Concerning organic microneedles grown on tungsten wires under intense electric fields

Abstract

Dendritic microneedles develop over a period of hours on the surface of a 10 mu m tungsten wire maintained at high potential (in the range 5-15 kV) in benzonitrile vapour. Auger spectra and X-ray diffraction patterns have been obtained from these microneedle-covered wires. The X-ray diffraction results for wires produced at high temperatures (>1000K) show that the wires themselves have been converted to tungsten monocarbide (WC). The Auger results indicate that the microneedles are composed of carbon; however, according to the X-ray diffraction, the structure is not that of graphite. The Auger spectra of microneedles grown with benzonitrile at room temperature also show only peaks due to carbon. A supply-type mechanism is put forward to account for the growth of these microneedles. It is proposed that the electric field focuses benzonitrile molecules on to the growing microneedle tips.