Kinetics of II-VI and III-V Colloidal Semiconductor Nanocrystal Growth:  “Focusing” of Size Distributions

Peng, Xiaogang; Wickham, and J.; Alivisatos, A. Paul

doi:10.1021/ja9805425

Cited by 1,844 publications

(1,926 citation statements)

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“…The molecular iron precursor (Fe(C 5 H 5 ) 2 ) facilitates diameter control and leads to diameter-uniform Fe 2 P@C nanocables, whereas the use of iron powder results in a wide size distribution of the Fe 2 P nanowires. The results are consistent with previously reported work, in which size-uniform 1-D nanocrystals were prepared from molecular metal precursors by the solution-based precursor injection method [14,15,[22][23][24][25][26]38]. Some prior studies have revealed that the size and size distribution of metal particles strongly affect those of the final products [24,[34][35][36].…”

Section: Resultssupporting

confidence: 92%

“…Recently, we replaced the elemental metal by a molecular metal precursor in the preparation of nanoscale transition metal phosphides and successfully obtained Fe 2 P@C core@shell nanocables [38]. Inspired by the precursor injection method [14,15,[22][23][24][25][26], we herein propose a suddentemperature-rise strategy for controlling the product size and shape. The experimental results show that a sudden rise in reaction temperature (from 220 to 400 °C ) can effectively control the diameter distribution of Fe 2 P@C nanocables obtained using a molecular precursor (ferrocene, Fe(C 5 H 5 ) 2 ) as the iron source, but had no influence on the diameter control of Fe 2 P nanowires synthesized from elemental Fe powder.…”

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confidence: 99%

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Magnetic Fe2P nanowires and Fe2P@C core@shell nanocables

et al. 2010

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We report the synthesis of one-dimensional (1-D) magnetic Fe 2 P nanowires and Fe 2 P@C core@shell nanocables by the reactions of triphenylphosphine (PPh 3 ) with Fe powder (particles) and ferrocene (Fe(C 5 H 5 ) 2 ), respectively, in vacuum-sealed ampoules at 380-400 °C . The synthesis is based on chemical conversion of micrometer or nanometer sized Fe particles into Fe 2 P via the extraction of phosphorus from liquid PPh 3 at elevated temperatures. In order to control product diameters, a convenient sudden-temperature-rise strategy is employed, by means of which diameter-uniform Fe 2 P@C nanocables are prepared from the molecular precursor Fe(C 5 H 5 ) 2 . In contrast, this strategy gives no obvious control over the diameters of the Fe 2 P nanowires obtained using elemental Fe as iron precursor. The formation of 1-D Fe 2 P nanostructures is ascribed to the cooperative effects of the kinetically induced anisotropic growth and the intrinsically anisotropic nature of hexagonal Fe 2 P crystals. The resulting Fe 2 P nanowires and Fe 2 P@C nanocables display interesting ferromagnetic-paramagnetic transition behaviors with blocking temperatures of 230 and 268 K, respectively, significantly higher than the ferromagnetic transition temperature of bulk Fe 2 P (T C = 217 K).

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Section: Resultssupporting

confidence: 92%

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confidence: 99%

Magnetic Fe2P nanowires and Fe2P@C core@shell nanocables

et al. 2010

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“…Since MSNs have low chemical potential and are also found at a local minima in the size dependent solubility curve, 15 they can not overcome the thermodynamic stability barrier to form RNCs through the Gibbs-Thompson growth mechanism at low temperature. 53,59 Therefore, we believe that the thermodynamic stability of (CdSe)19 at room temperature prevented the progression to RNCs. To confirm the identity of the CdSe nanocrystals and investigate the effects of surface ligand chemistry on the optical band gap, we purified samples withdrawn at one-hour time intervals, and analyzed the isolated product by LDI-MS (see Figure 2C).…”

Section: Resultsmentioning

confidence: 99%

Mechanistic Study of the Formation of Bright White Light-Emitting Ultrasmall CdSe Nanocrystals: Role of Phosphine Free Selenium Precursors

Dolai¹,

Dutta

Muhoberac³

et al. 2015

Chem. Mater.

