Atomic configurations of dislocation core and twin boundaries in 3C-SiC studied by high-resolution electron microscopy

The defects in 3C-SiC film grown on (001) plane of Si substrate were studied using a 200 kV high-resolution electron microscope with point resolution of 0.2 nm. A posterior image processing technique, the image deconvolution, was utilized in combination with the image contrast analysis to distinguish atoms of Si from C distant from each other by 0.109 nm in the [110] projected image. The principle of the image processing technique utilized and the related image contrast theory is briefly presented. The procedures of transforming an experimental image that does not reflect the crystal structure intuitively into the structure map and of identifying Si and C atoms from the map are described. The atomic configurations for a 30 degrees partial dislocation and a microtwin have been derived at atomic level. It has been determined that the 30 degrees partial dislocation terminates in C atom and the segment of microtwin is sandwiched between two 180 degrees rotation twins. The corresponding stacking sequences are derived and atomic models are constructed according to the restored structure maps for both the 30 degrees partial dislocation and microtwin. Images were simulated based on the two models to affirm the above-mentioned results.

High-frequency hydrogen-related infrared modes in silicon grown in a hydrogen atmosphere

High-frequency vibrational modes have been observed at liquid-helium temperature in silicon samples grown in a H-2 or D-2 atmosphere. The highest-frequency ones are due to the overtones and combination modes of SiH fundamentals. Others are CH modes due to (C,H) complexes, but the simultaneous presence of NH modes due to (N,H) complexes cannot be excluded. The present results seem to show also the existence of centers including both SiH and CH or NH bonds. One sharp mode at 4349 cm-l is related to a weak SiH fundamental at 2210 cm(-1). The related center is ascribed to a vacancy fully decorated with hydrogen with a nearest-neighbor C atom. [S0163-1829(99)00911-X].

Tuning the energy level and photophysical and electroluminescent properties of heavy metal complexes by controlling the ligation of the metal with the carbon of the carbazole unit

Four novel Ir-III and Pt-II complexes with cyclometalated ligands bearing a carbazole framework are prepared and characterized by elemental analysis, NMR spectroscopy, and mass spectrometry. Single-crystal X-ray diffraction studies of complexes 1, 3, and 4 reveal that the 3- or 2-position C atom of the carbazole unit coordinates to the metal center. The difference in the ligation position results in significant shifts in the emission spectra with the changes in wavelength being 84 nm for the Ir complexes and 63 nm for the Pt complexes. The electrochemical behavior and photophysical properties of the complexes are investigated, and correlate well with the results of density functional theory (DFT) calculations. Electroluminescent devices with a configuration of ITO/NPB/CBP:dopant/BCP/AlQ(3)/LiF/Al can attain very high efficiencies.

Controllable atom localization via double-dark resonances in a tripod system

We propose an atom localization scheme for a tripod-type atom making use of the sharp absorption peak resulting from interacting double-dark resonances. It is demonstrated that the probability of finding the atom at a particular position, as well as the localization precision, can be dramatically enhanced. The probability can be doubled by adjusting the Rabi frequency of the control field to the maximum Rabi frequency of the standing-wave field. Moreover, much better spatial resolution can be achieved for smaller detunings of the control and the standing-wave fields. (c) 2006 Optical Society of America.

Single-photon source in strong photon-atom interaction regime in quasiperiodic photonic crystals

The antibunching properties of the fluorescence from a two-level ideal system in a 12-fold quasiperiodic photonic crystal are investigated based on the calculated local density of states. We found that the antibunching phenomenon of the fluorescence from two-level ideal systems could be significantly changed by varying their positions, i.e., perfect antibunching and antibunching with damped Rabi oscillation phenomenon occurred in different positions and at different frequencies in photonic crystals as a result of the large differences in the local density of states. This study revealed that the multi-level coherence of fluorescence from a two-level ideal system could be manipulated by controlling the position of the two-level ideal system in photonic crystals and the emission frequency in the photonic band structure. Copyright (C) EPLA, 2008

