High energy ion beam modification of polymer films

Abstract

Studies on the effects of high energy ion beam irradiation in polymer films are reviewed in this paper. The studies reported in this review suggest exciting research in the field of ion-polymer interaction with impact on electronic transport in disordered systems, dynamical radiation chemistry and novel materials synthesis. p ]High energy ions (> 10 keV amu ) deposit a large amount of energy (several eV atom ) in ionizing the electrons of the target atoms. This results in significant destruction of bonds in the films as a result of which polymers undergo rapid dissociation. Using a quadrupole mass spectrometer, the study of transient emission of molecular species produced by an ion pulse has been shown to yield information about the diffusion and reaction kinetics of various molecules in the polymer. The fact that polymers undergo dissociation and those atoms which form volatile species are selectively depleted from the film could be utilized in producing useful inorganic composites by ion bombardment of polymers. For example, hard SiC composite films have been produced by ion beam irradiation of organo-silicon polymers. Eventually, polymer dissociation leads to a predominantly carbon containing film which exhibits interesting electronic transport properties. Experiments on ion irradiated, pure carbon films indicate that a metallic form of carbon is produced from the polymer films at high irradiation doses. While experiments on disordered conductors have involved the ion beam modification of highly conducting materials to form bad metals (with resistivity, ρ ∼ 10 −3−10 −4Ω cm ), comparable bad metals are formed in these experiments starting with insulating materials. There have been, in addition, interesting studies on polymer films using low energy ions (in the ion implantation regime) as well and a brief review of these studies have also been included in this paper.