Molecular Self-assembly Method Research Articles

Synthesis and characterization of new alkali-soluble polyimides and preparation of alternating multilayer nano-films therefrom

New alkali-soluble aromatic polyimides were prepared by a direct one-step polycondensation of 3,6-di(4-carboxyphenyl)pyromellitic dianhydride with common aromatic diamines in the presence of isoquinoline at 170 °C. The obtained polymers with inherent viscosities of the 0.62–1.01 g/dl range were all amorphous and highly soluble in dilute aqueous NaOH and tetramethylammonium hydroxide. Upon heating in TGA, the carboxylic acid groups degraded away at lower temperatures and the chain backbone did at higher temperatures. In DSC, no glass transition could be detected before decomposition. The alternating multilayer nano-films from the polyimides and poly(ethyleneimine) were prepared by the molecular self-assembly method and characterized by ellipsometry and X-ray reflectivity.

Guided molecular self-assembly: a review of recent efforts

This paper serves as an introductory review of significant and novel successesachieved in the fields of nanotechnology, particularly in the formation ofnanostructures using guided molecular self-assembly methods. Self-assembly is aspontaneous process by which molecules and nanophase entities may materializeinto organized aggregates or networks. Through various interactive mechanisms ofself-assembly, such as electrostatics, chemistry, surface properties, and via othermediating agents, the technique proves indispensable to recent functionalmaterials and device realizations. The discussion will extend to spontaneous andLangmuir–Blodgett formation of self-assembled monolayers on various substrates,and a number of different categories of self-assembly techniques based on thetype of interaction exploited. Combinatorial techniques, known as softlithography, of micro-contact printing and dip-pen nanolithography, whichcan be effectively used to up-size nanostructured molecular assemblies tosubmicrometer and micrometer scale patterns, will also be mentioned.

Novel properties of nanoscale organic–inorganic systems and photonic crystals — conducting polymers in nanoscale periodic structures, microcavities and photonic crystals

Conducting polymer/C60and C60doped conducting polymer/C60heterojunctions have been fabricated and found to exhibit remarkably enhanced photoresponse due to the highly effective photoinduced charge transfer at the interface. In conducting polymer/C60alkali metal nanoscale composite systems, multiphase superconductivity has been clarified and explained by taking the coupling of nanoscale grains by Josephson junctions into consideration. As examples of intramolecular organic-inorganic combined systems, unique electrical and optical characteristics have been revealed in oligosilanylene oligophenylene polymers. Electroluminescence has been demonstrated in organic-inorganic junction devices such as conducting polymer/porous Si and conducting polymer/diamond junctions. Conducting, polymer-based nanoscale multilayer systems have been studied utilizing molecular self-assembly method and novel photosensitive characteristics have been revealed. \\indent Novel optical and electrical properties of conducting polymers infiltrated in a photonic crystal, synthetic opal made of SiO2spheres of several hundred nm in diameter, and also a conducting polymer replica have been revealed. A clear diffraction pattern was observed in a photonic crystal infiltrated with conducting polymers, and transmission spectra are dependent on various ambient conditions. Their photoluminescence (PL) spectra, spectral narrowing of PL and lasing characteristics at relatively low optical excitation have also been clarified. Novel conducting characteristics of conducting polymers in a photonic crystal that was prepared by pyrolysis of a polymer replica of opal have also been observed.

Synthesis of nanoscale arrays of coupled metal dots

We report on a synthetic strategy for fabrication of close-packed planar arrays of nanometer diameter metal clusters. The clusters are single fcc crystals of gold, each encapsulated by a monolayer of alkyl thiol molecules. They are electronically coupled by means of aryl dithiol molecules. This structure, which is of interest for developing nanoscale electronics, is created using molecular self-assembly methods. It should prove possible to tune the conductivity of such arrays from the metallic limit to the insulating limit by controlling the size of the gold clusters and the strength of the electronic coupling between them.