Effect of Deposition Parameters on the Reactivity of Al/Ni Multilayer Thin Films

Nanoscale multilayers can be used as highly localized heat sources, making them attractive for several applications, in particular for joining and as igniters. Over the last decades, academia and industry have given particular emphasis to nanoscale multilayers from the Ni-Al system. In this study, Al/Ni (V) multilayer thin films with periods of nominally 25 and 50 nm (bilayer thickness) and near equiatomic average stoichiometry were produced by d.c. magnetron sputtering from Al (99.999% pure) and Ni (93 wt % Ni, 7 wt % V) targets (vanadium was added to the Ni target to make it non-magnetic). Deposition parameters such as the substrate rotation speed and substrate bias were varied in order to evaluate their effect on the reactivity of the multilayers. The influence of in situ ion bombardment of the multilayer thin films was also studied. Phase identification was carried out by X-ray diffraction, while the microstructure was analyzed in detail by transmission electron microscopy, distinguishing alternating layers throughout the entire thickness of the films. Although the films mainly consist of Al- and Ni-rich layers, the presence of the Al3Ni intermetallic phase was detected, except in the multilayers produced with the ion gun switched on during the deposition process. The ion bombardment, as well as the increase of the substrate bias, promote some microstructural disorder and thus affect the multilayers' reactivity.