Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY 11973, USA.
Nanotechnology. 2011 Jul 22;22(29):295605. doi: 10.1088/0957-4484/22/29/295605. Epub 2011 Jun 17.
We use in situ observations by variable temperature transmission electron microscopy on AuGe alloy drops at the tips of Ge nanowires (NWs) with systematically varying composition to demonstrate the controlled formation of metastable solid phases integrated in NWs. The process, which operates in the regime of vapor-liquid-solid growth, involves a size-dependent depression of the alloy liquidus at the nanoscale that leads to extremely Ge-rich AuGe melts at low temperatures. During slow cooling, these liquid AuGe alloy drops show pronounced departures from equilibrium, i.e., a frustrated phase separation of Ge into the adjacent solid NW, and ultimately crystallize as single-crystalline segments of metastable γ-AuGe. Our findings demonstrate a general avenue for synthesizing NW heterostructures containing stable and metastable solid phases, applicable to a wide range of materials of which NWs form by the vapor-liquid-solid method.
我们通过变温透射电子显微镜对锗纳米线（NWs）尖端的 AuGe 合金液滴进行了原位观察，系统地研究了合金液滴的成分变化，证明了亚稳固相的可控形成。该过程在汽-液-固生长的条件下进行，涉及纳米尺度上的合金液相线的尺寸依赖性降低，导致低温下的 AuGe 熔体中 Ge 非常丰富。在缓慢冷却过程中，这些液态 AuGe 合金液滴明显偏离平衡，即 Ge 向相邻的固态 NW 发生受阻的相分离，最终结晶为亚稳 γ-AuGe 的单晶段。我们的研究结果为合成包含稳定和亚稳固相的 NW 异质结构提供了一条通用途径，适用于通过汽-液-固方法形成 NW 的多种材料。
