Experiments are described in which a direct comparison was made between a conventional 2 kW water‐cooled sealed‐tube X‐ray source and a 30 W air‐cooled microfocus source with focusing multilayer optics, using the same goniometer, detector, radiation (Mo Kα), crystals and software. The beam characteristics of the two sources were analyzed and the quality of the resulting data sets compared. The Incoatec Microfocus Source (IµS) gave a narrow approximately Gaussian‐shaped primary beam profile, whereas the Bruker AXS sealed‐tube source, equipped with a graphite monochromator and a monocapillary collimator, had a broader beam with an approximate intensity plateau. Both sources were mounted on the same Bruker D8 goniometer with a SMART APEX II CCD detector and Bruker Kryoflex low‐temperature device. Switching between sources simply required changing the software zero setting of the 2θ circle and could be performed in a few minutes, so it was possible to use the same crystal for both sources without changing its temperature or orientation. A representative cross section of compounds (organic, organometallic and salt) with and without heavy atoms was investigated. For each compound, two data sets, one from a small and one from a large crystal, were collected using each source. In another experiment, the data quality was compared for crystals of the same compound that had been chosen so that they had dimensions similar to the width of the beam. The data were processed and the structures refined using standard Bruker and SHELX software. The experiments show that the IµS gives superior data for small crystals whereas the diffracted intensities were comparable for the large crystals. Appropriate scaling is particularly important for the IµS data.

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.

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We have investigated reactive phase formation in magnetron sputter-deposited NiyAl multilayer films with a 1 : 3 molar ratio and various periodicities, L, ranging from 320 nm down to a codeposited film with zero effective periodicity. The films were studied by x-ray diffraction, differential scanning calorimetry, electrical resistance measurements, and transmission electron microscopy. We find that Ni and Al have reacted during deposition to form the B2 NiAl phase and an amorphous phase. The formation of these phases substantially reduces the driving force for subsequent reactions and explains why nucleation kinetics become important for these reactions. Depending on the periodicity, these reactions result in the formation of NiAl3 or Ni2Al9 followed by NiAl3. Detailed calorimetric analysis reveals differences in the nucleation and growth behavior of NiAl3 compared with other studies.

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.

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The quantitative description of highly nonequilibrium processes for the preparation of metastable and unstable phases requires the determination of the thermodynamic functions of the system under investigation. However, in systems such as Cu–Cr which are immiscible in the equilibrium states, the determination of the thermodynamic functions over the entire concentration range is often difficult if not impossible because reliable experimental data are not available for the metastable or unstable regime. The present paper demonstrates that such data can be obtained by a combination of thin film deposition techniques and differential scanning calorimetry. It is concluded that the phase formation in such thin films can be described in terms of the thermodynamics of the system, even when the heats of mixing are highly positive. The results indicate that models of the regular solution type still provide a reasonable description of the thermodynamic functions of such alloys.

Amorphous metallic alloys, frequently observed to occur in systems with large negative heats of mixing, are much less common in systems which are immiscible in the equilibrium solid state, such as Nb-Cu. However, amorphous Nb-Cu alloys can be produced over a wide composition range by sputtering. Using isothermal and nonisothermal differential scanning calorimetry, both the kinetics and the thermodynamics of these amorphous Nb-Cu alloys were characterized quantitatively. It was found that the formation enthalpies of the amorphous alloys amounted to only 4.5-7.6 kJ/g atom. These data were combined with a modeling of the thermodynamic functions of the system. The unexpected low enthalpies and Gibbs energies of the amorphous phase demonstrate the thermodynamic stabilization of the liquid phase which develops with undercooling. This is connected with a change of sign in the heat of mixing of the liquid phase, which is positive at high temperatures and negative at low temperatures.