Molecular structure of a random copolymer film by plasma‐enhanced CVD from a mixture of cyclohexa hydrocarbons

Abstract

An important issue in the polymerization of a polymer film by plasma-enhanced chemical vapor deposition (PECVD) is how to control the polymer structure. As is generally recognized, it is extremely difficult to control the process because it is very complex. For example, various precursors in the plasma arise from fragmentation of source monomers, which can easily change by varying the plasma conditions. High-energy electrons and ions in the plasma bombard the surface of the deposited film and affect the chemical reaction on the film. Moreover, the droplets that arise from the reactor wall by sputtering will accumulate on the film. However, if we aim to fabricate only a photonically functional polymer film, we will be able to find a solution. In this paper, we propose copolymerization from two types of monomers; one type is used as jointing materials by cracking, and the other is used as a photonic functional segment without serious deformation. This difference of action arises from a difference in the formation enthalpy. To confirm this idea, as an initial step, we copolymerized a film from a mixture of benzene (C 6 H 6 ) as the functional segment and cyclohexene (C 6 H 10 ) as the jointing material under the low radio frequency power. The deposited film consists of sp 2 bonding clusters surrounded by sp 3 bonded (alkyl) networks. We confirmed that the sp 2 bonding clusters mostly belong to phenyl, with a few belonging to olefins arising from decomposed C 6 H 6 . In addition, the amount of sp 2 bonding increases proportionally with increasing ratio of C 6 H 6 in the mixture, and the ratio of phenyl in the film becomes comparable to that of polystyrene. From these facts, we speculate that C 6 H 10 acts as the jointing material and C 6 H 6 as the functional segment. Additionally, we introduced tetrafluorocarbon (CF 4 ) to the plasma. CF 4 decomposes with a smaller energy than C 6 H 10 , and it forms mainly fluorine and CF 3 radicals. The fluorine radical pulls out hydrogen from the film and reacts to form dangling bonds in the film. Moreover, we speculate that they will terminate the dangling bonds.

Photoluminescence of Polymer Film Fabricated by Plasma-Enhanced Chemical Vapor Deposition from Mixture of Benzene and Cyclohexene

“…In order to achieve this aim, at least, the segments of the polymer must remain unchanged so as to work as the optical functional segments and be incorporated into the molecular structures. However, we did not confirm, in our previous study 3) whether or not the segments change their structures for optical functional operation. The photoluminescence measurement of a polymer, as discussed, will give some significant information on its chemical structure, namely, electron states, substitution structures, defects, and other electron phonon interactions.…”

“…They were prepared by varying the ratio of C 6 H 6 to C 6 H 10 and the ratio of argon to CF 4 . By increasing the ratio of C 6 H 6 to C 6 H 10 in argon atmosphere, the amount of sp 2 bonding in the PECVD film increases, as determined by FT-IR measurement 3) and shown in the right-side columns of Table I. In the center columns of Table I, moreover, we show the elemental ratio of the film measured by XPS.…”

“…By FT-IR measurement, we confirmed that most sp 2 bonds are included in monosubstituted benzenes and that the number of bonds included in olefin is small. 3) The deposited film has an alkyl network structure that includes many branches. C 6 H 6 is incorporated into the network as substituted benzene or olefin because of its segmentation or fragmentation in plasma.…”

“…We have proposed the fabrication of a copolymer by PECVD to resolve this problem. 3) That is, we used two types of monomer in the polymerization. One type functions as an optical functional segment, and the other type functions as a joining material between the segments.…”

Nanophase‐separated poly(acrylic acid)/poly(ethylene oxide) plasma polymers for the spatially localized attachment of biomolecules

“…Mixing AA with other monomers was also investigated to produce thin films with variable chemical compositions . Such plasma copolymerization allows fluorocarbons, hydrocarbons, amine‐containing species, and other moieties to be added to the deposited film and produces coatings with unconventional chemistries that can be controlled by the ratio of the supplied precursors.…”