Akio Fuwa

Structural, optical and electrical properties of ZnTe thin films electrochemically deposited from a citric acid aqueous solution

ZnTe thin films were electrodeposited onto Au-coated Cu substrates from an electrolytic solution containing ZnSO4, TeO2, citric acid and sodium citrate, and the dependence of structure, composition and surface morphology on the solutions Zn concentration were investigated. Results of examinations for resistivity and optical absorption demonstrated, respectively, that as the Zn concentration in the electrolyte was reduced over the range of 5?50?mmol?dm?3, the resistivity of the films obtained continuously decreased and their band gap increased. Quantative analysis of energy dispersive x-ray analysis and inductively coupled plasma results indicated that the composition ratio (Zn?:?Te) was approximately stoichiometric under all conditions in this study. X-ray diffraction results revealed that all the ZnTe thin films obtained showed a preferred (111) orientation with cubic structure. ZnTe thin films we transferred onto nonconductive epoxy resin also showed the same structure.

Prediction for thermodynamic function of dioxins for gas phase using semi-empirical molecular orbital method with PM3 Hamiltonian

In this investigation, respective thermodynamic parameters of heats of formation, standard entropy and specific heat capacity at constant pressure for PCDDs, PCDFs, Co-PCB and PCBs as well as polychlorinated-benzenes and polychlorinated-phenols have been evaluated by quantum chemical calculation using a semi-empirical molecular orbital method with the PM3 Hamiltonian and statistical thermodynamic correlation.

Electrodeposition of ZnTe Film with High Current Efficiency at Low Overpotential from a Citric Acid Bath

The cathodic electrodeposition of ZnTe film was studied using an aqueous citric acid bath (pH 4; temperature 368 K) in which Zn(II) and Te(IV) species were dissolved to form Zn(Cit) 4- 2 and HTeO + 2 ions, respectively. The deposition mechanism was studied based on cyclic voltammetry. The influence of the deposition potential on the morphology, composition, and structure of the deposited film was also investigated. A smooth, dense polycrystalline ZnTe film with nearly stoichiometric composition was deposited at a constant cathode potential, ranging from -0.80 to -0.60 V vs. Ag/AgCl, from a solution containing 20 mmol dm -3 Zn(II), 0.16 mmol dm -3 Te(IV), 0.25 mol dm -3 H 3 Cit, and 0.25 mol dm -3 Na 3 Cit (Cit = C 6 H 5 O 7 ). Potentials in this range provided the deposited ZnTe film with high current efficiency (above 98%). During electrodeposition of the nearly stoichiometric crystalline ZnTe, the current density was approximately stationary.

Wettability control of a polymer surface through 126 nm vacuum ultraviolet light irradiation

The control of the surface wettability of poly (methyl methacrylate) (PMMA) substrates has been successfully demonstrated using an Ar2* excimer lamp radiating 126 nm vacuum ultraviolet (VUV) light. Each of the samples was exposed to 126 nm VUV light in air over the pressure range of 2×10−4–105 Pa. Although at the process pressures of 10, 103, and 105 Pa, the PMMA surfaces became relatively hydrophilic, the degree of hydrophilicity depended markedly on the pressure. The minimum water contact angles of the samples treated at 10, 103, and 105 Pa were about 50°, 33°, and 64°, respectively. These values were larger than those of PMMA substrates hydrophilized through 172 nm VUV irradiation conducted under the same conditions. On the other hand, after 126 nm VUV irradiation conducted under the high vacuum condition of 2×10−4 Pa, the PMMA substrate surface became carbon-rich, probably due to preferential cross-linking reactions, as evidenced by x-ray photoelectron spectroscopy. This surface was hydrophobic, showi...

Fabrication of microstructured copper on an indium–tin–oxide surface using a micropatterned self-assembled monolayer as a template

The difference in chemical reactivity between indium–tin–oxide (ITO) and self-assembled monolayer (SAM) surfaces was used to fabricate copper (Cu) microstructures. ITO substrates coated with octadecyltrimethoxysilane (ODS)–SAM were photolithographically micropatterned using vacuum ultraviolet (VUV) light. Each of the micropatterned samples was subsequently immersed in an electrodeposition bath in order to deposit Cu on its surface. As confirmed by atomic force microscopy, Cu electrodeposition proceeded selectively on the VUV-irradiated areas of the ITO surface while the ODS–SAM surface served effectively as a mask to block Cu deposition. Cu microstructures with 7.5 × 7.5 μm2 features were successfully fabricated on the ITO surface.

