Research on the Characteristic and Mechanism of Field Emission from Metal-Substrate Graphene Contact

Vacuum trigger switch is a widely used equipment in a wide voltage range, and recently researchers cover the conventional metal contacts with two-dimensional material trying to enhance the performance of the trigger switch. However, the characteristic and the mechanism of the field emission from metal-substrate two-dimensional material haven't been researched precisely. Besides, an agreement has not been reached whether the emission process of two-dimensional material follows the traditional Fowler-Nordheim theory or Murphy-Good theory or not. Confronted with these problems, we established an experimental system which can measure the current as low as Pico ampere. Furthermore, Advanced Performance Detector (PHOTONIS) which is composed of a high-gain microchannel plate connected with a phosphor screen is also used to capture the electron emission image to reveal the feature of emission process before breakdown. The results show that there exists a step effect in the V-I curve of the emission process of graphene which deviates from the FN theory. Besides, a hysteresis effect also occurs in the V-I characteristic of graphene. In order to illustrate this phenomenon, we proposed a qualitative model that the free electrons are first transferred to the $\mathrm{p}_{\mathrm{z}}$ orbital of carbon atom of graphene from metal substrate under the applied voltage. And with the applied voltage increasing, electrons will be released to the vacuum after the $\mathrm{p}_{\mathrm{z}}$ orbital of the carbon atom is all filled. This model explains the step effect pretty well but is invalid for hysteresis effect and thus need to be further improved. And we believed that our model and experimental results are surely to be helpful for later researchers and to enhance the performance of the vacuum trigger switch in the future.