Nanowires made of chalcogenide alloys are of interest for use in phase-change nonvolatile memories. For this application, insights into the thermal properties of such nanowires and, in particular, into the crystallization kinetics at the atomic level are crucial. Toward this end, we have performed large-scale atomistic simulations of ultrathin nanowires (9 nm in diameter) of the prototypical phase-change compound GeTe. We made use of an interatomic potential generated by the neural network fitting of a large ab initio database to compute the thermal properties of the nanowires. By melting a portion of a nanowire, we investigated the velocity of recrystallization as a function of temperature. The simulations show that the melting temperature of the nanowire is about 100 K below the melting temperature of the bulk, which yields a reduction by about a factor of 2 of the maximum crystallization speed. Further, analysis of the structural properties of the amorphous phase of the nanowire suggests a possible origin of the reduction of the resistance drift observed experimentally in nanowires with respect to the bulk.

Interfaces between different materials and phases play a crucial role in many physical and chemical phenomena. When performing simulations of matter at the atomic scale, however, it is often not trivial to characterize these interfaces, particularly when they are rough or diffuse. Here we discuss a generalization of a construction, due to Willard and Chandler, that allows one to obtain a smooth dividing surface that follows the irregular, ever changing shape of these fluctuating interfaces. We show how this construction can be used to study the surface that separates a solid material from its melt and how analyses of the Fourier modes for the capillary fluctuations of this instantaneous dividing surface can be performed. This particular analysis is useful as one can compute the specific free energy excess of the interface, and its dependence on orientation relative to the bulk phases, from the average amplitude of the Fourier modes. We therefore discuss the efficiency of this approach, both in terms of system size and statistical sampling.

The Ge2Sb2Te5 compound is of interest for applications in phase change non-volatile memories. First-principles calculations of phonon dispersion relations and electron-phonon coupling constant provide an estimate of the electron-phonon contribution to the thermal boundary resistance at the interfaces of Ge2Sb2Te5 with dielectrics (silica) and metal electrodes (Al and TiN). The diffuse mismatch model including full phononic dispersion has been used to compute the phononic contribution to the thermal boundary resistance. The calculated value of the electron-phonon contribution to the TBR at 300 K of about 14 m(2)K GW(-1) would dominate the TBR at the interfaces of hexagonal Ge2Sb2Te5 with the surrounding dielectrics and metals considered here once interdiffusion at the boundaries could be minimized.

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