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Silicon microparticles were formed by reduction of silicon tetrachloride by zinc. Chemical etching of these microparticles produced microparticles with a unique trench structure that showed visible photoluminescence. While we have previously reported the radially developed crystalline structure inside the as-synthesized microparticles, their crystalline structure was not clearly understood. In this study, we directly observed the cross sections of microparticles using a transmission electron microscope. We revealed the existence of a core inside the microparticles. The core showed a well-ordered electron diffraction pattern, which was readily explained by five single crystals rotated by 72° each. We also found that the observed radial lines and bands in the microparticles were caused by dislocations, mainly along the {111} planes. We consider that preferential etching along these radial dislocations is the origin of the formation of microparticles with trench structures.

The stability of photoluminescence (PL) intensity from chemically etched silicon microparticles is studied. Etched microparticles have many narrow and deep trenches on surface. They show visible orange–red PL, which decreases in intensity during continuous excitation by ultraviolet light. The intensity of PL partially recovers when the surrounding gas is changed from air to nitrogen. Thus PL quenching consists of both reversible and irreversible processes and we propose a kinetic model that consists of two quenching paths. Adsorption and desorption of oxygen followed by irreversible oxidation of emission sites are considered in the fast quenching pathway, while the slow pathway involves transport of oxygen molecules to emission sites in trenches with poor access. Our model agrees well with experimental data and rate constants of involved processes are determined, with which we discuss kinetics in PL quenching. Possible strategy to increase PL stability is also discussed.

While nanotechnology has been drawing a lot of attention in recent years, the “quantum size effect” is one of the properties unique to “nanosizes” that do not appear in either the bulk form or in the atomic and molecular levels. In this phenomenon when the size of a material becomes smaller than the effective Bohr radius (about 10 nm or less), the band levels become discrete and the bandgap becomes larger. In other words, because it is possible to control the bandgap of the material by controlling the size, it is possible to expect applications as a material with characteristics not present conventionally.

This paper presents a new direct simulation method for a drying colloidal suspension on a substrate. A key issue of the present method is the immersed free surface model proposed by the authors, which enables us to estimate accurately and efficiently capillary forces exerted on particles on a free surface. Using the immersed free surface model along with immersed boundary method and level set method, the present method leads to a three-way coupling of the fluid flow, the free surface motion and the particle motion. In addition, the present method includes a way of curvature estimation using virtual grid differencing to calculate accurately a surface tension. The way of curvature estimation is quantitatively validated through the simulation of a still droplet. The immersed free surface model is quantitatively validated through the simulation of a sphere moving across a free surface and the simulation of two spheres moving along a free surface. Finally, simulations of drying colloidal suspension containing 130 particles are performed to demonstrate the applicability of the present method to actual systems., This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

This article reviews scientific literature on computer-tailored interventions for adults that targeted physical activity and healthy eating. Systematic literature searches were performed using MEDLINE, CINAHL Plus, SPORTDiscus, and the Cochrane Library. Articles that were published in scientific journals were included if they evaluated an intervention for physical activity and healthy eating, or focused on weight loss, and used a randomized design. Thirty-eight articles were identified. Twenty-one (physical activity, 55%) and 22 (food intake, 57.9%) of the 38 studies showed that computer-tailored interventions were more effective than the control. Implications of inconsistency in results and future directions for research are discussed.

The older-generation dead-weight type force standard machines (DWMs) at the National Metrology Institute of Japan (NMIJ) were recently renovated with four aims: improving calibration uncertainty, enabling calibrations conforming to the latest standard, automating the calibration work, and reducing maintenance costs. Calibration uncertainties have been improved by removing eccentricity due to the incomplete tare balancing mechanism of the older 20 kN DWM and by eliminating extrapolation of calibration forces from kgf to N in the 54 kN DWM. Insufficient dead-weight division of the 54 kN DWM has been reformed to enable 8-step calibrations, along with expansion of its capacity to 100 kN. Working efficiency has been improved by automating dead-weight actuation and rotational position changes of force measuring instruments. Maintenance costs and labor have been reduced by electrifying the dead-weight actuation mechanism in the 54 kN DWM.

