Optoelectronic Material Section, Department of Chemical Engineering, Delft University of Technology , Julianalaan 136, 2628 BL Delft, The Netherlands.
ACS Nano. 2014 Nov 25;8(11):11499-511. doi: 10.1021/nn504679k. Epub 2014 Oct 31.
Ligand exchange is a much-used method to increase the conductivity of colloidal quantum-dot films by replacing long insulating ligands on quantum-dot surfaces with shorter ones. Here we show that while some ligands indeed replace the original ones as expected, others may be used to controllably remove the native ligands and induce epitaxial necking of specific crystal facets. In particular, we demonstrate that amines strip lead oleate from the (100) surfaces of PbSe quantum dots. This leads to necking of QDs and results in cubic superlattices of epitaxially connected QDs. The number of amine head-groups as well as the carbon chain length of linear diamines is shown to control the extent of necking. DFT calculations show that removal of Pb(oleate)2 from (100) surfaces is exothermic for all amines, but the driving force increases as monoamines < long diamines < short diamines < tetramines. The neck formation and cubic ordering results in a higher optical absorption cross section and higher charge carrier mobilities, thereby showing that the use of the proper multidentate amine molecules is a powerful tool to create supercrystals of epitaxially connected PbSe QDs with controlled electronic coupling.
配体交换是一种常用的方法，通过用较短的配体取代量子点表面上的长绝缘配体来提高胶体量子点薄膜的电导率。在这里，我们表明，虽然一些配体确实如预期的那样取代了原来的配体，但其他配体可能被用于可控地去除天然配体并诱导特定晶面的外延颈缩。特别是，我们证明胺可以从 PbSe 量子点的（100）表面剥离出 Pb 油酸酯。这导致 QD 的颈缩，并导致外延连接的 QD 的立方超晶格。胺的数量和线性二胺的碳链长度被证明可以控制颈缩的程度。DFT 计算表明，对于所有胺，从（100）表面去除 Pb(oleate)2 都是放热的，但驱动力随着单胺 <长二胺 <短二胺 <四胺而增加。颈缩形成和立方有序导致更高的光吸收截面和更高的电荷载流子迁移率，从而表明使用适当的多齿胺分子是一种强大的工具，可以创建具有受控电子耦合的外延连接 PbSe QD 的超晶体。
