Dominant precursor deposition

Assuming a dominant precursor for deposition simplifies tremendously the study of plasma-surface interactions. In spite of the oversimplification, it is worth examining the effects on the film structure and composition of growth simulations solely from a given chemically reactive radical. First, direct comparison with experimental data provides an assessment for the... 

The chemistry of the chalcogenolate compounds of these elements is dominated for the seek of molecular precursors for the deposition of 13/16 chalcogenide semiconductors by MOCVD or related techniques.159... 

After a general discussion of the production of supported catalysts, the theory of nuclcation and growth of solids is surveyed Next the interaction between supports and precipitating precursors of the active components, which is dominating the nuclcation with precipitation onto suspended supports, is discussed This is followed by a review of the loading of powdered supports suspended in an aqueous solution of the active precursor(s) by deposition-precipitation Highly prom-... 

The molar ratio of Fc203/Fe0 in the BIFs is less than 1.0 in all but one of the 28 analyses of Isua iron formation reported by Dymek and Klein (1988). In the one exception the ratio is 1.17. Unless the values of this ratio were reduced significantly during metamorphism, the analyses indicate that magnetite was the dominant iron oxide, and that hematite was absent or very minor in these iron formations. This, in turn, shows that some of the hydrothermal Fe was oxidized to Fe prior to deposition, but that not enough was oxidized to lead to the precipitation of Fc203 and/ or Fe oxyhydroxide precursors, or that these phases were subsequently replaced by magnetite. 

For a given deposit material there usually exist several possible reactions, of which all may be thermodynamically feasible. The reaction with the most negative value should dominate because it leads to the most stable reaction products. For example, in order to co-deposit Si3N4 and TiN, two systems of gaseous species are available. The first is TiCl4-SiH4-N2-H2, where N2 is used as nitrogen precursor. The chemical reactions are expressed as... 

Except for the slower demise of chlorophyl1-c, the alteration of chlorophyll-a during senescence and death can be attributed to cellular decompartmentalization and resultant action of cellular acids (Mg-loss) and enzymes (e.g chiorophyllase, phytol loss, 35) The relative amounts of pheophytin-a versus pheophorbide-a resulting from senescence-death has been shown to be species specific and is related to chlorophyllase activity (37). Sediment Trap Samples. The alteration of chlorophyll due to senescence/death phenomena, described above, yield a certain suite of pigments. Such arrays, dominated by pheophytin-a, might be expected to form the precursor complement in sediments deposited in an environment free of consumers. Such is obviously not the case in nature. Since the vast majority (e.g. 95-99%) of primary production serves as fodder in marine food webs (38) we must consider heterotrophic alteration of detrital tetrapyrrole pigments. 

In conclusion, the MD simulations of a-Si H him growth from the SiHa, SiH2, and SiH radicals as the sole deposition precursors support that SiHa is the dominant deposition precursor and have elucidated its role in determining the detailed him structure and him surface morphology and composition (Ramalingam, 2000). 

In spite of the role of the dominant deposition precursor in determining the structure and composition of the deposited him, it is also worth examining the possible roles of minority species that are present at low concentrations in the plasma and are not expected to have signihcant quantitative contribution to the hhn growth process. Of particular interest are species that are very reactive with the growth surfaces, such as SiH radicals and small Si H, clusters with n > 1. Indeed, such species may have both benehcial and detrimental effects on the structural quahty of the deposited him. 

---