Collisional quantum interference effect on rotational energy transfer in an atom-diatom system

The theoretical model of collisional quantum interference (CQI) in intramolecular rotational energy transfer is described in an atom-diatom system, based on the first Born approximation of time-dependent perturbation theory and considering a long-range interaction potential. The relation between differential and integral interference angles is obtained. For the CO A(1)Pi (v = 0)/e(3)Sigma (-)(v = 1)-He collision system, the calculated integral interference angles are consistent with the experimental values. The physical significance of interference angle and the essential factors it depends on as well as the influence of the short-range interaction on CQI are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

Synthesis and identification of Heterocyclic derivatives of fullerene C-60: Unexpected reaction of anionic C-60 with benzonitrile

During the reaction of reduced C-60 with benzyl bromide in benzonitrile, a novel cis-1 C-60 adduct, 1,4-dibenzyl-2,3-cyclic phenylimidate C-60 (1), Was obtained rather than the expected product of 1,4-dibenzyl C-60. The structure of compound 1 was analyzed by X-ray single-crystal diffraction, identifying the presence of a five-membered heterocycle at a [5,6] bond of C-60. One of the heteroatoms is assigned as a nitrogen atom; however, the identity of the other heteroatom cannot be determined unambiguously by crystallography due to similarity between the nitrogen and oxygen atoms.

Synthesis of Arm-6 polystyrene by atom transfer radical polymerization

A new initiator for atom transfer radical polymerization (ATRP), (Cl-2 HCCOO)(3) -C-6 H-3, (TrDCAP),has been designed and successfully synthesized. ATRP of styrene was carried out by using TrDCAP as hexafunctional initiator and the CuCl/bpy catalyst at 130 degrees C in 30% THF via core-first strategy. The Arm-6 PS-AAP was synthesized by etherealization of Arm-6 PS and 4-(4'-methoxyphenylazomethine) phenol (AAP). The initiator and the architectures of the Arm-6 PS were confirmed by H-1-NMR, FT-IR, UV-Vis and GPC.

Bonding quartz wafers by the atom transfer radical polymerization of the glycidyl methacrylate at mild temperature

In this paper, we presented a novel covalent bonding process between two quartz wafers at 300 degrees C. High-quality wafer bonding was formed by the hydroxylization, aminosilylation and atom transfer radical polymerization (ATRP) of glycidyl methacrylate (GMA), respectively, on quartz wafer surfaces, followed by close contact of the GMA functional wafer and the aminosilylation wafer, the epoxy group opening ring reaction was catalyzed by the amino and solidified to form the covalent bonding of the quartz wafers. The shear force between two wafers in all bonding samples was higher than 1.5 MPa. Microfluidic chips bonded by the above procedures had high transparency and the present procedure avoided the adhesive to block or flow into the channel.

Synthesis of asymmetric H-shaped block copolymer by the combination of atom transfer radical polymerization and living anionic polymerization

A new asymmetric H-shaped block copolymer (PS)(2)-PEO-(PMMA)(2) has been designed and successfully synthesized by the combination of atom transfer radical polymerization and living anionic polymerization. The synthesized 2,2-dichloro acetate-ethylene glycol (DCAG) was used to initiate the polymerization of styrene by ATRP to yield a symmetric homopolymer (Cl-PS)(2)-CHCCCCH2CH2OH with an active hydroxyl group. The chlorine was removed to yield the (PS)(2)-CHCOOCH2CH2OH ((PS)(2)-OH). The hydroxyl group of the (PS)(2)-OH, which is an active species of the living anionic polymerization, was used to initiate ethylene oxide by living anionic polymerization via DPMK to yield (PS)(2)-PEO-OH. The (PS)(2)-PEO-OH was reacted with the 2,2-dichloro acetyl chloride to yield (PS)(2)-PEO-OCCHCl2 ((PS)(2)-PEO-DCA). The asymmetric H-shaped block polymer (PS)(2)-PEO-(PMMA)(2) was prepared via ATRP of MMA at 130 degrees C using (PS)(2)-PEO-DCA as initiator and CuCl/bPy as the catalyst system. The architectures of the asymmetric H-shaped block copolymers, (PS)(2)-PEO-(PMMA)(2), were confirmed by H-1 NMR, GPC and Fr-IR.

