Polymorphism of GeSbTe superlattice nanowires

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Scaling-down of phase change materials to a nanowire (NW) geometry is critical to a fast switching speed of nonvolatile memory devices. Herein, we report novel composition-phase-tuned GeSbTe NWs, synthesized by a chemical vapor transport method, which guarantees promising applications in the field of nanoscale electric devices. As the Sb content increased, they showed a distinctive rhombohedral-cubic-rhombohedral phase evolution. Remarkable superlattice structures were identified for the Ge8Sb 2Te11, Ge3Sb2Te6, Ge 3Sb8Te6, and Ge2Sb 7Te4 NWs. The coexisting cubic-rhombohedral phase Ge 3Sb2Te6 NWs exhibited an exclusively uniform superlattice structure consisting of 2.2 nm period slabs. The rhombohedral phase Ge3Sb8Te6 and Ge2Sb 7Te4 NWs adopted an innovative structure; 3Sb2 layers intercalated the Ge3Sb2Te6 and Ge 2Sb1Te4 domains, respectively, producing 3.4 and 2.7 nm period slabs. The current-voltage measurement of the individual NW revealed that the vacancy layers of Ge8Sb2Te11 and Ge3Sb2Te6 decreased the electrical conductivity. © 2013 American Chemical Society.

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Nano Letters

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