Phase Transitions In Polymorphic In2Se3 Nanostructures

Elham Mafi

We show that the amorphization process in phase-change In2Se3 nanowires grown by chemical vapor deposition can be driven by electronic effects and does not require the conventional thermal melt-quench process. In particular, using transmission electron microscopy, in situ single-nanowire Raman spectroscopy, scanning Kelvin probe microscopy, and finite-element simulations, we demonstrate that the electronic amorphization can be achieved under optical excitations at temperatures far below the thermal melting point. The mechanism of this electronic amorphization is likely related to the presence of atomic bonds with different strengths in the crystalline phase In2Se3 and the weakening of the weaker bonds by nonequilibrium electrons. Our findings suggest that In2Se3is a promising candidate for phase-change memory applications, with potential advantages including energy-efficient memory switching due to the electronic amorphization process and highly stable data storage as a result of a high melting point compared to Ge/Sb–Te alloys. On a more general level, these results indicate the need to take into account the electronic effects in modeling and understanding the phase transition processes in phase-change memories. We report the observation of the generation of dislocations in single-crystal phase-change In2Se3 nanowires under electrical pulses and the impact of these dislocations on electrical properties. Particularly, we correlated the atomic-scale structural characteristics with local electrical resistance variations, by performing transmission electron microscopy and scanning Kelvin probe microscopy on the same nanowires. By coupling the experimental results with first-principles density functional theory calculations, we show that the immobile dislocations are generated via vacancy condensations. Importantly, these dislocations lead to several orders of magnitude increase in the electrical resistance, while maintaining the single crystallinity of the lattice. These results significantly advance the fundamental understanding of the structure-property relation in this phase-change material under transient electrical excitations. From a practical perspective, the significant increase in the electrical resistance, driven by the formation of dislocations and reversible via electrical pulses, can be exploited as a new electronic state in the single-crystalline phase in this phase-change material.

Phase Transitions In Polymorphic In2Se3 Nanostructures

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