Electron-beam polymerization

The pursuit of further miniaturization of electronic circuits has made submicrometer resolution Hthography a cmcial element in future computer engineering. LB films have long been considered potential candidates for resist appHcations, because conventional spin-coated photoresist materials have large pinhole densities and variations of thickness. In contrast, LB films are two-dimensional, layered, crystalline soHds that provide high control of film thickness and are impermeable to plasma down to a thickness of 40 nm (46). The electron beam polymerization of CO-tricosenoic acid monolayers has been mentioned. Another monomeric amphiphile used in an attempt to develop electron-beam-resist materials is a-octadecylacryUc acid (8). 

Methyl methacrylate can also be polymerized by radiation using either a cobalt-60 source or accelerated electrons at dose rates up to 3 megarads/sec. The activation energy for the electron beam polymerization is about 7.0kcal/ mole (Ref 12). Radical polymerization can also occur using diisocyanates or hydroperoxides as the initiating species (Ref 15)... 

Although being insulators in general at least one crystalline polydiacetylene DCH was found to be electrochemically dopable up to a conductivity of 10 (Qm) by applying an NaJ/J2 electrolytic contact One could think of combining this technique with electron-beam polymerization in order to produce a well-defined conducting pattern at the surface of a diacetylene crystal support or LB system. 

Morita, M. Imamura, S. Tamamura, T. Kogure, O. Murase, K. Direct pattern fabrication on silicon resin by vapor phase electron beam polymerization. J. Vac. Sci. Technol. B. 1983, 1 (4), 1171-1173. 

To investigate the effect of high-pressure CO2 on the polymerization reaction as well as to determine the amount of monomer inside the polymer particles, electron beam experiments have been performed [19]. Pulsed electron beam polymerization involves the generation of radicals in the aqueous phase, this being activated by an electron beam. These radicals initiate the polymerization of the residual monomer inside the latex particles. Based on the molecular weight of the newly formed polymer chains, the local monomer concentration in the polymer particles can be calculated. The growth time of a polymer chain is directly... 

I) Generation of a regular dot pattern of polymer by electron beam polymerization (top view)... 

Unfortunately we cannot give a value of the conversion for the electron beam polymerization. But from the similar value of the chain length (n = 400) it seems that also in the latter case we deal with conversions near the autocatalytic regime. 

There seems to be a discrepancy between our chain length data during electron beam polymerization and photopolymerization and the ones during thermal polymerization which were measured by Albouy et al. (5) and which were also presented at this meeting. They report... 

Use of dibutyltin diacrylate and its diisobutyl or dioctyl analogs in electron-beam polymerization to form tack-free films [147]. 

These are systems in which multilayer stmctures are fonned from molecules containing one or more double bonds and in which polymerization is subsequently initiated by appropriate means such as electron beam or UV light exposure. 

Other investigations dealt with straight-chain molecules (oi-tricosenoic acid) in which the penultimate and final carbon atoms at the hydrophobic end are connected by a double bond [91, 92]. The material does not polymerize as rapidly as those described before when irradiated by UV light, however, but it is readily polymerized when bombarded with an electron beam. It was thus thought to be an optimal material for the fabrication of electron beam resists. 

An analogous mechanism should also produce polymers on irradiation of epoxies. Crivello s recent mechanistic suggestions [29] are consistent with the mechanisms given above. One can conclude that radiation-induced polymerization of epoxies can proceed via several mechanisms. However, further work is needed to determine the relative contributions of the different mechanisms, which might vary from one epoxy to another. As part of the Interfacial Properties of Electron Beam Cured Composites CRADA [37], an in-depth study of the curing mechanism for the cationic-initiated epoxy polymerization is being undertaken. 

Davidson, S.R. and Wilkinson, S.A., electron-beam-induced polymerization of epoxides. J. Photochem. Photobiol. A Chem.,SS, 123-134 (1991). 

Janke, C.J., Dorsey, G.F., Havens, S.J. and Lopata, V.J., Electron beam curing of epoxy resins by cationie polymerization. 4Jsl International SAMPE Symposium, 196, 1996. 

Chemical alternation of the surface layer and deposition of a new layer on top of the silicone mbber can be achieved by physical techniques. For the inert surface of silicone rubber, the former requires the generation of high-energy species, such as radicals, ions, or molecules in excited electronic states. In the latter case, coatings of atoms or atomic clusters are deposited on polymer surfaces using technique such as plasma (sputtering and plasma polymerization) or energy-induced sublimation, like thermal or electron beam-induced evaporation. 

It is clear from this discussion that the dose requirement and unit cost will be lower if the material has a higher molar mass M and the reaction has a high G value. Thus, the best candidates will be a polymeric material and a chain reaction. Quite often, a free-radical irradiation is used. The radiation source of choice is usually a 60Co - y facility, although electron beam irradiation is also used. Since most radiation-chemical reactions used in industry can also be brought about by other conventional means such as thermal, or photochemical processes, the processing cost must be below 10irradiation cost one has to include the cost of operation, maintenance, and the like. (Danno, 1960). 

Chemical fixation for transmission electron microscopy prepares cells for the preservation of damage due to subsequent washing with aqueous solvents, dehydration with organic solvents such as ethanol or acetone, embedding in plastic resins, polymerization of the resins by heat, exothermic catalysts, or ultraviolet radiation, and imaging with high-energy electron beams in an electron microscope. 

A number of new resist materials which provide very high sensitivities have been developed in recent years [1-3]. In general, these systems owe their high sensitivity to the achievement of chemical amplification, a process which ensures that each photoevent is used in a multiplicative fashion to generate a cascade of successive reactions. Examples of such systems include the electron-beam induced [4] ringopening polymerization of oxacyclobutanes, the acid-catalyzed thermolysis of polymer side-chains [5-6] or the acid-catalyzed thermolytic fragmentation of polymer main-chains [7], Other important examples of the chemical amplification process are found in resist systems based on the free-radical photocrosslinking of acrylated polyols [8]. 

The hybridizing component can also be formed directly on the surface of a pristine or modified nanocarbon using molecular precursors, such as organic monomers, metal salts or metal organic complexes. Depending on the desired compound, in situ deposition can be carried out either in solution, such as via direct network formation via in situ polymerization, chemical reduction, electro- or electroless deposition, and sol-gel processes, or from the gas phase using chemical deposition (i.e. CVD or ALD) or physical deposition (i.e. laser ablation, electron beam deposition, thermal evaporation, or sputtering). 

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