Seed-mediated growth of palladium nanocrystals on indium tin oxide surfaces and their applicability as modified electrodes

Palladium nanoparticles (PdNPs) were successfully attached and grown on an indium tin oxide (ITO) surface using a seed-mediated growth method, i.e., via a simple two-step immersion of the ITO substrate into the seed and growth solutions. After the growth treatment for 24 h, PdNPs grew up to 60-80 nm, exhibiting crystal-like appearances and accompanying the formation of short rodlike nanocrystals as a minor product. Thus prepared PdNPs tend to stick each other, so that the dense gathering of PdNPs was observed on the ITO surfaces. Due to the dense attachment, the PdNPs directly attached to the ITO (PdNP/ITO) electrode had a significantly lowered charge-transfer resistivity compared with that of a bare ITO, and the redox reaction of [Fe(CN)6]3-/[Fe(CN)6]4- was observed as reversible in 0.1 M phosphate buffer solution. The electrocatalytic property of PdNPs was confirmed for the reduction of oxygen. In addition, some typical responses were observed in 0.5 M H2SO4 with the PdNP/ITO electrode, reflecting both the characteristics of NPs and the thin layer in nanoscale. The present preparation method of PdNP-attached surfaces would be promising for catalytic applications as well as electrochemical uses.     

Low-temperature elastic constants and piezoelectric coefficients of langasite (La3Ga5SiO14)

A complete set of elastic constants C _ij and piezoelectric coefficients e _ij of a La₃Ga₅SiO₁₄ (langasite) single crystal was determined from 5.5 to 275.5?K by resonant ultrasound spectroscopy. Unlike a conventional crystal, the elastic constants C _ij of the langasite crystal showed three types of temperature dependence: (i) monotonic elastic stiffening upon cooling (C ₄₄ and C ₁₄); (ii) monotonic elastic softening (C ₆₆); and (iii) a stiffening-to-softening transition below 150?K (C ₁₁, C ₁₂, C ₁₃ and C ₃₃). In addition, a strong correlation between C ₆₆ and the piezoelectric coefficient e ₁₁ was confirmed. Group theoretical lattice dynamics analysis revealed that the novel phenomena of elastic softening and strong correlation are explained on the basis of two types of optical mode internal displacements which have the totally symmetric A ₁ and doubly degenerated E symmetries in the point group D ₃.     

Accelerated long-range corrected exchange functional using a two-gaussian operator combined with one-parameter progressive correlation functional [LC-BOP(2Gau)]

Recently, we proposed a simple yet efficient method for the computation of a long-range corrected (LC) hybrid scheme [LC-DFT(2Gau)], which uses a modified two-Gaussian attenuating operator instead of the error function for the long-range HF exchange integral. This method dramatically reduced the computational time while maintaining the improved features of the LC density functional theory (DFT). Here, we combined an LC hybrid scheme using a two-Gaussian attenuating operator with one-parameter progressive correlation functional and Becke88 exchange functional with varying range-separation parameter values [LC-BOP(2Gau) with various μ values of 0.16, 0.2, 0.25, 0.3, 0.35, 0.4, and 0.42] and demonstrated that LC-BOP(2Gau) reproduces well the thermochemical and frontier orbital energies of LC-BOP. Additionally, we revised the scaling factors of the Gaussian multipole screening scheme for LC-DFT(2Gau) to correspond to the angular momentum of orbitals, which decreased the energy deviations from the energy with the no-screening scheme. © 2018 Wiley Periodicals, Inc.     

Oxygen bombardment effects on average crystallite size of sputter-deposited ZnO films

Zinc oxide (ZnO) film was deposited on a glass substrate by rf magnetron sputtering with O₂/Ar as working gases. Structural properties of the films were characterized by XRD. Average crystallite size in the films was strongly dependent on both the gas flow ratio of O₂/Ar and rf-power at a constant deposition pressure. During the deposition, energetic species in the plasma were in situ monitored using optical emission spectroscopy. An inverse correlation was observed between the average crystallite size and the emission intensity ratio of I_O^∗/I_Ar. Bombardment of atomic oxygen to the growing surface played an important role in determining the average crystallite size in the films. The average crystallite size could be controlled by the emission intensity ratio of I_O^∗/I_Ar.     

Characterization of atmospheric tritiated water concentration in the vicinity of the fukushima daiichi nuclear power plant

Journal of Radioanalytical and Nuclear Chemistry - This paper discusses the spatiotemporal variation in atmospheric tritiated water (HTO) concentration near the Fukushima Daiichi Nuclear Power...     

