Flux line lattice symmetries in the borocarbide superconductor LuNi2B2C

We compare the results of small angle neutron scattering on the flux line lattice (FLL) obtained in the borocarbide superconductor LuNi₂B₂C with the applied field along the c- and a-axes. For H‖c the temperature dependence of the FLL structural phase transition from square to hexagonal symmetry was investigated. Above 10 K the transition onset field. H ₂(T), rises sharply, bending away from H _c2(T) in contradiction to theoretical predictions of the two merging. For H‖a a first order FLL reorientation transition is observed at H _tr=3–3.5 kOe. Below H _tr the FLL nearest neighbor direction is parallel to the b-axis, and above H _tr to the c-axis. This transition cannot be explained using nonlocal corrections to the London model.     

Precision Lamb shift measurement in hydrogenic nitrogen by fast beam laser spectroscopy

A measurement of the 2S_1/2–2P_3/2 (fine structure–Lamb shift) transition in N⁶⁺ is under way. The technique involves fast beam spectroscopy with a transverse interaction geometry and uses an isotopic CO₂ laser and a resonant build up cavity. This revised version was published online in August 2006 with corrections to the Cover Date.     

On the solvolysis kinetics of amidoesters derived from β-aminoalcohols

To better understand reactivity in such systems, fifteen amidoesters derived from β-aminoalcohols were solvolyzed at the ester group in mildly basic methanol-d₄. All trials showed pseudo-first-order kinetics by ¹H NMR. The rate constants are about 2 to 140-fold larger than those found with simple alkyl esters. The least bulky N-acyl groups generally sponsor the largest rate constants, and strongly so in two cases, but apparently not as a result of lesser steric crowding between the amide and ester groups. Rate constants are also greater for those amidoesters favoring an anti conformation at the amide linkage.     

The growth of a single crystal of Sr3CuIrO6 and its magnetic behavior compared to polycrystals

We have grown single crystals of the psuedo-one-dimensional compound Sr₃CuIrO₆, a K₄CdCl₆-derived monoclinic structure with Cu-Ir chains along the [101] direction. We present the ac and dc magnetization behavior of the single crystals in comparison with that of the polycrystalline form reported earlier. There is a distinct evidence for at least two magnetic transitions, at 5 K (T ₁) and 19 K (T ₂), with different relative magnitudes in the single and polycrystals. The low temperature magnetic relaxation behavior of both the forms is found to be widely different, exhibiting unexpected time dependence.     

Chemical sensing and imaging with metallic nanorods

In this Feature Article, we examine recent advances in chemical analyte detection and optical imaging applications using gold and silver nanoparticles, with a primary focus on our own work. Noble metal nanoparticles have exciting physical and chemical properties that are entirely different from the bulk. For chemical sensing and imaging, the optical properties of metallic nanoparticles provide a wide range of opportunities, all of which ultimately arise from the collective oscillations of conduction band electrons ("plasmons") in response to external electromagnetic radiation. Nanorods have multiple plasmon bands compared to nanospheres. We identify four optical sensing and imaging modalities for metallic nanoparticles: (1) aggregation-dependent shifts in plasmon frequency; (2) local refractive index-dependent shifts in plasmon frequency; (3) inelastic (surface-enhanced Raman) light scattering; and (4) elastic (Rayleigh) light scattering. The surface chemistry of the nanoparticles must be tunable to create chemical specificity, and is a key requirement for successful sensing and imaging platforms.