The simplest metal carbene, BeCH2, is experimentally unknown. Its isomer, HBeCH, lies higher in energy, but has been detected by the infrared matrix isolation [J. Am. Chem. Soc. 1998, 120, 6097]. In the present study the ground and low-lying excited states of the BeCH2 and HBeCH isomers were investigated using state-of-the-art ab initio methods, including coupled-cluster theory with up to full quadruple excitations (CCSDTQ), and complete active space self-consistent field (CASSCF) with multireference configuration interaction with single and double excitations (MRCISD). The relative energies were obtained using the focal point analysis combined with large correlation-consistent cc-pCVXZ basis sets (X = D, T, Q, 5) and were extrapolated to the complete basis set (CBS) limit. The (3)B1 state of BeCH2 (C(2v) symmetry) is the global minimum on the ground triplet potential energy surface (PES). The (3)Σ(-) state of the linear isomer HBeCH is located 4.9 kcal mol(-1) above the global minimum, at the CCSDTQ/CBS level of theory. The BeCH2 and HBeCH isomers are connected through the (3)A" transition state lying 46.1 kcal mol(-1) above the global minimum. The higher-lying energy HBeCH structure has much larger Be-C bond dissociation energy (126.6 kcal mol(-1), cf. BDE(BeCH2) = 62.1 kcal mol(-1)). The lowest excited state of BeCH2 is the open-shell (1)B1 state, with a relative energy of only 4.9 kcal mol(-1) above the global minimum, followed by (1)A1 state (16.8 kcal mol(-1)) at the MRCISD/cc-pCVQZ level of theory. For the HBeCH isomer the lowest-energy excited states are (1)Δ and (1)Σ(+), lying about 30 kcal mol(-1) above the global minimum. For the ground state of BeCH2 the fundamental vibrational frequencies computed using second-order vibrational perturbation theory (VPT2) at the CCSD(T)/cc-pCVQZ level are reported. We hope that our highly accurate theoretical results will assist in the experimental identification of BeCH2.

In this study a systematic theoretical investigation of Ge2CH2 is carried out. The singlet potential energy surface (PES) was explored using state-of-the-art theoretical methods including self-consistent field (SCF), coupled cluster theory incorporating single and double excitation (CCSD), perturbative triple [CCSD(T)] and full triples [CCSDT] with perturbative quadruple (Q), together with a variety of correlation-consistent polarized valence basis sets cc-pVXZ (where X = D, T, and Q). A total of eleven stationary points have been located on the Ge2CH2 singlet ground state PES. Among them, seven structures are minima (1S-7S), two are transition states (TS1 and TS2), and two are second-order saddle points (SSP1 and SSP2). The global minimum is predicted to be an exotic hydrogen-bridged structure 1S. The energy ordering of the seven minima (in kcal mol(-1)) obtained from focal point analysis using the extrapolation to complete basis set (CBS) limit with zero point vibrational energy (ZPVE), core correlation, diagonal Born-Oppenheimer (DBOC) and relativistic correction is 1S [0.0]2S [17.2]3S [18.3]4S [31.7]5S [39.9]6S [58.1]7S [82.1].

Previous studies have proposed that silica has micropores or a “gel layer” on its surface; however, previous models of silica dissolution have considered only the top monolayer, and neglected the i...

We studied the growth kinetics of needle-like silicon wires formed in the reduction reaction of silicon tetrachloride (SiCl4) with zinc vapor. Real-time monitoring of the silicon wire growth was performed using a quartz tube reactor with a charge-coupled device (CCD) camera. The formation of silicon wires was observed when SiCl4 was mixed with zinc vapor; the wires grew at a constant rate, which reached 20 mm min–1. We did not prepare catalytic metal particles in the reactor; however, since zinc metal can form a liquid alloy with silicon at reaction temperatures of ca. 900–950 °C, we proposed that a vapor–liquid–solid (VLS) mechanism was responsible for the formation of the silicon wires. We consider that the zinc acted both as a reducing agent for SiCl4 and as a metal catalyst for the wire formation. On the basis of the VLS mechanism, a simple kinetic model for wire growth was proposed. Our model described the experimental data well, and the rate-limiting step for the wire growth is the gas-phase reducti...

