Raman microprobe analysis and ageing in dielectrics

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Description/Abstract

Subsurface voids in samples of electrically stressed low density polyethylene (LDPE) were analysed using confocal Raman microprobe spectroscopy (CRMS). An optical depth profiling technique was used to probe a void along the optic axis whilst a burst void was analysed at various lateral positions. Spectra from the voided samples showed signatures with similar features to those found in previous studies of electrical trees in polyethylene, including the presence of the D and G bands of disordered sp2 carbon. Results and spectra were then compared to the depth profiles and spectra from block and thin film samples of polyethylene and polystyrene which indicated that the established theory behind CRMS is oversimplified and that the detected signal is largely influenced by the optical properties of the material in question. Overall the study showed that despite some spatial resolution limitations of the technique, depth profiling is a useful tool in the analysis of aged polymers and dielectrics as it can show the variations in chemical composition with respect to position along the lateral and optic axis, a property especially relevant to electrical trees.