Kensuke Akamatsu

Preparation and characterization of polymer thin films containing silver and silver sulfide nanoparticles

Abstract Composite thin films consisting of nano-sized Ag particles dispersed in nylon 11 thin films have been prepared by using a thermal relaxation technique. The films obtained were characterized by transmission electron microscopy (TEM), electron diffraction (ED), energy-dispersive X-ray (EDX) microanalysis, and optical absorption spectroscopy. The Ag nanoparticles with 4.5–9.1 nm in diameter were found to be isolated individually and dispersed uniformly in the nylon 11 matrix. The volume fraction and the mean size of Ag nanoparticles in the film could be controlled by varying the initial amount of Ag deposition. Optical absorption peak due to the surface plasmon resonance of the Ag particles were observed around 430 nm and shifted to a longer wavelength with increasing the mean size of Ag nanoparticles, and absorbance increased simultaneously. We have also prepared Ag 2 S nanoparticles with 4.7–11.2 nm in diameter in nylon 11 films from exposing the Ag/nylon 11 films to H 2 S/O 2 mixed gas. ED patterns of the particles formed after the reaction with H 2 S were completely indexed as those of β -Ag 2 S with a monoclinic structure. The onset of the optical absorption spectra is similar to that of bulk β -Ag 2 S, suggesting that Ag 2 S nanoparticles with diameter of ca. 5nm preserve the band structure of bulk Ag 2 S.

Synthesis of titanium carbide from a composite of TiO2 nanoparticles/methyl cellulose by carbothermal reduction

Abstract Titanium carbide (TiC) was synthesized from a composite constituted of nano-sized TiO 2 particles (ca. 5 nm in diameter) and methyl cellulose (MC) via carbothermal reduction in an Ar flow. The composite was converted into titanium oxycarbide by heating at 1050°C. With the increase of heating temperature, the lattice parameter of the titanium oxycarbide phase increased while the oxygen content in the specimen decreased, especially above 1300°C. That is, low oxygen content (0.60–2.32 wt%) TiC could be prepared from the composite by heating above 1300°C, which was a considerably lower temperature compared to that employed in the conventional carbothermal reduction methods that use a mixture of TiO 2 and carbon powders.

Growth of metal oxide thin films from aqueous solution by liquid phase deposition method

Abstract The deposition process of iron oxyhydroxide (β-FeOOH) from aqueous solution system of FeOOH–NH 4 F·HF (aq.) with H 3 BO 3 by the liquid phase deposition (LPD) method has been investigated. The effect of initial concentration in the treatment solution and reaction time on microstructure and orientation of the deposited films were studied by means of scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM) observation. The films deposited were constructed by small particles having a crown-like and columnar structure, depending on the concentration range in the treatment solution. XRD measurements revealed that the deposited film preferred the specific direction normal to (211) plane and the dimension of the crystallites varied with the initial concentration of the solution. The deposition process and structure of the films appeared to be strongly affected by the hydrolysis reaction of Fe 3+ ions coordinated by F − and/or partial OH − ions by adding boric acid.

Synthesis and characterization of nano-sized gold-palladium bimetallic particles dispersed in polymer thin film matrix

We have prepared nano-sized Au/Pd bimetallic particles with various compositions dispersed in nylon 11 thin films by thermal relaxation technique. The films obtained were characterized by TEM, EDX, XPS and visible absorption spectroscopy. The Au/Pd molar ratio in the bimetallic particles could be varied over the entire composition range by controlling the initial deposition amount of constituent metals. It was found that the mean size of the dispersed particles decreased from 5.3 to 3.2 nm in diameter with increasing the Pd content in the bimetallic particles. Optical absorption due to surface plasmon resonance absorption of the Au particles decreased with decreasing the Au/Pd ratio, which can be caused by the changes in the band structure of the Au particles due to alloying with Pd.

Nanoscale metal particles dispersed in polymer matrix

Abstract Nanoscale Au, Ag and Pd particles dispersed in nylon 11 thin film matrix have been prepared by a vacuum evaporation technique followed by heat treatment. The metals vapor deposited on the nylon 11 surface could be dispersed in the matrix layer by the heat treatment at temperature above the glass transition temperature of nylon 11 matrix, with the effect of the structural relaxation of nylon molecules. The metal nanoparticles were well isolated individually and the mean size of the particles were increased with increasing the amount of metal deposition. The XPS depth profiling technique has shown that metal particles were also dispersed homogeneously in the depth scales of the matrix upon heat treatment. The absorption peak due to the surface plasmon resonance of Au and Ag particles shifted toward lower energy region as the thickness of the nylon matrix decreased, which can be due to dipole interaction of dispersed nanoparticles.

