Oriented polyoxometalate-polycation multilayers on a carbon substrate

In this paper, a new method of fabricating multilayers on a carbon substrate is presented. First, a uniformly charged carbon surface was prepared through molecular design. Then an ultrathin film consisting of layer-pairs of oppositely charged polymeric cationic poly(diallyldimethylammonium chloride) (PDDA) and silicotungstate, SiW12O404- (SiW12), was grown layer-by-layer onto the grafted carbon substrate using a molecular self-assembly technique and an electrochemical method. The technique allows one to prepare highly adherent, dense and smooth films of polyoxometalates with special properties. By combining cyclic voltammetry (CV) and X-ray (XR) reflectometry, it was determined that the average surface density of SiW12 was 2.10 x 10(-10) mol cm(-2), and the thickness increase per adsorption of PDDA-SiW12 was 1.7 +/- 0.2 nm, indicating that the amount of SiW12 anion per one layer adsorption corresponded to a monolayer coverage. Atomic force microscopy (AFM) was also used to examine the surface morphology and determine the grain size distribution and roughness for multilayer films. An increase in root-mean-square (RMS) surface roughness from 7 to 9 Angstrom was observed as the number of layer-pairs in the film increased from 2 to 6. FTIR results showed that the good stability of the multilayer films was due to Coulomb interactions between the SiW12 anion and the polymeric cations PDDA. Moreover, the multilayer films, in acidic aqueous solution, showed good electrocatalytic activity toward the reduction of NO2-, and the catalytic currents increased with increasing the layer numbers of SiW12 adsorption. These characteristics of the multilayer films might find potential applications in the field of sensors and microelectronics devices.

Electrocrystallized platinum nanoparticle on carbon substrate

Platinum nanoparticles were electrocrystallized on a 4-aminophenyl monolayer-grafted carbon substrate. These Pt-modified surfaces were characterized by scanning tunneling microscopy (STM). The characterization by STM revealed that the platinum nanoparticles obtained had good size monodispersity and were well separated from one another on HOPG surfaces. (C) 2000 Elsevier Science S.A. All rights reserved.

A mica-modified quartz resonator for a quartz crystal microbalance study

Mica, as a bridge of the study for combining between quartz crystal microbalance (QCM) and atomic force microscope (AFM), was successfully modified onto the piezoelectric quartz crystal (PQC). This mica-modified piezoelectric quartz crystal (mica-PQC) can be stably oscillated with a shift frequency of +/-1 Hz per half an hour in air. Using this mica-PQC, the processes of DNA adsorbed onto the mica surface were studied in liquid phase. The results show that a bivalent cation, such as Mn2+, can be used as an ionic bridge to immobilize DNA on mica surface. The image of DNA on the mica surface was also obtained by AFM. Mica-PQC gives the possibility of a combination between QCM and AFM in situ.

Preparation, structures, and electrochemistry of a new polyoxometalate-based organic/inorganic film on carbon surfaces

The preparation, structure, and electrochemical and electrocatalytical properties of a new polyoxometalate-based organic/inorganic film, composed of cetyl pyridinum 11-molybdovanadoarsenate (CPMVA) molecules, have been studied. Cyclic potential scanning in acetone solution led to a stable CPMVA film formed on a highly oriented pyrolytic graphite (HOPG) surface. X-ray photoelectron spectroscopy, scanning tunneling microscopy, and cyclic voltammetry were used for characterizing the structure and properties of the CPMVA film. These studies indicated that self-aggregated clusters were formed on a freshly cleaved HOPG surface, while a self-organized monolayer was formed on the precathodized HOPG electrode. The CPMVA film exhibited reversible redox kinetics both in acidic aqueous and in acetone solution, which showed that it could be used as a catalyst even in organic phase. The CPMVA film remained stable even at pH > 7.0, and the pH dependence of the film was much smaller than that of its inorganic film (H4AsMo11VO40) in aqueous solution. The CPMVA film showed strong electrocatalysis on the reduction of bromate, and the catalytic currents were proportional to the square of the concentration of bromate. The new kind of polyoxometalate with good stability may have extensive promise in catalysis.

The single crystal-like banded textures in the films of a thermotropic liquid crystalline poly(aryl ether ketone) containing a lateral chloro group

The banded textures in the films of a thermotropic liquid crystalline poly(aryl ether ketone) containing a lateral chloro group have been studied by means of transmission electron microscopy(TEM), electron diffraction(ED) and atomic force microscopy (AFM). The crystallization-induced Landed texture without external shear can be formed when the thin films were annealed at the temperature range(320-330 degrees C) of the liquid crystalline state from the melt, The results show that the banded regions have high orientation of single crystal based on the orthorhombic packing and the growing direction of the Lands is along the b axis of the crystals, This kind of single crystal-like bands is due to the different orientation of the packing molecular chains, The molecular chains of the dark bands in the bright field electron micrograph are perpendicular to the film plane, while the ones of the bright Lands are tilt along the b axis with the tilt angle upto +/-20 degrees.

