Shape control of CdSe nanocrystals

Abstract

Nanometre-size inorganic dots, tubes and wires exhibit a wide range of electrical and optical properties that depend sensitively on both size and shape, and are of both fundamental and technological interest. In contrast to the syntheses of zero-dimensional systems, existing preparations of one-dimensional systems often yield networks of tubes or rods which are difficult to separate. And, in the case of optically active II-VI and III-V semiconductors, the resulting rod diameters are too large to exhibit quantum confinement effects. Thus, except for some metal nanocrystals, there are no methods of preparation that yield soluble and monodisperse particles that are quantum-confined in two of their dimensions. For semiconductors, a benchmark preparation is the growth of nearly spherical II-VI and III-V nanocrystals by injection of precursor molecules into a hot surfactant. Here we demonstrate that control of the growth kinetics of the II-VI semiconductor cadmium selenide can be used to vary the shapes of the resulting particles from a nearly spherical morphology to a rod-like one, with aspect ratios as large as ten to one. This method should be useful, not only for testing theories of quantum confinement, but also for obtaining particles with spectroscopic properties that could prove advantageous in biological labelling experiments and as chromophores in light-emitting diodes.

Colloidal Quantum Nanostructures: Emerging Materials for Display Applications

“…Besides using size to control their optical and electronic properties, SCNCs can be synthesized in a variety of shapes and dimensionalities (see below);17, 18, 19, 20, 21, 22 these characteristics govern the polarization and the directionality of the emission of the NCs. The surface of the NCs is easily processed, and hence NCs can be introduced onto various phases/substrates such as hydrophobic or hydrophilic media, and onto or into flexible or rigid substrates 23, 24, 25, 26.…”

Molecular Control of the Nanoscale: Effect of Phosphine–Chalcogenide Reactivity on CdS–CdSe Nanocrystal Composition and Morphology

“…18 Nearly spherical to rod-like shapes are produced using ligands such as hexyl phosphonic acid. 19 Aspect ratio is sensitive to phosphonic acid alkyl chain length; the shorter the chain, the more elongated and branched are the nanorods. 18,20 Aspect ratio control has been studied for ZnS, ZnSe,16,21 ABSTRACT We demonstrate molecular control of nanoscale composition, alloying, and morphology…”

Nanocrystals: Solution-based synthesis and applications as nanocatalysts

“…Actually, controlled synthesis of nanostructured materials has been achieved by many solution-based methods [40 45]. For example, Peng et al demonstrated that control of the growth kinetics of the II IV semiconductor CdSe via adjusting monomer concentration could be used to vary the shapes of the resulting particles from a nearly spherical morphology to a rodlike one, with aspect ratios as large as ten to one [46]; the O'Brien group synthesized monodisperse MnO nanocrystals by thermal decomposition of manganese acetate in the presence of oleic acid at 320 °C and showed that the particle size could be adjusted from 12 to 20 nm by controlling the aging time [47]; Hyeon and co-workers also reported a one nanometer-level diameter-controlled synthesis of monodisperse magnetic iron oxide nanocrystals obtained by seed-mediated growth of previously synthesized monodisperse nanoparticle seeds [48]. Although these exciting results provide effective strategies for the synthesis of nanocrystals with controllable shape and size, what is still required is much more rational control over the nanocrystals, namely, the ability to design and optimize nanostructures at will.…”