Investigating the temperature and Al doping effect on the O2 adsorption Process on ZnO nanowire surface: A ReaxFF-MD approach

Abstract

ZnO nanostructures have garnered significant attention from researchers and industries due to their outstanding properties as gas-sensing materials. Aluminium (Al) doping, in particular, can further fine-tune or optimize these gas-sensing properties. In this research, we investigate the adsorption of O₂ molecules on undoped and Al-doped ZnO nanowires at $5\text{\%}$ and $10\text{\%}$ doping concentrations using advanced reactive force field (ReaxFF)-based molecular dynamics (MD) simulations. The adsorption process is studied at temperatures of 100 K, 300 K, and 500 K, with 300 O₂ molecules in each case, and the influences of these factors on the adsorption type are analyzed through radial distribution function (RDF) analysis. The adsorption behavior of O₂ molecules on both undoped and Al-doped ZnO nanowires is compared by calculating system energy, adsorption energy, and the number of adsorbed molecules. The results show that the binding distances between O₂ molecules and Zn and Al atoms on the nanowire surfaces are 2.18 Å and 1.78 Å, respectively, as determined from RDF analysis. The O₂ adsorption process on undoped and Al-doped ZnO nanowire surfaces occurs in two distinct stages, with higher temperatures leading to an increased number of adsorbed molecules. As Al doping increases, it significantly accelerates O₂ adsorption in the initial stage, while pure ZnO shows greater adsorption number in the second stage. Chemisorption dominates the interaction in both undoped and Al-doped ZnO.