Mössbauer Study of the Ferroelectric State in Ga-Substituted CuFeO2

57Fe Mossbauer spectroscopic measurements have been conducted on CuFe1−xGaxO2 single crystals, in order to investigate the magnetic structures and hyperfine parameters in ferroelectric CuFe0.965Ga0.035O2 and paraelectric CuFeO2. We confirmed that the Mossbauer spectrum at 4.2 K in CuFeO2 is explained by the collinear antiferromagnetic structure with spins along the hexagonal c-axis. In the ferroelectric phase in CuFe0.965Ga0.035O2, the spectrum consists of three magnetic components, where magnetic hyperfine fields distribute in three different directions within the (110) plane. This configuration is not completely consistent with a simple proper screw structure with a uniform spin distribution. The quadrupole coupling constants e2qQ/2 are unexpectedly large for both specimens. In the ferroelectric state in CuFe0.965Ga0.035O2, e2qQ/2 becomes noticeably smaller than that in the paraelectric phase in CuFeO2. We discuss the difference in quadrupole coupling constant between the ferroelectric and paraelectric ...

Assembly of hydrothermally synthesized tin oxide nanocrystals

We have successfully assembled highly crystalline tin oxide nanoparticles, which were synthesized through a simple hydrothermal approach, onto the chemical template of octadecyltrimethoxysilane self-assembled monolayer (OTS-SAM). Tin oxide nanoparticles were synthesized by refluxing ethanol containing 0.1M of tin (IV) chloride pentahydrate at 70°C for 3h, and subsequently hydrothermally treating the resulted precipitates at 200°C for 80h. As a result, we could obtain the highly crystalline tin oxide nanoparticles. The average particle size and its distribution were estimated by high-resolution transmission electron microscopy observation to be about 5.8nm and 27.6%. Area-selective assembly of tin oxide nanoparticles was performed by dipping a few drops of the suspension containing the nanoparticles onto the OTS-SAM template-covered silicon substrates, and then sonicating the substrate covered with the dried suspension in absolute toluene for 10min. The nanoparticles assembled on the methyl-covered regions...

Site-selective electroless plating on amino-terminated diamond substrate patterned by 126 nm vacuum ultraviolet light lithography

A chemically inert diamond surface was modified through photo-oxidation with 126 nm vacuum ultraviolet (VUV) light followed by chemical vapor deposition (CVD) of an amino (NH2)-terminated organosilane. When VUV irradiation was conducted under a residual pressure of 10 or 103Pa, the sample surface became hydrophilic, with its water contact angle dropping from about 92.5° to about 13° or less than 5°, respectively. In contrast, samples treated at 105Pa were less wettable than those prepared at 10 or 103Pa due to insufficient light intensity. The contact angle of the sample treated at 105Pa was about 82°. With all the samples, after 126 nm VUV irradiation, photo-oxidation was found to be greatly enhanced in the topmost region close to the surface (i.e., at a depth of around 3 nm from the surface), while photo-oxidation reactions did not proceed in the deeper regions (i.e., around 10 nm from the surface), as evidenced by angle-resolved x-ray photoelectron spectroscopy (XPS). Following photo-oxidation, the hyd...

Photoinduced decomposition of alkyl monolayers using 172 nm vacuum ultraviolet light

The photoinduced stability of two alkyl monolayers on Si has been investigated using a Xe2 excimer lamp radiating 172 nm vacuum ultraviolet (VUV) light. The photoinduced stability of 1-octadecene monolayer (ODM) was compared with that of alkylsilane monolayer. 1-octadecene was employed as a starting precursor of alkyl monolayer on Si. The alkylsilane monolayer was formed from otadecyltrimethoxysilane monoalyer (OTSM) onto the SiO2/Si substrate. The decomposition of ODM was investigated under VUV irradiation conducted at 10 and 105 Pa. The VUV light decomposed ODM at both 10 and 105 Pa. The photodecomposition rate at 105 Pa was smaller than that at 10 Pa. The decomposed methyl and ethyl groups from the alkyl chain formed carboxyl groups. The carboxyl coverage on the surface of Si increased with increasing VUV irradiation time ranging from 0 to 60 s at 10 Pa, and decreased after 60 s. In contrast, the Si–O component in x-ray photoelectron Si 2p spectrum drastically increased after the VUV irradiation time o...

Catalytic effects of copper on dibenzo‐p‐dioxin and polychlorinated dibenzo‐p‐dioxin generations using ab initio molecular orbital method

The roles played by copper in dibenzo‐p‐dioxin formation from the precursor phenol have been investigated using ab initio molecular orbital calculation, and the following catalytic roles of copper has been identified: (i) stabilization of the total energy owing to the absorption of phenol, (ii) reduction of oxygen‐hydrogen bond strength in phenol, and (iii) reduction of steric effect of hydrogen atom in pre‐dioxin. The catalytic effect of copper has been shown in terms of the smaller apparent activation energy. In the case of polychlorinated dibenzo‐p‐dioxins generation from precursor polychlorinated phenols, the catalytic roles (i), i.e., the stabilization of the total energy of precursor, would become even stronger. On the other hand, the catalytic roles (ii) and (iii) are unchangeable regardless of the existence of substituted chlorine atom.