Electrical characteristics of nanometer gaps in vacuum under direct voltage

The electrical characteristics of nanometer gaps in vacuum were studied with the tungsten electrodes under dc and pulsed voltage. A novel experimental technique to study the electrical characteristics of nanometer gaps was presented in the paper. In the experimental setup, the tungsten was fabricated and shaped to be a perfect sphere through the electrochemical etch and Joule melting method, and the nanogap was controlled precisely by the scanning electron microscope (SEM) and nanometer manipulator. The effects of electrode geometry, gap separation and injected voltage waveform were investigated. The current-voltage curves and Fowler-Nordheim plots showed the difference of the field emission process before breakdown between the sphere-sphere electrodes and needlesphere electrodes. The gap separation dependence of dielectric strength demonstrated the similar trend to the previous work but better performance. The breakdown voltage for pulsed voltage was 4-5 times higher than that for the dc voltage. The analysis of the physical damage indicated that the current, duration time and electrode geometry played important roles in electrode modification. In addition, a possible mechanism of nanoscale vacuum breakdown was also proposed in the paper.