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ABSTRACT:We have designed a new non-phosphinated reaction pathway, which includes synthesis of a new, highly reactive Se-bridged organic species (chalcogenide precursor), to produce bright white light-emitting ultrasmall CdSe nanocrystals of high quality under mild reaction conditions. The detailed characterization of structural properties of the selenium precursor through combined 77 Se NMR and laser desorption ionization-mass spectrometry (LDI-MS) provided valuable insights into Se release and delineated the nanocrystal formation mechanism at the molecular level. The 1 H NMR study showed that the rate of disappearance of Se-precursor maintained a single-exponential decay with a rate constant of 2.3 x 10 -4 s -1 at room temperature. Furthermore, the combination of LDI-MS and optical spectroscopy was used for the first time to deconvolute the formation mechanism of our bright white light-emitting nanocrystals, which demonstrated initial formation of a smaller key nanocrystal intermediate (CdSe)19. Application of thermal driving force for destabilization resulted in (CdSe)n nanocrystal generation with n = 29-36 through continuous dissolution and addition of monomer onto existing nanocrystals while maintaining a living-polymerization type growth mode. Importantly, our ultrasmall CdSe nanocrystals displayed an unprecedentedly large fluorescence quantum yield of ~27% for this size regime (<2.0 nm diameter). These mixed oleylamine and cadmium benzoate ligand-coated CdSe nanocrystals showed a fluorescence lifetime of ~90 ns, a significantly large value for such small nanocrystals, which was due to delocalization of the exciton wavefunction into the ligand monolayer. We believe our findings will be relevant to formation of other metal chalcogenide nanocrystals through expansion of the understanding and manipulation of surface ligand chemistry, which together will allow the preparation of "artificial solids" with high charge conductivity and mobility for advanced solid-state device applications.3

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“…During the growth of the particles, smaller particles will dissolve and become the constituents of larger particles, a process known as Ostwald ripening. 28 An effect of the Ostwald ripening is the increase in size distribution, a phenomenon termed "defocusing". This effect is seen clearly in the "flattening" of the exitonic peak as particles increase in size during the growth phase.…”

Section: Resultsmentioning

confidence: 99%

Silica-Coated CdTe Quantum Dots Functionalized with Thiols for Bioconjugation to IgG Proteins

et al. 2006

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Quantum dots (QDs) have been increasingly used in biolabeling recently as their advantages over molecular fluorophores have become clear. For bioapplications QDs must be water-soluble and buffer stable, making their synthesis challenging and time-consuming. A simple aqueous synthesis of silica-capped, highly fluorescent CdTe quantum dots has been developed. CdTe QDs are advantageous as the emission can be tuned to the near-infrared where tissue absorption is at a minimum, while the silica shell can prevent the leakage of toxic Cd 2+ and provide a surface for easy conjugation to biomolecules such as proteins. The presence of a silica shell of 2-5 nm in thickness has been confirmed by transmission electron microscopy and atomic force microscopy measurements. Photoluminescence studies show that the silica shell results in greatly increased photostability in Tris-borate-ethylenediaminetetraacetate and phosphate-buffered saline buffers. To further improve their biocompatibility, the silica-capped QDs have been functionalized with poly(ethylene glycol) and thiol-terminated biolinkers. Through the use of these linkers, antibody proteins were successfully conjugated as confirmed by agarose gel electrophoresis. Streptavidin-maleimide and biotinylated polystyrene microbeads confirmed the bioactivity and conjugation specificity of the thiolated QDs. These functionalized, silica-capped QDs are ideal labels, easily synthesized, robust, safe, and readily conjugated to biomolecules while maintaining bioactivity. They are potentially useful for a number of applications in biolabeling and imaging.

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Kinetics of II-VI and III-V Colloidal Semiconductor Nanocrystal Growth: “Focusing” of Size Distributions

Cited by 1,844 publications

References 20 publications

Magnetic Fe2P nanowires and Fe2P@C core@shell nanocables

Magnetic Fe2P nanowires and Fe2P@C core@shell nanocables

Mechanistic Study of the Formation of Bright White Light-Emitting Ultrasmall CdSe Nanocrystals: Role of Phosphine Free Selenium Precursors

Silica-Coated CdTe Quantum Dots Functionalized with Thiols for Bioconjugation to IgG Proteins

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