2015 Vol. 28, No. 6

Special Issue
2015, 28(6): 0-0.
The phase separation and magnetic-field-induced transition of the antiferromagnetic charge-ordered insulator (AFI) phase into the ferromagnetic metal (FM) phase in an anisotropically-strained manganite thin film is directly imaged using a home-built magnetic force microscope (MFM). The MFM images at 10 K show that the two competing phases already coexist in zero magnetic field. Remarkably anisotropic distribution of the stripe-like phase domains are observed, which can qualitatively account for the anisotropic transport. Above 2.2 T, the AFI phase starts to transform into FM phase gradually. The melting of AFI phase is completed at 3.2 T. The FM phase can be retained after the magnetic field is removed, suggesting the metastable nature of the AFI phase at this temperature.
Anatase TiO2(001) surface arouses lots of research interests since it is believed to be the most reactive surface. However, recent STM measurements showed that except the defect sites, anatase TiO2(001) (1×4) reconstructed surface is inert to H2O adsorption. It was indicated that oxidation could be the reason which induces the inert surface reactivity. Therefore, it is strongly motivated to understand the oxidation structures as well as the oxidation process on this surface. In this work, based on first principles calculations, we investigated the oxidized structures and processes of TiO2 anatase (001) surface with (1×4) reconstruction. We have discovered two kinds of oxidized structures through the molecular adsorption and dissociated adsorption with different oxidation ratio. To understand the oxidation process, we studied the reaction barrier of oxidation process. We conclude the stability of different oxidized structures with different oxidation ratio by comparing the free energy of the system as a function of oxygen chemical potential. Based on that, a first-principles-based phase diagram of the low-energy oxidized surface structures is provided. The effects of the lattice stress are also studied. Results show that the oxidized structure and oxidation ratio strongly depend on the temperature and pressure. The lattice stress also plays an important role.
On the basis of first-principles calculations, we have designed a novel type of molecular systems in which a single-walled carbon nanotube (SWNT) is encapsulated by acyclic CB[n]-type molecular container. The electronic structures and coherent electron transportation properties of the molecules were simulated at the density functional theory level. Due to the weak interactions between the inner SWNT and outer molecular container, the acyclic part can slide along the nanotube direction, which in turn effectively changes the electron tunneling ability through the SWNT. The dependences of tunneling conductance on the position of the acyclic container attached to the SWNT were examined, which reflect clearly a Bloch form distribution of molecular wavefunction along the nanotube direction. We thus proposes a convenient way to scan the one-dimensional electron wavefunction in carbon nanotubes.
A programmable algorithm using bond dissociation energies has been proposed for the prediction of reaction pathways. It has been successfully applied to a gas-phase reaction of F2+CH3Cl, with the accurate revelation of the most favorable product CF4 and its corresponding reaction pathway. This acts as an inspiring example of chemical empiricism 2.0, and may open the door for the large-scale prediction of reaction pathways at the age of big data.
The effects of doping concentration, position and oxygen vacancy defect on the stability, electronic and optical properties of La-doped anatase TiO2 have been investigated based on DFT+U method. The calculations indicated that the doping concentration and sites of La affected the stability and band gap of La-doped TiO2 significantly due to the lattice distortion, which obey the ionic Pauling’s rules and crystal field theories; moreover, the simulated adsorption spectrum shows an obviously increase in the photocatalysis properties, which are in good agreement with recently experimental measurements. The oxygen vacancy defect will enhance the structural stability and the adsorption of visible light in La-doped TiO2 system, which is important in photocatalytic application.
Optical tomography system based on modified simultaneous iterative reconstruction tech-nique is designed to real-time monitor spatial distribution and diffusion process of smoke plume in a power plant. Concentration profiles, rather than just a point value, of smoke plume concentrations are the goal of this method, and the tomography algorithm is ana-lyzed. According to incomplete projection data in the process of reconstruction and exiting noise interference, the modified simultaneous iterative reconstruction technique (SIRT) is adopted to extract the information of the trace gas concentration by a fan beam scanning and is compared to the conventional SIRT. Three evaluation indexes show that the recon-struction effect is the best by choosing proper relaxation factor, which reduces the index d to 0.044 from 0.435 and reduces the index r to 0.044 from 0.376 for 5500 iterations. Hence, the modified algorithm performs better in estimating the shape of the plume, this method is used to process the measured spectra in field campaign, the reconstruction results and the measured data are basically consistent, which is further confirmed by the experimental results.
