Multireference character in some small boron clusters could be significant, and a previous all-electron fixed-node diffusion quantum Monte Carlo (FN-DMC) calculation with the single-determinant-Jastrow (SDJ) trial wavefunction shows that the atomization energy (AE) of B4 + is overestimated by about 1.4 eV compared with the coupled cluster method with single, doubles, and perturbative triples [CCSD(T)] results. All-electron FN-DMC calculations and those with the pseudopotential (PP) using SDJ and multi-determinant-Jastrow (MDJ) trial wavefunctions with B3LYP orbitals as well as CC calculations at different levels are carried out on Bn Q (n = 1-5, Q = -1, 0, 1) clusters. The obtained FN-DMC energies indicate that the node error of the employed SDJ trial wavefunction in all-electron calculations is different from that with the PP for some clusters. The error of AEs and dissociation energies (DEs) from all-electron FN-DMC calculations is larger than that with the PP when the SDJ trial wavefunction is employed, while errors of CC methods do not depend on whether the PP is used. AEs and DEs of the boron clusters are improved significantly when MDJ trial wavefunctions are used in both all-electron calculations and those with the PP, and their error is similar to that of CCSD(T) compared with CCSDT(Q) results. On the other hand, reasonable adiabatic electron detachment energies (ADEs) and ionization potentials (AIPs) are achieved with FN-DMC using SDJ trial wavefunctions and MDJ is less effective on ADEs and AIPs. Furthermore, the relative energy between two structures of B9 - is predicted reliably with FN-DMC using the SDJ trial wavefunction and the effect of MDJ is negligible, while density functional theory results using different exchange-correlation functionals differ significantly.

Recently, memristors have attracted considerable attention because of their potential applications in artificial neural networks which will promote the future development of artificial intelligence. In this work, the analogue memristive and related synaptic behavior of memristors based on single crystalline LiNbO3 thin films have been studied. Low energy Ar+ ions irradiation was applied to locally dope the LiNbO3 thin films by controllably introducing oxygen vacancies acting as donors. The resistive switching performance and synaptic plasticity can be tuned by changing the size or the number of the irradiated regions below the top electrode. Linear regression, an important fundamental function belonging to the machine learning in artificial intelligence, was emulated using memristors with different synaptic plasticity. It has been shown that the local doping method significantly influences the linear regression process.

Polycrystalline bismuth ferrite (BiFeO3, BFO) thin films are fabricated by pulsed laser deposition technique on Pt/Ti/SiO2/Si substrates, the current-voltage (I-V) and capacitance-voltage (C-V) measurements show that the Au/BFO/Pt structure simultaneously show resistive and capacitive switchings. By tuning the amplitude of the external voltage, multiple resistance states and capacitance states are obtained. The conduction mechanism of the Au/BFO/Pt is analyzed to explain the switchings, and temperature-dependent I-V and C-V measurements are performed to demonstrate that ferroelectric switching is not the root cause of the resistive and capacitive switching in the examined BFO thin films. (C) 2018 The Japan Society of Applied Physics

Low magnetic loss ferrite composites consisting of Ba(CoTi)1.2Fe9.6O19 and BiFeO3 (BFO) ferrite were investigated for permeability, permittivity, and high frequency losses at 10 MHz–1 GHz. The phase fraction of BiFeO3 was quantitatively analyzed by X-ray diffraction measurements. An effective medium approach was employed to predict the effective permeability and permittivity for the ferrite composites, which was found to be in good agreement with experimental data. The experiment demonstrated low magnetic losses (<0.128), modified by BFO phase fraction, while retaining high permeability (∼10.86) at 300 MHz. More importantly, the BFO phase resulted in a reduction of magnetic loss by 32%, as BFO phase increased from 2.7 vol. % to 12.6 vol. %. The effect of BFO phase on magnetic and dielectric properties revealed great potential for use in the miniaturization of high efficiency antennas.

Co-Ti substituted M-type hexaferrite composites, consisting of Ba(CoTi)(1.2)Fe9.6O19 with various amounts of Bi2O3 (0-8 wt%), were successfully synthesized by conventional ceramic processes. The effects of Bi2O3 upon the composite microstructure, magnetic properties, and magnetic and dielectric properties sintered at low temperatures were systematically investigated. The present studies aim to develop magneto-dielectric materials possessing equivalent values of permeability and permittivity, as well as low magnetic and dielectric losses, which allow for miniaturizing efficient antennas at the very high frequency band (VHF, 30-300 MHz). The present experiments show that addition of BiFeO3, observed in the polycrystalline hexaferrite composites, acts to reduce loss factors (i.e., tan delta mu/mu' = 0.014, tan delta epsilon/epsilon' = 0.00071) while concomitantly retaining high and equivalent values of permeability and permittivity (i.e., mu' similar to 12 and epsilon' similar to 12 at 300 MHz). (C) 2015 Elsevier B.V. All rights reserved.