We have constructed statistical models that predict thermal resistance after fouling layer formation in a heat exchanger, in which a slurry of stearic acid in toluene was cooled. Chemoinformatics w...

We studied the formation dynamics of low-molecular-weight organic semiconducting molecules of N,N′-bis[4-[bis(3-methylphenyl)amino]phenyl]-N,N′-diphenylbenzidine (DNTPD) during solvent evaporation. We dropped the DNTPD–toluene solution on a glass substrate and performed in situ measurements of mass, temperature, scattered light intensity, and photoluminescence (PL). We found that both light scattering and PL measurements were able to detect the onset of solid film formation from dissolved organic semiconducting materials. When a solid thin film forms during drying, sudden changes in scattered light and PL are observed. Furthermore, we also found that a period of time after the onset was necessary for completion of thin solid film formation. Observations and in situ PL measurement during thin-film formation by spin coating revealed that this period of time affected the optical properties of the film. This result indicates that quantitative information on the film formation process is quite important to obt...

The global minimum among possible structures of SiC2H2 has been experimentally and theoretically determined to be 1-silacyclopropenylidene (1S). In 1994 Maier and Reisenauer reported the generation of 1-silacyclopropenylidene and its three isomers (2S–4S) by pulsed-flash pyrolysis followed by matrix-spectroscopic identification. Reliable quartic force fields for 1-silacyclopropenylidene and its three isomers are determined employing ab initio coupled-cluster theory with single, double, and perturbative triple excitations [CCSD(T)] and the correlation-consistent core-valence quadruple zeta (cc-pCVQZ) basis set. Second-order vibrational perturbation theory (VPT2) has been utilized to determine equilibrium and zero-point vibration corrected rotational constants, centrifugal distortion constants, and harmonic and anharmonic vibrational frequencies. The distances between the average nuclear positions (r α ) are also determined. The predicted rotational constants, centrifugal distortion constants, and anharmoni...

Theoretical investigations of three equilibrium structures and two associated isomerization reactions of the GeCH(2) - HGeCH - H(2)GeC system have been systematically carried out. This research employed ab initio self-consistent-field (SCF), coupled cluster (CC) with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] wave functions and a wide variety of correlation-consistent polarized valence cc-pVXZ and cc-pVXZ-DK (where X = D, T, Q) basis sets. For each structure, the total energy, geometry, dipole moment, harmonic vibrational frequencies, and infrared intensities are predicted. Complete active space SCF (CASSCF) wave functions are used to analyze the effects of correlation on physical properties and energetics. For each of the equilibrium structures, vibrational second-order perturbation theory (VPT2) has been utilized to obtain the zero-point vibration corrected rotational constants, centrifugal distortion constants, and fundamental vibrational frequencies. The predicted rotational constants and anharmonic vibrational frequencies for 1-germavinylidene are in good agreement with available experimental observations. Extensive focal point analyses, including CCSDT and CCSDT(Q) energies and basis sets up to quintuple zeta, are used to obtain complete basis set (CBS) limit energies. At all levels of theory employed in this study, the global minimum of the GeCH(2) potential energy surface (PES) is confirmed to be 1-germavinylidene (GeCH(2), 1). The second isomer, germyne (HGeCH, 2) is predicted to lie 40.4(41.1) ± 0.3 kcal mol(-1) above the global minimum, while the third isomer, 2-germavinylidene (H(2)GeC, 3) is located 92.3(92.7) ± 0.3 kcal mol(-1) above the global minimum; the values in parentheses indicate core-valence and zero-point vibration energy (ZPVE) corrected energy differences. The barriers for the forward (1→2) and reverse (2→1) isomerization reactions between isomers 1 and 2 are 48.3(47.7) ± 0.3 kcal mol(-1) and 7.9(6.6) ± 0.3 kcal mol(-1), respectively. On the other hand, the barriers of the forward (2→3) and reverse (3→2) isomerization reactions between isomers 2 and 3 are predicted to be 55.2(53.2) ± 0.3 kcal mol(-1) and 3.3(1.6) ± 0.3 kcal mol(-1), respectively.

