Sandia National Laboratories, Albuquerque, NM 87185, USA.
Cornell High Energy Synchrotron Source, Cornell University, Ithaca, NY 14853, USA.
Sci Adv. 2017 May 5;3(5):e1602916. doi: 10.1126/sciadv.1602916. eCollection 2017 May.
Oriented attachment (OA) of synthetic nanocrystals is emerging as an effective means of fabricating low-dimensional nanoscale materials. However, OA relies on energetically favorable nanocrystal facets to grow nanostructured materials. Consequently, nanostructures synthesized through OA are generally limited to a specific crystal facet in their final morphology. We report our discovery that high-pressure compression can induce consolidation of spherical CdSe nanocrystal arrays, leading to unexpected one-dimensional semiconductor nanowires that do not exhibit the typical crystal facet. In particular, in situ high-pressure synchrotron x-ray scattering, optical spectroscopy, and high-resolution transmission electron microscopy characterizations indicate that by manipulating the coupling between nanocrystals through external pressure, a reversible change in nanocrystal assemblies and properties can be achieved at modest pressure. When pressure is increased above a threshold, these nanocrystals begin to contact one another and consolidate, irreversibly forming one-dimensional luminescent nanowires. High-fidelity molecular dynamics (MD) methods were used to calculate surface energies and simulate compression and coalescence mechanisms of CdSe nanocrystals. The MD results provide new insight into nanowire assembly dynamics and phase stability of nanocrystalline structures.
取向附着（OA）合成纳米晶体作为一种有效的方法来制造低维纳米材料。然而，OA 依赖于能量有利的纳米晶面来生长纳米结构材料。因此，通过 OA 合成的纳米结构通常限于其最终形态的特定晶面。我们报告了我们的发现，高压压缩可以诱导球形 CdSe 纳米晶阵列的固结，导致意想不到的一维半导体纳米线，不显示典型的晶面。特别地，原位高压同步加速器 X 射线散射、光学光谱和高分辨率透射电子显微镜表征表明，通过外部压力操纵纳米晶之间的耦合，可以在适度的压力下实现纳米晶组装和性质的可逆变化。当压力增加到超过阈值时，这些纳米晶开始相互接触并固结，不可逆地形成一维发光纳米线。高保真度分子动力学（MD）方法被用来计算表面能和模拟 CdSe 纳米晶的压缩和聚结机制。MD 结果为纳米线组装动力学和纳米晶结构的相稳定性提供了新的见解。
