Quasi-one-dimensional quantized states in an epitaxial Ag film on a one-dimensional surface superstructure

The in-plane energy dispersion of quantized states in an ultrathin Ag film formed on the one-dimensional (1D) surface superstructure Si(111)-(4 x 1)-In shows clear 1D anisotropy instead of the isotropic two-dimensional free-electron-like behavior expected for an isolated metal film. The present photoemission results demonstrate that an atomic layer at the film-substrate interface can regulate the dimensionality of electron motion in quantum films.     

2-azaadamantane N-oxyl (AZADO) and 1-Me-AZADO: highly efficient organocatalysts for oxidation of alcohols

Development of a stable nitroxyl radical class of catalysts, 2-azaadamantane N-oxyl (AZADO) and 1-Me-AZADO, for highly efficient oxidation of alcohols is described. AZADO and 1-Me-AZADO exhibit superior catalytic proficiency to TEMPO, converting various sterically hindered alcohols to the corresponding carbonyl compounds in excellent yields.     

Fifth-order two-dimensional Raman spectroscopy of liquid water, crystalline ice Ih and amorphous ices: sensitivity to anharmonic dynamics and local hydrogen bond network structure

The theoretical study of off-resonant fifth-order two-dimensional (2D)-Raman spectroscopy is made to analyze the intermolecular dynamics of liquid and solid water. The 2D-Raman spectroscopy is susceptible to the nonlinear anharmonic dynamics and local hydrogen bond structure in water. It is found that the distinct 2D-Raman response appears as the negative signal near the t(2) axis. The origin of this negative signal for t(2)<15 fs is from the nonlinear polarizability in the librational motions, whereas that for 30 fs相似文献   

Total synthesis of enantiopure (+)-gamma-lycorane using highly efficient Pd-catalyzed asymmetric allylic alkylation

[reaction: see text] A highly efficient short total synthesis of (+)-gamma-lycorane (>99% ee, 41% overall yield) was achieved by using the asymmetric allylic alkylation in the key step catalyzed by palladium complexes with novel chiral biphenol-based monodentate phosphoramidite ligands.     

Radial excitation of hadronic states with null pontryagin index

Radial excitations of hadrons carrying zero instanton number are investigated. The mass relations among relevant non-strange and strange mesons and baryons have been derived consistently with the observed data.     

Metallic transport in a monatomic layer of in on a silicon surface

We have succeeded in detecting metallic transport in a monatomic layer of In on an Si(111) surface, Si(111)-sqrt[7]×sqrt[3]-In surface reconstruction, using the micro-four-point probe method. The In layer exhibited conductivity higher than the minimum metallic conductivity (the Ioffe-Regel criterion) and kept the metallic temperature dependence of resistivity down to 10?K. This is the first example of a monatomic layer, with the exception of graphene, showing metallic transport without carrier localization at cryogenic temperatures. By introducing defects on this surface, a metal-insulator transition occurred due to Anderson localization, showing hopping conduction.     

Ion beam modification of silicide-silicon interfaces

We have modified the contact interface between Pd₂Si and n-Si by ion implantation and investigated the effect of the implantation on Schottky barrier height and rate of silicide formation by electrical current-voltage measurements and Rutherford backscattering spectroscopy. Various ions, As. P, B. O and Si at 50 keV and up to a dose of 5 × 10¹⁴ ions/cm² were implanted into Si wafers before the Pd-deposition to form Pd₂Si. In the case of As and P, the implantation showed a large erect on the subsequent Pd₂Si formation; the formation is enhanced in the as-implanted samples, but it is retarded if an annealing at 600°C precedes the Pd-deposition. Silicide formation was found generally to help reduce the implantation damage (with or without the 600°C annealing) and showed improvements on the electrical characteristics of the contact interface. Consumption of the entire implanted region by silicide formation is found necessary for obtaining a good diode performance. In the case of As implantation, a lowering of the Schottky barrier height of Pd₂Si has been observed.     

A Flexible Approach to Grandisine Alkaloids: Total Synthesis of Grandisines B,D, and F

This article describes in detail the first total synthesis of grandisine alkaloids, grandisines B, D, and F, which show affinity for the human δ‐opioid receptor. The key steps in this synthesis are construction of the isoquinuclidinone moiety of 2 by intramolecular imine formation and the tetracyclic ring system of 4 by stereoselective ring closure of the enolate of amine 8 generated by 1,4‐addition of ammonia to 9 . Synthesis of key intermediate 9 featured a highly stereoselective Brønsted acid mediated Morita–Baylis–Hillman (MBH) reaction via the N‐acyl iminium ion.     

Conformational phase diagram of poly(l-lysine) in sodium alkanesulfonate aqueous solutions at various temperatures

The conformation of poly(l-lysine) (PLL) was investigated in sodium alkanesulfonate C_nSO₃Na (n=8, 7) at various temperatures by circular dichroism spectrum measurements. C₈SO₃Na induced a double-step conformational change from a coil, to a β-sheet, and then to an α-helix, in which C₇SO₃Na induced a single-step coil-to-helix conformational change. Binding isotherms of C₈SO₃Na by PLL were constructed from the potentiometry of equilibrium concentration of the surfactant using a surfactant ion-selective electrode. The curves indicated the cooperative binding characteristic and were analyzed by a linear lattice model using the Bethe approximation. The thermodynamic parameters obtained from the model revealed that the binding of C₈SO₃Na by PLL was an entropy-driven process. The conformational change was observed at nearly full binding, presumably due to the surfactant clustering of the ordered conformation.     

Interaction between adatom-induced localized states and a quasi-two-dimensional electron gas

Using angle-resolved photoemission spectroscopy, we investigate changes in the band dispersion of a free-electron-like surface state of [FORMULA: SEE TEXT], induced by adsorption of submonolayer Au adatoms. At room temperature, where the adatoms are in a two-dimensional adatom-gas phase, electrons are transferred from the Au adatoms to the substrate, shifting the surface band downwards and causing it to deviate from a parabolic dispersion. At 135 K where the Au adatoms are frozen at specific sites of the substrate, the band splits into two. This band splitting can be explained in terms of hybridization between the unperturbed surface band and the localized virtual bound states induced by the Au adatoms.