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.

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.

Networked films comprising gold nanoparticles (4 nm core diameter) and dodecanedithiol were deposited via layer-by-layer self-assembly. The film thickness was controlled by the number of deposition cycles and ranged from submonolayer to multilayer coverage with up to 60 nm thickness. FE-SEM and XPS revealed island growth during the first four to five deposition cycles. At room temperature, films based on islands showed slightly nonlinear current-voltage curves, whereas thicker films gave Ohmic behavior. Between 100 and 300 K, the temperature dependence of conductance was consistent with an Arrhenius model for activated charge transport. The chemical sensitivity of the films was characterized by dosing them with vapors of toluene, 4-methyl-2-pentanone, 1-propanol, and water while monitoring their relative differential resistances. Thin films responded with a decrease in the resistance, whereas thicker films responded with a resistance increase. The results indicate that swelling along the film normal may be important for the underlying sensing mechanism of homogeneous multilayer films. Changes in permittivity and/or swelling-induced decrease of the interisland distance can be responsible for the observed decrease in resistance of the thinner films.

Gold-nanoparticle/organic films were prepared via layer-by-layer self-assembly using dodecylamine-stabilised Au-nanoparticles and poly(propyleneimine) (PPI) dendrimers of generation one to five (G1-G5) or hexadecanedithiol (HDT) as linker compounds. TEM and FE-SEM images revealed that the bulk of the films consisted of nanoparticles with diameters of about 4 nm. XPS was used to study the chemical composition of the films. The C 1s and N 1s signals of an AuPPI-G4 film were interpreted qualitatively according to the dendrimer structure. The absence of the nitrogen signal in case of an AuHDT film indicated that the dodecylamine ligands were quantitatively exchanged during film assembly. About 76% of the sulfur atoms were bound to the nanoparticles. the remainder being present as free thiol (S H) groups. All films displayed linear current voltage characteristics and Arrhenius-type activation of charge transport. The conductivities of the AuPPI films decreased exponentially over approximately two orders of magnitude (6.8 x 10(-2) to 1.0 x 10(-3) ohms(-1) cm(-1)) with a five-fold increase of the dendrimer generation number. Dosing the films with solvent vapours caused their resistances to increase. Using different solvent vapours demonstrated that the sensitivity of this response was determined by the solubility properties of the linker compounds. Microgravimetric measurements showed that absorption of analyte was consistent with a Langmuir adsorption model. These measurements also revealed a linear correlation between the electrical response (deltaR/Rini) and the concentration of absorbed analyte. The absorption of d4-methanol from a saturated vapour atmosphere was studied by neutron reflectometry with an AuPPI-G4 film. This measurement indicated condensation of methanol on top of the film and a uniform distribution of the analyte across the film thickness.