Narrow Nanorods Research Articles

Evolution of morphology and magnetic properties of α-Fe2−xCrxO3 nanoparticles in dependence on Cr concentration

Hematite, α-Fe2O3, one of the most widely studied magnetic compounds known to mankind since ancient times, has amazing properties and continues to puzzle researchers to this day. In this work, we found exceptionally strong changes in the morphology and magnetic properties of hematite nanoparticles upon doping with rather low concentrations of chromium. Nanoparticles α-Fe2−xCrxO3 with x varied from zero to 0.15 were prepared by solvothermal method using FeCl3·6H2O, CrCl3·6H2O, and 1,2-diaminopropane, (CH2)3(NH2)2, as precursors and temperature 180 °C for 6 h. The X-ray diffraction data showed the presence of only one crystal phase α-Fe2O3 for all x meanings with growing average crystalline size as the x increases. For the parent α-Fe2O3 powdered samples, the transmission electron microscopy revealed very long narrow nanorods with rounded ends that transform into spindles of increasing volume and cross section diameter as the Cr concentration increases. Vibrating sample magnetometry (VSM) and magnetic circular dichroism (MCD) study of the nanoparticles behavior in dependences on temperature and magnetic field revealed many unusual peculiarities. Among them there are strong increase of NPs magnetization with x increase (usually opposite picture is observed), the Morin transition temperature TM dependence on magnetic field, VSM sees the Morin transition in samples with small x only while MCD – in all samples, magnetization field dependences also are different when measured with VSM and MCD, and so on. Qualitative considerations were proposed to explain the observed phenomena.

Effect on SmBa2Cu3Oy films of lattice strain induced by BaHfO3 nanorods

BaMO3 (BMO, M=Zr, Sn, Hf, etc.) is well known to undergo self-organisation into many nanorods in a REBCO film grown by vapour phase epitaxy. However, REBCO experiences strain resulting from the BMO nanorods and this strain causes the superconducting properties to deteriorate. In this study, we prepared SmBCO films containing 16 vol% BaHfO3 (BHO) using a pulsed laser deposition method. Deposition was accomplished by using a low-temperature growth (LTG) technique to grow the films even at low substrate temperatures. By decreasing the substrate temperature, the number density of the BHO nanorods, which is estimated from the critical current density in magnetic fields and the irreversibility line, increased and their diameter decreased. The lattice strain exerted upon SmBCO and BHO could conveniently be evaluated by conventional X-ray diffraction owing to the substantial BHO content. This evaluation indicated that, as the substrate temperature decreased, the tensile strain exerted upon SmBCO decreased, whereas the compressive strain experienced by BHO increased. These results indicate that the effect of stress exercised by the narrow nanorods on REBCO is small. Our findings suggest LTG to be an effective technique to prepare REBCO films with a high number density of BMO nanorods owing to the small amount of stress induced by these nanorods.

Superconducting properties and microstructures for Ba2SmNbO6 and BaHfO3 co-doped SmBa2Cu3Oy thin films

Recently, we observed that Ba2SmNbO6 (BSNO), which has a double perovskite structure, forms wide nanorods in a SmBa2Cu3Oy (SmBCO) film when compared with BaHfO3 (BHO) nanorods. These wide nanorods can trap flux quanta effectively in low magnetic fields; on the other hand, narrow nanorods can trap flux quanta in high magnetic fields. In this paper, we doped SmBCO films with BSNO and BHO with the aim of introducing both wide and narrow nanorods and bringing out the flux pinning properties in low and high magnetic fields simultaneously. We investigated their microstructures and superconducting properties, and as a result, we confirmed that wide and narrow nanorods could coexist in the SmBCO films. The wide and narrow nanorods trapped the flux quanta in different magnetic fields. We also explored the optimal composition for BSNO + BHO co-doped SmBCO films. These findings indicate that flux pinning properties can be tuned by the multiple doping of BMO materials.

Nucleation of single GaN nanorods with diameters smaller than 35 nm by molecular beam epitaxy

Nucleation mechanism of catalyst-free GaN nanorod grown on Si(111) is investigated by the fabrication of uniform and narrow (<35 nm) nanorods without a pre-defined mask by molecular beam epitaxy. Direct evidences show that the nucleation of GaN nanorods stems from the sidewall of the underlying islands down to the Si(111) substrate, different from commonly reported ones on top of the island directly. Accordingly, the growth and density control of the nanorods is exploited by a “narrow-pass” approach that only narrow nanorod can be grown. The optimal size of surrounding non-nucleation area around single nanorod is estimated as 88 nm.