We have synthesized macrocyclic polystyrene- (PS-) terminated PS star polymers via a core-cross-linking approach in this work. A tadpole-shaped macrocyclic PS-linear-PS copolymer was synthesized at first via click chemistry and ATRP polymerization method. The "living" ATRP initiating chain-ends of the tadpole-shaped copolymers were linked together via ATRP polymerization with divinylbenzene to form a core-cross-linked macrocyclic star polymer. The number of arms attached to the macrocyclic star polymers was measured with NMR. and absolute molecular weights with gel permeation chromatography (GPC) with multiangle laser light scattering detector. These macrocyclic star polymers had a highly cross-linked core and many radiating arms. The shorter tadpole-shaped precursors caused core-cross-linked star polymers with higher molecular weights and more arm numbers. The macrocycle-terminated core-cross-linked star polymers showed two glass transition temperatures, one arising from the linear branches and another from the macrocycles.

In this work, novel star-hyperbranched block copolymers containing four polystyrene arms and hyperbranched polyglycidol at the end of each arm (SPS-b-HPG) have been synthesized. The polystyrene arms were prepared through atom transfer radical polymerization of styrene starting from a four-arm initiator. The hydroxyl-terminated PS star polymers served as precursors for the cationic ring-opening polymerization of glycidol using BF3 center dot OEt2 as the catalyst. The chemical structures of these block copolymers were characterized by using H-1 and C-13 NMR. DSC analysis indicated that the star-hyperbranched block copolymers exhibited two distinct glass transition temperatures corresponding to the linear PS and the HPG segments, respectively. The addition of LiClO4 increased the T-g of HPG segments at low concentrations, however, decreased the T-g at high concentrations. The T-g of PS segments was not affected by the addition of salts at all. Furthermore, the interaction of sPS-b-HPG with LiBr was studied by using viscosity analysis based on the Jones-Dole equation. The star-like PS core strengthened the interaction of sPS-b-HPG with Li ions that could facile the inhomogeneous distribution of Li cations and anions in different phases, which is important in polymeric electrolytes for lithium chemical power sources. The ionic conductivity of one sPS-b-HPG/LiClO4 electrolyte was measured to be higher than that of HPG/LiClO4 electrolyte. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 949-958, 2009

Carbon nanotubes (CNTs) are used as templates to synthesize regioselective polymers from enzymatic polymerization of phenol in water. About 90% of total polymeric units in the obtained polymers are the highly thermally stable oxyphenylene units. The polymer-yields are dependent on the quantities of CNTs used. On the basis of MWNT-templated enzymatic polymerization of phenol, covalent attachment of polyphenol chains to the surface of MWNT by way of a linking molecule, hydroquinone, is achieved. This approach supplies a novel way for producing high-performance polymers and for functionalization of the surface of CNT. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1627-1635, 2009

We studied the effects of H2O2 oxidation without metal catalysts and under neutral conditions on morphologies and structures of the multiwalled carbon nanotubes (MWNTs). The formation of surface functional groups and changes in nanotube structures, morphology, and thermal stability during oxidation were analysized by X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectra, high-resolution transmission electron microscopy, and thermogravimetric analysis. Several functional groups such as carboxylic (−COOH), carbonyl (−CO), and hydroxyl (−OH) groups were formed on the surface of MWNTs; however, hydroxyl groups were preferentially formed and reached a maximum atomic concentration of about 46% in 4 days of oxidation. The graphitization degree decreased in the first day of oxidation; however, it readily increased in the continued oxidation days.

Doping dependence of the anisotropic resistivity and in-plane thermopower have been systematically studied for Bi2Sr2Ca1−xGdxCu2O8+δ single crystals (x=0, 0.09, 0.19, 0.32 and 0.41), whose hole concentration changes from overdoped to underdoped level. For the underdoped crystals, the in-plane resistivity ρab(T) exhibits an obvious downturn from the T-linear behavior at characteristic temperature T*, whose value increases with x, which manifests the opening of the spin gap in the normal state. The c-axis resistivity ρc(T) and the anisotropy ρc(T)/ρab(T) increase rapidly with increasing Gd-doping concentration. The in-plane thermopower S increases monotonously with decreasing the carrier concentration, and its temperature dependence for the underdoped crystals shows a deviation from the T-linear dependence at high temperature region. By assuming a characteristic temperature Tscale where the thermopower S begins to deviate from T-linear behavior, S(T)/S(Tscale) vs. T/Tscale can be well scaled into a universal curve for all the underdoped crystals. The Tscale, which is supposed to relate with pseudogap, shows the similar doping dependence to that of T*. However, there are quantitatively difference between T* and Tscale.