Ion fraction

Fig. 3.53. Ion fraction of He and He ions (open and full symbols, respectively) in LEIS from Cu (v,T) and different types of C (carbidic carbon , graphitic carbon O, 0,- -, ) as a function of the sum of the reciprocal velocities of the incoming and the scattered ion [3.139],...

At high energies (small values of l/v ) the ion fraction is high, because there is little time for neutralization. 

For a given geometry, the ion fraction decreases exponentially with the inverse of the velocity. 

Although it is, in principle, feasible to quantify LEIS results, the determination of absolute ion fractions is far from trivial. In LEIS experiments, the surface composition is therefore generally obtained in a relative measurement by comparison of signals of the element in the sample of interest with those of reference samples, assuming that the matrix does not have a significant role and that the surface roughness is similar. 

Of the remaining second-order terms, the terms with the coefficient XAXBXx are exactly the same as those which occur in the binary system AX-BX multiplied by the ion fraction of X, A x the terms with the coefficient XAXBXY are the same as for the system AY-BY multiplied by XY and, similarly, the terms in XAXxXY or XBXxXY are the same as for the system AX-AY or BX-BY multiplied by the factors XA or XB respectively. These four collections of terms are the linearly additive binary... 

Bissot, T.C. (1985) Sulfate ion transport through perfluorinated chlor-alkali membranes an example of co-ion fractionation in membrane. Paper presented at the meeting of the Electrochemical Society, Toronto, Canada. 

The same evolution of the absorption spectrum with the dose has been found in a high dose rate for various values of the Ag and Au ion fraction in the initial solution. Clusters Agi. Au are alloyed with the same composition. The maximum wavelength and the extinction coefficient Smax of the alloy depend on x. The experimental spectra are in good agreement with the surface plasmon spectra calculated from the Mie model at x values for which optical data are available (Fig. 12) [102]. Similar calculations were carried out for the alloy Ag Pdi obtained at a moderate dose rate [180]. 

Salt particles whose chemical composition reflects that of seawater have been observed in many clean air locations. However, in a number of other cases, the ratio of the elemental mass of some elements to that of sodium differs from that in seawater. It has been suggested that ion fractionation may occur during particle formation at the surface as discussed shortly, chemical reactions may also occur on the particle sur-... 

Fluorine exists as F and MgF+ in seawater in approximately equal concentrations. The free ion fractions of Cl and Br- are essentially 100%. Iv in the form IO3 is the thermodynamically favoured (stable) form of iodine in oxygenated seawater. In the upper ocean, where thermodynamic disequilibria are common, a significant fraction of total iodine is present as iodide (I-). IO3, like I , is weakly interactive. 

A practical problem is that the sputtered chemical complexes often exhibit only a transitory existence. Traditional mass spectrometric techniques provide information on gross removal but little understanding of the mechanism involved. Data requirements in this area include gross removal rates, nature of ejected species, and changes to surface stoichiometry. In Sect. 6.5.1., the influence of surface chemistry on the nature of the sputtered species, and in particular on secondary ion fractions will be discussed. The role of surface chemistry and surface modification procedures on impurity control will be elucidated there. 

A variety of techniques leading to increased ion fractions are under investigation with a view to assessing the potential of this approach for impurity control in Tokamaks167 171. ... 

In the remaining part of this chapter one such approach, the nitriding of metal surfaces, will be discussed in some detail since it could lead both to higher ion fractions and to a lower effective-Z than that of the pure metal. 

The GD plasma environment is an interesting vessel to study gas-phase chemical properties. The gettering qualities of carbon, silver, tantalum, titanium, and tungsten were compared by Mei and Harrison [40] on the basis of the atomic ion fraction of all of the observed lanthanum species R = La+/(La+ + LaO+) X... 

Table V. Cation molar and after ion fractions in exchange the original cancrinite samples ...

Fig. 18. (a) Negative ion fraction of scattered O versus exit angle for 1 keV oxygen atoms incident on Mg, Al, and Ag. (b) Ion fractions for different metals as a function of the metal s workfunction (from Ref. 78). 

Fig. 11. Experimental ion fractions for random scattering direction for the Ag(l 10) (open dots) and Ag(lll) (full dots) surfaces. The lines labelled ion and neutral correspond to calculated Auger survival probabilities for two types of trajectories.

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