Integration of Gold Nanoparticles to Modulate the Ignitability of Nanothermite Films

Thermite multilayered films composed of alternating thin layers of metal/oxidizers have various uses in microelectromechanical systems (MEMS), microelectronics, and materials bonding applications. Recently, applied research especially on the microinitiator applications has engendered an urgent need to improve ignitability without changing the layering and reactant spacing that both affect the combustion characteristics. This work describes an innovative nanoengineering solution to reduce the energy barriers for mass transport, making it possible to substantially lower ignition energy of CuO/Al reactive multilayers without manipulating the fuel and oxide layers thickness. To that end, gold nanoparticles exhibiting high thermal diffusivity properties are in situ grown uniformly inside the first CuO layer to produce localized hot-spots and promote the Al + CuO reaction. The CuO/Al reactive films with embedded gold nanoparticles exhibit earlier and optimized reaction than standard ones. The effect of gold nanoparticles on the thermite ignition mechanisms and the detailed reaction pathways were characterized by a host of characterization techniques including microscopy, thermal analysis, spectroscopy, and X-ray diffractometry. Altogether, results show that the gold nanoparticles are seeding nodular defects with conical shapes provoking (under thermal stimulation) high stressed zones in the multilayer where the Al + CuO reaction is quickly triggered. The analysis of reaction products showed that the multilayers break the unreacted Al droplets early allowing them to burn into the environment. The results provide a behavioral baseline for future studies of interface engineering to tune internal stress-induced reaction in reactive thin films at large.