Adsorption of NO (x = 1, 2) Molecules on the CoFeMnSi(001) Surface: First-Principles Insights

In this article, the adsorption of NO (x = 1, 2) gas molecules on the (001) surface of CoFeMnSi quaternary Heusler alloys has been investigated theoretically with density functional theory (DFT) calculations. The adsorption strength was estimated with adsorption energy (E _a), magnitude of charge transfer (ΔQ), charge density difference (CDD), minimum distance between molecule and surface (d), and adsorption mechanism was analyzed with density of states. The results showed that unlike half-metallic nature of the bulk phase, the pristine CoFeMnSi(001) surface exhibited metallic character caused by the emergence of electronic states of the atoms in the top-most layer of the surface. It was found that both NO and NO₂ molecules undergo chemical adsorption and strongly interact with the surface evidenced by the large value of E _a and ΔQ. In particular, the NO molecule dissociates into N and O atoms for some adsorption configurations. Bader charge analysis reveals that NO molecules act as charge acceptors by drawing charge from the surface atoms through p-d hybridization. Such findings might be useful in the development of Heusler alloys based gas sensors.