Controllable Gas Adsorption via Inter-Coupled Ferroelectricity in In₂Se₃ Monolayer

Abstract

Recently, two-dimensional ferroelectrics with spontaneous electric polarization have attracted growing interest for application in gas sensors and other electronic devices. This study proposes an in-plane polarization-induced sensor based on the α-In$_2$Se$_3$ ferroelectric material with reversible gas capture or release. A comprehensive quantum mechanical analysis on the characteristics of the device is presented by employing density functional theory calculations, ab initio molecular dynamic simulations, and the non-equilibrium Green's function formalism. The ferroelectricity of α-In$_2$Se$_3$ results in different surface polarizations, leading to different adsorption behaviors on surfaces with opposite polarizations. Based on the adsorption energy, charge transfer, and recovery time, the negatively polarized surface is better suited for gas capture than the positively polarized surface. Consequently, by applying a vertical electric field, which changes the out-of-plane polarization, reversible capture or release of NH$_3$ and NO$_2$ molecules can be achieved. However, applying vertical electric fields in transistor-based gas sensors is rather challenging. Meanwhile, the unique interlocking feature of electric dipoles in α-In$_2$Se$_3$ monolayer can be used to control gas adsorption or desorption by an in-plane bias voltage (electric field). The sensitivities of the positive and negative surfaces to the NH$_3$ molecule are 107.6% and 11.3%, respectively, when an appropriate in-plane bias voltage is applied. The proposed sensor that allows manipulating the out-of-plane polarization by an in-plane bias is of special importance and opens up a new pathway for sensing applications.