Antibacterial Activities of Short Designer Peptides: a Link between Propensity for Nanostructuring and Capacity for Membrane Destabilization

Amphiphilic peptides A(3)K, A(6)K, and A(9)K displayed an increasing propensity for nanoaggregation with increasing the size of hydrophobic alanine moiety, and the size and shape of the aggregates showed a steady transition from loose peptide stacks formed by A(3)K, long nanofibers by A(6)K, to short and narrow nanorods by A(9)K. This size and shape transition was broadly consistent with the trend predicted from interfacial packing and curvature change if these peptide surfactants were treated as conventional surfactants. The antibacterial capacity, defined by the killing of percentage of bacteria in a given time and peptide concentration, showed a strong correlation to peptide hydrophobicity, evident from both microscopic and fluorescence imaging studies. For A(9)K, the power for membrane permeation and bacterial clustering intensified with peptide concentration and incubation time. These results thus depict a positive correlation between the propensity for self-assembly of the peptides, their membrane penetration power, and bactericidal capacity. Although the exposure of A(9)K to a preformed DPPC membrane bilayer showed little structural disturbance, the same treatment to the preformed DPPG membrane bilayer led to substantial disruption of model membrane structure, a trend entirely consistent with the high selectivity observed from membrane hemolytic studies.

Correlation in narrow nanorods: a variational potential–configuration interactionscheme

Full configuration interaction calculations for two electrons in narrow semiconductornanorods are carried out employing different orbital basis sets. It is shown that the usualconfigurations built from single-particle states cannot yield a correct singlet–tripletenergetic order regardless of the basis size, as they miss the correlation energy.Mean-field optimized orbitals partially correct this drawback. A new approach isintroduced, based on a simple variational procedure, which yields robust results.

CdSe quantum dots in ZnSe nanowires as efficient source for single photons up to 220 K

ZnSe nanowire heterostructures were grown by molecular beam epitaxy in the vapour–liquid–solid growth mode assisted by gold catalysts. Size, shape and crystal structure are found to strongly depend on the growth conditions. Both, zinc-blende and wurtzite crystal structures are observed using transmission electron microscopy. At low growth temperature, cone-shaped nano-needles are formed. For higher growth temperature, the nanowires are uniform and have a high aspect ratio with sizes of 1– 2 μ m in length and 20–50 nm in width as observed by scanning electron microscopy. Growing a nanowire on top of a nano-needle allows us to obtain very narrow nanorods with a diameter less than 10 nm and a low density of stacking fault defects. These results allow us the insertion of CdSe quantum dots in a ZnSe nanowire. An efficient photon anti-bunching was observed up to 220 K, demonstrating a high-temperature single-photon source.

Ultra Narrow PbS Nanorods with Intense Fluorescence

We report on the narrowest "free" quantum rods of PbS with 1.7 nm diameter produced in a single step under bench-top reaction conditions. The nanorods exhibit molecule-like discrete narrow optical behavior with high fluorescence quantum yield. We propose a new macroscopic vortex assembly formation by simple spin casting route. Interestingly, the pattern generates fluorescence along its line from the nanorod domains. The ultra narrow nanorods with strong discrete fluorescence and robust stability could be useful in biological labeling, fluorescence resonance energy transfer, and optoelectronics applications, as well as to verify the theories in the very strong confinement regime.

Stimulated emission from ZnO nanorods

AbstractBy means of time resolved spectroscopy we compare two samples of ZnO nanorods with respect to their suitability as stimulated emitters. In the case of narrow nanorods their wave guiding quality causes a suppression of exciton–exciton scattering whereas no laser emission is detectable. Unlike their narrow counterparts, wide nanorods not only benefit from a larger overlap of the guided mode with the gain medium but a variation in VLS growth results in gold nanoparticles being present at the bottom of nanorods. Consequently, laser emission from single wide rods is evidenced up to 150 K. In addition to experimental studies we carry out 3D numerical simulations of the electric field distribution to evaluate the influence of gold nanoparticles at the nanorod/substrate interface. This finite element analysis confirms that gold leads to an enhancement of confinement within the resonator. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)