODELS. We selected two criteria to characterize the structure of the mono- and di-cations. The wavefunctions of the cations at their respective optimized geometries were used to determine Mayer s bond indices which reflect the strength of the interatomic bonds. The differences in the cations and also the neutral molecule emerge very clearly from Table III. 

Fe4Sni2S32) to 2.319 A in the Si-doped compound studied here. This may be due to the doping of Si atoms. The size of Si" is smaller in comparison to the size of Cu and this would lead to the smaller Cu-S bond length in the Si-doped compound [22]. The Fe/Sn-S distances do not show much change, being 2.536 A in the pure compound and 2.5365 A in the Si-doped sample. Selected bond distances are given in Table 15.2. 

Fig. 1(b) represents the selectivity to styrene as a ftmcfion of time fijr the above catal ts. It is observed that the selectivity to styrene is more than 95% over carbon nauofiber supported iron oxide catalyst compared with about 90% for the oxidized carbon nanofiber. It can be observed that there is an increase in selectivity to styrene and a decrease in selectivity to benzene with time on stream until 40 min. In particrdar, when the carbon nanofiber which has been treated in 4M HCl solution for three days is directly us as support to deposit the iron-precursor, the resulting catalyst shows a significantly lows selectivity to styrene, about 70%, in contrast to more than 95% on the similar catalyst using oxidized carbon nanofiber. The doping of the alkali or alkali metal on Fe/CNF did not improve the steady-state selectivity to styrene, but shortened the time to reach the steady-state selectivity. 

Figure 2. Effects of altervalent cation doping of Ti02 on a) CO selectivity and b) H2 selectivity under concentrated feed conditions, CH4/02=66.7/33.3 vol.% (Ti02 doped with lwt% of ZnO A CaO 0 La203 Li O undoped).

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