Electrospinning of polyvinylidene difluoride with carbon nanotubes: synergistic effects of extensional force and interfacial interaction on crystalline structures

Polyvinylidene difluoride (PVDF) solutions containing a very low concentration of single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) of similar surface chemistry, respectively, were electrospun, and the nanofibers formed were collected using a modified rotating disk collector. The polymorphic behavior and crystal orientation of the nanofibers were studied using wide-angle X-ray diffraction and infrared spectroscopy, while the nanotube alignment and interfacial interactions in the nanofibers were probed by transmission electron microscopy and Raman spectroscopy. It is shown that the interfacial interaction between the SWCNTs and PVDF and the extensional force experienced by the nanofibers in the electrospinning and collection processes can work synergistically to induce highly oriented beta-form crystallites extensively. In contrast, the MWCNTs could not be well aligned along the nanofiber axis, which leads to a lower degree of crystal orientation.     

Growth of vertically aligned carbon-nanotube array on large area of quartz plates by chemical vapor deposition

A simple method has been developed for growth of well-aligned carbon nanotubes (CNTs) on nickel-film quartz plates by chemical vapor deposition (CVD) with organic ethylenediamine as a precursor. High-density carbon nanotubes were vertically aligned on a large area of the quartz plates. The height of the nanotube array could be controlled by varying the CVD time. High-resolution transmission electron microscopy analysis revealed that the multiwalled CNTs were composed of crystalline graphitic sheets with a bamboo structure. Received: 28 May 2001 / Accepted: 3 December 2001 / Published online: 4 March 2002     

PEG-POSS assisted facile preparation of amphiphilic gold nanoparticles and interface formation of Janus nanoparticles

A general approach to transfer water-soluble nanoparticles with different shapes, sizes, and surface charges into organic solvents, retaining their surface charge properties was developed, and its application in fabrication of hybrid Janus particles with opposite charges in solution was also demonstrated.     

Charge-storage effects in a metal-insulator-semi-conductor structure containing germanium nano-crystals formed by rapid thermal annealing of an electron-beam evaporated germanium layer

Charge-storage effects in a metal-insulator-semi-conductor device containing germanium (Ge) nano-crystals were investigated. The Ge nano-crystals were formed by rapid thermal annealing (RTA) of an evaporated, ultra-thin Ge layer at 1000 °C in argon. Capacitance–voltage measurements shows that the amount of electrical charge which can be stored in the device varies with the duration of the RTA treatment. The charge shows a maximum value for 200 s RTA treatment, and then decreases with longer annealing time up to 400 s. Atomic force microscopy analysis indicates that there is a correlation between the density of Ge nano-crystals in the devices, and the amount of electrical charge stored. For an RTA treatment of 300 s, capacitance–time measurements show a time dependence, which indicates a dispersive carrier relaxation. The retention time is dependent on the applied bias, and a maximum retention time of 115 s was observed at -7 V. The value of the stored electrical charges in the device decreases with increasing ambient temperature. A possible charging/discharging mechanism for the device was discussed to explain the capacitance–time measurements and the temperature stored charge results. PACS 81.07.Ta; 81.15.Jj; 73.63.Kv; 85.35.Be; 81.40.Ef     

Size of the freeze-out source in high energy heavy ion collisions

Based on a hydro-inspired azimuthally symmetric emission function, we analyze the HBT radius Rs and the single-particle transverse momentum spectra in Au+Au collisions measured by the STAR Collaboration at SNN = 200 GeV. The results show that consistent assumptions about transverse density (and/or flow profile) in the calculation of the HBT radius Rs and single-particle spectral analyses play an important role for understanding the size of the freeze-out source.     

Periodic wavetrains for systems of coupled nonlinear Schrödinger equations

Exact, periodic wavetrains for systems of coupled nonlinear Schrödinger equations are obtained by the Hirota bilinear method and theta functions identities. Both the bright and dark soliton regimes are treated, and the solutions involve products of elliptic functions. The validity of these solutions is verified independently by a computer algebra software. The long wave limit is studied. Physical implications will be assessed.