Shallow donor state due to nitrogen-hydrogen complex in diamond

Based on an ab initio calculation, we propose a possible shallowing of a nitrogen (N) donor in diamond, in contrast to the traditional thinking that it is very deep. A complex defect of N and hydrogen (H), N-H-N, should be much shallower than an isolated N donor. A qualitative scenario for formation of the N-H-N defects is presented. The existence of this complex is strongly suggested by a recent discovery of a new muonium center in N-rich diamond.     

Amine-salt-controlled, catalytic asymmetric conjugate addition of various amines and asymmetric protonation

The combined use of chiral Pd complex 2 and amine salt enabled completely regulated release of free nucleophilic amine. Under these conditions, an efficient catalytic asymmetric conjugate addition of various amines was achieved to afford beta-amino acid derivatives in high chemical yields with up to 98% ee. Furthermore, a highly enantioselective protonation in 1,4-addition of amine was also developed. [reaction: see text]     

Semiconductor Optical Amplifier (SOA)-Fiber Ring Laser for Sensor Application

A bi-directional fiber ring laser with a semiconductor optical amplifier has been developed in which a frequency difference between the counter-propagating oscillations is controlled by an introduced birefringent medium. With the material which causes the retardation change by a physical phenomenon to be measured, the laser in this study is applicable to a novel fiber sensor of which the sensing signal is obtained in a frequency domain.     

Viscoelastic behaviors and molecular motions of highly syndiotactic poly(vinyl alcohol) fibers

The viscoelastic behavior and molecular motion of highly syndiotactic poly(vinyl alcohol) (S‐PVA) fibers with a dyad syndiotacticity (r) of 69% were studied by dynamic mechanical thermal analysis and wide‐angle X‐ray diffraction and compared with those of atactic poly(vinyl alcohol) (A‐PVA) fibers with r = 54%. The β_c dispersion, based on the molecular motion of the chain molecules in the crystalline regions, was observed for A‐PVA around 120–140 °C, and the only primary (α_c) dispersion was observed for S‐PVA around 180 °C. The thermal expansion coefficients for the a and c axes of the A‐PVA crystal changed discontinuously around 120 °C, which corresponded to the β_c dispersion. For S‐PVA, the coefficient for the (002) plane changed discontinuously around 100 °C, similarly to A‐PVA, but that for the (100) plane remained unchanged between 20 and 220 °C. These results showed that the intermolecular hydrogen bonding of S‐PVA was stronger in the direction of the a axis than in the other directions, suppressing the β_c dispersion. The storage modulus and thermal expansion coefficient of the (020) plane (molecular axis) of S‐PVA decreased markedly around 180 °C, and this indicated that the α_c dispersion was due to the torsional motion of the molecular chains in the crystalline regions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 800–808, 2004     

Substitutional disorder effects on optical spectra of extremely heavily doped Si : P obtained by ion implantation and laser annealing

The optical reflectivity spectrum (2500–5000 Å) of extremely heavily phosphorus (P)-doped Si has been studied. The E₁ and E₂ peaks, which represent the completeness of the Si crystal, are slightly affected when doping concentrations are less than 10²¹ cm^-3 (2% Si : P). However,they appreciably degrade as the doping concentration increases from 10²¹ to 5×10²¹cm^-3 (10% Si : P). As the result of band calculations using a supercell configuration and pseudopotential method, we have been able to ascribe this behavior to the substitutional disorder effect.