Metal Nanoparticle Films Research Articles

A new approach to molecular devices using SAMs, LSMCD and Cat-CVD

This paper proposes a new technology for the fabrication of molecular devices using nanotechnology based on liquid and surface sciences recently developed, such as the direct patterning of solid surfaces using the difference of hydrophobic and hydrophilic properties of self-assembled mono-layers and self-assembly films of metal nanoparticles, the fine fabrication of films by the method of Liquid Source Misted Chemical Deposition, and the Langmuir–Blodgett self-assembly films. In these liquid-based technologies, various kinds of organic compounds in solutions, including biological systems, can be used as functional materials in molecular devices. In addition, it has been found that the insulating inorganic films obtained by catalytic chemical vapor deposition are quite effective in the protection of molecular devices against water and/or oxygen. We confirm, from the experimental results presented in this report, that this new approach is practically promising in future.

Preparation and electrochemical polymerization of new multifunctional pyrrolethiolate-stabilized gold and palladium nanoparticles.

New pyrrolylalkanethiolate-stabilized gold and palladium nanoparticles have been prepared: electrochemical polymerization of their metal nanoparticles and their TEMPO-derivatized metal nanoparticles gave the remarkably stable poly(pyrrole metal nanoparticle) films on metal electrodes.

Controlled Electroless Deposition of Noble Metal Nanoparticle Films on Germanium Surfaces

Thin noble metal films have been prepared as a result of the immersion of germanium substrates into dilute, aqueous solutions of AuCl4-, PdCl42-, or PtCl42-, respectively. Deposition proceeds via galvanic displacement in the absence of fluoride, pH adjusters, complexing agents, or external reducing agents. This manner of metal deposition serves as a cost-effective, high-throughput methodology with control over surface morphology and deposition rate by modulation of plating parameters such as concentration, temperature, and immersion time.

Percolation model for electron conduction in films of metal nanoparticles linked by organic molecules

We have investigated theoretically and experimentally the temperature dependence of the conductance of films of Au nanoparticles linked by alkane dithiol molecules in the temperature range between 5 and 300 K. Conduction in these films is due to tunneling of single electrons between neighboring metal nanoparticles via the linker molecules. During tunneling an electron has to overcome the Coulomb charging energy. We find that the observed temperature dependence of the conductance is non-Arrhenius-like and can be described in terms of a percolation theory which takes account of disorder in the system. Disorder in our nanoparticle films is caused by variations in the nanoparticle size, fluctuations in the separation gaps between adjacent nanoparticles and by offset charges. To explain in detail our experimental data, a wide distribution of separation gaps and charging energies has to be assumed. We find that a wide Coulomb charging energy distribution can arise from random offset charges even if the nanoparticle size distribution is narrow.

A Versatile Surface Modification Scheme for Attaching Metal Nanoparticles onto Gold: Characterization by Electrochemical Infrared Spectroscopy

A simple method for preparing metal nanoparticle films immobilized on gold substrates is described. A variety of nanoparticle films are characterized by electrochemical infrared reflection-absorption spectroscopy (EC-IRAS) in which the anomalous negative-absorbance properties commonly observed in metal particle arrays can be completely controlled. Such anti-absorbance v C O band components obfuscating the EC-IRAS data interpretation are associated with the complex dielectric behavior induced by metal nanoparticles aggregates. To achieve a well distributed metal nanoparticle array, the substrates were pretreated with 3-mercaptopropyltrimethoxysilane before anchoring gold, platinum or platinum-ruthenium alloy nanoparticles on the gold substrates. The prepared nanoparticle films displayed excellent electrochemical properties implying facile electronic communication through the organic glue matrix between the nanoparticle arrays and the gold substrates. Coating of the gold nanoparticle arrays with platinum via copper underpotential deposition (UPD) steps furthermore demonstrates optimal electronic response between the nanoparticle arrays and the underlying substrate. These findings will facilitate better nanoparticle analysis by electrochemical and optical spectroscopic means.

Pressure-induced insulator conductor transition in a photoconducting organic liquid-crystal film.

Intermolecular separation determines the extent of orbital overlap and thus the rate of electron transfer between neighbouring molecules in an organic crystal. If such a crystal is compressed, the resistivity decreases owing to a diminishing intermolecular distance. Metal insulator transitions have been observed by applying hydrostatic pressure to, for example, Langmuir films of metal nanoparticles. But previous attempts to observe a clear transition point in organic crystals, such as anthracene and tetracene, were not successful owing to difficulties with electrically insulating the high-pressure cell. Here we report a different approach by using a sample that is photoconductive and forms an organized film. A cylindrical tip (approximately 100 microm in diameter) was used to compress the sample instead of a piston/cylinder structure, entirely eliminating the problem of electrical insulation. Furthermore, by illuminating the sample with a laser, the conductivity of the sample is increased by several orders of magnitude. By monitoring the photocurrent with sensitivity at the 10(-13) A level, changes in resistivity at very low pressure could be monitored. We observe a sharp increase in current that could indicate a transition from hopping to delocalized conduction.

Nanostructural composites of phthalocyanine and metals

Thin composite films of metal nanoparticles incorporated into a phthalocyanine matrix were prepared by simultaneous vacuum deposition of copper and phthalocyanine from two evaporation sources. Absorption spectra in both the IR and UV/VIS regions were measured in order to study changes of structure and properties with different volume fractions of copper in the films. The effective medium theory (EMT) approach was used to model optical spectra. A pronounced aging of composite layers was observed after the deposition.