Continuous Shape Tuning of Nanotetrapods: Toward Shape-Mediated Self-Assembly

Abstract

We describe a surfactant-driven method to synthesize highly monodisperse CdSe-seeded CdS tetrapods with differing arm lengths and diameters in order to examine their effects on self-assembly. We exploited the phenomena of weak-and strong-binding capping groups to tune the arm length and diameter with uniform shape and achieved >95% yield. Afterward, we utilize these particles to overcome some of the key problems in the assembly of anisotropic shaped particles. Intriguingly, we found that tetrapods with certain arm lengths pack like fishbone chains, which was greatly dependent on particle shape and size. These ordered assembly phenomena were understood with the assistance of computer simulations, which strongly support our experimental observations. Importantly, this work presents a synthetic route toward shape tuning in CdSe-seeded CdS tetrapod structures, which has great influence on their self-assembly behavior at the solution/substrate interface.

Type I vs. quasi-type II modulation in CdSe@CdS tetrapods: ramifications for noble metal tipping

“…Previously identified self-assembly mechanisms for tetrapods have highlighted the interdigitation of TP arms to form aggregated structures or "fishbone" type assemblies. 59 For the materials reported herein, we observed two new types of assembly for TP nanocrystals, which can be classified as "tip-to-tip" (as seen in Fig. 2 and 3) or "tip-to-core" (as seen in minority in Fig.…”

“…A major challenge for the synthesis of monodisperse CdSe@CdS tetrapods was the strict need for ZB CdSe NCs to maintain their crystallographic phase purity both prior to, and during, W CdS arm growth, which becomes increasingly challenging with decreasing particle size. 38,40,41,59 A major technical challenge that remained in the preparation of CdSe@CdS TPs was the ability to fully map the transition between type I vs. quasi-type II energetics by preparing uniform model tetrapods where only the size of the ZB CdSe was systematically varied from 2-6 nm.…”

“…Using this technique, arm length was controlled through a binary weak/strong binding ligand system consisting of carboxylic/phosphonic acids in ∼4 : 1 ratio, which previously has been demonstrated by Chan to affect final tetrapod dimensions. 59 An attractive feature of the reported synthetic methods was the ability to prepare tetrapods of uniform length (∼35 nm) from a wide range of zincblende CdSe seeds (2-6 nm) at large scale (500-1000 mg). As confirmed through detailed manual sizings, each tetrapod sample exhibits a wide (∼8-9 nm) CdS base which tapers to a small diameter (∼2-3 nm) tip, regardless of CdSe seed size (Fig.…”

Optical Properties, Synthesis, and Potential Applications of Cu-Based Ternary or Quaternary Anisotropic Quantum Dots, Polytypic Nanocrystals, and Core/Shell Heterostructures

“…Several excellent reviews have covered the theoretical and experimental investigations of the synthesis, optical properties, and multimodal applications in the past several years in great detail [1,2,3,4]. The most well-explored systems are the II-VI type Cd-based QDs [5,6], and corresponding Cd-based heterostructures [7,8,9]. More recently, Cu-based multicomponent (ternary, quaternary, and quasi-quaternary) QDs have become an area of great attention due to their specific advantages relative to its Cd-based counterparts and a range of other unique and important properties.…”

“…It is well known that the optical properties of QDs are not only size and composition dependent, but are also strongly determined by the resulting shape, with several morphologies demonstrating this, including nanorods (NRs), nanoplatelets (NPLs), and tetrapods (TPs). Their synthesis is well explored for Cd-based systems [7,13,14,15,16,17,18], with these nanostructures, especially NRs and TPs, showing increased electrical conductivity compared to core, quasi-spherical nanoparticles, and therefore are very appealing for applications requiring efficient charge transfer [19]. CdSe/CdS dot in rods, rod in rods, and CdSe nanoplatelets have been shown to demonstrate polarized emission for use in a liquid crystal display, acting as optical funnels, absorbing across a significant range of unpolarised wavelengths and then emitting strongly linearly polarised emission at a specific wavelength depending on the specific nanostructure [20].…”