Evaluation of the 3D-PIV standard images (PIV-STD project)

Particle Imaging Velocimetry (PIV) offers many advantages for studies of fluid flows. Lots of PIV techniques have been developed and applied to various flow fields. However, there are no standard tools for evaluation of the PIV system effectiveness and accuracy. To popularize the PIV for practical use, the PIV system should have some standard.     

Control of structure and electric properties of amorphous organic semiconductive thin films prepared by excimer laser ablation

Excimer laser ablation (ELA) of 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) with ArF (193 nm), KrF (248 nm), XeCl (308 nm), and XeF (351 nm) beams under optimized conditions enables us to obtain organic semiconductor thin films with various structures such as amorphous carbon, polyperinaphthalene (PPN), and PTCDA itself. Electric conductivity and carrier species of the films depend strongly on the ablation wavelength, fluence, substrate temperature, and ambient vapor species. It is found that electric conductivities of the films are controllable, ranging from 10^-6 to 10¹ S cm^-1 with the selection of appropriate ablation conditions. An organic pn junction is successfully constructed by the change of ablation conditions during ELA. Furthermore, ELA of PTCDA at 248 nm in iodine vapor leads to formation of tetraiodoallene in the film.     

Pulsed laser deposition of photosensitive a-Si thin films

Si films have been fabricated by pulsed KrF excimer laser deposition (PLD) through the use of various Si targets and deposition conditions. The deposits consisted of droplets and homogeneous films, which were assigned to be crystalline and amorphous silicon, respectively, by the micro Raman scattering measurements. Not only the crystalline but also the amorphous Si part scarcely (<1 atomic %) contained hydrogen regardless of whether or not the films are prepared in the presence of H₂ gas. Conditions were explored to reduce the droplet formation and to produce photosensitive films. Amorphous Si films with photosensitivity (C_ph/C_d) exceeding 10³ were obtained, and they exhibited high stability against light soaking. Thus, PLD is a promising method to fabricate photosensitive and photostable a-Si films.     

Structural Analysis and Properties of Organic-Inorganic Hybrid Ionic Conductor Prepared by Sol-Gel Process

Organic-inorganic hybrid lithium ion conductors were prepared by the sol-gel process. The hybrid ion conductor will be used as the electrolyte for Li based high-energy density batteries. The hybrid ion conductor was prepared from a mixture of tetramethyl orthosilicate (TMOS), polyethylene glycol 200 (PEG₂₀₀), lithium perchlorate (LiClO₄) and water. A wet gel was prepared at room temperature. The gels dried at 80°C under vacuum did not contain water. The dried hybrid ion conductor gel had homogeneity and high transparency. Ionic conductivity of the hybrid sample was measured by the complex impedance method and it increased with increasing PEG₂₀₀ content. The dried hybrid gel that contained no LiClO₄ did not show ion conduction. Conductivity on the order of 10^–5 S·cm^–1 at room temperature was obtained. Structural characterization was done by Fourier Transform Infrared Spectra (FTIR) and NMR measurement of ¹³C and ¹H, and the thermal stability and glass transition properties were studied by DSC. Glass transition temperature decreased with increasing PEG₂₀₀ content and increased with increasing [Li]/[O] ratio (the oxygen considered is from the polyethylene glycol). Existence of the Si–O–(C₂H₄O) _n –bond and the C–OH bond in the framework of the organic and inorganic phases was confirmed. TMOS and PEG₂₀₀ were hydrolyzed and condensed. The organic and inorganic phases were chemically bonded and the microstructure of the hybrid matrix was shaped as comb. The comb shape leads to high ionic conduction.     

Dual Catalysis of Gold Nanoclusters: Photocatalytic Cross-Dehydrogenative Coupling by Cooperation of Superatomic Core and Molecularly Modified Staples**

Thiolate-protected gold nanoclusters (AuNCs) have attracted significant attention as nano-catalysts, revealing a superatomic core and gold-thiolate staples as distinct structural units. Here, we demonstrate the unprecedented dual catalytic activity of thiolate-protected [Au₂₅(SR)₁₈]⁻ nanoclusters, involving both photosensitized ¹O₂ generation by the Au₁₃ superatomic core and catalytic carbon-carbon bond formation facilitated by Au₂(SR)₃ staples. This synergistic combination of two different catalytic units enables efficient cross-dehydrogenative coupling of terminal alkynes and tertiary aliphatic amines to afford propargylamines in high yields of up to 93 %. Mixed-ligand AuNCs bearing both thiolate and alkynyl ligands revealed the intermediacy of the alkynyl-exchanged AuNCs toward both photosensitization and C−C bond-forming catalytic cycles. Density functional theory calculations also supported the intermediacy of the alkynyl-exchanged AuNCs. Thus, the use of ligand-protected metal nanoclusters has enabled the development of an exceptional multifunctional catalyst, wherein distinct nanocluster components facilitate cooperative photo- and chemo-catalysis.     

