City Research Online

Abstract

The photo-injection of electrons from thin metal films into a liquid insulant, subjected to an electric stress, is an established method of enhancing the natural conduction current. The interpretation and analysis of the waveshape of the current transient produced by this injection leads to a clearer understanding of the mechanism of charge transport.

This work introduced some new techniques to this field of study. Two grids were incorporated in the test cell containing the liquid. One grid shuttered the charge carriers, which were injected into a vapour gap to improve photo-emission, the second defined the drift field in the liquid. A grid shutter combined with back-illumination of the photo-cathode obviates the effects of bulk ionisation but it introduces its own distortion of the wave-shapes in the form of spreading on the current response to a pulse stimulus.

Instrumentation techniques and signal processing methods, in the form of digital correlation and cumulative averaging, were applied to the problems of measuring small signals in a noisy environment. On-line analytical programs were produced to interpret the results in terms of the criteria for electrohydrodynamic stability in the liquid.

A differential light-sensitive amplifier was constructed which enabled correlation to be established between the current and e.h.d. convection by measuring changes of light intensity, not detectable by the human eye, in a schlieren image of the drift field. Impure hexane has been found to be electrohydrodynamically unstable at low fields in accordance with recent theories. Purified hexane was stable over the range of low-stress which was applied, but displayed instability when charge was injected even at currents as low as 1 pA and an electric stress of 150 V cm-1.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > QC Physics
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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