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Jung, Chan Su,Kim, Han Sung,Im, Hyung Soon,Park, Kidong,Park, Jeunghee,Ahn, Jae-Pyoung,Yoo, Seung Jo,Kim, Jin-Gyu,Kim, Jae Nyeong,Shim, Ji Hoon American Chemical Society 2015 NANO LETTERS Vol.15 No.6
<P>Phase-change nanowires (NWs) have emerged as critical materials for fast-switching nonvolatile memory devices. In this study, we synthesized a series of <I>m</I>GeTe·Bi<SUB>2</SUB>Te<SUB>3</SUB> (GBT) pseudobinary alloy NWsGe<SUB>3</SUB>Bi<SUB>2</SUB>Te<SUB>6</SUB> (<I>m</I> = 3), Ge<SUB>4</SUB>Bi<SUB>2</SUB>Te<SUB>7</SUB> (<I>m</I> = 4), Ge<SUB>5</SUB>Bi<SUB>2</SUB>Te<SUB>8</SUB> (<I>m</I> = 5), Ge<SUB>6</SUB>Bi<SUB>2</SUB>Te<SUB>9</SUB> (<I>m</I> = 6), and Ge<SUB>8</SUB>Bi<SUB>2</SUB>Te<SUB>11</SUB> (<I>m</I> = 8)and investigated their composition-dependent thermal stabilities and electrical properties. As <I>m</I> 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 <I>m</I> = 3–8. <I>In situ</I> temperature-dependent transmission electron microscopy reveals the higher thermal stability of the compositions with lower <I>m</I> values, and a phase transition from the H phase into the single-crystalline C phase at high temperatures (400 °C). First-principles calculations, performed for the superlattice structures (<I>m</I> = 1–8) of GBT and <I>m</I>GeTe·Sb<SUB>2</SUB>Te<SUB>3</SUB> (GST), show an increasing stability of the H phase (versus the C phase) with decreasing <I>m</I>; 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 mΩ·cm, and the resistivity of the H phase is lower than that of the C phase, which has been supported by the calculations.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2015/nalefd.2015.15.issue-6/acs.nanolett.5b00755/production/images/medium/nl-2015-007559_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl5b00755'>ACS Electronic Supporting Info</A></P>