Morphology of single-wall carbon nanotube aggregates generated by electrospray of aqueous suspensions

Airborne single-wall carbon nanotubes (SWCNTs) have a high tendency to agglomerate due to strong interparticle attractive forces. The SWCNT agglomerates generally have complex morphologies with an intricate network of bundles of nanotubes and nanoropes, which limits their usefulness in many applications. It is thus desirable to produce SWCNT aerosol particles that have well-defined, unagglomerated fibrous morphologies. We present a method to generate unagglomerated, fibrous particles of SWCNT aerosols using capillary electrospray of aqueous suspensions. The effects of the operating parameters of capillary electrospray such as strength of buffer solution, capillary diameter, flow rate, and colloidal particle concentration on the size distributions of SWCNT aerosols were investigated. Results showed that electrospray from a suspension of higher nanotube concentration produced a bimodal distribution of SWCNT aerosols. Monodisperse SWCNT aerosols below 100 nm were mostly non-agglomerated single fibers, while polydisperse aerosols larger than 100 nm had two distinct morphologies: a ribbon shape and the long, straight fiber. Possible mechanisms are suggested to explain the formation of the different shapes, which could be used to produce SWCNT aerosols with different morphologies.     

Domain growth and aging scaling in coarsening disordered systems

We explore the electronic and transport properties out of a biased multilayer hexagonal boron nitride (h-BN) by first-principles calculations. The band gaps of multilayer h-BN decrease almost linearly with increasing perpendicular electric field, irrespective of the layer number N and stacking manner. The critical electric filed (E ₀) required to close the band gap decreases with the increasing N and can be approximated by E ₀ = 3.2 / (N ? 1) (eV). We provide a quantum transport simulation of a dual-gated 4-layer h-BN with graphene electrodes. The transmission gap in this device can be effectively reduced by double gates, and a high on-off ratio of 3000 is obtained with relatively low voltage. This renders biased MLh-BN a promising channel in field effect transistor fabrication.     

Electric field control of nonvolatile four-state magnetization at room temperature

We find the realization of large converse magnetoelectric (ME) effects at room temperature in a magnetoelectric hexaferrite Ba0.52Sr2.48Co2Fe24O41 single crystal, in which rapid change of electric polarization in low magnetic fields (about 5 mT) is coined to a large ME susceptibility of 3200 ps/m. The modulation of magnetization then reaches up to 0.62μ(B)/f.u. in an electric field of 1.14 MV/m. We find further that four ME states induced by different ME poling exhibit unique, nonvolatile magnetization versus electric field curves, which can be approximately described by an effective free energy with a distinct set of ME coefficients.     

Self‐formed Schottky barrier induced selector‐less RRAM for cross‐point memory applications

We propose a selector‐less Pr_0.7Ca_0.3MnO₃ (PCMO) based resistive‐switching RAM (RRAM) for high‐density cross‐point memory array applications. First, we investigate the inhomogeneous barrier with an effective barrier height (Φ_eff), i.e., self‐formed Schottky barrier. In addition, a scalable 4F² selector‐less cross‐point 1 kb RRAM array has been successfully fabricated, demonstrating set, reset, and read operation for high cell efficiency and high‐density memory applications. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cutoff characteristics of dielectric-filled circular holes embedded in dispersive plasmonic medium

The cutoff characteristics of dielectric-filled circular holes embedded in a dispersive plasmonic medium are investigated. Since two distinctive operating modes, surface plasmon polariton and circular waveguide modes, can exist in the slow and fast wave regions, respectively, the cutoff characteristics for each are separately investigated for linear and radial polarizations of the guided fields. As a result, the cutoff wavelengths for the linear and radial polarizations with very small subwavelength hole radii are found to be limited by the plasma resonance wavelength and plasma wavelength, which in turn are dependent and independent, respectively, of the dielectric constant of the dielectric filler material.     

A sonochemical-assisted synthesis and annealing temperature effect of La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> nanoparticles

This paper reports on the sonochemical-assisted synthesis of La_0.7Sr_0.3MnO₃ (LSMO) nanoparticles (NPs) which have a single-crystalline perovskite structure. The average particle size of LSMO NPs was controlled from about 40 to 120 nm by changing the annealing temperatures from 750 to 1050°C. The particle size, electrical resistivity, and ferromagnetic transition temperature of LSMO NPs were strongly dependent on the annealing temperature. A substantial decrease in resistivity and an enhancement in the insulator–metal transition temperature were found on increasing the annealing temperature. Furthermore, the enhancement in magnetization and paramagnetic–ferromagnetic (PM–FM) transition temperatures was observed as the annealing temperature increases.     

A strip-shield improves the efficiency of a solenoid coil in probes for high-field solid-state NMR of lossy biological samples

A strip-shield inserted between a high inductance double-tuned solenoid coil and the glass tube containing the sample improves the efficiency of probes used for high-field solid-state NMR experiments on lossy aqueous samples of proteins and other biopolymers. A strip-shield is a coil liner consisting of thin copper strips layered on a PTFE (polytetrafluoroethylene) insulator. With lossy samples, the shift in tuning frequency is smaller, the reduction in Q, and RF-induced heating are all significantly reduced when the strip-shield is present. The performance of 800 MHz ¹H/¹⁵N and ¹H/¹³C double-resonance probes is demonstrated on aqueous samples of membrane proteins in phospholipid bilayers.     

Measure permutation formulas in Feynman’s operational calculi

In Jefferies-Johnson’s theory of Feynman’s operational calculi for noncommuting operators, the two operators T _{µ 1,µ 2} f(Ã, \(\tilde B\)) and T _{µ 2},µ₁ f(Ã, \(\tilde B\)) are not equal. Relationships between these two operators are given, i.e., “measure permutation formulas” in Feynman’s operational calculi are developed; they correspond to the “index permutation formula” in Maslov’s discretized version of Feynman’s operational calculus.     

Drug release from various thicknesses of layered mats consisting of electrospun polycaprolactone and polyethylene oxide micro/nanofibers

A new drug delivery system (DDS) consisting of electrospun nanofibers is proposed. Layered mats of hydrophobic polycaprolactone (PCL) and polyethylene oxide (PEO) nanofibers were prepared successfully in a layer-by-layer manner using an electrospinning process. The PEO mat and drug were co-electrospun as a drug reservoir. Drug release rate was controlled physically by the thickness of the electrospun nanofibrous PCL layer, and its release behavior was examined over time. Release tests showed that the release behavior and the amount of initial burst of the drug were critically dependent on the thickness of the nanofibrous PCL mat. The release of drug showed a linear relationship with the thickness of the porous electrospun PCL mat. In addition, to demonstrate the feasibility of this type of DDS, the release behavior of the antimicrobial peptide HPA3NT3 from the nanofiber system was examined. The release of the peptide was easily controlled by the PCL nanofiber thickness and the released peptide did not lose biological activity.