Formation of PbS Nanowire Pine Trees Driven by Screw Dislocations
Formation of PbS Nanowire Pine Trees Driven by Screw Dislocations
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DOI：
10.1021/ja906499a
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发表时间：
2009-11-18
影响因子：
15
通讯作者：
Jin, Song
中科院分区：
文献类型：
--
作者：
Lau, Y. K. Albert;Chernak, Davin J.;Jin, Song
以PbCl2和S为前驱体，采用化学气相沉积法制备了层状硫化铅(PbS)纳米线“松树”，并系统观察了氢气流量、温度、压力和生长衬底等生长参数对螺位错驱动纳米线生长的影响。统计结果表明，在600℃、900Torr、氢气流量为1.5sccm的典型反应条件下，位错驱动的主干生长速率约为6µm/min，而气-液-固(VLS)驱动的分支纳米线的生长速率约为1.2µm/min。氢气流动的开始加上新鲜硅的存在已经被确定为可重现地产生PbS纳米线树的关键因素。为了在经典晶体生长理论的背景下解释实验结果，前者被建议在实际硫前体H_2S的过饱和度中产生尖峰，并与螺杆组分引发位错，然后以各向异性的方式传播，形成PbS纳米线干。保持合适的氢气流量提供了有利的低过饱和度，促进了位错断裂的主干纳米线的生长，并使分支的VLS纳米线能够同时生长。此外，热力学考虑和实验表明，硅通过与H_2S可逆反应生成SiS_2来控制过饱和度，并且SiS_2也可以作为PbS纳米线生长的可行前驱体。总结了螺位错驱动纳米线生长的关键要求。这项研究为螺位错驱动的纳米线的进一步生长提供了一些一般性的指导。
The basic characteristics of nanowire growth driven by screw dislocations were investigated by synthesizing hierarchical lead sulfide (PbS) nanowire "pine trees" using chemical vapor deposition of PbCl2 and S precursors and systematically observing the effects of various growth parameters, such as hydrogen flow, temperature, pressure, and the growth substrates employed. Statistical surveys showed that the growth rate of the dislocation-driven trunk is about 6 mu m/min and that of the vapor-liquid-solid (VLS) driven branch nanowire is about 1.2 mu m/min under the typical reaction conditions at 600 degrees C, 900 Torr, and a hydrogen flow rate of 1.5 sccm. The onset of hydrogen flow plus the presence of fresh silicon have been identified as the critical ingredients for generating PbS nanowire trees reproducibly. To explain the experimental findings in the context of classical crystal growth theory, the former is suggested to create a spike in supersaturation of the actual sulfur precursor H2S and initiate dislocations with screw components that then propagate anisotropically to form the PbS nanowire trunks. Maintaining suitable hydrogen flow provides a favorable low supersaturation that promotes dislocation-cl riven trunk nanowire growth and enables the simultaneous VLS nanowire growth of branches. Furthermore, thermodynamic consideration and experiments showed that silicon fortuitously controls the supersaturation by reversibly reacting with H2S to form SiS2 and that SiS2 can also be a viable precursor for PbS nanowire growth. The key requirements of screw dislocation-driven nanowire growth are summarized. This study provides some general guidelines for further nanowire growth driven by screw dislocations.