Achieving Ultrafast Growth of Large-Scale Single-Phase Ni Silicide by Controlling the Bilayer Thickness of a Reactive Multilayer

A reactive multilayer is a nanoscale interlaced material that is able to release stored energy with proper ignition sources. In this study, the equiatomic Ni/Si RMLs with bilayer thicknesses of 13, 17, 28, 31, 52, 86, 138, 173, and 291 nm were fabricated by magnetron sputtering. The free-standing Ni/Si RMLs were ignited by an infrared LASER, and two-step self-propagation wavefronts were observed. When the bilayer thickness was less than 90 nm, the major products were verified as NiSi2, accompanied by the Ni2Si and amorphous Ni/Si mixture. In contrast, when the bilayer thickness exceeded 130 nm, the primary products were identified as NiSi along with the amorphous Ni/Si mixture. The formation of a single-phase silicide across a large area induces potential applications. A new one-dimensional model was constructed to understand the two-step self-propagation behaviors, simultaneous Ni/Si interdiffusion, and underlying heat loss rate. In our simulation model, the self-propagation velocity depends on the bilayer thickness. The premixed thickness dominates the reaction mechanism because it represents the energy loss during fabrication. When the premixed thickness was low, we observed the immediate ignition of the second wavefront after the ignition of the first wavefront. On the other hand, we observed the ignition and propagation of the first wavefront with high premixed thickness. The two critical temperatures roughly range from 450 to 500 K and from 850 to 1000 K.