When a mixture of liquid crystal (LC) and photo reactive monomer is irradiated by UV light, polymerization occurs and LC droplets form through phase separation, producing polymer dispersed LCs (PDLCs). Although size control of LC droplets and reduced amounts of LC in PDLC films are important in applications, precise size control of LC droplets at a low LC fraction has not yet been accomplished. In this study, the phase diagrams of the LC/initial monomer and the LC/polymer during polymerization were used to control LC droplet size at various LC fractions. Both the relative position of the sample in the initial phase diagram and the shift of the phase separation line during polymerization were shown to be important in determining the size of LC droplets. Our results are expected to provide a new strategy for precise size control of LC droplets especially at a low LC fraction range, which would be a great help for PDLC applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Three equilibrium structures and two associated isomerization transition states for the SiCH 2 –HSiCH–CSiH 2 system have been theoretically investigated using highly correlated ab initio methods combined with the correlation-consistent polarized core-valence basis sets. Vibrational second-order perturbation theory (VPT2) has been employed to obtain the zero-point vibration corrected rotational constants, centrifugal distortion constants, and fundamental vibrational frequencies for each equilibrium structure. The comparison of the theoretically predicted rotational constants and fundamental frequencies for silylidene (SiCH 2 ) with existing experimental observations shows excellent agreement. The CH 2 (CD 2 ) rocking modes ( ν 6 ) are the most anharmonic among the six vibrational modes, consistent with limited experimental observations. The five stationary point structures and their relative energies on the ground state potential energy surface (PES) are accurately determined using the focal point extrapolation technique. Silylidene (SiCH 2 ) has been confirmed to be the global minimum. Silaacetylene (HSiCH) with a trans -bent structure is located 34.8 ± 0.3 kcal mol −1 (with zero-point vibrational energy, scalar relativistic effects, and DBOC corrections) above the global minimum. The barrier height for the critical reverse isomerization process [HSiCH → SiCH 2 ] is predicted to be 4.1 ± 0.3 kcal mol −1 . The third isomer silavinylidene (CSiH 2 ) is predicted to lie 84.6 ± 0.3 kcal mol −1 above the global minimum, with the barrier height for the reverse isomerization process [CSiH 2 → HSiCH] being only 2.6 ± 0.3 kcal mol −1 . The present research should assist the future experimental characterization of silylidene (SiCH 2 ) isomers.

Post-transcriptional regulation of gene expression by RNA-binding proteins has pivotal roles in many biological processes. We have shown that Stau1, a conserved RNA-binding protein, negatively regulates myogenesis in C2C12 myoblasts. However, its target mRNAs in regulation of myogenesis remain unknown. Here we describe that Stau1 positively regulates expression of Dvl2 gene encoding a central mediator of Wnt pathway in undifferentiated C2C12 myoblasts. Stau1 binds to 3′ untranslated region (UTR) of Dvl2 mRNA and Stau1 knockdown shortened a half-life of the mRNA containing Dvl2 3′ UTR. After induction of myogenic differentiation, association of Stau1 with 3′ UTR of Dvl2 mRNA was decreased. Correlated with the decrease in the association, the Dvl2 mRNA level was reduced during myogenesis. A forced expression of Dvl2 markedly inhibited progression of myogenic differentiation. Our results suggest that Dvl2 has an inhibitory role in myogenesis and Stau1 coordinates myogenesis through the regulation of Dvl2 mRNA.

Simulation models for a variety of new water heater systems were developed and the models were integrated into a city-level residential energy end-use model for Osaka City. Using the model, the potential of energy conservation and CO2 emission-reduction by introducing new residential water heaters was evaluated at the city-level. Optimal water-heating systems for each household category for primary energy reduction, CO2 emission-reduction, or cost reduction were identified by applying the end-use demand model. The effect of subsidies for installing more efficient systems and the influence of diffusion of these systems on electricity load curves were also discussed.

