title: Fast Crystallization of the Phase Change Compound GeTe by Large-Scale Molecular Dynamics Simulations.
abstract: Phase change materials are of great interest as active layers in rewritable optical disks and novel electronic nonvolatile memories. These applications rest on a fast and reversible transformation between the amorphous and crystalline phases upon heating, taking place on the nanosecond time scale. In this work, we investigate the microscopic origin of the fast crystallization process by means of large-scale molecular dynamics simulations of the phase change compound GeTe. To this end, we use an interatomic potential generated from a Neural Network fitting of a large database of ab initio energies. We demonstrate that in the temperature range of the programming protocols of the electronic memories (500-700 K), nucleation of the crystal in the supercooled liquid is not rate-limiting. In this temperature range, the growth of supercritical nuclei is very fast because of a large atomic mobility, which is, in turn, the consequence of the high fragility of the supercooled liquid and the associated breakdown of the Stokes-Einstein relation between viscosity and diffusivity.
authors: †Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi 53, I-20125 Milano, Italy.|‡Department of Chemistry and Applied Biosciences and Facoltà di Informatica, ETH Zurich and Università della Svizzera Italiana, Istituto di Scienze Computazionali, Via G. Buffi 13, CH-6900 Lugano, Switzerland.
authors: Gabriele C
authors: GC
authors: Sosso
authors: ¶Chaire de Simulation à l'Echelle Atomique (CSEA), Ecole Polytechnique Fèdèrale de Lausanne (EPFL), PH H2 482 Station 3, CH-1015 Lausanne, Switzerland.
authors: Giacomo
authors: G
authors: Miceli
authors: †Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi 53, I-20125 Milano, Italy.
authors: Sebastiano
authors: S
authors: Caravati
authors: ‡Department of Chemistry and Applied Biosciences and Facoltà di Informatica, ETH Zurich and Università della Svizzera Italiana, Istituto di Scienze Computazionali, Via G. Buffi 13, CH-6900 Lugano, Switzerland.
authors: Federico
authors: F
authors: Giberti
authors: §Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, Universitätstrasse 150, D-44780 Bochum, Germany.
authors: Jörg
authors: J
authors: Behler
authors: †Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi 53, I-20125 Milano, Italy.
authors: Marco
authors: M
authors: Bernasconi
keywords: density functional theory; homogeneous crystallization; molecular dynamics simulations; neural networks; phase change materials; supercooled liquids