Phase Transformation and Characterization of 3D Reactive Microstructures in Nanoscale Al/Ni Multilayers

Abstract

Reactive multilayer systems represent an innovative approach for potential usage in chip joining applications. As there are several factors governing the energy release rate and the stored chemical energy, the impact of the morphology and the microstructure on the reaction behavior is of great interest. In the current work, 3D reactive microstructures with nanoscale Al/Ni multilayers were produced by alternating deposition of pure Ni and Al films onto nanostructured Si substrates by magnetron sputtering. In order to elucidate the influence of this 3D morphology on the phase transformation process, the microstructure and the morphology of this system were characterized and compared with a flat reactive multilayer system on a flat Si wafer. The characterization of both systems was carried out before and after a rapid thermal annealing treatment by using scanning and transmission electron microscopy of the cross sections, selected area diffraction analysis, and differential scanning calorimetry. The bent shape of multilayers caused by the complex topography of silicon needles of the nanostructured substrate was found to favor the atomic diffusion at the early stage of phase transformation and the formation of two intermetallic phases Al0.42Ni0.58 and AlNi3, unlike the flat multilayers that formed a single phase AlNi after reaction.

Microstructural Characterization and Self‐Propagation Properties of Reactive Al/Ni Multilayers Deposited onto Wavelike Surface Morphologies: Influence on the Propagation Front Velocity

“…The formation of these two phases was already observed in Al/Ni RMS with an atomic composition rich in nickel. [ 10,15 ] Note that these small spots of the second phase are aligned with the direction of the patterns. To confirm the presence of the L3 phase and elucidate the phase formation process, it is necessary to perform further analyses.…”

“…[6,12] The influence of the substrate surface on the RMS structure and phase transformation was recently explored, showing the impact of the substrate roughness on the premixed thickness of the asdeposited RMS and on the phase transformation during annealing. [14,15] However, the dynamics of the reaction promoted by slow heating rates, such as annealing or differential scanning calorimetry (DSC), differs from a self-propagating reaction, where the formation of the AlNi intermetallic phase occurs directly from a liquid-solid state, whereas during annealing the diffusion of the reactants occurs in the solid state. [16] Schultz et al recently showed the influence of the substrate topography on the propagation velocity by depositing RMS on low-temperature co-fired ceramic (LTCC) with previous surface modification.…”

Influence of Initial Temperature and Convective Heat Loss on the Self-Propagating Reaction in Al/Ni Multilayer Foils

“…The samples were heated with a constant rate of 0.333 K s −1 from 200 to 823 K. A second run with the reacted material under identical conditions allowed for determining the baselines, which were subtracted from the first up-scan. The calorimeter was calibrated by measuring the melting temperatures and melting enthalpies of In and Zn [52]. Multiple pieces of the thin films have been stacked to reach a sufficient total mass for a good signal to noise ratio.…”