Plasma, impurity concentration effective

Comparision of Techniques. A figure-of-merit for the impurity concentration that exists in a plasma is a parameter based on the classical resistivity of the plasma (24), the "effective Z" ... 

The measured erosion of a beryllium surface will therefore be dependent not only on the impurity concentration in the incident plasma, but also on the temperature of the sample surface during the plasma exposure. An example of this effect is shown in Fig. 14.5, where the deposition of a carbon impurity... 

Spectroscopic methods for the deterrnination of impurities in niobium include the older arc and spark emission procedures (53) along with newer inductively coupled plasma source optical emission methods (54). Some work has been done using inductively coupled mass spectroscopy to determine impurities in niobium (55,56). X-ray fluorescence analysis, a widely used method for niobium analysis, is used for routine work by niobium concentrates producers (57,58). Paying careful attention to matrix effects, precision and accuracy of x-ray fluorescence analyses are at least equal to those of the gravimetric and ion-exchange methods. 

Plasma impurities may also have a beneficial effect by cooling the plasma edge in the vicinity of the first wall. But this is partially offset by the fact that the sputtering yields due to impurities are higher as compared with that of hydrogen. Consequently, a relatively small concentration of impurities can significantly increase the wall erosion and plasma contamination. 

Neither the dopant distribution coefficient nor the catalytic effect on growth rate is understood in detail. It is reasonable to expect that the dissociation rate of an impurity molecule might be higher than for SiH4, enhancing the concentration in the film. When the plasma contains molecular species a and and the dissociation rate is higher for p by a factor d, then a simple model predicts a distribution coefficient of... 

There are many methods for metal determination (Standard Methods, 1998 section 3000). Some, for example as gravimetric, titrimetric or colorimetric methods, are most effective at high metal concentrations. Others, for example atomic absorption (AA), inductively coupled plasma (ICP) or inductively coupled plasma mass spectrometry (ICPMS) are far more sensitive. The latter are used for typical textile applications, such as compliance testing for water quality or detection of trace impurities in high-volume raw materials. 

---