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Exothermic reactions can self-propagate rapidly in multilayered foils, and the properties of these reactions depend strongly on the heat of reaction, the average atomic diffusion distance, and the degree of intermixing at the layer interfaces prior to ignition. By performing low-temperature anneals on sputter-deposited Al/Ni nanolaminate foils, the thickness of the intermixed region between layers was increased and its effects on the heats and velocities of reactions were measured. The intermixed region consisted of the metastable Al9Ni2 phase while the final phase of the foil was Al3Ni2. Analytical and empirical models were used to predict reaction velocities as a function of bilayer thickness and intermixing thickness, and the predictions are in good agreement with the experimental results. Increasing the average thickness of the intermixed region from 2.4 to 18.3 nm reduced the reaction velocity for all of the foils but was most significant for the foils with bilayer thicknesses less than 25 nm. The results indicate that the reaction velocity can be separated into two distinct regimes. The first regime occurs for thicker bilayers in which the average atomic diffusion distance is large. In this regime, reaction temperatures are high and reducing the bilayer thickness increases the reaction velocity. The second regime occurs for thinner bilayers where reaction velocity is dominated by the reduction in available energy due to intermixing. In this regime, reducing bilayer thickness results in a decrease in reaction velocity.

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Combustible multilayer foils can be fabricated by sputter depositing alternate layers of materials which react exothermically during thermally induced intermixing. Current models for these reactions consider pure materials which only intermix during the self-propagating stage of the reaction, though in reality during fabrication the materials undergo partial intermixing. An analytical model dealing with the premixing is presented and compared with experimental results for Al/Ni and Al/(Ni:Cu) multilayers. The model and the results indicate that premixing lowers the propagation velocity both by slowing the rate of atomic diffusion between layers and by lowering the temperature of the reaction. The lower temperature can cause solid/liquid phase changes to dominate the reaction path. It is concluded that to use these foils in commercial and engineering applications, the method of fabrication and the phase changes occurring during the reaction must be controlled to give the desired characteristics.

In this paper we demonstrate the utility of differential scanning calorimetry for investigating the thermodynamics and kinetics of a broad range of thin film reactions. We begin by describing differential scanning calorimeters and the preparation of thin film samples. We then cite a number of examples that illustrate how enthalpies of crystallization, heats of formation and enthalpies of interfaces can be measured using layered thin films of Ni/Al, Cu/Zr and Zr/Al and homogeneous thin films of Co-Si, Nb-Cu, Cr-Cu and Ge-Sn. Following these examples of thermodynamic measurements, we show how kinetic parameters of nucleation, growth and coarsening can also be determined from differential scanning calorimetry traces using layered thin films of Ni/Al, Ti/Al and Nb/Al and homogenous thin films of Co-Si and Ge-Sn. The thermodynamic and kinetic investigations highlighted in these examples demonstrate that one can characterize phase transformations that are relevant to commercial applications and scientific studies both of thin films and of bulk materials.