Field emission from nanometer protuberances at high current density

The results of experimental and theoretical investigations of high-current-density field emission from nanometer objects on the tungsten cathode surface are presented. Such objects were microprotuberances, and spots of Zr or ZrO, produced by a thermal-field buildup process (microtips) and selective adsorption (spots). The limiting values of stable emission current densities from local areas of the cathode surface were determined. The process of the cathode heating was numerically simulated in terms of a heat transfer equation approach for three-dimensional axial-symmetric model. The dependencies of the equation's coefficients upon temperature and mutual influence of the temperature and current distributions were taken into account. The main feature of the calculated temperature distribution consists in forming the overheated region in the inner emitter's volume. It was established that the limiting current densities of stable emission for nanometer objects can be almost an order of magnitude higher than for the traditional field emitter, in accordance with the experimental results.