.In situ temperature-dependent trainsmission electron microscopy studies of pseudobinary mGeTeBi2Te3 nanowires and first principles calculations
- .In situ temperature-dependent trainsmission electron microscopy studies of pseudobinary mGeTeBi2Te3 nanowires and first principles calculations
- 정찬수; 김한성; 임형순; 박기동; 박정희; 안재평; 유승조; 김진규; 김재녕; 심지훈
- Nanowire; in-situ TEM; Phase-change materials; GeTe center dot Bi2Te3; nanowires; superlattice; electrical conductivity
- Issue Date
- Nano letters
- VOL 15, NO 6, 3923-3930
- 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.
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