Department of Materials Science and Engineering, University of California, Los Angeles , Los Angeles, California 90024, United States.
Nano Lett. 2013;13(12):6009-15. doi: 10.1021/nl4032023. Epub 2013 Dec 2.
The vapor-liquid-solid (VLS) mechanism is the predominate growth mechanism for semiconductor nanowires (NWs). We report here a new solid-liquid-solid (SLS) growth mechanism of a silicide phase in Si NWs using in situ transmission electron microcopy (TEM). The new SLS mechanism is analogous to the VLS one in relying on a liquid-mediating growth seed, but it is fundamentally different in terms of nucleation and mass transport. In SLS growth of Ni disilicide, the Ni atoms are supplied from remote Ni particles by interstitial diffusion through a Si NW to the pre-existing Au-Si liquid alloy drop at the tip of the NW. Upon supersaturation of both Ni and Si in Au, an octahedral nucleus of Ni disilicide (NiSi2) forms at the center of the Au liquid alloy, which thereafter sweeps through the Si NW and transforms Si into NiSi2. The dissolution of Si by the Au alloy liquid mediating layer proceeds with contact angle oscillation at the triple point where Si, oxide of Si, and the Au alloy meet, whereas NiSi2 is grown from the liquid mediating layer in an atomic stepwise manner. By using in situ quenching experiments, we are able to measure the solubility of Ni and Si in the Au-Ni-Si ternary alloy. The Au-catalyzed mechanism can lower the formation temperature of NiSi2 by 100 °C compared with an all solid state reaction.
蒸气-液体-固体（VLS）机制是半导体纳米线（NWs）生长的主要机制。我们在这里报告了一种使用原位透射电子显微镜（TEM）在 Si NWs 中形成硅化物相的新的固-液-固（SLS）生长机制。新的 SLS 机制类似于依赖于液体介导生长种子的 VLS 机制，但在成核和质量输运方面却有根本的不同。在 Ni 双硅化物的 SLS 生长中，Ni 原子通过 Si NW 中的间隙扩散从远程 Ni 颗粒中提供，然后到达 NW 尖端的预先存在的 Au-Si 液态合金滴。当 Au 中 Ni 和 Si 达到过饱和时，八面体 Ni 双硅化物（NiSi2）核在 Au 液态合金的中心形成，此后该核在 Si NW 中扫过并将 Si 转化为 NiSi2。通过接触角在 Si、Si 的氧化物和 Au 合金相遇的三点处进行振荡，溶解 Si 的 Au 合金液态中介层进行溶解，而 NiSi2 则以原子逐步的方式从液态中介层中生长。通过使用原位淬火实验，我们能够测量 Ni 和 Si 在 Au-Ni-Si 三元合金中的溶解度。与全固态反应相比，Au 催化机制可以将 NiSi2 的形成温度降低 100°C。