Formation of Co filled carbon nanocapsules by metal-template graphitization of diamond nanoparticles

Co filled carbon nanocapsules, which are formed by a heat treatment of the mixture of Co and diamond nanoparticles, have been studied by in situ transmission electron microscopy (TEM), x-ray diffraction, and Raman spectroscopy. Raman studies show that the heat treatment reduces the surface native oxide (Co3O4) of Co nanoparticles. The reduction is accompanied by graphitization of diamond nanoparticles, indicating that diamond nanoparticles being in contact with the metallic Co are transformed into graphitic coating. The in situ TEM studies show that the graphitic coating is formed in the heating process, not in the cooling process. Furthermore, once the coating is completed, the number of the graphitic layers is almost constant on further heating and cooling. These results allow us to conclude that metallic Co particles simply act as templates for graphitic coating.

Preparation and characterization of Au/Co nano-alloys

Abstract In this work we attempted to prepare binary alloy nanoparticles consisting of Au and Co, which is a typical phase-separation system in a bulk phase diagram, via a vacuum co-evaporation method. The crystal structure and lattice constant of the Au/Co nano-alloys obtained were investigated by means of a high-resolution transmission electron microscope and selected area electron diffraction. We obtained thermodynamically stable Au/Co nano-alloys with A1 structure upon heat-treatment at a certain temperature, and a partial transition from A1 to an ordered L1 0 structure also took place. The results in the present study demonstrated the thermodynamical differences on alloying behavior between bulk and nanoscopic materials.

Fabrication and characterization of PAN-derived carbon thin films containing Au nanoparticles

Abstract We have prepared polyacrylonitrile (PAN) thin films containing Au nanoparticles by heat treatment of Au/PAN stacking films. The effect of heat treatment on the microstructure of the composite films was investigated by means of transmittance electron microscopy (TEM), Fourier-transform infrared (FT-IR) and Raman spectroscopy. The Au nanoparticles initially deposited on the PAN film were found to be dispersed into the PAN layer by heat treatment at 200 °C, after which structural changes in the PAN matrix were observed, i.e. decomposition of methylene and nitrile groups into CN conjugation. It was also found that heat treatment of the films at higher temperatures caused change of the PAN matrix into amorphous carbon. The mean size of the Au nanoparticles increased with increasing heat-treatment temperature.

Single-electron tunneling effects in thin Nylon 11 films containing gold nanoparticles

Abstract Very thin Nylon 11 films (≤20 nm in thickness) containing Au nanoparticles were prepared, and current–voltage (I–V) characteristics in the vertical direction of the films were studied. The plan and cross-sectional transmission electron microscopic images revealed that Au particles are spontaneously aligned in the middle of the upper and lower electrodes and Nylon 11 tunneling barriers are naturally formed between Au nanoparticles and electrodes. Clear Coulomb staircases were observed in the I–V characteristics.

Fabrication of Copper Film on Aluminum Nitride by Novel Electroless Plating

A detailed study aimed at investigating the interfacial structure of Cu films deposited on high purity aluminum nitride (AIN) substrate, which controls the adhesive strength of the deposited Cu film, is described. In this system, the Cu films are deposited by uniform coating of nanosized Cu 2 O particles onto the substrate, oxidation of Cu 2 O to CuO by heat-treatment in air, and subsequent reduction to metallic Cu followed by electroless Cu plating. Effect of the treatment condition on the structure of composite layer formed on the A1N substrate was investigated by means of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, which show that the interfacial structure depends significantly on the annealing conditions. Upon heat-treatment above 800°C in air, an CuAl 2 O 4 and/or α-Al 2 O 3 phase is formed on the AIN surface. The adhesive strength of the deposited Cu film increased with increasing the annealing temperature, and maximum strength observed is ca. 4 kg per 2X2 mm 2 (kg/4 mm 2 ), much greater than that obtained by conventional electroless plating process. The formation of an interfacial oxide layer is suggested to be responsible for high adhesive strength through chemical interaction. The use of Cu 2 O particles as deposition seeds having chemical bonding with AIN substrate can be crucial in this methodology, which has important implications for practical manufacture of Cu-based electronic devices fabricated on A1N substrate.