Electrochemical synthesis of polyaniline nanoparticles

Polyaniline nanoparticles were prepared on a highly oriented pyrolytic graphite (HOPG) surface from dilute polyaniline acidic solution (1 mM aniline + 1 M HClO4) using a pulsed potentiostatic method. Electrochemistry, Fourier transform infrared external reflection spectroscopy (FT-IR-ERS), X-ray photoelectron spectroscopy (XPS) and tapping-mode atomic force microscopy (TMAFM) were: used to characterize the composition and structure of the polyaniline nanoparticles. FT-IR-ERS and XPS results revealed that the polyaniline was in its emeraldine form. TMAFM measurement showed that the electropolymerized polyaniline nanoparticles dispersed on the:HOPG surface with a coverage of about 10(10) cm(-2). These nanoparticles were disk-shaped having a height of 10(-30) Angstrom and an apparent diameter varying from 200 to 600 Angstrom. The particle dimensions increased with the electropolymerization charge (Q) over the interval from 5.7 to 19.3 mu C cm(-2) (C) 2000 Elsevier Science S.A. All rights reserved.

Deoxyribonucleic acid sample preparation in scanning probe microscope

The process of deoxyribonucleio acid (DNA) sample preparation in scanning tunneling microscope (STM) and atomic force microscope (AFM) is reviewed. The main discussions are devoted to the methods, advantages or drawbacks and improvement of the DNA sample's immobilization and spreading.

Simple preparation method of multilayer polymer films containing Pd nanoparticles

A simple route to the fabrication of multilayer films containing Pd nanoparticles is described. Following layer-by-layer assembly of PdCl42- and polycation, QPVP-Os (a quaternized poly(4-vinylpyridine) complexed with [Os(bpy)(2)Cl](2+/+)), on 4-aminobenzoic acid-modified glassy carbon electrodes, the three-dimensional Pd nanoparticle multilayer films are directly formed on electrode surfaces via electrochemical reduction of PdCl42- sandwiched between polymers. The growth of PdCl42- is easy on electrode surfaces by electrostatic interaction, and the assembly processes are monitored by cyclic voltammetry and UV-vis spectroscopy. The depth profile analyses by X-ray photoelectron spectroscopy verify the constant composition of the Pd nanoparticle multilayer films. Atomic force microscopy proves that the as-prepared Pd nanoparticles are uniformly distributed with an average particle diameter of 3-7 mn. The resulting Pd nanoparticle multilayer-modified electrode possesses high catalytic activity for the reduction of dissolved oxygen and oxidation of hydrazine compounds in aqueous solution.

Shear-induced spiral-like morphology of a main-chain liquid crystalline poly(aryl ether ketone)

The shear-induced spiral-like morphology of a main-chain thermotropic liquid crystalline poly(aryl ether ketone) is observed and characterized by means of polarizing light microscopy, atomic force microscopy, transmission electron microscopy and electron diffraction techniques. The spiral-like texture is formed during shearing in the temperature range of liquid crystalline to isotropic transition (335-340 degreesC), and dispersed discontinuously in the mosaic matrix. Electron diffraction results indicate that the spiral exhibits orthorhombic lateral packing of the crystals and homeotropic alignment of the molecules. The spiral formation process and possible affecting factors are discussed.

Controlled nucleation and growth of surface-confined gold nanoparticles on a (3-aminopropyl)trimethoxysilane-modified class slide: A strategy for SPR substrates

The thickness of the gold film and its morphology, including the surface roughness, are very important for getting a good, reproducible response in the SPR technique. Here, we report a novel alternative approach for preparing SPR-active substrates that is completely solution-based. Our strategy is based on self-assembly of the gold colloid monolayer on a (3-aminopropyl)trimethoxysilane-modified glass slide, followed by electroless gold plating. Using this method, the thickness of films can be easily controlled at the nanometer scale by setting the plating time in the same conditions. Surface roughness and morphology of gold films can be modified by both tuning the size of gold nanoparticles and agitation during the plating. Surface evolution of the Au film was followed in real time by UV-vis spectroscopy and in situ SPRS. To assess the surface roughness and electrochemical stability of the Au films, atomic force microscopy and cyclic voltammetry were used. In addition, the stability of the gold adhesion is demonstrated by three methods. The as-prepared Au films on substrates are reproducible and stable, which allows them to be used as electrodes for electrochemical experiments and as platforms for studying SAMs.