Palladium(II)‐Catalyzed Dehydroboration via Generation of Boron Enolates

The Pd^II‐catalyzed dehydroboration of boron enolates generated from ketones and 9‐iodo‐9‐borabicyclo[3.3.1]nonane was achieved, providing a synthetically versatile protocol from ketones to α,β‐unsaturated ketones. The Pd^II compound employed in this reaction worked catalytically in the presence of Cu(OAc)₂. The high trans‐selectivity of the olefinic moiety was observed. Aryl halide moieties (‐Br and ‐Cl) remained intact for this reaction in spite of the presence of a Pd species. An ester substrate could also be applied when a stoichiometric amount of Pd^II was used. The crossover reactions using boron and silyl enolates revealed that the oxidation reaction is much faster than the Saegusa‐Ito reaction.     

Structural characterization of amorphous silicon nitride by molecular dynamics simulation

Computer simulation, using the molecular dynamics (MD) technique, has been carried out on amorphous silicon nitride (a-Si₃N₄) with simple Busing-type potentials. From the MD simulation, the following points have been deduced. (1) The average Si---N bond length obtained from MD results is r_Si---N=1.74 Å, and its coordination number, N_Si---N, is 3.95. The bond angles around a Si and a N atom, N---Si---N and Si---N---Si, are found to be 109.8° ± 12.36° and 127.08° ± 16.63°, respectively. The N---Si---N value obtained is in very good agreement with the tetrahedral bond angle (= 109.47°). Hence, the short-range structural arrangement of a-Si₃N₄ comprises tetrahedral SiN₄ units. The MD results presented in this study also indicate that there exist only a small number of defects such as dangling bonds. (2) These MD results are in good agreement with the reported X-ray and neutron data. The a-Si₃N₄ structure can be reproduced by the MD simulation given in this study.     

Tetrahedral Oligothiophenes; Synthesis,X‐ray Analysis,and Optoelectronic Properties of Highly Symmetrical, 3D‐Branched Oligothiophenes

Tetrakis(bithienyl)methane and tetrakis(terthienyl)methane have been synthesized from tetrakis(2‐thienyl)methane by use of Suzuki–Miyaura coupling as a key reaction. Their trimethylsilyl (TMS) derivatives are also synthesized. X‐ray analysis reveals that each oligothiophene moiety tends to adopt anti‐conformations and show relatively small torsion angles between the adjacent thiophene rings. While the longest absorption maxima of these tetrakis(oligothienyl)methanes exhibit only a slight bathochromic shift compared to the corresponding linear oligothiophene derivative, tetrakis(bithienyl)methane and its TMS derivative exhibit an appreciable red‐shift in their fluorescence spectra. The intramolecular interaction between thienyl groups of tetrakis(2‐thienyl)methane is supported by DFT calculation.     

Vibrational quasi-degenerate perturbation theory: applications to fermi resonance in CO2, H2CO, and C6H6

A quasi-degenerate perturbation method with vibrational self-consistent field (VSCF) reference wavefunction is developed. It simultaneously accounts for strong anharmonic mode-mode coupling among a few states (static correlation) by a configuration interaction theory and for weak coupling with a vast number of the other states (dynamic correlation) by a perturbation theory. A general formula is derived based on the van Vleck perturbation theory. An algorithm that selects a compact set of the most important VSCF configurations which contribute to the static correlation is proposed and a scheme to limit the number of configurations considered for dynamic correlation is also implemented. This method reproduces the vibrational frequencies of CO2 and H2CO that are subject to the strongest anharmonic mode-mode coupling within 10 cm(-1) of vibrational configuration interaction results in a computational expense reduced by a factor of one to two orders of magnitude. The method also reproduces the infrared absorption of C6H6 in the CH stretching (nu12) frequency region, in which combination tones nu13nu16 and nu2nu13nu18 appear on account of an intensity borrowing from nu12via the anharmonic coupling.     

A dual-level state-specific time-dependent density-functional theory

A highly efficient new algorithm for time-dependent density-functional theory (TDDFT) calculations is presented. In this algorithm, a dual-level approach to speed up DFT calculations (Nakajima and Hirao, J Chem Phys 2006, 124, 184108) is combined with a state-specific (SS) algorithm for TDDFT (Chiba et al., Chem Phys Lett 2006, 420, 391). The dual-level SS-TDDFT algorithm was applied to excitation energy calculations of typical small molecules, the Q bands of the chlorophyll A molecule, the charge-transfer energy of the zincbacteriochlorin-bacteriochlorin model system, and the lowest-lying excitation of the circumcoronene molecule. As a result, it was found that the dual-level SS-TDDFT gave correct excitation energies with errors of 0.2-0.3 eV from the standard TDDFT approach, with much lower CPU times for various types of excitation energies of large-scale molecules.