CdSe Nanocrystals
The synthesis of CdSe nanocrystals by the reaction of dimethylcadmium with trioctylphosphine selenide in a trioctylphosphine oxide-trioctylphosphine TOPO-TOP coordinating solvent at 250-300 C Eq. 4 allows the preparation of colloidal nanocrystals with sizes from 1.7 to 15 nm soluble in a variety of organic solvents such as toluene, hexane, chloroform, etc. 23, 56 . The solubility of the particles is provided by the shell of TOPO molecules passivating the Cd surface sites whereas the selenium...
Nonaqueous Media
In most of the aqueous systems studied to date, sonochemical synthesis of metal colloids was achieved by the reactions of solute with primary and secondary radicals in the bulk solution phase. Suslick et al. 94-97 followed a different technique in order to synthesize metal nanoparticles in non-aqueous solvents. The general procedure followed by Suslicks group and others who have used the method is schematically shown in Fig. 4.13. Ultrasonic irradiation of organic liquids containing dissolved...
Info Dcl
1 K. Cornish, D.J. Silber, O.-K. Grosjean, N. Goodman, J. Nat. Rubb. Res. 1993, 8, 275-285. 2 H. Mooibroek, K. Cornish, Appl. Microbiol. Biotechnol. 2000, 53, 355-365. 3 D.C. Blackley, Polymer Lattices, Vol. 1, 2nd edn, Chapman amp Hall, London, 4 D. Hosler, S.L. Burkett, M.J. Tarka-nian, Science 1999, 284, 1988-1991. 5 H.-G. Elias, Gro e Molek le, Springer, Berlin Heidelberg New York Tokyo, 1986, pp. 5-7. 6 C. de i Condamine, F. Fresneau, Memoires de l'Academie Royale des Sciences, 1751, pp....
High Aspect Ratio Particles
The LbL method is essentially insensitive to template shape when polyelectrolytes are being used to modify particles that are larger than about 50 nm. The LbL method has been applied to modify the surface of nickel nanorods of average diameter 65nm and length 1.5 m Fig. 8.7a . The nickel nanorods were coated with eight layers of PDADMAC and PSS Fig. 8.7b 71 . TEM images of the modified particles reveal that the nickel nanorods were coated with polyelec-trolyte multilayers, the thickness of the...
CaP and GaAs Nanocrystals
The synthesis of gallium-related nanocrystals is more complex than that of indium-related ones. Very high temperatures are required to achieve satisfactory particle crystallinity. Thus, the synthesis of crystalline GaP particles from GaCl3 and tris- trimethylsilyl phosphine in TOPO-TOP medium was possible only after long-term annealing at 370-400 C 106 . The GaP nanocrystals prepared by this approach show interesting and unusual quantum size effects arising from the interplay between the direct...
PbSe
PbSe nanocrystals are of great potential interest due to the unique properties of bulk PbSe. Thus, bulk PbSe has a cubic rock salt crystal structure, a narrow direct band gap 0.26 eV and a large exciton Bohr radius 46 nm, about eight times larger than that of CdSe . As a result, size-quantization effects are much more pronounced in PbSe than in cadmium chalcogenides 96 , and the value of the band gap energy makes the PbSe nanocrystals interesting as emitters in the near-IR region. High-quality...
Emulsion Stability Against Ostwald Ripening Collisions and Coalescence
A stable emulsion of very small droplets is for historical reasons called a miniemulsion as proposed by Chou et al. 7 . To create such a state, the droplets must be stabilized both against molecular diffusion degradation Ostwald ripening - a monomolecular process or x1 mechanism and against coalescence by collisions a bimolecular process or t2 mechanism . When an oil-in-water emulsion is created by mechanical agitation of a heterogeneous fluid containing surfactants, a distribution of droplet...
Postpreparative Sizeselective Fractionation of Nanoparticles
As already mentioned above, the nanoparticle size distribution can often be improved through the post-preparative size fractionation which is based on the size-dependent variation of particle properties. The most frequently used size-selective Fig. 2.22 Absorption spectra of size-selected fractions thin lines obtained from crude solutions thick lines of various ll-VI and lll-V nanocrystals by applying the size-selective precipitation technique. Details of preparation and solvent nonsolvent...
