Ion enhancement

C2.18.3.2 EXPERIMENTAL STUDIES OF ION-ENHANCED ETCHING REACTION KINETICS AND DYNAMICS... 

Chang J P, Arnold J C, Zau G C H, Shin H-S and Sawin H H 1997 Kinetic study of low energy ion-enhanced plasma etching of polysilicon with atomic/molecular chlorine J. Vac. Sc/. Technol. A 15 1853-63... 

E. Chason, B. K. Kellerman. Monte Carlo simulations of ion-enhanced island coarsening. Nucl Instrum and Meth in Phys Res B 0 225, 1997. 

The nature of the gegen ion is probably of the greatest importance in determining the rate of propagation in ionic polymerization. However, it is not clear whether the presence of the gegen ion enhances or inhibits the propagation. One may argue that the... 

Figure 20 shows the plot of the surface tension vs. the logarithm of the concentration (or-lg c-isotherms) of sodium alkanesulfonates C,0-C15 at 45°C. In accordance with the general behavior of surfactants, the interfacial activity increases with growing chain length. The critical micelle concentration (cM) is shifted to lower concentration values. The typical surface tension at cM is between 38 and 33 mN/m. The ammonium alkanesulfonates show similar behavior, though their solubility is much better. The impact of the counterions is twofold First, a more polarizable counterion lowers the cM value (Fig. 21), while the aggregation number of the micelles rises. Second, polarizable and hydrophobic counterions, such as n-propyl- or isopropylammonium and n-butylammonium ions, enhance the interfacial activity as well (Fig. 22). Hydrophilic counterions such as 2-hydroxyethylammonium have the opposite effect. Table 14 summarizes some data for the dodecane 1-sulfonates.

Macdonald et al.25 28 maintained that the adsorption of chloride ions enhances the formation of cation vacancies of metal ions and their transfer... 

Sotomatsu, A., Tanaka, M., Lizuka, T. and Hirai, S. (1993). Aluminum ions enhance production of superoxide anions by the cultured microglia. J. Neurochem. 59, Suppl. S6. 

Standard addition experiments can be used to check for matrix effects such as ion enhancement or suppression. 

Matrix effect is a phrase normally used to describe the effect of some portion of a sample matrix that causes erroneous assay results if care is not taken to avoid the problem or correct for it by some mechanism. The most common matrix effects are those that result in ion suppression and subsequent false negative results. Ion enhancement may lead to false positive results.126 127 Several reports about matrix effects include suggestions on what can cause them and how to avoid them.126-147 While various ways to detect matrix effects have been reported, Matuszewski et al.140 described a clear way to measure the matrix effect (ME) for an analyte, recovery (RE) from the extraction procedure, and overall process efficiency (PE) of a procedure. Their method is to prepare three sets of samples and assay them using the planned HPLC/MS/MS method. The first set is the neat solution standards diluted into the mobile phase before injection to obtain the A results. The second set is the analyte spiked into the blank plasma extract (after extraction) to obtain the B results. The third set is the analyte spiked into the blank plasma before the extraction step (C results) these samples are extracted and assayed along with the two other sets. The three data sets allow for the following calculations ... 

Fig. 4.5 gives data on the rate of water loss of aquo metal ions. It is well known that hydrolysis of the metal ion enhances the rate of water loss from the metal ion. Usually a monohydroxo complex has a k-w that is two to three orders of magnitude larger than that of a non-hydrolyzed species. 

Relaxation studies have shown that the attachment of an ion to a surface is very fast, but the establishment of equilibrium in wel1-dispersed suspensions of colloidal particles is much slower. Adsorption of cations by hydrous oxides may approach equilibrium within a matter of minutes in some systems (39-40). However, cation and anion sorption processes often exhibit a rapid initial stage of adsorption that is followed by a much slower rate of uptake (24,41-43). Several studies of short-term isotopic exchange of phosphate ions between aqueous solutions and oxide surfaces have demonstrated that the kinetics of phosphate desorption are very slow (43-45). Numerous hypotheses have been suggested for this slow attainment of equilibrium including 1) the formation of binuclear complexes on the surface (44) 2) dynamic particle-particle interactions in which an adsorbing ion enhances contact adhesion between particles (43,45-46) 3) diffusion of ions into adsorbents (47) and 4) surface precipitation (48-50). 

