Metal Microparticles Research Articles

Microparticle-initiated vacuum breakdown—Some possible mechanisms

It is known that micron- and submicron-sized metallic particles are released from the electrode surfaces when a vacuum gap is subjected to a high dc stress. It is also well known that larger particles (> 10 μm) are generated within the interelectrode gap when a vacuum gap is subjected to conditioning or severe prebreakdown current flow. This paper examines the role of such particles in inducing the breakdown of a vacuum gap. While the larger particles induce breakdown by way of a trigger discharge, it is shown that the smaller particles can initiate breakdown because of effects associated with impact. The various effects associated with the high-speed impact of a metallic microparticle on a target electrode, viz., cratering, production of metal vapor, and production of thermally generated plasma and their relative significance on vacuum breakdown, are examined.

Electrical Conduction between Metallic Microparticles

Electrical conduction in very thin metal films deposited onto single-crystal sodium chloride substrates has been investigated. The conduction for annealed films is found to be thermally activated with a negative temperature coefficient of resistance. Inspection of the films in an electron microscope shows them to consist of separated microparticles. Electron tunneling through the vacuum between microparticles is generally assumed to be the mechanism of electrical conduction. In this work an attempt has been made to show that conduction can occur in the substrate surface. The conduction is believed to be electron tunneling between regions in the substrate surface immediately under the metallic particles. The current carriers can be contributed to the insulator surface regions by the metallic microparticles. In addition, an activation energy is thought to be necessary before tunneling can occur. This energy is electrostatic in nature and is dependent upon the average size and separation of the microparticle regions.