The stable conformations of a series of bioactive molecules, (?)-alboatisins A?C, are identified via Monte Carlo searching with the MMFF94 molecular mechanics force field. Then, the optical rotation (OR) values, vibrational circular dichroism (VCD), and electronic circular dichroism (ECD) spectra were calculated using the gradient-corrected density functional theory method. The vibrational and transition modes of molecular chirality were explored in terms of their microscopic origin. The calculated specific rotations are in agreement with the experimental values. From the OR analysis, it was concluded that optical rotation values areregulated by hydroxyl substitution. Vibrations occurring on the chiral skeleton may cause strong absorption in VCD spectra; VCD spectra are thus the spectral response to deformation vibrations on the chiral carbon skeleton. The lowest-energy negative Cotton effect is caused by σ→π* transition. Frontier molecular orbital analysis showed that strong ECD absorptions are produced when the dominant transition on the chiral skeleton is asymmetric; ECD spectra show the result of transitions lacking asymmetry on the chiral skeleton.
The inverse sandwiches [E-C{5-n}H{5-n}Nn-E]+ and [E-C{5-n}H{5-n}Pn-E]+ (n=1, 2, 3; E=Al, Ga, In, Tl) with low-valent boron group elements are studied. The (η5,η5) coordinated inverse sandwich [E-C{5-n}H{5-n}Nn-E]+ is unstable in energy or nonexistent. However, the (η5,η5) coordinated [E-C{5-n}H{5-n}Pn-E]+ is not only stable in energy, but also stable against dissociation. The dissoction stability [E-C{5-n}H{5-n}Pn-E]+ with the same E element decreases as the number n increases, while for the certain n number, the dissociation energies with different E elements are close to each other. [E-C4H4P-E]+ has similar dissocition stability to the well-known [E-C5H5-E]+. The inteaction between C{5-n}H{5-n}Pn and lowvalent E element is mainly ionic. Since lone pairs of electrons locate on both E and P atoms, the (η5, η5) coordinated inverse sandwich [E-C{5-n}H{5-n}Pn-E]+ would act as multi electron-donors.
Metal cations as well as water are important factors to control the synthesis of MnO2 crystal nanostructures. In this work, systemic Density functional theory calculations aboutα,β,δ-MnO2 are presented to show the importance of metal cations and water for the structure stability and energy stability of MnO2. It is shown that the α-MnO2 crystal and its (110) surface will crash without the tunnel cations such as K+, and the distance between the layers of the δ-MnO2 will be significantly lower than that of the experimental results without the interlayer metal cations and water. At the same time, α-MnO2 and δ-MnO2 can be more stable than β-MnO2 with metal cations and water, and vice versa.
We report ab initio scattering calculations results of electron-methanethiol collisions using R-matrix approach within the static-exchange and static-exchange-polarization approximations. The calculated elastic integral cross sections are in agreement with the experimental data. Two shape resonances of 2A' symmetry located at 4.06 and 8.32 eV are detected within static-exchange-polarization model. For this dipole molecule, Born-closure procedure was used to account for the higher partial waves (l>4) for the convergence of the cross section. The effective collision frequencies over a wide electron temperature range (200?30000 K) are calculated using the data of the momentum-transfer cross section.
The mono and dihydrated complexes of 2'-deoxyguanosine have been used to elucidate the importance of the 2'-hydroxy group in the hydration. Density functional theory and time-dependent density functional theory methods were performed to investigate the ground-and excited-state hydrogen bonding properties of 2'-deoxyguanosine-water (2'-dG-W) and 2'-deoxyguanosine-2water (2'-dG-2W). Infrared spectra, geometric optimizations, frontier molecular orbitals and Mulliken charges have also been studied. The results demonstrated that the excited-state intramolecular hydrogen bonding dynamics of complexes 2'-dG-W and 2'-dG-2W behaves differently upon photoexcitation, while their intermolecular hydro-gen bonding dynamics behaves similarly. Moreover, the significant weakening of the inter-molecular hydrogen bond O4···H1?N1 and the formation of the new strong hydrogen bond O4···H3?N2 in the 2'-dG-2W upon photoexcitation were due to the geometric structure bending of guanine and the rigidity of related molecules. In addition, the charge transfer properties were theoretically investigated by analysis of molecular orbital.
