Origin of charge density at LaAlO3 on SrTiO3 heterointerfaces: possibility of intrinsic doping

As discovered by Ohtomo and Hwang, a large sheet charge density with high mobility exists at the interface between SrTiO3 and LaAlO3. Based on transport, spectroscopic, and oxygen-annealing experiments, we conclude that extrinsic defects in the form of oxygen vacancies introduced by the pulsed laser deposition process used by all researchers to date to make these samples is the source of the large carrier densities. Annealing experiments show a limiting carrier density. We also present a model that explains the high mobility based on carrier redistribution due to an increased dielectric constant.     

Choreographic solution to the general-relativistic three-body problem

We reexamine the three-body problem in the framework of general relativity. The Newtonian N-body problem admits choreographic solutions, where a solution is called choreographic if every massive particle moves periodically in a single closed orbit. One is a stable figure-eight orbit for a three-body system, which was found first by Moore (1993) and rediscovered with its existence proof by Chenciner and Montgomery (2000). In general relativity, however, the periastron shift prohibits a binary system from orbiting in a single closed curve. Therefore, it is unclear whether general-relativistic effects admit choreography such as the figure eight. We examine general-relativistic corrections to initial conditions so that an orbit for a three-body system can be choreographic and a figure eight. This illustration suggests that the general-relativistic N-body problem also may admit a certain class of choreographic solutions.     

Sublimation phenomena of Lennard-Jones fluids in slit nanopores

Using molecular dynamics simulations, The authors studied the solid-vapor coexistence states of Lennard-Jones methane confined in slit-shaped graphite nanopores. Both the intrapore solid and extrapore vapor were simulated using a unit cell which they previously developed. Frozen critical condensates in the pores were cooled stepwise, and the equilibrium vapor pressure was determined at each temperature. The obtained solid-vapor coexistence curves were remarkably lower than that of the bulk phase. Their thermodynamic model successfully predicts the simulation results without the need to introduce any adjustable parameter, and thus proves its reliability.     

Synthesis of highly-ordered mesoporous silica particles using mixed cationic and anionic surfactants as templates

We applied a molecular assembly formed in an aqueous surfactant mixture of cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium octylsulfate (SOS) as templates of mesoporous silica materials. The hexagonal pore size can be controlled between 3.22 and 3.66 nm with the mixed surfactant system. In addition, we could observe the lamellar structure of the mixed surfactants with precursor molecules, which strongly shows the possibility of precise control of both the pore size and the structure of pores by changing the mixing ratio of surfactants. Moreover, use of the cationic surfactant having longer hydrophobic chain like stearyltrimethylammonium bromide (STAB) caused the increase in d(100) space and shifted the point of phase transition from hexagonal phase to lamellar phase to lower concentration of SOS.     

Selective defluorination approach to N-Cbz-3,3-difluoro-2-difluoromethylenepyrrolidine and its application to 3,3-difluoroproline dipeptide synthesis

Mg-promoted defluorination of N-(p-methoxyphenyl)bis(trifluoromethyl)imine 1 gave perfluoroenamine 2, which was readily transformed to N-Cbz-2-trifluoromethyl-3,3-difluoropyrrolidine 10. Chemoselective defluorination from the trifluoromethyl group of 10 by LHMDS-promoted dehydrofluorination in THF provided 3,3-difluoro-2-difluoromethylenepyrrolidine 11. The product 11 was converted to 3,3-difluoroproline dipeptides 16 upon treatment with aminoesters.     

Observation of a small number of molecules at a metal nanogap arrayed on a solid surface using surface-enhanced Raman scattering

In situ Raman spectroscopic measurements with 785 nm excitation were carried out in aqueous solutions containing bipyridine derivatives. Intense Raman signals were observed when the Ag dimer structure was optimized. The SERS activity was dependent upon on the structure of the Ag dimer with a distinct gap distance, suggesting that the intense SERS originates from the gap part of the dimer. Characteristic time-dependent spectral changes were observed. Not only a spectrum which was the superposition of two bipyridine spectra but also spectra which can be assigned to one of the bipyridine derivatives were frequently observed. Observation using solutions with different concentrations proved that the spectra originated from very small numbers of molecules at the active SERS site of the dimer.     

Hydrogen-bond interaction in organic conductors: redox activation, molecular recognition, structural regulation, and proton transfer in donor-acceptor charge-transfer complexes of TTF-imidazole

Hydrogen-bond interaction in donor-acceptor charge-transfer complexes of TTF-imidazole demonstrated the electronic effects in terms of control of component ratio and redox activation. These unprecedented effects of hydrogen bonds renewed the criteria giving "a high probability of being organic metals" and produced a number of highly conductive complexes with various acceptors having a wide range of electron-accepting ability. In p-chloranil complex, both molecules were linked by hydrogen bonds and formed a D-A-D triad, regulating the donor-acceptor composition to be 2:1. Theoretical calculations have revealed that the polarizability of hydrogen bonds controls the redox ability of the donor and p-benzoquinone-type acceptors and afforded different ionicity in complexes from those expected by the difference of redox potentials between donor and acceptors. In the p-chloranil complex, this electronic and structural regulation by hydrogen bond realized the first metallic donor-acceptor charge-transfer complex based on hydrogen bond functionalized TTF. Hydrogen bonds controlled also molecular arrangements in charge-transfer complexes, giving diverse and highly ordered assembled structures, D-A-D triad in the p-chloranil complex, one-dimensional zigzag chain in I(5) salt, alternating donor-acceptor chain in chloranilic acid complex, and D-A-D-A cyclic tetramer in nitranilic acid complex. Furthermore, TTF-imidazole acted as electron donor as well as proton acceptor in anilic acid complexes and realized the simultaneous charge- and proton-transfer complexes. These investigations demonstrated the new and intriguing potentials of the hydrogen bond in the development of organic conductors and multifunctional molecular materials.     

Weak ferromagnetism in a semiconducting (ethylenedithiodiselena- dithiafulvalenoquinone-1,3-diselenolemethide)2.FeBr4 salt

The 2:1 salts of a new bent donor molecule, ethylenedithiodiselenadithiafulvalenoquinone-1,3-diselenolemethide (EDT-DSDTFVODS) and either an FeBr(4)- or a GaBr(4)- ion exhibit semiconducting properties and had small activation energies. The Fe(III) d spins of the FeBr(4)- salt are initially subject to a strong antiferromagnetic interaction and afterward exhibited a weak ferromagnetism at 3.8 K with a very small remanent magnetization of ca. 4 x 10(-2) mu(B) and a spin-flop near 25 kOe along the intercolumnar direction.