The early stages of solid-state reactions in Ni/Al multilayer films

Abstract

Ni/Al multilayer films with pair thicknesses of 10 and 20 nm and with overall compositions in the range 48–88 at. % Al were prepared by sputtering. For comparison, Ni-Al alloy films in the same concentration range were prepared by co-deposition of the elements. The films were studied by x-ray diffraction, electron diffraction, and differential scanning calorimetry. It was found that the B2 NiAl phase with a metastable concentration of approximately 63 at. % Al was the first phase to grow upon annealing of the multilayer films. The growth of this phase could be described by Johnson–Mehl–Avrami kinetics with an activation energy of 0.8 eV and an Avrami exponent of 0.5. This low activation energy was consistent with the observation that the phase had formed during deposition and continued to grow upon annealing at low temperatures to thicknesses of a few nanometers. If the reactant phases were not fully consumed by the B2 phase growth, the subsequent reaction was the formation of NiAl3, previously thought to be the first product phase in the Ni-Al system. The reduction of driving force by the preceding B2 phase growth explains why the formation of NiAl3 takes place by a nucleation-and-growth process, an observation that has been discussed controversially in the recent literature. The nucleation and growth of NiAl3 had an activation energy of 1.5 eV in agreement with previous studies.

Atomic layer deposited ultrathin metal nitride barrier layers for ruthenium interconnect applications

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Phase transformations and thermodynamic properties of nanocrystalline FePt powders

“…Rietveld analysis of the samples after the measurements reveals the presence of the L1 0 FePt and, in the case of the 2 h milled powder, additional Fe 3 Pt and FePt 3 phases. The apparent absence of a peak in the isothermal DSC measurements has been ascribed to transformations starting with fast nucleation from random positions followed by a comparatively slow diffusion-controlled growth [19] and [20]. Slow growth rates could be supported, for instance, by the data shown in Fig.…”

Non-equilibrium intermixing and phase transformation in severely deformed Al/Ni multilayers

“…This is explained by the asymmetry of the interdiffusion coefficients, with Ni diffusing much more rapidly into Al than Al into Ni [22,23]. However, depending on the nominal composition of the multilayer and on the processing history, also different initial intermediate phases such as AlNi [19,20,[24][25][26], AlNi 3 [10] or a metastable Al 9 Ni 2 -phase [24,27] Argon flow for 2 min at 250°C. This temperature was chosen because it is close to the onset for the Al 3 Ni formation [12,14,17,18], and the duration was sufficiently short to avoid significant grain growth.…”