Bifunctional, conjugated oligomers for orthogonal self-assembly: selectivity varies from planar substrates to nanoparticles

A diphenylacetylene containing two different end groups (isonitrile and thioacetate) was synthesized, showing that the chemistry used to install each end group is compatible with that of the others. The isonitrile group binds preferentially to platinum, and the thiol group binds preferentially to gold. However, the selectivity was different when nanoparticles were compared to planar substrates.     

Characterization of rodlike aggregates generated from a cationic surfactant and a polymerizable counterion

The polymerization of elongated micellar structures offers a novel approach to the production of high-aspect-ratio, water-soluble amphiphilic nanorods. A cationic surfactant with a vinyl-containing counterion, cetyltrimethylammonium 4-vinylbenzoate, has been synthesized and polymerized to produce high-aspect-ratio nanoparticles which are insensitive to changes in solution conditions. Aggregates are polymerized over a range of initiator concentrations allowing for control of the product length. Small-angle neutron scattering and light scattering are used to characterize the dimensions of the polymerized aggregates, showing them to have a fixed radius of 2 nm and contour lengths varying from 96 to 340 nm. Proton NMR verifies the chemical structure and provides insight into the mobility of the aggregate components. Finally, gel permeation chromatography of the polymer extracted from the aggregates indicates that the polymerization reaction controls the aggregate dimensions.     

Fiber bragg gratings made with a phase mask and 800-nm femtosecond radiation

High-quality retroreflecting fiber Bragg gratings were written in standard Ge-doped telecom fiber (Corning SMF-28) after a few minutes exposure with pulsed 800-nm, 120-fs laser radiation by use of a deep-etch silica zero-order nulled phase mask optimized for 800 nm. Induced index modulations of 1.9 x 10(-3) were achieved with peak power intensities of 1.2 x 10(13) W/cm2 without any fiber sensitization. The fiber gratings are stable and did not erase after 2 weeks at 300 degrees C. The primary mechanism of induced index change results from a structural modification to the fiber core.     

Multiphonon vibrations at high angular momentum in 182 Os

Evidence is presented for multiphonon excitations based on a high-spin (25 Planck) intrinsic state in the deformed nucleus 182 Os. Angular momentum generation by this mode competes with collective rotation. The experimental data are compared with tilted-axis cranking calculations, supporting the vibrational interpretation. However, the lower experimental energies provide evidence that more complex interactions of states are playing a role.     

Nondestructive spatial heterodyne imaging of cold atoms

We demonstrate a new method for nondestructive imaging of laser-cooled atoms. This spatial heterodyne technique forms a phase image by interfering a strong reference laser beam with a weak probe beam that passes through the cold atom cloud. The figure of merit equals or exceeds that of phase-contrast imaging, and the technique can be used over a wider range of spatial scales. We show images of a dark-spot magneto-optic trap taken with imaging fluences as low as 61 pJ/cm(2) at a detuning of 11? , resulting in 0.0004 photons scattered per atom.     

Optical frequency conversion by a rotating molecular wave plate

We demonstrate efficient four-wave mixing in low-pressure molecular deuterium without the need for phase matching. We use two laser fields with opposite circular polarizations to produce a strong excitation of a rovibrational transition at a frequency of 3167 cm(-1) . The coherent molecular motion, in turn, modulates a third laser field (also circularly polarized) and results in highly efficient single-sideband conversion.     

Frequency-narrowed external-cavity diode-laser-array bar

We demonstrate that appropriately designed external cavities can be used to frequency narrow high-power diode-array bars. Using a commercial 20-W array, we narrow the linewidth to 50 GHz with 14 W of cw output power. A magnifying telescope and a cylindrical collimating lens minimize broadening owing to curvature in the alignment of the diode-array elements.     

Mössbauer study of magnetic ordering and superconductivity in YBa2(Cu1−xFex)3O7

We have made superconducting samples of the Y?Ba?Cu?O system with Fe substituted for the Cu. The percentage of Fe substituted varied from 2 to 100. The samples have been verified by x-ray diffraction to be single-phase 1–2–3 compounds. The 6% Fe substitution reduces T_c from 94 K to 80 K. The room temperature Mössbauer spectrum shows two pairs of doublets, indicating there are two distinct Cu sites in the sample. The most surprising result is that magnetic ordering of the Fe coexists with superconductivity of the material at 4.2 K.     

Synthesis and Characterization of a Ruthenium(II) Complex for Photovoltaic Cells

We have designed and synthesized a new ruthenium complex, [(5‐amino‐1,10‐phenanthroline)bis(4,4′‐dicarboxylic acid‐2,2′‐bipyridine)]ruthenium(II) by introducing two types of ligands, 5‐amino‐1,10‐phenanthroline and 4,4′‐dicarboxylic acid‐2,2′‐bipyridine. We investigated the electronic, spectroscopic, electrochemical, and photovoltaic properties of the Ru(II) complex. The short‐circuit current density and overall solar‐to‐electric energy conversion efficiency of photovoltaic cells made with this Ru(II) complex were found to be 8.9 mA/cm² and 2.1%, respectively. A series of analogous Ru(II) complexes have also been synthesized and investigated to compare the effects of functional groups on various ligands. HOMO‐LUMO energies and molecular orbital surfaces have been investigated using semiempirical quantum chemical methods.