Poly(amidoamine) (PAMAM) dendrimers can be used as a polymeric template/stabilizer/ reservoir to prepare stable gold-dendrimer nanocomposites by reducing PAMAM-tetrachloroaurate polysalts using hydrazine. In the gold-dendrimer nanocomposite, the presence of elemental gold is indicated by its characteristic plasmon absorption peak at 529 nm in aqueous solution and is visualized by transmission electron microscopy (TEM) equipped with energy-dispersive X-ray spectroscopy (EDXS). Electrostatic layer-by-layer assembly of the gold-dendrimer nanocomposite using poly(sodium 4-styrenesulfonate) (PSS) as the oppositely charged polyelectrolyte leading to nanoscale uniform multilayers of gold-dendrimer nanoclusters is reported. UV-vis absorption spectra from the consecutive multilayers indicated that each bilayer growth is regular, even though a 20 nm absorption bathochromic shift takes place in the film. TEM of PSS/gold-dendrimer nanocomposite film demonstrates that gold nanoparticles (5-20 nm) appear as aggregates within a gold-dendrimer nanocomposite monolayer, an observation borne out by crystalline gold electron diffraction patterns obtained from PSS/gold-dendrimer nanocomposite. Atomic force microscopy (AFM) of PSS/gold-dendrimer nanocomposite film indicates that the nanoclusters are arrayed with high uniformity at the nanometer scale.

Nanocrystalline TiO2 amphoteric colloidal charged particles and polyelectrolytes have been used to fabricate a dye-sensitized solar cell. Two weak polyelectrolytes, poly(allylamine hydrochloride) and poly(acrylic acid), and two strong polyelectrolytes, poly(dimethyldiallylammonium chloride) (PDAC) and poly(sodium 4-styrenesulfonate), have been utilized to assemble polyion/TiO2 nanocomposite multilayered films by the electrostatic layer-by-layer deposition technique. The layer-by-layer assembly of the TiO2 nanoparticles proceeds linearly as shown by sequential UV−vis absorption and thickness measurements. The morphology of these assemblies was characterized using atomic force microscopy. The nanoporous polyion/TiO2 films were sintered and used as working electrodes for cis-di(thiocyanato)-N,N-bis(2,2‘-bipyridyldicarboxylate)-ruthenium(II) (N3) sensitized solar cells. I−V characteristics of the solar cells made by the calcinated polyelectrolyte/TiO2 electrodes show several interesting results. (i) The short-circuit current does not linearly increase with the thickness of the TiO2 electrode, even though the adsorption behavior of the N3 dye shows a linear increase. (ii) The precursor polyelectrolytes used to assemble TiO2 play a major role in the photovoltaic performance of the solar cells. Thermogravimetric analysis studies show that the thermal stability of the polyelectrolytes may have a direct effect on the overall device efficiency. (iii) The photovoltaic performance of these solar cells is comparable to that of cells made by other methods such as spin casting, the layer-by-layer technique offers unsurpassed control in manipulating the final device thickness. An efficiency of 7.2% was obtained for the solar cell made from PDAC/TiO2 (200 bilayers) precursor film, under 1 sun at simulated Air Mass 1.5 direct irradiation.

The purple membrane (PM) containing bacteriorhodopsin (BR) is a promising biomaterial for many potential optical and optoelectronic device applications. Organized, heterogeneous assemblies using polycationic poly(dimethyldiallylammonium chloride) (PDAC) and PM fragments have been successfully constructed by the spontaneous alternating adsorption of PDAC and PM. The fabrication process of the multilayers was followed by UV−vis absorption spectroscopy and ellipsometry. The results indicate that the deposition process is linear and highly reproducible from layer to layer and that a monomolecular film of PM may be obtained in each PDAC/PM bilayer by controlling the adsorption time. Second harmonic generation measurements from the composite films gave a second-order susceptibility χ(2) of 8.1 × 10-9 esu and confirm that the PM fragments are arrayed with a high degree of orientation and acentric polar order in the films. Atomic force microscopy images provided the surface morphology of sequential layers of PDAC and PM fragments. Relative PDAC/PM bilayer thicknesses of 55 Å were observed, and the homogeneity of the layers was found to improve as the number of layers increased.

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