Oxidation and ablation of polymers by vacuum-UV radiation from low pressure plasmas

Low-pressure glow discharge plasmas are increasingly used as an effective method for the surface modification of polymers; they can also serve in the laboratory to simulate low Earth orbital environment (LEO). Although Vacuum-Ultraviolet (VUV, λ < 200 nm) is an important component of plasma environment, only few studies have focused on its effects so far. The emission from low-pressure microwave plasma in the VUV-UV regions was investigated in order to use this plasma as light sources for the study of the VUV/UV effects on various polymers (polyethylene, polymethylmethacrylate, etc.) or high molecular weight oligomers (hexatriacontane). We have employed a quartz crystal microbalance (QCM) in order to measure in situ the net mass change of the polymeric films exposed to VUV/UV radiation originating from hydrogen plasmas. Measurements were made with the specimens in vacuum, or immersed in low-pressure oxygen, directly exposed to the VUV/UV (perpendicular to the radiation flux), or only to the VUV-generated atomic oxygen, AO (parallel to the radiation flux). Following irradiation, samples were analysed by X-ray Photoelectron Spectroscopy (XPS), in order to study the evolution of the oxygen content and of the various functional groups.