Implications of positive ion layer formation across highly injecting metal contacts: current instabilities and electrostatic repulsion

This paper is a theoretical and experimental investigation of the implications for the contact resistance of highly injecting metal contacts, whenever monolayers of positive ions are formed over the cathode. The major ion neutralization processes for a metal+oxide+gas interface are theoretically discussed since they principally determine whether fixed positive ion monolayers can or cannot form. The formation of positive ion monolayers on cathode surfaces will reduce the effective barriers required for electronic field emission. Practical implications may appear as additional current components, current instabilities and blow-open forces between the joints. Current instabilities have been experimentally investigated for a variety of components operating in the air or in high vacuum environment. The obtained results clearly demonstrate non-linear conductivity phenomena and hysteresis effects between the interfacial field and the injected charge in the examined structures. The evolution of blow-open forces between highly injecting metals has been investigated by analyzing transient current and voltage waveforms during spontaneous contact opening at reduced clamping forces. The importance of interfacial cavities and screening charges between the electrodes has been investigated as they may determine the over-current values during the spontaneous contact opening process. Fundamental aspects in controlling the above effects on heavy duty industrial components are pointed out.