Nanostructured phase-change materials (PCMs) are promising candidates for next generation memory technologies. Despite the essential role the crystallization kinetics of PCMs play in the switching of the memory, this kinetics have hardly been studied, since its investigation is highly challenging. This thesis presents a facile method to synthesize in a single-step ligand-free Ge-Sb-Te based phase-change nanoparticles, with excellent size, crystallinity and composition control. Subsequently the amorphous PCMs were crystalized by slow and fast heating using transmission electron microscopy and ultrafast differential scanning calorimetry (DSC). The slow heating resolved the size dependence of the crystallization temperature for Ge2Sb2Te5 nanoparticles with average diameter from 15 down to 7 nm, where the crystallization temperature slightly decreases with the reduction of nanoparticle size. Surface-induced heterogeneous nucleation is considered responsible for this effect. Ultrafast heating with heating rates up to 40000 K/s have allowed us to study the crystallization kinetics of Ge-Sb thin films, GeSbTe and GeTe nanoparticles. A breakdown of Arrhenius behavior was observed for the crystallization of all these PCMs. Associated with numerical modeling using JMAK theory, we unraveled the crystal growth rate as well as the viscosity for these PCMs between the glass transition and melting temperatures of these PCMs. Especially for the GeSbTe and GeTe nanoparticles, a viscosity model with fragile-to-strong crossover was used to well interpret the observed crystallization kinetics for the amorphous nanoparticles. It was also found that proper incorporation of methane gas during nanoparticles deposition improved the performance of the PCMs in applications such as memories.
|Translated title of the contribution||Ge-Sb-Te gebaseerde phase-change nanodeeltjes|
|Qualification||Doctor of Philosophy|
|Place of Publication||[Groningen]|
|Publication status||Published - 2017|