Surface induced crystallization/amorphization of phase change materials

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Materials Science

Background:

• Phase transformations in nanolayers are critical for materials applications.
• Surface effects significantly influence material properties at the nanoscale.
• Understanding crystallization and amorphization dynamics is key for device performance.

Purpose of the Study:

• To investigate surface-induced crystallization and amorphization in Germanium-antimony-tellurium (Ge2Sb2Te5) nanolayers.
• To model the effect of an external surface layer (ESL) on phase transformation kinetics.
• To determine an optimal ESL width for controlling surface-induced phase changes.

Main Methods:

• Utilized a phase field model incorporating Ginzburg-Landau (GL) equations.
• Introduced an external surface layer (ESL) with distributed surface energy and elastic properties.
• Solved coupled GL and elasticity equations to simulate crystallization and amorphization.

Main Results:

• The ESL width significantly impacts crystallization, with optimal growth observed for widths ≤ 1 nm.
• ESL accelerates surface nucleus growth but does not alter bulk crystallization rates.
• Amorphization temperature decreases with ESL presence, stabilizing for widths ≥ 0.5 nm.
• A linear relationship (Δsat/Δη ≅ 6.235Δγ/γin) was established for predicting ESL effects.

Conclusions:

• An external surface layer (ESL) plays a crucial role in surface-induced phase transformations of Ge2Sb2Te5 nanolayers.
• The optimal ESL width for controlling these transformations is determined to be between 0.5 nm and 1 nm.
• The derived linear relationship provides a predictive tool for estimating ESL effects in various surface-induced transformations.