Plasma Sensitivity of Elements

What happens in a low-pressure plasma process cannot be determined in an a priori manner based only on the nature of the plasma gas or on the objective of the process. The plasma sensitivity series of elements involved, in both the luminous gas phase and the solids, that make contact with the luminous gas phase seems to determine the balance between ablation and polymerization by influencing the fragmentation pattern of molecules in the luminous gas environment. 

In order to elucidate the mechanisms by which a polymeric material deposits and also those by which surface modification of a polymeric material by plasma 

Material deposition occurs via plasma formation of reactive species however, it is not a simple step of forming a polymeric material from a set of reactive species. The reactive species do not necessarily originate from the monomer because the ablation process can and does contribute. Gaseous reactive species can originate from once-deposited material (plasma polymer) and also from the reactor wall or any other solid surfaces that are in contact with the luminous gas. How these complex reactive species lead to the material deposition is described in Chapter 5. 

Ablation, which is fragmentation or dissociation, is involved in every proeess, i.e., monomer to reaetive speeies, plasma polymer to reaetive speeies, wall surface to reactive speeies, and eseape of fragmented speeies from the system. Fragmentation of moleeules is the primary effeet of plasma exposure to a material. The importanee of ablation can be visualized in the well-established fragmentation patterns of many organic materials, whieh eonstitute the foundation of seeondary ion mass spectroscopy (SIMS). 

The reactive species (preeursors in the precursor concept) are ereated not only by fragmentation of the monomer but also by fragmentation of the plasma polymer formed and of materials existing on the various surfaces that come into contact with the plasma. 

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The decrease of Si due to F-containing contaminants and the role of the oxygen plasma treatment can be explained by the principle of CAP. The key factor to explain the change of elementary composition at the interface is the plasma sensitivity of elements involved on the surface and in the plasma phase. The ablation of materials exposed to plasmas appears to follow the plasma sensitivity series of the elements involved, which is in the order of the electronegativity of the elements, i.e., elements with higher electronegativity in the condensed phase are more prone to ablate in plasma that contains elements with lower electronegativity [5]. 

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