The effect of time delay on a genetic toggle switch, whose undelayed dynamics shows low protein expression states (L-states), high expression states (H-states) and coexistence of them different transcription-factor binding rates α, is investigated by using the delayed stochastic simulation method. Interestingly, we find that the delay induces a transition from the coexistence state to L-state or H-state by suppressing the other state. Moreover, the phase diagram on the α-τ plane is obtained by extensive simulations. It is observed that, the coexistence state is remarkably narrowed by increasing delay time, and completely disappearsabove a triple-point-like point where direct transitions between H-state and L-state are possible.
Ab initio calculation is performed to investigate the uranium solubility in different sites of Gd2Zr2O7 pyrochlore. The Gd2Zr2O7 maintains its pyrochlore structure at low uranium dopant levels, and the lattice constants of Gd2(Zr{2-y}Uy)O7 and (Gd{2-y}Uy)Zr2O7 are gen-erally expressed as being linearly related to the uranium content y. Uranium is found to be a preferable substitute for the B-site gadolinium atoms in cation-disordered Gd2Zr2O7 (where gadolinium and zirconium atoms are swapped) over the A-site gadolinium atoms in orderedGd2Zr2O7 due to the lower total energy of (Gd{2-y}Zry)(Zr{2-y}Uy)O7.
Poly(ethylene glycol) (PEG) macromolecular brushes were synthesized directly via re-versible addition-fragmentation chain transfer polymerization cyclopolymerization of diacry-late monomers bearing PEG functional groups through the formation of 11-member rings. The diacrylate monomers bearing PEG functional groups are the 1,2,3-triazole-tethered di-acrylate macromolecular monomers with different PEG lengths synthesized via the so-called “click” chemistry. The bulky hindrance of PEG chains affected the polymerization behavior of the diacrylate macromolecular monomers, and the diacrylate monomers showed strong tendency to cyclopolymerization rather than crosslinking. NMR analysis and gel perme-ation chromatography profiles proved the high e ciency of cyclopolymerization without sidereactions. The aqueous solutions of the obtained PEG macromolecular brushes were fluores-cent under UV excitation. The uorescence depended dramatically on the concentration of brush-like polymers due to the aggregation of cyclopolymer in water, and could be quenched by the addition of DNA.
Cu(In,Al)(Se,S)2 thin films were successfully obtained through a simple low-cost non-vacuum process. The Cu(In,Al)Se2 raw material powder was firstly synthesized by a tra-ditional solvothermal route. Then, the precursor coatings were prepared by drop-coating Cu(In, Al)Se2 slurry. Finally, the Cu(In,Al)Se2 and Cu(In,Al)(Se,S)2 films were achieved by the selenization and/or sulfuration process. Through X-ray diffraction (XRD), scanning electron microscope, X-ray fluorescence, and absorption spectroscopy measurement, it was found that all the films show the single chalcopyrite phase structure and have the preferred(112) orientation. Meanwhile, after substituting selenium by sulfur, the main XRD peaks shift to higher 2θ degrees and the porous films become more compact. The energy band gap also increases to a suitable range for light absorption from 1.21 eV to 1.33 eV, which indicates that the additional sulfuration process is much more favorable for improving the quality of Cu(In,Al)(Se,S)2 films.
A polyurethane/silver sulfide nanocomposite film was synthesized by a biomineralization sim-ulated method. The effect of the Ag2S nanoparticles on the physical properties of the com-posite was studied by Fourier transform infrared, differential scanning calorimetry (DSC), scanning electron microscopy. The thermal stability of the composite was measured by DSC. The fluorescence emission of the nanocomposite films was found to be very sensitive to Ni(II) ions, with a small amount of Ni(II) ions making the emissions increase dramatically. The films are predicted to have the potential to be developed into excellent sensing films of Ni(II) ions in the water.
