Gold nanoparticle/alkanedithiol films were prepared via layer-by-layer self-assembly. For the assembly process, dodecylamine-stabilized Au nanoparticles with an average size of 4 nm and alkanedithiols with different alkylene chain lengths (C 6 , C 9 , C 12 , C 16 ) were used. The thickness of the films was determined by AFM and ranged between 26 and 34 nm. FE-SEM and TEM images indicate that the particle size within the film materials was similar to that of the dodecylamine-stabilized particles used for film preparation. The composition of the films was analyzed by XPS. The absence of the nitrogen signal indicated that the dodecylamine ligands were quantitatively exchanged by alkanedithiol molecules during film assembly. Two sulfur signals were observed, which could be assigned to sulfur bound to gold (S-Au) and to free thiol groups (S-H). As indicated by the relative signal intensities, about 60% of the alkanedithiol molecules were bound with both ends to the nanoparticles, whereas 40% were bound with only one thiol group. The C/S ratio was in good agreement with the stoichiometry of the alkanedithiol molecules. All films showed linear current-voltage characteristics. Conductivity measurements at variable temperature were consistent with an Arrhenius-type activation of charge transport. Using an activated tunneling model for describing the charge transport properties, we obtained an electron tunneling decay constant of β N ) 0.61 or 0.71, depending on the method used for data analysis. When the films were dosed with vapors of toluene and tetrachloroethylene, the resistance of the films increased reversibly. This response increased exponentially with increasing length of the alkanedithiol molecules. The chemical selectivity of the films corresponded essentially to the solubility properties of the alkanedithiol molecules.

Vapor-sensitive thin-film resistors comprising gold nanoparticles and different types of organic dendrimers (polyphenylene, poly(propylene imine) and poly(amidoamine)) were prepared via layer-by-layer self-assembly and characterized by UV/vis spectroscopy, atomic force microscopy, and conductivity measurements. While the metal nanoparticles were utilized to provide the film material with electric conductivity, the dendrimers served to cross-link the nanoparticles and to provide sites for the selective sorption of analyte molecules. Dosing the films with vapors of toluene, 1-propanol, and water significantly increased the film resistances. The chemical selectivity of this response was controlled by the solubility properties of the dendrimers.

We report on the electrical alignment of ZnO nanorods and their electrical properties. The ZnO nanorods were wet-chemically synthesized, and their length and diameter were adjusted to about 200−300 nm and 15−30 nm, respectively. The nanorods were deposited onto electrode structures and directed into 200- to 800-nm-wide electrode gaps by using alternating electric fields at frequencies between 1 and 10 kHz and field strengths between 106 and 107 V/m. The nanorods align parallel to the electric field lines and make electrical contact with the gold electrodes. Clear photoresponse to 366-nm ultraviolet light irradiation was demonstrated. The current−voltage characteristics of the aligned rods are strongly nonlinear and asymmetrical, showing rectifying, diode-like behavior and asymmetry factors up to 25 at 3-V bias voltage.

Layer‐by‐layer assembly of gold nanoparticle/dendrimer composite films is described in this article. Crosslinking the nanoparticles through disulfide‐functionalized polyphenylene dendrimers enables well‐controlled film deposition and serves to mechanically reinforce the film material. Chemiresistors based on such films (see Figure) display short response times, high sensitivity to volatile organic compounds, and a desirable low sensitivity to humidity.

Tris(hydroxymethyl)phosphine-capped gold nanoparticles (ca. 1−2 nm diameter) bind densely to DNA, although both species are negatively charged. The particles are also active catalysts for electroless plating of gold. Electroless plating after adsorption to calf thymus DNA immobilized on silicon provides nanowires as narrow as ca. 30−40 nm and electrical conductivities ca. one-thousandth that of bulk gold. Here we summarize our physical characterization of the particles and their DNA conjugates and initial electrical measurements after plating.

The power conversion efficiency of dye-sensitized solar cells crucially depends on the ability of the sensitizer to absorb light in a broad range of the solar spectrum. In order to increase this range of absorption, a tandem structure with two different sensitizer dyes in two different compartments of the cell, respectively, was realized. Overall power conversion efficiencies as high as η=10.5% and short circuit current densities of JSC=21.1 mA/cm2 were achieved under air mass 1.5 illumination with red dye and black dye in the upper and lower compartment of the cell, respectively.

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Mixed oxides Ti(1-x)Zr(x)O2 with 0 < x < or = 0.2 were synthesized by means of thermal hydrolysis for use in dye-sensitized solar cells. The lattice parameter d is observed to increase linearly with Zr content x. The band gap of the mixed oxides was measured to increase by up to 0.2 eV. The respective shift of the conduction band edge leads to an increase of the open circuit voltage (V(OC)) by up to 0.1 V. Among others, temperature-dependent measurements of V(OC) clearly identify the correlation between band edge shift and change in V(OC).