Directional Charge Transport in Layered Two‐Dimensional Triazine‐Based Graphitic Carbon Nitride

Triazine‐based graphitic carbon nitride (TGCN) is the most recent addition to the family of graphene‐type, two‐dimensional, and metal‐free materials. Although hailed as a promising low‐band‐gap semiconductor for electronic applications, so far, only its structure and optical properties have been known. Here, we combine direction‐dependent electrical measurements and time‐resolved optical spectroscopy to determine the macroscopic conductivity and microscopic charge‐carrier mobilities in this layered material “beyond graphene”. Electrical conductivity along the basal plane of TGCN is 65 times lower than through the stacked layers, as opposed to graphite. Furthermore, we develop a model for this charge‐transport behavior based on observed carrier dynamics and random‐walk simulations. Our combined methods provide a path towards intrinsic charge transport in a direction‐dependent layered semiconductor for applications in field‐effect transistors (FETs) and sensors.     

Investigating molecular charge transfer complexes with a low temperature scanning tunneling microscope

Electron donor-acceptor molecular charge transfer complexes (CTCs) formed by alpha-sexithiophene (6T) and tetrafluoro-tetracyano-quinodimethane (F4TCNQ) on a Au(111) surface are investigated by scanning tunneling microscopy, spectroscopy, and spectroscopic imaging at 6 K. New hybrid molecular orbitals are formed in the CTCs, and the highest occupied molecular orbital of the CTC is mainly located on the electron accepting F4TCNQ while the lowest unoccupied molecular orbital is predominantly positioned on the electron donating 6T. We observed the conductance switching of F4TCNQ inside CTCs, which may find potential applications in novel molecular device operations.     

Measurement of the branching fractions of exclusive _B-->D(*)(pi)l-_nu l decays in events with a fully reconstructed B meson

We report a measurement of the branching fractions for _B-->D(*)(pi)l- _nu(l) decays based on 341.1 fb(-1) of data collected at the Upsilon(4S) resonance with the BABAR detector at the SLAC PEP-II e+ e- storage rings. Events are tagged by fully reconstructing one of the B mesons in a hadronic decay mode. We obtain B(B- -->D(0)l-_nu(l)=(2.33+/-0.09(stat)+/-0.09(syst)%, B(B- -->D(*0)l-_nu(l)=(5.83+/-0.15(stat) +/-0.30(syst) %, B(_B(0)-->D+l-_nu(l)=(2.21+/-0.11(stat) +/-0.12(syst)%, B(_B(0)-->D(*)l-_nu(l)=(5.49+/-0.16(stat)+/-0.25(syst)%, B(B- -->D+pi-l-_nu(l)=(0.42+/-0.06(stat)+/-0.03(syst)%, B(B- -->D(*)+pi-l-_nu(l)=(0.59+/-0.05(stat)+/-0.04(syst)%, B(_B(0)-->D(0)pi+l-_nu(l)=(0.43+/-0.08(stat)+/-0.03(syst)%, and B(_B(0)-->D(*0)pi+l-_nu(l)=(0.48+/-0.08(stat)+/-0.04(syst)%.     

Controlling the spontaneous emission of a superconducting transmon qubit

We present a detailed characterization of coherence in seven transmon qubits in a circuit QED architecture. We find that spontaneous emission rates are strongly influenced by far off-resonant modes of the cavity and can be understood within a semiclassical circuit model. A careful analysis of the spontaneous qubit decay into a microwave transmission-line cavity can accurately predict the qubit lifetimes over 2 orders of magnitude in time and more than an octave in frequency. Coherence times T1 and T_{2};{*} of more than a microsecond are reproducibly demonstrated.     

Single- and double-pion production in nucleon collisions on the nucleon and on nuclei—the ABC effect and its origin in a dibaryonic resonance

The ABC effect-an intriguing low-mass enhancement in the ππ invariant mass spectrum-is known from inclusive measurements of two-pion production in nuclear fusion reactions. First exclusive measurements carried out at CELSIUS-WASA for the fusion reactions leading to d or ³He reveal this effect to be a σ-channel phenomenon associated with the formation of a ΔΔ system in the intermediate state and combined with a resonance-like behavior in the total cross-section. Together with the observation that the differential distributions do not change in shape over the resonance region the features fulfill the criteria of an isoscalar s-channel resonance in pn and NNππ systems, if the two emitted nucleons are bound. It obviously is robust enough to survive in nuclei as a dibaryonic resonance configuration. In this context also the phenomenon of NΔ resonances is reexamined.     

8-羟基喹啉过渡金属配合物电子光谱和二阶非线性光学性质的 DFT研究

使用含时密度泛函理论(TDDFT)B3LYP方法计算了IB, IIB, VIIIB过渡金属与8-羟基喹啉络合(MQ)后, 配合物的电子光谱以及二阶非线性光学性质. 结果表明, 掺杂过渡金属后, 形成络合物的能隙值减小100～150 kJ/mol, 最大吸收波长红移150～200 nm左右. 电子从基态到激发态的跃迁主要为p→p*, n→p*跃迁, 属于LLCT, MLCT过程. IB的络合物MQ以及VIIIB的络合物MQ3表现出良好的非线性光学性质.     

Reversibly Crosslinked Networks of Nanoparticles in Metallocene‐Catalyzed Olefin Polymerization

A hierarchic build‐up of functional nano‐ and microparticles allows the generation of smart organic supports for metallocene catalysts. Latices, well defined in size and surface structure, are made by emulsion polymerization using poly(ethylene oxide)‐containing surfactants. Micron‐sized catalyst beads are formed by reversible loading/crosslinking with a metallocene/methylaluminoxane complex. As a result of the network fragmentation during ethylene polymerization, the catalysts achieve very high productivities, hard polyethylene particles and homogeneous distributions of nanometer‐sized fragments in the product.     

A Polymorph Crystal Structure of Hexaphenyl Observed in Thin Films

Highly oriented thin films of hexaphenyl — which are used in organic opto‐electronic applications — are characterised in terms of their crystal structures. Two different crystal structures of hexaphenyl (C₃₆H₂₆) are observed when the films are prepared by physical vapour deposition at various substrate temperatures. If the substrate is kept at room temperature, hexaphenyl crystallises within a structure which is already known from single crystal investigations. However, when the thin films are grown at a substrate temperature of 160°C a new crystalline phase appears. This structure was characterised by X‐ray and transmission electron diffraction. Due to the strong preferred orientation of the crystallites within the thin films, the lattice constants as well as main features of the new crystal structure could be determined. The lattice is indexed as monoclinic with: a = 7.98Å, b = 5.54Å, c = 27.64Å and β = 99.8°. The new crystal structure has high similarity to the already known crystal structure: Both structures are built by layers of hexaphenyl molecules, within one layer the aromatic planes of the hexaphenyl molecules are packed in a herringbone pattern. The characteristic feature of the new structure is that the long axes of the hexaphenyl molecules are arranged absolutely perpendicular to the layers, whereas, within the already known structure the long axes show an tilt angle of 17° to the layer normal direction.     

Grand European Chemical Conferences: The Whole is More than the Sum of the Parts

National chemical society conferences are major platforms for communication and the exchange of ideas among the various chemical communities. However, in light of increasing efforts to create a true European research area in chemistry, there is an obvious need to establish such a platform on the European level. The GDCh has recently come up with a concept for achieving this goal.