Enhanced NH₃ and NO sensing performance of Ti₃C₂O₂ MXene by biaxial strain: insights from first-principles calculations

Abstract

In this study, we investigate the adsorption properties of CO, NH₃, and NO gases on Ti₃C₂O₂ MXene surfaces through density functional theory (DFT) calculations. A comprehensive analysis of the adsorption preferences, electronic properties, work function (<i>φ</i>), sensitivity (<i>S</i>), and recovery time (<i>τ</i>) was conducted, focusing on the effects of biaxial strain (<i>ε</i>) ranging from -2% to 4%. At free strain, toxic gases can adsorb onto the Ti₃C₂O₂ surface, with adsorption energies (<i>E</i>_ad) of -0.096 eV (CO), -0.344 eV (NH₃), and -0.349 eV (NO), indicating moderate interactions between NH₃, NO and the Ti₃C₂O₂ surface, while CO displays weaker physisorption. Electron density difference (EDD) and electron localization function (ELF) analyses underscore the electron transfer mechanisms, supporting the enhanced sensitivity of Ti₃C₂O₂ for NH₃ and NO detection. The influence of <i>ε</i> on gas adsorption behaviour was also studied, demonstrating that tensile strain enhances NH₃ adsorption (<i>E</i>_ad = -0.551 eV at <i>ε</i> = 4%), while NO exhibits an inverse trend under compressive strain (<i>E</i>_ad = -0.403 eV at <i>ε</i> = -2%). The <i>S</i> based on a change rate of <i>φ</i> was evaluated to be around 12% and 6% for NH₃ and NO, respectively, within the calculated strain range, indicating sufficient detection capability. Additionally, the <i>τ</i> for NH₃ and NO detection was computed. At 0% strain and 300 K, the <i>τ</i> values for NH₃ and NO are in the microsecond range, suggesting that detecting these gases under normal conditions poses a challenge. However, strain-tuned Ti₃C₂O₂ and lowered temperature enhance the gas sensing performance, with increased <i>τ</i> values at tensile strain for NH₃ and compressive strain for NO. These results suggest that Ti₃C₂O₂ MXene, when tuned with biaxial strain, is a promising candidate for detecting NH₃ and NO at low to room temperatures.