Effects of Pentavalent Sb Ions on the Adsorption of Divalent Co-57 on Hematite. Benjamin and Bloom reported that arsenate ions enhance the adsorption of cobaltous ions on amorphous iron oxyhydroxide (J 6). Similarly, when divalent Co-57 ions were adsorbed on hematite together with pentavalent Sb ions, an increase of adsorption in the weakly acidic region was observed. For example, when 30 mg of hematite was shaken with 10 cm3 of 0.1 mol/dm3 KC1 solution at pH 5.5 containing carrier-free Co-57 and about 1 mg of pentavalent Sb ions, 95 % of Co-57 and about 30 % of Sb ions were adsorbed. The emission spectra of the divalent Co-57.ions adsorbed under these conditions are shown in Figure 8 together with the results obtained under different conditions. As seen in Figure 8, the spectra of divalent Co-57 co-adsorbed with pentavalent Sb ions are much different from those of Co-57 adsorbed alone (Figure 3). These observations show a marked effect of the.co-adsorbed pentavalent Sb ions on the chemical structure of adsorbed Co-57. 

The most important mechanistic aspects regarding ion suppression have been investigated in deeper detail than those regarding ion enhancement, which, in general, are less frequent. Ion suppression can occur both in the solution or in the gas phase [35],... 

It is this authors opinion, that ion and electron enhanced chemical reactions of the type described above are probably important in MOST situations. Nevertheless, to our knowledge, neither a theoretical understanding nor well defined experiments have been reported on this subject. Therefore, several experiments which have been performed recently in this laboratory will be described and then possible explanations for the ion-enhanced, chemical reactions will be discussed. 

Similar conclusions can be drawn from the data shown in Fig. 27 where the partial pressure of SiF4 is monitored mass spectrometrically as an Si sample is rotated into a jet of XeFj gas with and without ion bombardment. The ion-enhanced etching of silicon is indicated by the much larger evolution of SiF4 when the sample is exposed... 

Another clue to why this branching ratio changes in this counterintuitive way with laser intensity is to note that the three-photon signal is peaked near v = 15, while the two-photon signal is peaked near v = 7. This implies that high vibrational excitation of the ion enhances the curve crossing necessary to produce the two-photon signal. This is exactly the trend observed in the Landau-Zener formula calculations performed by Zavriyev et al. [50], In their calculations on H2 the probability to cross the... 

Nitrogen protonation or incorporation of high oxidation state metal ions facilitates nucleophilic substitution (especially at Craeso) whereas N-deprotonation or coordination to low valent metal ions enhances the electrophilic reaction (especially at Cme50). The effects of electron-donating substituents (alkyl) are less than those of electron-withdrawing groups (especially n acceptors, N02, COR). 

As shown in Fig. 2, the Gd3+ ion enhances the relaxation rate of the protons of water molecules located at a distance r from the metal center in the first coordination sphere of the metal ion. The relaxivity is thus primarily affected by the hydration of the metal ion. Toxicity reasons however limit the maximum num-... 

Cardiac glycosides cause a positive inotropic effect which means an increase of the cardiac beat volume by enhanced contraction ability. The reason for this is supposed to be aligned with the direct inhibition of the transport enzyme sodium/ potassium-ATPase. The decrease of sodium ions enhances the calcium ion concentration, which activates the myofibrillic enzyme and inactivates proteins like tropo-myocine and tropomine. Till present, a final proof for this hypothesis is lacking, the toxicity, however, is definitely aligned with these effects [97]. 

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