Inorganic Colloids through Controlled Precipitation
Colloids made of inorganic materials are usually prepared via precipitation, a process that involves at least two steps nucleation and growth. To achieve monodispersity, these two steps must be separated into sequential stages that is, nucleation should be strictly avoided once growth has started. In a typical process, the monomer usually existing as a complex or a solid precursor must be added or released slowly at a well-controlled rate in order to keep it from passing the critical...
Miniemulsions Stabilized with Inorganic Nanoparticles
Addition of water-dispersible inorganic nanoparticles, e.g. colloidal silica, throughout miniemulsification leads to a potential structural complexity which covers the whole range from embedded particles as in the case of calcium carbonate and carbon blacks to surface bound inorganic layers as in the case of clays . The structure created by the ternary system oil water nanoparticles follows the laws of spreading thermodynamics, as they hold for ternary immiscible emulsions Fig. 6.16 TEM...
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This work has been supported in part by the AFOSR-MURI program at the UW, a Career Award from the National Science Foundation DMR-9983893 , a Research Fellowship from the Sloan P. Foundation a Fellowship from the David and Lucile Packard Foundation, and a Camille Dreyfus Teacher Scholar Award from the Dreyfus Foundation. Y. Y. and Y. L. thank the Center for Nanotechnology at the UW for Student Fellowship Awards. 312 9 Colloidal Crystals Recent Developments and Niche Applications 9.10 1 a D. H....
Transient Regime of Particle Growth Focusing and Defocusing of Particle Size
As mentioned in the previous section, nano-OR results in a particle size distribution above 15 which is still rather broad. Narrower size distributions can be achieved if the growth of nanoparticles occurs in a transient regime and is terminated before the equilibrium between particles and monomer is attained. If only a part of the precursors is converted to nanoparticles at the nucleation stage and a considerable amount of precursors is still present in the colloidal solution in the form of...
Inverse Miniemulsions
The concept of miniemulsion stabilization is not restricted to direct miniemul-sions, but can also be extended to inverse miniemulsions where the osmotic pressure is built up by an agent insoluble in the continuous oily phase, a so-called lipophobe. Ionic compounds, simple salts, or sugars show a low solubility in organic solvents and can be used as lipophobes in water-in-oil miniemulsions 71 . Another adaptation of the process is that for the dispersion of polar monomers in non-polar...
Nanoparticle Assembly
As an alternative to liquid structure-forming precursors that solidify in the voids of colloidal crystals, solid particles may be used as precursors provided that they are significantly smaller than the sphere templates. Macroporous materials can be prepared by introducing nanoparticle precursors with sizes of about 10 nm into the voids of colloidal crystals with sphere sizes of hundreds of nanometers , followed by removal of the colloidal crystal template. This is a relatively flexible...
Chemical Reactions
In this section, the use of sol-gel reactions coupled with the infiltration method see Section 8.3.1 is described. Although metal oxide precursors are widely used to form thin inorganic coatings on surfaces, the vast majority of them are extremely water sensitive, hydrolyzing and condensing upon direct contact with water 128 . An exception to this is the TALH precursor discussed in Section 8.2.1.3. When applied directly to modifying colloids, it is often difficult to control the precipitation...
Semiconductor Nanoparticles Synthesized in Aqueous Media
Various II-VI nanoparticles have been prepared in aqueous solutions using different thiols as stabilizing agents CdS 35 , CdSe 36 , CdTe 33 , CdxHg1-ATe 37 and HgTe 38 . Fig. 2.7 illustrates a typical aqueous synthesis using CdTe see Eq. 3 as an example. In the first stage, a hydrogen chalcogenide produced by reaction between Al2Te3 and H2S04 is introduced as gas at room temperature into the reaction vessel containing the aqueous solution of a metal salt and a suitable stabilizer at the...
Nanoparticles 1
The importance of modifying the surface properties of nanoparticles lies in modulating the unique size-dependent properties afforded by colloids in this size range, as well as their surface characteristics. Reducing the size of the particles to the Fig. 8.7 TEM images of a bare nickel nanorods b a nickel nanorod coated with eight layers of polyelectrolyte PDADMAC PSS c PDAD-MAC PSS nanotubes eight layers of polyelectrolyte obtained upon dissolution of the sacrificial nickel nanorod from the...