Maier et al. found that photolysis of singlet cyclopropenylidene (1S) in a matrix yields triplet propargylene (2T), which upon further irradiation is converted to singlet propadienylidene (vinylidenecarbene, 3S). Their discovery was followed by interstellar identification of 3S by Cernicharo et al. An accurate quartic force field for propadienylidene (3S) has been determined employing the ab initio coupled-cluster (CC) with single and double excitations and perturbative triple excitations [CCSD(T)] method and the correlation-consistent core-valence quadruple-ζ (cc-pCVQZ) basis set. Utilizing vibrational second-order perturbation theory (VPT2), vibration-rotation coupling constants, rotational constants, centrifugal distortion constants, vibrational anharmonic constants, and fundamental vibrational frequencies are determined. The predicted fundamental frequencies for 3S as well as its (13)C and deuterium isotopologues are in good agreement with experimental values. The theoretical zero-point vibration corrected rotational constants B0 are consistent with experimental values within 0.3% of errors. The isotopic shifts of B0 are in close to exact agreement with experimental observations. The mean absolute deviation between theoretical anharmonic and experimental fundamental vibrational frequencies for 24 modes (excluding CH2 s-str.) is only 2.6 cm(-1). The isotopic shifts of the vibrational frequencies are also in excellent agreement with the available experimental values. However, a large discrepancy is observed for the CH2 symmetric stretch, casting doubt on the experimental assignment for this mode.

A model is developed that simulates nationwide energy consumption of the residential sector by considering the diversity of household and building types. Since this model can simulate the energy consumption for each household and building category by dynamic energy use based on the schedule of the occupants’ activities and a heating and cooling load calculation model, various kinds of energy-saving policies can be evaluated with considerable accuracy. In addition, the average energy efficiency of major electric appliances used in the residential sector and the percentages of housing insulation levels of existing houses is predicted by the “stock transition model.” In this paper, energy consumption and CO2 emissions in the Japanese residential sector until 2025 are predicted. For example, as a business – as-usual (BAU) case, CO2 emissions will be reduced by 7% from the 1990 level. Also evaluated are mitigation measures such as the energy efficiency standard for home electric appliances, thermal insulation code, reduction of standby power, high-efficiency water heaters, energy-efficient behavior of occupants, and dissemination of photovoltaic panels.

This article reviews recent contributions to mesoscale modeling for self-organization of colloidal systems. The review covers both off-lattice models and off-lattice–on-lattice hybrid models that are able to describe the motion of colloidal particles with hydrodynamic interaction. All the models are compared with one another in terms of accuracy, applicable scope, robustness and efficiency.

We report on the formation of silicon nanowires via the gas-phase reaction of silicon tetrachloride with zinc vapor at ca. 1000 °C. In this method, metal catalysts do not have to be prepared before...

When suspensions containing colloidal particles of two different sizes are coated on substrates to form films by evaporating the host fluids, the smaller particles can segregate to the top surface of the films. We investigate the effects of the evaporation rate on the segregation by use of Langevin dynamics simulations. The evaporation rate is scaled by the Brownian diffusion rate of the particles, yielding a dimensionless number which we define as the particle drying Peclet number. We show that there is a Peclet number at which the segregation is the most enhanced. Our result indicates the need for the regulation of the evaporation rate to control the segregation.

The effect of surface deprotonation of colloidal silica particles on settling mode transition has been studied quantitatively. We observed the settling mode transitions of silica aqueous suspensions by adding a pH controlled CaCl2 electrolyte solution as a coagulant. Depending on the solution pH, three types of settling modes were observed, i.e. “no settling mode”, “free settling mode” and “hindered settling mode”. In these observations, a large pH drop occurred immediately after mixing of the coagulant. To describe the pH drop, we developed a simple mathematical model consisting of a 1-pK Stern model and a mass balance equation of protons on silica particles. The model shows excellent agreement with experiments in the number of dissociated protons from a silica surface (np). Furthermore, the boundaries of the three setting modes in the pH-φ phase diagram are also well explained by the value of np. Our results clarify that the extent of colloidal instability is quantitatively described by np.

In pioneering matrix isolation experiments, Maier and Reisenauer reported and identified infrared spectra for 1-silacyclopropenylidene and three of its isomers. These experiments were followed by microwave spectroscopy identification of two of the structures. Seven low-lying isomers of SiC2H2 are systematically investigated here using ab initio restricted Hartree−Fock (RHF), coupled cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] methods and the correlation-consistent polarized valence cc-pVXZ/cc-pV(X+d)Z (X = D, T, and Q) basis sets. Full valence complete active space self-consistent field (CASSCF) wave functions are used for interpretation. All levels of theory employed in this study confirm the global minimum of the SiC2H2 potential energy surface (PES) to be 1-silacyclopropenylidene (1S). Among the seven singlet stationary points, six isomers are found to be minima, whereas one structure (6S) is a second-order saddle point. For the lowest-lyin...

