Comparative Study of Cold Electron Emission from 2D Ti₃C₂T_X MXene Nanosheets with Respect to Its Precursor Ti₃SiC₂ MAX Phase

Abstract

2-D Ti3C2TX MXene nanosheets are obtained by etching Ti3SiC2 MAX phase that is synthesized by heating the elemental Ti, Si, and C mixture at high temperature. The electron emission behavior of both Ti3C2TX MXene and Ti3SiC2 MAX phase is studied. MXene exhibits excellent field emission characteristics with a turn-on field of 4.7 V μm–1, and that for the Ti3SiC2 MAX phase is 6.5 V μm–1. The turn-on electric field corresponding to an emission current density of 10 μA cm–2 is 5.0 V μm–1 for Ti3C2TX MXene and 7.5 V μm–1 for the Ti3SiC2 MAX phase. The calculated enhancement factor of MXene nanosheets is ∼4280, which is one of the highest reported enhancement factors to date. In order to get theoretical insight into the field emission properties for Ti3C2 and OH-terminated Ti3C2 MXene in comparison to the Ti3SiC2 MAX phase, we have presented the structure and electronic properties from state of the art density functional theory (DFT) simulations. The interaction of – OH with Ti3C2 involves charge transfer from the “Ti” 3d orbital to −OH. The computed work function follows the trend Ti3SiC2 > Ti3C2 > Ti3C2/OH, which supports the maximum field emission in −OH-terminated Ti3C2 MXene and the minimum field emission in the Ti3SiC2 MAX phase.