Overview of Electron Emission Laws from 2D Materials

In this paper, we present an overview of the novel scaling laws of thermionic emission (TE), field emission (FE) and photoemission (PE) for two-dimensional (2D) materials. For these emerging materials, we express the emission models in the form of $\ln(J/K^{\beta})\propto 1/K$, where J is the emission current density, $K$ is temperature (T) for TE and $K$ is dc or optically field for FE and PE. Here, the scaling is $\beta = 3/2$ and $\beta = 1$ for electron emission in lateral (or edge) and vertical (or surface) direction, respectively, which is different from the traditional scaling of $\beta = 2$ for bulk 3D materials.