Thermal Stability of (Mg/NbOx)82 Multilayer Nanostructure

Thermal stability of the multilayer (Mg/NbOx)82 nanostructure and the effect of heat treatment on its electrical properties and phase composition depending on the bilayer thickness are studied. The studied (Mg/NbOx)82 samples contain 82 bilayers whose thickness varies in the range from 2.2 to 6.2 nm. The NbOx layer thickness in the multilayers is the same (0.96 nm) in all samples, while the magnesium layers thickness is varied. It is established that the magnesium layers are either discrete (a set of nanosized particles) or continuous depending on their thickness. A metallothermic reaction occurs in (Mg/NbOx)82 multilayer nanostructures at a temperature of 430 °C: niobium oxide decomposes and the released oxygen partly oxidizes the magnesium layers. That leads to the conductive magnesium metal layers breaking and to the sharp increase of the nanostructures’ resistance by more than two orders. Despite the metallothermic reaction, the layering of the (Mg/NbOx)82 nanostructures as a whole and the presence of unoxidized magnesium inclusions remain even after heating up to 450 °C. The annealing effect on the (Mg/NbOx)82 multilayers with extremely small bilayers thickness (varied from 2.2 to 6.2 nm) has been studied. The thinnest Mg layers are discrete while thicker layers are continuous. A metallothermic reaction occurs in the multilayer (Mg/NbOx)82 nanostructures during heat treatment: the nanosized pure Nb clusters are formed while the continuous Mg layers are oxidized and destroyed.