Electrical control of the direction of spin accumulation

We are able to continuously change the direction of polarization of spin accumulation in a nonmagnetic metal by varying the currents injected by two ferromagnetic spin injectors. From measurements made at a distance from the injection area, we find a cosvarphi variation of the spin signal. This confirms that the angle of polarization of the nonlocal spin polarization with respect to the magnetization of the fixed spin detector is continuously varied as we change the injection currents. We give an explanation for the origin of this simple cosvarphi variation of the spin signal.     

Reversible photomechanical switching of individual engineered molecules at a metallic surface

We have observed reversible light-induced mechanical switching for individual organic molecules bound to a metal surface. Scanning tunneling microscopy (STM) was used to image the features of individual azobenzene molecules on Au(111) before and after reversibly cycling their mechanical structure between trans and cis states using light. Azobenzene molecules were engineered to increase their surface photomechanical activity by attaching varying numbers of tert-butyl (TB) ligands ("legs") to the azobenzene phenyl rings. STM images show that increasing the number of TB legs "lifts" the azobenzene molecules from the substrate, thereby increasing molecular photomechanical activity by decreasing molecule-surface coupling.     

Magnetic-field effects on the size of vortices below the surface of NbSe2 detected using low energy beta-NMR

A low energy radioactive beam of polarized 8Li has been used to observe the vortex lattice near the surface of superconducting NbSe2. The inhomogeneous magnetic-field distribution associated with the vortex lattice was measured using depth-resolved beta-detected NMR. Below Tc, one observes the characteristic line shape for a triangular vortex lattice which depends on the magnetic penetration depth and vortex core radius. The size of the vortex core varies strongly with the magnetic field. In particular, in a low field of 10.8 mT, the core radius is much larger than the coherence length. The possible origin of these giant vortices is discussed.     

Effects produced by metal-coated near-field probes on the performance of silicon waveguides and resonators

We study the effects of metal-coated fiber near-field probes on the performance of nanophotonic devices. Employing a heterodyne near-field scanning optical microscope and analyzing transmission characteristics, we find that a metal-coated probe can typically introduce a 3 dB intensity loss and a 0.2 rad phase shift during characterization of a straight waveguide made in a silicon-on-insulator system. In resonant nanophotonic structures such as a 5 mum radius microring resonator, we demonstrate that the probe induces a 1 nm shift in resonant wavelength and decreases the resonator quality factor, Q, from 1100 to 480.     

Thermoluminescence and radiation-induced volume changes in CaF2 (Mn,RE) materials

The thermoluminescence properties of various CaF₂ materials (natural fluorite, CaF₂-glass ceramics and enamels) doped with RE oxides and Mn are investigated in details. Volumetric measurements show that γ-irradiation leads to a change in the volume density of powder samples of these materials. Depending on the character of the sample, positive (increased volume) or negative dilatation (decreased volume) can be observed during irradiation with doses within the range 1 C/kg–9 C/kg. As time elapses, the radiation-induced alteration of the sample volume is relaxed and after 2–3 months reaches again the initial volume density of the sample. The unexpected result of radiation-induced volume changes are discussed in details accounting for supplementary X-ray, electron microscopy and EPR studies.     

New synthetic technology for efficient construction of alpha-hydroxy-beta-amino amides via the Passerini reaction

[reaction: see text] The Passerini reaction of N-protected amino aldehydes, isonitriles, and TFA using pyridine-type bases proceeds under mild conditions and directly affords alpha-hydroxy-beta-amino amide derivatives in moderate to high yields. These adducts are readily hydrolyzed to alpha-hydroxy-beta-amino carboxylic acids. Application of these key intermediates to concise syntheses of P(1)-alpha-ketoamide protease inhibitors is illustrated.     

New exact relations for improving the exchange and correlation potentials

For the purpose of improving present approximations to the exchange and correlation potentials, newly derived properties of the exact exchange and correlation potentials are summarized. Present approximations are not expected to generally satisfy these properties. The summarized properties include relations at the Fermi level, low-density requirements, and a new density functional formula for computing ionization energies. © 1995 John Wiley & Sons, Inc.     

Automerizations in benzenoid hydrocarbons. New mechanistic insights from the thermal rearrangement of benz[a]anthracene-5-13C.

Scrambling of the carbon atoms in benz[a]anthracene between positions 5 and 6 has been shown to occur at high temperatures; a mechanism involving thermal generation of a carbene is proposed.