Beam damage of polypropylene in the environmental scanning electron microscope: an FTIR study

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Abstract
The environmental scanning electron microscope allows the examination of virtually any specimen in a gaseous environment without the need for coating or drying. Experimental evidence, however, suggests that significant electron beam damage occurs in hydrated specimens. It is thought that water molecules, ionized by the electron beam, produce hydrogen and hydroxyl free radicals which attack the organic material of the sample. In order to elucidate the beam damage mechanisms, areas of polypropylene films were exposed to the electron beam at varying doses and exposure times under both hydrating and dehydrating conditions. The chemical changes occurring as a result of electron‐beam irradiation were determined using Fourier transform infra‐red microscopy. Direct interaction of the electron beam with the polymer results in extensive cross‐linking. In the presence of water, free‐radical‐initiated reactions lead to hydrolysis and oxidation of the polymer.