Phase-change materials were highly promising for next-generation nonvolatile data storage technology and their properties were usually improved by doping. In this paper, the pronounced effects of Sn doping (0%, 10%, 30%) on crystallization behaviors of Ge2Sb2Te5 (GST) film induced by a picosecond pulsed laser were investigated in detail. The TEM observations presented the crystallization threshold, melting threshold and ablation threshold all decreased with the increasing of Sn doping while the crystal structure and crystallization behavior has not been changed. After single pulse Gaussian laser irradiation, the morphology of crystallized films for GST and Sn-doped GST all presented an ingot-like microstructure at higher laser fluence and equiaxed crystal microstructure at lower laser fluence, which was mainly caused by the temperature gradient. The local grain refinement was found in GSTSn30% films because weaker Sn-Te bond (359.8 kJ/mol) replaced the stronger Ge-Te bond (456 kJ/mol), which was also proved by X-ray photoelectron spectroscopy (XPS). This eventually led to a decline in nucleation energy barrier and increased nucleation rate.
Nano particle embedded thin film has great potential application in tuning the optical properties of phase change material. In this paper, we prepared GeTe nano particle embedded Cu composite thin film (GeTe@Cu) by magnetic co-sputtering GeTe and Cu targets. High-resolution transmission electron microscopy (HR-TEM) was used to characterize the local structure of the composite thin film and the GeTe nano particles. It was found that the composite thin film was constituted of net-like Cu-Cu bonds, Ge (Te)-Cu bonds as well as GeTe nano particles. Optical reflectivity of the composite thin film was also measured. Ab initio molecular dynamics (AIMD) simulations was employed to investigate the forming mechanism of GeTe nano particles and the local features in detail. Simulation results revealed that Ge-Te-Ge-Te four-fold ring promote the formation of GeTe atom cluster and large amount of free electrons from Cu atoms make the Ge-Te bonds stronger, in further leading to the formation of GeTe nano particles. These results in this paper paved the way for further research about multi-level optical storage of nano particles embedded phase change composite thin film.
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