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

In this article, the adsorption of NO x ( 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 (Δ Q ), 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 NO 2 molecules undergo chemical adsorption and strongly interact with the surface evidenced by the large value of E a and Δ Q . In particular, the NO x molecule dissociates into N and O atoms for some adsorption configurations. Bader charge analysis reveals that NO x 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.