Self-assembled monolayer of ssDNA on Au(111) substrate

Self-assembled monolayer of natural single-stranded DNA (ssDNA) from dl:natured plasmid DNA and pBR322/PstI marker was first observed on Au(111) by low-current STM (Lc-STM). The width of ssDNA stripe measured is 0.9 +/- 0.1 nm, which is just half of the theoretical width of double-stranded DNA (dsDNA). Each ssDNA stripe consists of bright and dark parts. alternatively; the period of two adjacent bright parts in the same ssDNA stripe measured is 0.4 +/- 0.1 nm, which is consistent with the theoretical distance between two adjacent base pairs in ssDNA. The stripe orientations in ssDNA domains are predominately at angles of 0 degrees, 60 degrees or 120 degrees relative to crystallographically faceted steps on the gold surface. The electrochemical experiment indicated that it was ssDNA but not dsDNA that was absorbed on Au(111)surface. (C) 2001 Elsevier Science B.V. All rights reserved.

Langmuir-Blodgett film formation from surfactant-capped zinc sulfide nanoparticles spread on water surface

The surfactant-capped ZnS nanoparticulate multilayer film has been fabricated by Langmuir-Blodgett(LB) technique. ZnS LB firm was investigated by the small-angle x-ray diffraction(XRD), atomic force microscopy(AFM) and transmission electron microscopy(TEM). The results indicate that ZnS nanoparticulate LB film is one-dimensional superlattice.

Structural and optical properties of distyrylbenzene derivative thin films

In order to understand the relationship between the molecular orientation and optical properties of oligophenylenevinylene film, oriented thin films of 1,4-di(p-methoxystyryl)benzene (DSB-1) and 1,4-di(p-methoxystyryl)-2,5-dimethoxybenzene (DSB-2) were fabricated on a potassium bromide (KBr) (001) surface by the vacuum-evaporation method. The structures and optical properties of DSB films have been investigated by transmission electron microscopy (TEM), atomic force microscopy (AFM) and polarized photoluminescence (PL) spectroscopy, respectively. DSB-1 molecules orient obliquely and/or parallel to the substrate surface depending on the substrate temperature. On the other hand, DSB-2 molecules tend to grow epitaxially with the molecular plane parallel to the substrate surface. The anisotropic molecular orientations represent the polarized PL. The epitaxial growth and molecular orientations observed by TEM and AFM at the local and microscopic scale are confirmed by polarized PL measurement on a macroscopic scale. (C) 1999 American Institute of Physics. [S0021-8979(99)01523-6].

Fabrication and characterization of heteropolyanion Langmuir-Blodgett films

The possibility of the formation of Langmuir-Blodgett (LB) films with dimethyldioctadecylammonium (DODA) after the addition of cobalt(II)-substituted Dawson-type tungstodiphosphate anion (briefed as (H2O)(CoP2W17O618-)-P-11) in the subphase has been explored. Marked modifications of the compression isotherms are observed when this anion is dissolved in the subphase, which demonstrates that the polyanions interact with the monolayers. LB films have been readily obtained from this system. The adsorption Fourier transform IR (FT IR) spectroscopy, atomic force microscopy (AFM), X-ray diffraction (XRD) and cyclic voltammetry (CV) have been used to investigate the morphological and molecular structure of the deposited film. The FT IR results showed the presence of the polyanion within the LB films, and the shift for its characteristic bands may be related to the presence of positively charged DODA. AFM measurement reveals that the LB films of DODA/(H2O)(CoP2W17O618)-P-II are regularly and uniformly deposited on the substrate. XRD experiments prove that the lamellar structure of the LB films of DODA/(H2O)(CoP2W17O618-)-P-II is well-defined. The LB films of DODA/(H2O)(CoP2W17O618-)-P-II immobilized onto an indium-oxide (ITO) glass, in aqueous solutions of pH 2.0-5.0, show quite facile redox reactions even for multilayers. All the experiments carried out in the present study suggest that the new materials of heteropolyanions can be formed by LB techniques and beneficial physicochemical properties of heteropolyanions can be maintained/enhanced through molecular-level design. (C) 1999 Elsevier Science S.A. All rights reserved.

IN-SITU AFM STUDY OF THE SURFACE-MORPHOLOGY OF POLYPYRROLE FILM

In this paper we focus on the surface morphology of polypyrrole film by using in situ atomic force microscopy (AFM). The formation process of polypyrrole film and the transformation process of the film from the oxidized to reduced state were clearly observed.