CdTe nanocrystals capped with 1-mercapto-2,3-propandiol, CdSe nanocrystals capped with sodium citrate, and core-shell CdSe/CdS nanocrystals capped with sodium citrate were synthesized in aqueous solutions, and their surface was modified by 3-mercaptopropyltrimethoxysilane (MPS) in water-ethanol mixtures. By addition of sodium silicate, "raisin bun"-type composite particles were formed, with either CdTe, CdSe, or CdSe/CdS nanocrystals being homogeneously incorporated as multiple cores into silica spheres of 40-80 nm size, accompanied by some alteration of optical properties of the nanoparticles and, in particular, the reduction of the luminescence quantum yield. Further, growth of larger silica spheres (100-700 nm) can be performed by the Sto ¨ber technique using either MPS-modified semiconductor nanocrystals or "raisin bun"-type composite particles as seeds, which gives semiconductor-doped silica globules of desirable sizes in the submicrometer range. The composite spheres can be used as building blocks for 3D colloidal crystals, prepared in this study for CdS/CdSe-doped 250 nm silica colloid. The shift of the photonic band gap to the red was observed in photonic crystals made of nanoparticles-doped silica due to the high refractive index of the semiconductors.

The structure of the multilayer assemblies of yttrium iron garnet nanoparticles (YIG) with polyelectrolytes was investigated with the emphasis on the control of the particle density in the adsorption layers. It was found that the growth of YIG films prepared by the layer-by-layer assembly can occur via two deposition modes: (1) sequential adsorption of densely packed adsorption layers (normal growth mode) and (2) in-plane growth of isolated particle domains (lateral expansion mode). Importantly, the dependence of the optical density on the number of deposition cycles remains linear in both cases. Microscopy results indicate that the origin of the lateral growth is in the interplay of particle/particle and particle/polyelectrolyte interactions rather than in a substrate effect. The lateral expansion mode is a general attribute of the layer-by-layer deposition and can be observed for various aqueous colloids. For the preparation of sophisticated multifunctional assemblies on nanoparticles, the film growth via domain expansion should be avoided, and therefore, one must be able to control the growth pattern. The switch from lateral to normal growth mode can be effected by grafting charged organic groups to YIG nanoparticles. Hydrophobic interactions between the hydrocarbon groups of the modified YIG and polyelectrolyte significantly increase the attractive component of the particle/polyelectrolyte and particle/particle interactions. The films from modified YIG display densely packed nanoparticle layers with a greatly reduced number of defects.

We report formation of polyelectrolyte/multiwall carbon nanotube (MWNT) multilayers by the layer-by-layer assembly technique. Both "hollow" and "bamboo" type MWNTs were employed. Scanning electron and atomic force microscopy indicate high structural homogeneity of the prepared composites. Ellipsometry and the absorbance spectroscopy confirm sequential adsorption of oppositely charged nanotubes and the polyelectrolyte resulting in uniform growth of the polyelectrolyte/MWNT films. Measurements of the mechanical properties show that these are strong composite hybrid films with mechanical properties exceeding many carbon nanotube composites made by mixing, or in-situ polymerization. Bamboo-type carbon nanotube composites display ultimate tensile strength of 150 ± 35 MPa and Young modulus of 4.5 ± −0.8 GPa as compared to 110 ± 25 MPa and 2 ± 0.5 GPa in composites made from common hollow MWNTs. This indicates that the morphology of the fibers can substantially improve matrix connectivity on the material mitigating "telescopic effect" in MWNTs. The films made from bambootype MWNTs approach in strength recently reported layer-by layer composite films from single wall carbon nanotubes, while being substantially less expensive. These results confirm the potential of the layering method for the manufacturing of composites with high load of strong filler and importance of uniform distribution and good interconnectivity between carbon nanotubes and the polymer matrix.

