Theoretical investigation of gas sensing properties of a monolayer gallenene: First-principles insight

Abstract

Two dimensional (2D) materials exhibit potential to be used in thin film electronic devices. In present paper, we explore 2D polymorphs of α-Ga by performing ab−initio calculations based on density functional theory. Phonon calculations show that Ga100 and Ga010 planes are dynamically stable at 6% and 2% bi-axial tensile strain. The ab-initio molecular dynamics calculations show that while Ga100 plane retain structural stability in a free standing state for temperature up to 500 K, Ga010 plane shows structure distortion which further increases with increase in temperature. We find total energy of Ga010 plane is smaller (−1.09 eV/f.u.) than Ga100 plane, indicating that Ga010 plane is energetically more stable. We next follow the adsorption of toxic gas molecule over Ga010 plane, referred as gallenene sheet. The negative adsorption energy shows that adsorption of phosgene (CCl2O), hydrogen cyanide (HCN), phosphine (PH3), and hydrogen selenide (H2Se) gas molecule over gallenene sheet is feasible. We find that (CCl2O) H2Se gas (weakly) strongly interact with gallenene with adsorption energy of (−0.39 eV) −0.52 eV. Bader charge calculation shows transfer of electronic charge between adsorbed gas molecule and gallenene sheet, which further confirmed by plot of electron localization function (ELF). The recovery time of desorption for CCl2O (PH3) gas comes 3.90×10−6 s (2.85×10−4 s) due to greater (smaller) out of plane distance of 2.93 Å (2.75 Å). The current–voltage (I–V) characteristic shows small deviation due to lower concentration of gases over gallenene, which further confirmed by transmission spectra. We hope that our theoretical predictions will help experimentalists to synthesize gallenene based gas sensors.