Plasma processing of soft materials for development of flexible devices

Plasma-polymer interactions have been studied as a basis for development of next-generation processing of flexible devices with soft materials by means of low-damage plasma technologies (soft materials processing technologies). In the present article, interactions between argon plasmas and polyethylene terephthalate (PET) films have been examined for investigations of physical damages induced by plasma exposures to the organic material via chemical bonding-structure analyses using hard X-ray photoelectron spectroscopy (HXPES) together with conventional X-ray photoelectron spectroscopy (XPS). The PET film has been selected as a test material for investigations in the present study not merely because of its specific applications, such as a substrate material, but because PET is one of the well defined organic materials containing major components in a variety of functional soft materials; C-C main chain, CH bond, oxygen functionalities (O=C-O bond and C-O bond) and phenyl group. Especially, variations of the phenyl group due to argon plasma exposures have been investigated in the present article in order to examine plasma interactions with π-conjugated system, which is in charge of electronic functions in many of the π-conjugated electronic organic materials to be utilized as functional layer for advanced flexible device formations. The PET films have been exposed to argon plasmas sustained via inductive coupling of RF power with low-inductance antenna modules. The HXPES analyses exhibited that the degradations of the oxygen functionalities and the phenyl group in the deeper regions up to 50 nm from the surface of the samples were insignificant indicating that the bond scission and/or the degradations of the chemical bonding structures due to photoirradiation from the plasma and/or surface heating via plasma exposure were relatively insignificant as compared with damages in the vicinity of the surface layers.