Pretreatment biasing

For total mercury, two sets of low results were rejected owing to the suspicion of mercury losses the laboratories concerned had experienced the same difficulty in the interlaboratory study and were encouraged to investigate the source of error leading to biased results. The certified value is mainly based on results obtained by CVAAS as final determination (except one set by CVAFS and two sets by ICPMS) however, the pretreatment techniques were widely different from one laboratory to another. 

In an effort to enhance diamond nucleation and to control film morphology, extensive work on the nucleation and early growth stages has been performed. As a result, technology problems associated with the nucleation of polycrystalline diamond films have been adequately addressed. A number of nucleation enhancement methods have been developed that enable the control of nucleation density over several orders of magnitude. Nucleation density has been increased from < 10 cm on untreated substrates up to 10 cm on scratched or biased substrates. The effects of surface conditions on nucleation processes have been investigated to provide the guideline for the selection of optimum surface pretreatment methods. In this chapter, substrate materials, surface pretreatment methods and their influences on diamond nucleation are discussed. 

In an in-depth study of diamond nucleation on Si in MW PACVD,0 1 substrates were pretreated by negative biasing in a 2 vol.%CH4-H2 plasma. The biasing enhanced diamond nucleation density on unscratched Si wafers, up to 10 cm" , as compared to 10 cm" on scratched Si wafers and 10 -10 cm-2[279] Qjj untreated Si wafers (Fig. 6). 

Stoner et al.l l proposed a model to explain diamond nucleation mechanism on Si during biasing pretreatment, as displayed in Fig. 7 ... 

Finally, the process parameters used in biasing pretreatments are summarized in Table 3 for an overview. 

Table 3. Process Parameters Used in Biasing Pretreatments...

The ingredients for pretreatments can range from simple to complex, with particular formulations for particular dye types or fabrics, or combinations of these. This chapter is an overview of pretreatment as a process, rather than a specific chemical or physical analysis of a particular step in that process. References are included for those interested to further their own research. Specific ingredients tend to be confidential as commercially sensitive, but some recipes are publicly available for use as a starting point for experimentation (Bae, 2007, p. 46 Hawkyard, 2006 Provost et al., 2003). Many of the pretreatment formulations have been aimed at fashion fabrics, so they are biased toward fiber types such as cotton, silk, nylon, and wool. The principle and most common ingredients for pretreatments are thickeners, alkalis, and urea ... 

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