Theoretical investigations of the equilibrium structures and associated isomerization reactions of the hydrogen clusters H(6)(+) have been carried out. Three equilibrium structures and three isomerization transition states were located on the electronic doublet and quartet states of the respective potential energy surfaces. The research employed ab initio self-consistent-field (SCF), coupled cluster (CC) with single and double excitations (CCSD), CCSD with perturbative triple excitations (CCSD(T)), and full triple excitations (CCSDT) wave functions and a wide variety of correlation-consistent polarized valence cc-pVXZ and aug-cc-pVXZ (where X = D, T, Q) basis sets. For each structure the geometry, energy, dipole moment, harmonic vibrational frequencies, and infrared intensities are predicted. Complete active space SCF (CASSCF) and multireference configuration interaction (MRCI) wave functions are used to analyze the effect of correlation on physical properties and energetics. Extensive focal point analyses (including CCSDTQ and full CI energies and basis sets up to sextuple zeta) are used to obtain complete basis set (CBS) limit energies. The H(2)(+)-core H(6)(+) cluster with D(2d) symmetry is the global minimum, lying 3.9 (4.2) +/- 0.1 kcal mol(-1) below the H(3)(+)-core H(6)(+) cluster with C(s) symmetry, where zero-point vibrational energy (ZPVE) corrected value are shown in parentheses. The barrier of the isomerization reaction between these two structures is 7.4 (5.2) +/- 0.1 kcal mol(-1). The dissociation energies for the H(2)(+)-core H(6)(+) isomer [H(6)(+) (D(2d)) --> 2H(2) + H(2)(+)] and the H(3)(+)-core H(6)(+) isomer [H(6)(+) (C(s)) --> H(3)(+) + H(2) + H] are 57.5 (50.9) +/- 0.1 and 12.3 (8.3) +/- 0.1 kcal mol(-1), respectively.

The equilibrium structures of P(2)H(2) isomers and the associated isomerization transition states have been investigated systematically starting from self-consistent-field theory and proceeding to coupled cluster methods using a wide range of basis sets. For each structure, the geometry, energy, dipole moment, harmonic vibrational frequencies, and infrared intensities have been predicted. The global minimum has been confirmed to be planar trans-HPPH diphosphene, lying 3.2 kcal mol(-1) below cis-HPPH with the aug-cc-pVQZ CCSD(T) method upon inclusion of zero-point vibrational energy corrections. Diphosphinylidene, which has the connectivity PPH(2) and C(2v) symmetry, lies 25.2 kcal mol(-1) above the global minimum. The trans-cis isomerization reaction occurs via internal rotation with a barrier of 35.2 kcal mol(-1) using the cc-pVQZ Mk-MRCCSD (2e/2MO) method. This transition state exhibits multireference character and consequently properties were evaluated using CASSCF, MRCI, CASPT2, and Mk-MRCCSD methods with various basis sets. At the aug-cc-pVQZ CCSD(T) level, the transition state for the isomerization reaction between trans-HPPH and diphosphinylidene (planar PPH(2)) is predicted to be nonplanar with a torsional angle of 101.1 degrees . The corresponding barrier is estimated to be 48.2 kcal mol(-1).

Colloidal silica films, formed by the drop evaporation method, showed birefringent spherulite optical properties. They displayed a Maltese cross pattern under crossed polarizers, and interference colors, such as blue and orange-red, under crossed polarizers with a compensator. The difference in refractive index was estimated to be 9x10(-4) from the interference colors. Scanning electron microscopy (SEM) results revealed anisotropic structures in the colloidal films. Particles formed radially ordered hexagonal arrays. The drop evaporation method used in this report, which dries from the edge to the center, resulted in a radially ordered colloidal film. When a colloidal silica film was prepared using a unidirectional drying method, particles were packed in an ordered structure corresponding to the drying direction and the resulting film showed different birefringent optical properties. Our results show that a variety of birefringent films can be obtained from spherical colloidal dispersions through control of the drying method.

