.In situ temperature-dependent trainsmission electron microscopy studies of pseudobinary mGeTeBi2Te3 nanowires and first principles calculations

Title
.In situ temperature-dependent trainsmission electron microscopy studies of pseudobinary mGeTeBi2Te3 nanowires and first principles calculations
Authors
정찬수김한성임형순박기동박정희안재평유승조김진규김재녕심지훈
Keywords
Nanowire; in-situ TEM; Phase-change materials; GeTe center dot Bi2Te3; nanowires; superlattice; electrical conductivity
Issue Date
2015-06
Publisher
Nano letters
Citation
VOL 15, NO 6, 3923-3930
Abstract
Phase-change nanowires (NWs) have emerged as critical materials for fast-switching nonvolatile memory devices. In this study, we synthesized a series of mGeTe.Bi2Te3 (GBT) pseudobinary alloy NWsGe(3)Bi(2)Te(6) (m = 3), Ge4Bi2Te7 (m = 4), Ge5Bi2Te8 (m = 5), Ge6Bi2Te9 (m = 6), and Ge8Bi2Te11 (m = 8)and investigated their composition-dependent thermal stabilities and electrical properties. As m decreases, the phase of the NWs evolves from the cubic (C) to the hexagonal (H) phase, which produces unique superlattice structures that consist of periodic 2.2-3.8 nm slabs for m = 3-8. In situ temperature-dependent transmission electron microscopy reveals the higher thermal stability of the compositions with lower m values, and a phase transition from the H phase into the single-crystalline C phase at high temperatures (400 degrees C). First-principles calculations, performed for the superlattice structures (m = 1-8) of GBT and mGeTe.Sb2Te3 (GST), show an increasing stability of the H phase (versus the C phase) with decreasing m; the difference in stability being more marked for GBT than for GST. The calculations explain remarkably the phase evolution of the GBT and GST NWs as well as the composition-dependent thermal stabilities. Measurement of the current-voltage curves for individual GBT NWs shows that the resistivity is in the range 3-25 mO.cm, and the resistivity of the H phase is lower than that of the C phase, which has been supported by the calculations.
URI
http://pubs.kist.re.kr/handle/201004/51201
ISSN
15306984
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KIST Publication > Article
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