electron-bearn-assisted etching has been proposed as source of low-damage etching. oj M.S. student in the Physics Dept. Coburn and Winters demonstrated that Si 3 N4 and Si0 2 2463

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A pulsed drift tube has been employed for measurement of the electron attachment coefficient, alpha a in pure sulphur dioxide over the E/N range 3.03<or=E/N<or=242.4 Td. A pressure dependence of alpha a/(SO2) has been observed for E/N<40.0 Td, indicating the existence of a three-body attachment process, whilst for values of E/N>40 Td the results indicate a dissociative attachment process. Measurements of the mobility of the negative ions formed indicate the presence of at least four ions with reduced mobilities of 0.69, 0.62, 0.55 and 0.39 cm2 V-1 s-1 respectively. Using a drift tube mass spectrometer system the ion spectra produced in pure SO2 and in SO2-O2 mixtures have been studied. In pure SO2 at pressures around 1 Torr a number of large cluster ions are observed. At much lower pressures the predominant ion is SO2 - which rapidly clusters to form SO2.SO2 - as the pressure increases. When SO2 is added to oxygen the following reactions are observed: O-+SO2 to SO3+e; O2 -+SO2 to SO2 -+O2. The rate for the first reaction has been measured over a range of E/N and has been found to vary between 2.0*10-9 cm3 s-1 and 8*10-10 cm3 s-1. The second reaction has a rate of 3.9*10-9 cm3 s-1 at E/N=117.2 Td.

A time-dependent, two-dimensional model is used to study internal heating effects and possible device failure in ZnO varistors in response to a high-voltage pulse. The physics and qualitative trends discussed here should hold for materials with internal microstructured grain boundaries. Our analysis is based on an electro-thermal, random Voronoi network. It allows for the dynamic predictions of internal failure and to track the progression of hot-spots and thermal stresses. Results here show that application of high voltage pulses can lead to the attainment of Bi 2 O 3 melting temperatures in the grain boundaries and an accelerated progression towards failure. Comparisons between uniform and normally distributed barrier breakdown voltage showed relatively small difference. Physically, this is shown to be associated with the applied bias regime and grain size. It is argued that reduction in grain size would help lower the maximum internal stress. This is thus a desirable feature, and would also work to enhance the hold-off voltage for a given sample size.Index Terms -Energy absorption, ZnO varistor, electro-thermal failure, voronoi network, high voltage pulsing.