Electrochemical Deposition
In many of the methods previously described, complete filling of the interstitial spaces of the colloidal crystal is not achieved owing to factors such as the loss of solvent during sol-gel processing, decomposition of the precursor to a smaller structure-forming species, or the presence of void spaces between nanoparticle precursors. A method that solves this problem is template-directed electrochemical deposition 89 presented schematically in Fig. 15.6 . This technique typically begins with...
Twodimensional Arrays of Monodisperse Nanocrystals Formed by Selfassembly
Monodisperse nanoparticles easily organize themselves in ordered structures because of dispersive attractions caused by van der Waals forces 21, 119 . Both 2D and 3D arrays can be prepared simply by placing a drop of a colloidal solution of monodisperse nanoparticles on a suitable support and allowing the carrier solvent to evaporate slowly. Fig. 2.27 shows HRTEM images of 2D arrays of CdSe nanocrystals on carbon-coated copper TEM grids. A long-range hexagonal ordering is observed in all cases...
Polymers on Metals
Organic polymeric shells have also been successfully applied to encapsulating metal nanoparticles. These procedures can in principle be used for the stabilization and nanostructuration of the nanoparticles, just as in the case of metal oxides, but suffer from some limitations, such as dissolution in some organic solvents, or much higher sensitivity to high-temperature processing. Marinakos and coworkers 154-156 coated gold particles by the conducting polymers poly N-methylpyrrole and poly...
Teos Ethanol Ammonia Dye
3 Single dye layer single silica layer shell particles, solvent 25 ethanol in water 4 Prepared using APS-dye conjugate TEOS ratio of 1 54, 1.7-4.4 mol dye g silica. 3 Single dye layer single silica layer shell particles, solvent 25 ethanol in water 4 Prepared using APS-dye conjugate TEOS ratio of 1 54, 1.7-4.4 mol dye g silica. conjugate to TEOS affects the brightness or intensity of fluorescence as well as the particle size Imhof et al., 1999 Matthews et al., 2001 . Imhof et al. 1999 observed...
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Department of Chemical and Biomolecular Engineering The University of Melbourne Victoria 3010 Australia This book was carefully produced. Nevertheless, editor, authors and publisher do not warrant the information contained therein to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate. Library of Congress Card No. applied for A catalogue record for this book is available from the British...
Nanocrystals for Biolabeling
Recently, the possibility of employing semiconductor nanoparticles as fluorescence labeling reagents for biological imaging experiments has been demonstrated by the attachment of CdSe CdS 13 and CdSe ZnS 14, 146 core-shell nanocrystals to DNA molecules 13, 14 and proteins 146 . Semiconductor nanocrystals are photostable and have nearly continuous excitation spectra above the threshold of absorption, together with a strong, narrow and symmetric emission band which depends on the particle size....
IIIV Nanocrystals
While II-VI semiconductor nanocrystals have been studied extensively during the last two decades, much less information is available about their III-V analogues. The reason is that III-V semiconductors are more-covalent compounds and high temperatures are usually required for their synthesis. For covalent semiconductors, the synthesis of nanocrystals by colloidal techniques becomes increasingly difficult 98 . On the other hand, III-V nanocrystals can exhibit even more pronounced quantum size...
Saltprecipitation and Chemical Conversion
An alternative to the use of sol-gel precursors for the fabrication of macroporous materials by colloidal crystal templating employs metal salt precursors in conjunction with in situ chemical reactions 64-67 . In this method, a metal salt is first deposited in the voids of a colloidal crystal by precipitation from a saturated solution. This salt may be further converted to a form capable of undergoing high-temperature decomposition to a structure-forming solid. This approach is especially...
Electroless Deposition
A number of macroporous metals, including Ni, Cu, Ag, Au, and Pt, can be prepared by electroless deposition around colloidal crystals modified with catalytic particles 104 . Colloidal silica spheres are first functionalized with thiol groups via siloxane coupling agents, and are then organized into a colloidal crystal by convective self-assembly. The colloidal crystal is then immersed in a toluene solution containing gold nanoparticles, followed by drying and high-temperature treatment to...