can also be molded into macroporous structures by the templating method presented here. By appropriate modification and optimization of the templating procedure we expect that it will be possible to vary the pore-size range significantly. The macroporous metals may themselves be used as templates on which other materials could be deposited or grown. ExperimentalMonodisperse PS spheres were synthesized and packed into colloidal crystals by centrifugation as described previously [6]. Sphere diameters in various batches ranged from 420 ± 50 nm to 660 ± 30 nm. To prepare macroporous nickel oxide, nickel(II) acetate (2 g) was dissolved in either acetic acid (5 mL) or a mixture of H 2 O (5 mL)and ethanol (5 mL) at 60 C. After cooling to room temperature, any undissolved solid was removed by filtration. Centimeter-scale, close-packed, colloidal polystyrene crystals (1 g) were soaked in this solution for 3±5 min. Excess solution was removed from the impregnated colloidal crystals by vacuum filtration. The samples were dried at 60 C for 2 h. The dried composites were soaked in 10 mL of a saturated solution of oxalic acid in ethanol (ca. 25±30 g in 100 mL) for 3±5 min. After additional vacuum filtration and drying, the PS spheres were removed by calcination in flowing air at 360±575 C for 7±10 h (heating rate: 1 C/ min). Macroporous Ni was prepared by heating macroporous NiO in flowing H 2 at 300 C for 2±5 h (heating rate: 1 C/min) or by heating the nickel oxalate/PS composite in flowing nitrogen at 450±500 C for 10 h. Preparation of partially reduced samples containing both NiO and Ni was possible by decreasing the reduction time or temperature, or by carrying out a fast calcination, for example at 360 C for 1 h in fast flowing air.Electrochemical tests were performed in two electrode cells using 1 M aqueous KOH as the electrolyte and nickel pellets as both electrodes. Pellets were made by pressing a mixture of 10 wt.-% poly(vinylidene fluoride) binder with 90 wt.-% nickel to 1500 psi for 30 s.

Three-dimensional colloidal crystals have been grown by electrophoretic deposition on ITO glass supports from aqueous-ethanol colloidal solutions of monodisperse submicrometer-sized negatively charged polystyrene latex spheres. The technique offers the possibility to produce uniform single-crystal colloidal multilayers on the time scale of minutes, which is a drastic acceleration in comparison with the gravity sedimentation technique that needs weeks or even months. SEM and AFM images of colloidal crystals reveal that close-packed 3D fcc ordering of the latex spheres extends over large areas. Electrophoretically deposited colloidal crystals show a pronounced photonic stopband in the visible spectral range in the normal incidence transmission spectra with a position depending on the size of latex spheres. The electrophoretic deposition has also been used for the impregnation of 3D colloidal crystals with luminescent CdTe nanocrystals. The luminescence spectrum of CdTe nanocrystals shows a dip at the wavelengths corresponding to the spectral position of the photonic stopband of the colloidal crystal.

Hybrid thin films are prepared from 8 to 10 nm Fe3O4 nanoparticles and exfoliated montmorillonite clay by using layer-by-layer assembly on poly(diallyldimethylammonium bromide), PDDA. Distinct stratification of the Fe3O4/PDDA/clay films is obtained due to the sheetlike structure of the clay particles. This feature distinguishes these assemblies from their polyelectrolyte-polyelectrolyte analogues, where the layers of individual polyelectrolytes are strongly interdigitated. Being adsorbed on PDDA strictly parallel to the substrate surface, montmorillonite produces a dense layer of overlapping alumosilicate sheets, which virtually flawlessly separates one magnetite layer from another. The difference in magnetic properties between assemblies of various architectures is attributed to the insulation effect of clay layers inserted between magnetic layers. The montmorillonite sheets disrupt the electron exchange interactions between the magnetite nanoparticles in adjacent layers, thereby limiting the magnetization reversal to two dimensions. Some optical properties of Fe3O4/PDDA films are investigated as well. When they are deposited on thin plastic substrate, oscillations of optical density were observed in the red part of the UV-vis spectrum. This effect, which was never been observed for conventional, thick substrates such as glass slides, stems from the interference of the light beams passed through and reflected off of the assembled film.

Magnetization-induced second-harmonic generation (SHG) in layer-by-layer assembled films containing yttrium iron garnet nanoparticles is observed. The SHG intensity, including its magnetoinduced component, linearly increases with the number of self-assembling layers, which indicates along with diffuseness of the SHG radiation that SHG occurs in its incoherent form: hyper-Rayleigh scattering (HRS). The nonlinear magneto-optical Kerr effect in HRS has a noticeable magnetic contrast brought about by the internal homodyne mechanism.

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