Observation and characterization of periodic structure formation in dielectric breakdown channels of electron-irradiated polymethyl methacrylate

Dielectric breakdown of insulators is a common failure mode in high-radiation environments and could be used for novel materials processing, but the mechanisms governing channel formation remain poorly understood. When electron-irradiated polymethyl methacrylate undergoes breakdown, the resulting channels exhibit striking periodic structures in the recently identified ivy-mode channels. Optical and electron microscopy revealed the presence of a boundary region that is also periodic, and Raman spectroscopy determined that carbon deposition correlates with channel width variations. We therefore conclude that the instability must occur during the plasma discharge phase. We systematically evaluated three candidate instability mechanisms and demonstrate that the z-pinch entropy mode governs the formation of periodic structures in the breakdown channels. This work represents, to our knowledge, the first direct observation of plasma instabilities creating persistent morphological features in solids. Our findings establish a predictive framework for discharge characteristics in insulators.