Carbon nanotubes (CNTs) were grown directly on substrates by alcohol catalytic chemical vapor deposition using a Co–Mo binary catalyst. Optimum catalytic and reaction conditions were investigated using a combinatorial catalyst library. High catalytic activity areas on the substrate were identified by mapping the CNT yield against the orthogonal gradient thickness profiles of Co and Mo. The location of these areas shifted with changes in reaction temperature, ethanol pressure and ethanol flow rate. Vertically aligned single-walled CNT (SWCNT) forests grew in several areas to a maximum height of ca. 30 μm in 10 min. A pure Co catalyst yielded a vertically aligned SWCNT forest with a bimodal diameter distribution. The effects of Mo on the formation of catalyst nanoparticles and on the diameter distribution of SWCNTs are discussed and Mo as thin as a monolayer or thinner was found to suppress the broadening of SWCNT diameter distributions.

Images from scanning electron microscopy, transmission electron microscopy and X-ray diffraction profiles of typical magnesium diethoxide (MGE) particles obtained by the reaction of ethanol, metal magnesium and iodine showed the round MGE particle (tertiary particle) had a layer structure consisting of many crystalline fragments (secondary particles) comprising many minute crystals (primary particles). It was clearly shown that each precipitated secondary particle had not agglomerated, but had repeatedly grown and combined with others. From the investigation of the course of a reaction, it was suggested the MGE crystals grown on Mg metal exfoliated as “lump-like” seeds, and crystal growth on seeds proceeded such that the shapes of the final MGE particles were more spherical than those of their seeds. It was presumed from a model reaction that the enhancement of MGE solubility by I2 addition to form the quasi-stable complex nMg(OEt)2·MgI2·mEtOH was the key process in the formation of plate crystals. The relationship between the size of crystalline fragments and crystallization rate (reaction rate, MGE solubility) was discussed. The catalyst, when prepared using MGE as the carrier material, exhibited exceptionally high polymerization activity than when it was prepared with MgCl2 alcohol complex (MgCl2·ROH). We presume that this is because particles of the MGE-based catalyst are porous, and because the formation of active species of the supported Ti and monomer diffusion progressed adequately from the surface of the particle to its internal parts.

Our group recently reproduced the water-assisted growth method, so-called "super growth", of millimeter-thick single-walled carbon nanotube (SWNT) forests by using C2H4/ H2/ H2O/ Ar reactant gas and Fe/ Al2O3 catalyst. In this current work, a parametric study was carried out on both reaction and catalyst conditions. Results revealed that a thin Fe catalyst layer (about 0.5 nm) yielded rapid growth of SWNTs only when supported on Al2O3, and that Al2O3 support enhanced the activity of Fe, Co, and Ni catalysts. The growth window for the rapid SWNT growth was narrow, however. Optimum amount of added H2O increased the SWNT growth rate but further addition of H2O degraded both the SWNT growth rate and quality. Addition of H2 was also essential for rapid SWNT growth, but again, further addition decreased both the SWNT growth rate and quality. Because Al2O3 catalyzes hydrocarbon reforming, Al2O3 support possibly enhances the SWNT growth rate by supplying the carbon source to the catalyst nanoparticles. The origin of the narrow window for rapid SWNT growth will also be discussed., Comment: 6 pages, 6 figures. Submitted to J. Nanosci. Nanotech

A simulation model of concentrated colloidal rod-like nanoparticles is developed. As the governing equation of motion of a nanoparticle, the Langevine equation with external force is used. The external force includes capillary force, contact force, electrostatic force, van der Waals force, and elastic force which occurs inside an elastic rod. Numerical simulations are performed for the system of concentrated colloidal rod-like nanoparticles, which experiences solvent evaporation with a constant rate. Consequently, some structures of self-organized rod-like nanoparticles are obtained for the specified aspect ratios. The time evolution of the system is quantitatively analyzed by using the orientational order parameter and the non-dimensional boundary area. Moreover the two quantities are found to resolve the structures obtained in the simulation.