Optimized structures of Cr2(CO)6+ with three different symmetries by density functional calculation

Density functional calculations have been made on a binuclear metal carbonyl ion Cr₂(CO)₆⁺ found in our laser ablation–molecular beam (LAMB) experiment. Optimized structures are calculated for three different conformations: T33 of D_3d symmetry with three terminal carbonyl groups on each chromium atom, B2T22 of D_2h symmetry with two bridging carbonyl groups and two terminal carbonyl groups on each chromium atom, and B4T11 of D_4h symmetry with four bridging carbonyl groups and one terminal carbonyl group on each chromium atom. The most stable conformation is T33 which is 36.76 and 286.44 kJ mol⁻¹ lower in energy than B2T22 and B4T11, respectively. The difference of conformation exerts a significant influence on the internuclear distance between chromium and the carbon of terminal CO, but hardly on the Cr–Cr bond length. For B2T22 and B4T11, longer C–O distances for bridging carbonyls compared with those for terminal ones indicate effective π*-back donation from the chromium atom to the bridging carbonyl groups. Furthermore, the relative abundance of Cr₂(CO)_n⁺ (n = 0–6) observed in our previous experimental study can be explained qualitatively by comparison of the excess energy produced in the formation of a Cr⁺–Cr bond with the CO dissociation energy of Cr₂(CO)₆⁺. © 1998 John Wiley & Sons, Ltd.     

Improved stability of molecular organic EL devices

Influence of emission sites on emission efficiency and running durability of molecular organic electroluminescent devices was investigated. When fluorescent dye rubrene was doped into TPD diamine hole transport layer, rubrene molecule emitted bright yellow light with a max. luminance of 61 000 cd/m². The device had the highest efficiency of 9.8 Im/W at 100 cd/m². Half-decay time of the device from initial luminance of 530 cd/m² under constant direct current was 3 600 h. On the other hand, when rubrene was doped into BeBq₂ complex electron transport layer, the efficiency was 4.4 Im/W and the half-decay time was 110 h. Thus doping site is found to exert significant influence both on the emission efficiency and the running durability.     

Utilizing nonlinear phenomena to locate grazing in the constrained motion of a cantilever beam

Grazing behavior in soft impact dynamics of a harmonically based excited flexible cantilever beam is investigated. Numerical and experimental methods are employed to study the dynamic behavior of macro- and micro-scale cantilever beam–impactor systems. For off-resonance excitation at two and a half times the fundamental frequency, the response of the oscillating cantilever experiences period doubling as the separation distance or clearance between the beam axis and the contact surface is decreased. The nonlinear phenomenon is studied by using phase portraits, Poincaré sections, and spectral analysis. Motivated by atomic force microscopy, this general dynamic behavior is studied as a means to locating the separation distance corresponding to grazing where the contact force is minimized.     

Photocycloaddition Reactions of Alkyl and Aryl 2‐Thioxo‐3H‐benzoxazole‐ 3‐carboxylates to Alkenes

The photochemical reactions of alkyl and aryl 2‐thioxo‐3H‐benzoxazole‐3‐carboxylates 1 have been examined. Irradiation of 1 in the presence of tetra‐ and trisubstituted alkenes 2a and 2b , 2‐methylprop‐2‐ene nitrile 2e , and dienes 2f and 2g gave [2+2] cycloadducts of the CS bond of 2‐thioxobenzoxazoles and the CC bond of alkenes, spiro[benzoxazole‐thietanes] 3, 4, 8 – 13, 15, 18, 20, 23 – 26 in moderate‐to‐good yields. The photoaddition reactions proceed in a regiospecific manner. The spirocyclic compounds obtained are indefinitely stable at room temperature. Irradiation of 1a in the presence of 1,1‐ and 1,2‐disubstituted alkenes 2c and 2d yielded the products 5 – 7 of oxazole‐ring cleavage. Compound 1d also underwent photoaddition with alkenes to yield spiro[benzoxazole‐thietanes] and/or 2‐substituted benzoxazoles and/or iminothietanes, depending on the nature of the substituents present in the alkenes. On intramolecular [2+2] photoadduct, tetracyclic 27 , was obtained, when ethenyl 2‐thioxobenzoxazole‐3‐carboxylate 1e was irradiated.