Design and Fabrication of Rocketlike Tetrapodal CdS Nanorods by Seed-Epitaxial Metal−Organic Chemical Vapor Deposition

Abstract

Single-crystalline rocketlike tetrapodal CdS nanorods were synthesized via a one-step seed-epitaxial MOCVD approach by thermal decomposition of Cd(S 2 CNEt 2 ) 2 powders. This bottom-up method uses silver particles to initiate and guide the preferential orientation of the axial nanorods, whereas the epitaxial growth of wurtzite-structured branches occurs on the cubic CdSe seeds. This controlled seedepitaxial method has potential as a general means of forming complex branching structures and may also offer opportunities for applications as building blocks for optoelectronic devices.Significant efforts have been made to control the size and shape of inorganic nanocrystals, because these parameters primarily determine their electronic and optical properties. 1-5 One way to achieve shape control is to enhance anisotropic nanocrystals growth using a liquid medium such as the vapor-liquid-solid (VLS) method. 6 Another common approach is to use surfactants or micelles (regular or inverse) as regulating agents or templates to facilitate anisotropic crystal growth. 7-9 More recently, complicated nanostructures, such as tetrapodlike, hierarchical, dendritic, etc., are highly desired considering their applications as interconnections in the "bottom-up" self-assembly approach toward future nanocircuits and nanodevices. Among them, tetrapodal branched nanostructures are typical because they present promising properties in field emission, mechanical reinforcement of polymer, infrared adsorption, photovoltaic devices, and so on. 10-15 Until now, tetrapodal crystals have frequently occured in several materials such as ZnO, 6 ZnS, 16 ZnSe, 2 CdS, 17 CdSe, 18 and CdTe, 10,19 which are generated through epitaxial growth of wurtzite-structured arms out of the zinc-blende-phased core. 20 In all above cases, however, harsh conditions such as reactions in organic solvents or chemical vapor deposition at high temperatures are normally required. Obviously, seeking new and versatile synthetic routes may be very important.In forming the tetrapodal structure, phase control and switching (nucleation in the zinc blende phase while growing in the wurtzite phase) are key steps. To control these steps, it is necessary to change the nucleation and growth environments and separate the nucleation and growth processes, 21 and the epitaxial growth has long been regarded as the best strategy. Epitaxial growth, however, usually takes place two-dimensionally on a planar substrate; recently, it has been built three-dimensionally on the nanowire surfaces between two materials with the same crystal structure. 22 In addition, the epitaxial growth of wurtzite layers out of a tetrahedral zinc core has been observed before. 23 The growth of these self-assembled nanoarchitectures is based on the crystallographic characteristics. This motivated us to design and fabricate 3D CdS nanoarchitectures. It is well-known that zinc blende CdSe and wurtzite CdS have similar crystal structures and close lattice constants. In accordance with the lattice-matching theory, eff...

ZnS nanostructures: From synthesis to applications

“…These experimental results showed a direct evidence of the zinc blende octahedron nucleus model, which could give a clue for explaining the formation of ZnS tetrapod nanostructures [244]. Using cubic CdSe nanocrystals as the seeds, Yao and co-workers fabricated size-tunable ZnS tetrapods via a one-step seed-epitaxial MOCVD approach [245][246][247]. The ZnS tetrapods had a CdSe nanocrystal core at the center with four wurtzite ZnS arms growing out from the core along four [0 0 0 1] directions.…”

Synthesis and Cathodoluminescence of Morphology-Tunable SiO2 Nanotubes and ZnS/SiO2 Core−Shell Structures Using CdSe Nanocrystals as the Seeds

“…In recent years, we have done some research on the growth of various semiconductor nanostructures by introducing CdSe nanocrystals (NCs) into the gas-phase growth process. 43,44 Our method relies on a buffer layer of cubic CdSe NCs on the silicon substrate on which branched ZnSe nanowires and rocketlike CdS tetrapods are grown. As we know, with the additional of complex structures to nanostructures the potential for synthesizing materials with interesting electrical, optical, and mechanical properties is even greater.…”

Microwave-Assisted Synthesis of Cadmium Sulfide Nanoparticles: Effect of Hydroxide Ion Concentration

“…There are many reports about synthesis of CdS nanoparticles such as spray-pyrolysis [8,9], chemical vapor deposition [10,11], solvothermal [12,13] and sol-gel [14,15]. Nevertheless, a rapid and inexpensive alternative is the microwave-assisted synthesis [5,16,17].…”