Tri-n-octylphosphine oxide (TOPO)-capped colloidal cadmium selenide (CdSe) quantum dots (QDs) in octane formed a QD film under laser irradiation. The film was formed at a constant rate of deposition after an incubation period. The deposition rate increased linearly with increasing laser intensity and QD concentration. Addition of TOPO molecules into the suspension significantly retarded film formation. The TOPO molecules are thought to desorb from the QD surface under laser irradiation because well-capped QDs with TOPO molecules did not form a film. We propose that absorbed photons induce desorption of TOPO molecules from QDs and destabilized QDs are formed in the suspension. The formed unstable QDs attach to the substrate, resulting in the formation of a QD film. A model is proposed to analyze the kinetics of film formation. It consists of three steps: the diffusion of QDs from the bulk suspension, the photoinduced desorption reaction of TOPO molecules, and the mass transport of unstable QDs onto the sub...

The relationships among the nominal thickness of Co catalyst, the structure of the catalyst particles, and the structure of carbon nanotubes (CNTs) growing from the catalyst during chemical vapor deposition were investigated. Various morphologies of CNTs such as individuals, random networks parallel to the surface of the substrate (‘grasses’), and vertically aligned forests of single- and multi-walled carbon nanotubes were grown by only varying the nominal thickness of catalyst under the same reaction condition. These different morphologies at the same growth time were due to the different areal density rather than to the length of CNTs. With increasing nominal thickness of catalyst, the catalyst particles changed in diameter while their areal density remained relatively almost constant. The change in diameter possibly affected the number ratio of active catalyst particles to the whole particles, which in turn affected the areal density of CNTs and yielded the various morphologies. Longer growth time increased the CNT length, which caused further change in CNT morphologies from individuals to grasses and grasses to forests.

Photoluminescence (PL) changes in cyano-substituted poly p-phenylene vinylene (PPV) derivatives caused by photooxidation are discussed. PL blue shift of ordinary PPVs due to photooxidation is usually known to involve a significant quenching of PL intensity. In the case of cyano-substituted poly p-phenylene vinylene (CN-PPVs), we found that photooxidation at higher temperature results in blue shift without a significant PL quenching, and that photooxidation at lower temperature results in quenching with little blue shift. Our results indicated that photooxidation of CN-PPVs at an appropriate temperature can attach PL blue shift without a quenching of PL intensity, from the PL peak wavelength of solid film state to the PL peak wavelength of solution state. The appropriate temperature is different for each of the CN-PPVs. It is demonstrated that the PL peak wavelength of MEH-CN-PPV solid film can be changed with little significant PL quenching, from the 594 nm, which is the PL peak wavelength of bulk MEH-CN-PPV, to the blue limit of the PL peak wavelength of 547 nm, which is the PL peak wavelength of a well-dispersed state of MEH-CN-PPV. The changed PL properties can be preserved under a reduced pressure atmosphere, even if samples are irradiated by a light source. The dominant factor of the blue shift to the PL peak wavelength of solution state is considered to be expanding of distance between planes (d-space) of the CN-PPV-layered structure, which determines the intermolecular interaction. Controlling d-space of cyano-PPV derivatives by photoirradiation is suggested to be a useful method of creating various PL or EL color patterns of CN-PPVs.

Field emission properties of single-walled carbon nanotubes (SWCNTs), which were prepared through alcohol catalytic chemical vapor deposition for 10–60 s, were characterized in a diode configuration. Protrusive bundles at the top surface of samples act selectively as emission sites. The number of emission sites was controlled by emitter morphologies combined with texturing of Si substrates. SWCNTs grown on a textured Si substrate exhibited a turn-on field as low as 2.4 V/µm at a field emission current density of 1 µA/cm2. Uniform spatial luminescence (0.5 cm2) from the rear surface of the anode was revealed for SWCNTs prepared on the textured Si substrate. Deterioration of field emission properties through repetitive measurements was reduced for the textured samples in comparison with vertically aligned SWCNTs and a random network of SWCNTs prepared on flat Si substrates. Emitter morphology resulting in improved field emission properties is a crucial factor for the fabrication of SWCNT-electron sources. Morphologically controlled SWCNTs with promising emitter performance are expected to be practical electron sources.