Synthesis of eight-arm polystyrene by atom transfer radical polymerization

A new initiator for atom transfer radical polymerization (ATRP), (Cl2HCCOOCH2)(4)C(TDCAP) was designed and successfully synthesized. The initiator was,used to initiate,the polymerization of styrene via ATRP to method yield an eight-arm polystyrene with functional end-group chlorides. The different polymers could be prepared via ATRP of different monomers at 130 degrees C using TDCAP/CuCl/bPy as the initiating system. The initiator and eight-armed polymer were characterized by means of H-1 NMR, FTIR and GPC.

Temperature dependence of the distribution of the first passage time: Results from discontinuous molecular dynamics simulations of an all-atom model of the second beta-hairpin fragment of protein G

More than 22 000 folding kinetic simulations were performed to study the temperature dependence of the distribution of first passage time (FPT) for the folding of an all-atom Go-like model of the second beta-hairpin fragment of protein G. We find that the mean FPT (MFPT) for folding has a U (or V)-shaped dependence on the temperature with a minimum at a characteristic optimal folding temperature T-opt*. The optimal folding temperature T-opt* is located between the thermodynamic folding transition temperature and the solidification temperature based on the Lindemann criterion for the solid. Both the T-opt* and the MFPT decrease when the energy bias gap against nonnative contacts increases. The high-order moments are nearly constant when the temperature is higher than T-opt* and start to diverge when the temperature is lower than T-opt*. The distribution of FPT is close to a log-normal-like distribution at T* greater than or equal to T-opt*. At even lower temperatures, the distribution starts to develop long power-law-like tails, indicating the non-self-averaging intermittent behavior of the folding dynamics. It is demonstrated that the distribution of FPT can also be calculated reliably from the derivative of the fraction not folded (or fraction folded), a measurable quantity by routine ensemble-averaged experimental techniques at dilute protein concentrations.

Electrocatalytic performance of Pt-TiO2/C complex catalysts for oxidation of methanol

It is reported for the first time that the Pt-TiO2/C catalyst prepared with chemical reduction and sol-gel method showed the excellent electrocatalytic activity and stability for the electrooxidation of methanol. When the atom ratio of Ti to Pt in the catalysts is 1/2, the catalysts showed the best electrocatalytic properties. After the catalyst is treated at 500 degreesC, the performance is further improved. It is hopeful to use the catalyst in the pratical DMFC.

A novel dimer - Heteropolytungstate with a vanadium atom as the centre - Synthesis and structural characterization of (H3O)(4)[VW12O40Na (H2O)(4)](2)

A novel dimer-tungstovanadate, (H3O)(4)[VW12O40Na (H2O)(4)](2), was hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction, IR spectra, TGA-DSC thermal analysis and polarograpy. The yellowish crystal crystallized in the triclinic system, space group P1, a = 1.464 5(3) nm, b = 1.468 6(3) nm, c = 1.411 1(3) nm, alpha = 111.82(2)degrees, beta = 93.17(3)degrees, gamma = 117.47(3)degrees, V = 2.210 6(8) nm(3), Z = 1, D-c = 4.552 g . cm(-3), lambda (Mo K alpha) = 0.071 073 nm, mu = 31.402 mm(-1) F(000) = 2 6481 R = 0.078 0. The title compound consists of two Keggin structure units linked together with two hydrated sodium cations to form a dimer with a porous structure with the pore dimension of 0.766 nm X 0.778 5 nm.