Negative radiation-induced

Turning to the pulse radiolysis data for further information, it is fairly obvious that any attempt to explain the radiation-induced polymerization of a-methylstyrene on the basis of a single ionic species, be it a positive or a negative ion, is faulted by the data. Certainly several species are formed in detectable quantities. It is unfortunate that they all absorb in essentially the same region of the spectrum, but this is not unexpected (11). What it means, however, is that neither identities nor concentration can be established solely on the basis of the spectrum that one obtains. Thus, it would appear that ascribing the spectrum of a-methylstyrene to the radical anion, as Hirota has done (13), is at best an oversimplification. 

The scheme of radiation-induced reactions of CMS, negative electron resist, is proposed as follows on the basis of the present pulse radiolysis data. 

These results indicate that n-butylvinylether forms the cation radicals through positive charge transfer rather than by capturing an electron to form the anion radical and suggests that the ionization potential of n-butylvinylether is lower than that of 3-methylpentane (according to the measurements by the present authors, this is the case) and its electron affinity is negative. The observed behavior of n-butylvinylether seems to coincide with its cationic nature in the radiation-induced polymerization. Though the formation of carbonium ions from the cation radicals has not yet been elucidated, the cation radicals may play an important role in the initiation process of polymerization. 

Application of pulse radiolysis to polymers and polymerization was motivated at first by the success of radiation-induced polymerization as a novel technique for polymer synthesis. It turned out that a variety of monomers could be polymerized by means of radiolysis, but only a little was known about the reaction mechanisms. Early studies were, therefore, devoted to searching for initiators of radiation-induced polymerization such as radicals, anions and cations derived from monomers or solvents. Transient absorption spectra of those reactive intermediates were assigned with the aid of matrix isolation technique. Thus the initiation mechanisms were successfully elucidated by this method. Propagating species also were searched for enthusiastically in some polymerization systems, but the results were rather negative, because of the low steady state concentration of the species of interest. 

Many reports have been published on negative electron-beam resists. Most of these resists utilize radiation-induced gel-formation as the insolubilzation reaction. However, a major problem with these resists, is that their resolution is limited by swelling which is induced by the developer during development. 

By analogy with free-radical polymerizations, Eqs. (6.93) and (6.94) can be used also to calculate the radiation-induced rate of formation of initiating positive and negative ions by replacing R by R" " or R. ... 

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