Optical harmonic generation from periodically arrayed hexagonal structure of silver nanoparticles.

A self-assembled method was successfully exploited to fabricate a close-packed hexagonal structure of nano-silver clusters by deposition of silver films on polystyrene micro-spheres in conjunction with lift-off the micro spheres. An enhancement of the optical second-harmonic susceptibility was observed from these periodically arrayed silver particles with an intensity of several folds larger than that is generated from a uniform silver-film of the same thickness. The quasi-phase matching condition contributed from the Bragg wave vectors of the periodically arrayed silver nano-particles can satisfactorily express this enhancement.

Magnetic properties of multi-walled carbon nanotubes.

The magnetic properties of multiwall carbon nanotubes (MWCNTs) grown by microwave plasma enhanced chemical vapor deposition (MPECVD) were studied by electron paramagnetic resonance and magnetization measurements. The ferromagnetic characters of virgin grown MWCNTs are mainly attributed to the catalyst nanoparticles embedded on the tips. After acid etching for purification, the trace of magnetic resonance prominently distributed from the remnant of catalyst nanoparticles within the lower sectional parts of the tubes and partially might come from the unpaired spins of CNTs. The free radicals from the unbounded carbons and the itinerant conduction electrons of metallic CNTs also contribute to the electron spin resonance. Magnetization measured by a superconducting quantum interference device (SQUID) reveals fairly a small hysteretic loop with small coercive field for both virgin and purified MWCNTs.

Dielectric constants of single-wall carbon nanotubes at various frequencies.

A cylindrical rod composed of a uniform mixture of single-wall carbon nanotubes and alumina powders dissolved in paraffin was inserted in the center of a radio frequency cavity. The complex dielectric constant of carbon tubes at various frequencies was measured by a resistance-inductance-capacitance (RLC) meter and a microwave network analyzer. The cylindrical rod benefits the protection of the sample from adsorbing moisture and preventing the rod from filling with air, thus making accuracy experiment values. The real part and the imaginary part of the dielectric constants of single-wall carbon nanotubes are, respectively, increase and decrease in magnitudes as frequency increases satisfactorily in complying with the portray from the free electron Drude model.

Magnetoreception system in honeybees (Apis mellifera).

Honeybees (Apis mellifera) undergo iron biomineralization, providing the basis for magnetoreception. We showed earlier the presence of superparamagnetic magnetite in iron granules formed in honeybees, and subscribed to the notion that external magnetic fields may cause expansion or contraction of the superparamagnetic particles in an orientation-specific manner, relaying the signal via cytoskeleton (Hsu and Li 1994). In this study, we established a size-density purification procedure, with which quantitative amount of iron granules was obtained from honey bee trophocytes and characterized; the density of iron granules was determined to be 1.25 g/cm(3). While we confirmed the presence of superparamagnetic magnetite in the iron granules, we observed changes in the size of the magnetic granules in the trophycytes upon applying additional magnetic field to the cells. A concomitant release of calcium ion was observed by confocal microscope. This size fluctuation triggered the increase of intracellular Ca(+2) , which was inhibited by colchicines and latrunculin B, known to be blockers for microtubule and microfilament syntheses, respectively. The associated cytoskeleton may thus relay the magnetosignal, initiating a neural response. A model for the mechanism of magnetoreception in honeybees is proposed, which may be applicable to most, if not all, magnetotactic organisms.

Electrical conductance in a single carbon nanofiber.

A microwave-plasma enhanced chemical-vapor-deposition (MPECVD) method was used to grow a solo multi-wall carbon nanofiber, which plays as a bridge across nickel electrodes that were separated by the photolithographic process. The length and diameter of carbon nanofiber are 3 microm and 100 nm, respectively. The single wire across the electrodes reveals a step current-voltage characteristic measured at high currents and low temperatures while shows a continuous behavior for multiple nanofibers. This stepwise conductance can be successfully dwelled by the quasi one-dimensional transport theory of conductors without considering the electron-phonon interaction at low temperatures and is expected to play a crucial role to determine the electrical behavior of these nanodevices.

Growth of carbon nanotubes at low powers by impedance-matched microwave plasma enhanced chemical vapor deposition method.

A solo carbon nanotube (CNT) was successfully grown on nickel electrodes by a microwave plasma enhanced chemical vapor deposition (MPECVD) method equipped with an impedance-matched substrate holder with the reaction gases composed of hydrogen (H2), carbon dioxide (CO2), and methane (CH4) mixtures. An introduction of carbon dioxide gas before CNTs growth, the substrate temperature can easily be reached above 610 degrees C even heated at a low microwave power. This can be enunciated from fact that carbon dioxide inherits with higher bond energy for molecular dissociation, lower thermal conductivity, and higher heat capacity in comparing to other gases. The electron field emissions for randomly aligned CNTs and well-aligned CNTs grown by MPECVD and by radio frequency assisted hot-filament methods, respectively, are measured and compared. The higher field emission characteristic of the randomly aligned CNTs is presumed to be due to the protruded CNTs, which inheriting with less screening effect and manifesting with defects are crucial to play the effective emission sites.