Depletion-Mediated Interfacial Assembly of Semiconductor Nanorods,Nano Letters

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Depletion-Mediated Interfacial Assembly of Semiconductor Nanorods
Nano Letters ( IF 9.6 ) Pub Date : 2019-01-25 00:00:00 , DOI: 10.1021/acs.nanolett.8b04198
Dahin Kim ₁ , Wan Ki Bae ₂ , Shin-Hyun Kim ₁ , Doh C. Lee ₁

Affiliation

Electronic devices comprised of nanocrystal (NC) thin film are projected to demonstrate enhanced figure of merit if NC building blocks self-assemble into highly uniform, 2-dimensional (2-D) superstructures with long-range order. Despite intensive research efforts and remarkable progress, long-range assembly of colloidal anisotropic NCs into thin films with orientational and positional order has remained to be addressed. One of the most promising approaches is to dissolve excess free molecules into NC solution, which has enabled the formation of NC monolayers with exceptional quality at air/solution interface. Nevertheless, the assembly mechanism and the role of free molecules have not been comprehensively elucidated, restricting the use of the approach. Here, we find that the interfacial assembly of CdSe/CdS core/shell nanorods (NRs) results in various ordered structures in the presence of free oleic acid molecules. The structures include a bundle of standing NRs, a belt of multilayered lying NRs, and a monolayer smectic phase, obtained by simple change in density of surface ligands on the NRs. Experimental observation and theoretical calculation reveal that the assembly is initiated at the air/solution interface due to the preferential depletion attraction of NRs to the interface. However, subsequent growth is significantly altered depending on the ligand density that determines the relative magnitude of interface-NR depletion attraction to inter-NR attraction. Highly ordered structures of NRs, especially for the monolayer smectic phase, are promising as a polarized light-emitting layer for thin-film optical devices. In addition, our findings on the depletion-mediated NR assembly provide important and universal design criteria for 2-D structuring of NCs with diverse geometries and compositions.

中文翻译：

耗尽介导的半导体纳米棒的界面组装

预计由NC薄膜组成的电子设备将展示出，如果NC构件自组装成具有长程有序的高度均匀的二维（2-D）上层结构，则会提高品质因数。尽管进行了大量的研究工作并取得了显着进展，但胶体各向异性NCs长距离组装成具有取向和位置顺序的薄膜仍然有待解决。最有前途的方法之一是将多余的自由分子溶解到NC溶液中，这使得能够在空气/溶液界面形成具有卓越品质的NC单层。然而，尚未全面阐明组装机制和游离分子的作用，从而限制了该方法的使用。这里，我们发现CdSe / CdS核/壳纳米棒（NRs）的界面组装在存在游离油酸分子的情况下导致各种有序结构。该结构包括一束直立的NR，一束多层的NR以及单层近晶相，这是通过简单改变NR上表面配体的密度而获得的。实验观察和理论计算表明，由于NR优先消耗到界面上，所以在空气/溶液界面开始组装。但是，随后的生长会根据配体密度而发生显着变化，而配体密度决定了界面NR耗竭吸引力与NR间相互作用的相对强度。NR的高度有序结构，尤其是对于单层近晶相，作为薄膜光学器件的偏振发光层，它们是有希望的。此外，我们关于耗尽介导的NR组装的发现为具有不同几何形状和成分的NC的二维结构化提供了重要且通用的设计标准。

更新日期：2019-01-25

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