The Prussian blue/ionic liquid-polyaniline/multiwall carbon nanotubes (PB/IL-PANI/MWNTs) composite film was fabricated by using cyclic voltammetry. The ion liquid acting as a lubricating agent, could enhance the electron delocalization degree and reduce the struc-tural defects of the polyaniline. The surface morphology of the composite film revealed that the PB nanoparticles have smaller size than that in pure PB film. Due to the introduction of ion liquid, the PB/IL-PANI/MWNTs composite film showed wonderful synergistic effect which can remarkably enhance sensitivity, expand linear range and broaden acidic adapt-ability for hydrogen peroxide detection. The composite film demonstrated good stability in neutral solution contrast to pure PB film, with a linear range from 2.5 μmol/L to 0.5 mmol/Land a high sensitivity of 736.8 μA·(mmol/L)-1·cm-2 for H2O2 detection. Based on the com-posite film, an amperometric glucose biosensor was then fabricated by immobilizing glucose oxidase. Under the optimal conditions, the biosensor also exhibits excellent response to glucose with the linear range from 12.5 μmol/L to 1.75 mmol/L and a high sensitivity of 94.79 μA (mmol/L)-1·cm-2 for H2O2. The detection limit was estimated 1.1 μmol/L. The resulting biosensor was applied to detect the blood sugar in human serum samples without any pretreatment, and the results were comparatively in agreement with the clinical assay.
A superhydrophobic steel mesh film was prepared by combination of macro-scale rough sur-face and low surface energy material treatment through a facile coating method. The contact angle for seawater is measured to be as high as 130.16o. A reformed Cassie-Baxter equation was applied for the theoretical predictions of this novel material for the first time. Good agreement between the predictions and experiments was obtained. The loading capacities of these boats, fabricated from the resulting hydrophobic steel meshes, were also character-ized. The highest loading weight about 17.50 g was obtained by the steel mesh treated by 2.0wt% (heptadecafluoro-1,1,2,2,-tetradecyl)trimethoxysilane solution. The striking loading capacity of this miniature boat may be attributed to the air film trapped around the mesh surface. This novel superhydrophobic steel mesh material have wide applications on medical materials, marine materials and smart materials.
A new X-shaped compound (SiPy) functionalized with acetylene bonds in the 1-, 3-, 6-, and 8-positions of the pyrene core has been synthesized by Sonogashira coupling reactions. Its photophysical, thermal, and organic field effect transistor (OFET) properties as well as the film morphologies have been investigated. SiPy exhibits high stability which is evidenced by thermal gravimetric analysis. The atomic force microscopy images reveal that the morphol-ogy of thin films depends on the substrate temperature. The film OFET devices based on SiPy were constructed and exhibited p-type performances.
The Sr4Al14O25:M and doped Sr4Al14O25:M+Sm3+ (M=Mn4+, Cr3+) phosphors were syn-thesized by a solid-state reaction method and their luminescent properties were investi-gated. The results showed that the co-doping of Sm ions did not change the positions of excitation band and emission band but signi cantly improved the luminescent properties of Sr4Al14O25:Cr3+ phosphors; whereas, the emission intensity of Sr4Al14O25:Mn4+ was re-dueced remarkably when Sm ions were co-doped. In addtion, a radiative-form energy transfer from Sm3+ to Cr3+ was observed for the first time in the Cr, Sm co-doped Sr4Al14O25 phos-phors. The results indicated that Sm ions could signi cantly improve the emission intensity of Sr4Al14O25:Cr3+, making the Sm3+co-doped Sr4Al14O25:Cr3+ phosphor a promising can-didate for the applications in display and solid state lightening.
SiO2/TiO2 double-layer films with antireflective and self-cleaning properties were prepared by dip-coating glass substrate into cost-effective SiO2 and TiO2 sol successively and subse-quently being calcined at 500 oC. The optical and structural properties of films have been in-vestigated by UV-visible spectrophotometer and field emission scanning electron microscope, respectively. At the same time, self-cleaning property generated from superhydrophilicity and photocatalysis was obtained. The results indicated that the as-prepared SiO2/TiO2 double-layer films show maximum transmittance of 95% and self-cleaning property.
Chinese Abstracts
2015, 28(6): 781-781.