Synthesis and mechanism of polyaniline nanotubes with rectangular cross section via in situ polymerization

Polyaniline (PANI) nanotubes with rectangular cross section, which had 90–500 nm in outer diameter and 30–400 nm in inner diameter, were synthesized via a self‐assembly process in the presence of chiral acid (1S)‐(+)‐10‐camphorsulfonic (D‐CSA) and non‐chiral hydrochloric acid (HCl) coordinating with sodium dodecylbenzenesulfonate (SDBS), respectively. By using SEM, TEM, OM, FTIR, and WAXD, the as‐prepared PANI nanotubes with diversified morphologies were also characterized so as to investigate the formation mechanism of such tubular nanostructures with square cross sections. The results showed that the bilayer‐lamellar micelles formed by anilinium cations and CSA anions acted as the primary templates in the formation of the flat oligomer flakes, and the flakes finally united together to form rectangular nanotubes initiated by the reaction of the active centers on their edges. This study sheds light on the formation process of the PANI nanotubes with rectangular holes and outer contours and may be instructive to the controllable growth of certain nanostructures with unique morphologies. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis and optical characterization of submicrometer gold nanotubes grown on goethite rods

Goethite (FeOOH) rods were used as templates for growing gold nanotubes with a length of a few hundred nanometers and an aspect ratio between 3 and 4. Successful uniform growth required surface modification, followed by the attachment of small Au seeds and one-step seeded growth using formaldehyde as a reducing agent, as previously reported for the growth of Au shells on silica spheres and hematite spindles. The thickness and surface roughness of the obtained shells could be adjusted by simply varying the concentration ratio between seeds (modified goethite rods) and growth reagents (HAuCl 4 and formaldehyde). The morphology of the synthesized gold nanotubes was thoroughly characterized by TEM, SEM, and AFM/MFM. The resulting gold nanotubes display well-defined plasmon resonances, with a strong longitudinal mode centered around ca. 1400 nm and a broad band in the visible resulting from the overlap of a transverse mode and a multipolar mode, as was found from theoretical modeling using the boundary element method, which provides reasonable agreement with the experimental results.     

Synthesis of single crystalline tellurium nanotubes with triangular and hexagonal cross sections

Single crystalline tellurium (Te) nanotubes with triangular cross sections were successfully synthesized for the first time by a simple approach of vaporizing tellurium metal and condensing the vapor in an inert atmosphere onto a suitable substrate. Tellurium gas was evaporated by heating at 350 degrees C and was condensed on the Si (100) substrate at 150-200 degrees C, in the downstream of argon (Ar) gas at a flow rate of 25 sccm for 10 min. This led to the production of nanotubes of triangular cross section along with some hexagonal ones. The formation of the nanotubes was highly dependent upon the structure of the substrate surface, Ar gas flow rate, and the deposition temperature. When the substrate is Si (111) or sapphire (0001) or when the argon flow rate is increased to 500 sccm, nanowires and nanorods were exclusively formed. Irrespective of the morphologies, all the observed Te nanostructures grew in a regular [0001] direction. The facile approach to nanotubes with a triangular cross section may facilitate some new applications as well as stimulate theoretical studies pertaining to the stability of this high-energy configuration.     

Synthesis of nearly uniform single-walled carbon nanotubes using identical metal-containing molecular nanoclusters as catalysts

Uniform and small-diameter single-walled carbon nanotubes (SWNTs) have been produced using identical molecular nanoclusters containing Fe and Mo atoms with a defined molecular formula and a specific structure as catalysts in a chemical vapor deposition method. The average diameter of the SWNTs produced in these experiments is 1.0 nm with a standard deviation for the diameter distribution of 17%. The diameters of SWNTs were obtained by atomic force microscopy and Raman spectroscopy.     

Spectrophotometric errors associated with cells of circular cross section

It is shown that the use of spectrophotometric cells having circular cross sections leads to errors that depend on the absorbance, on the ratio of beam width to cell diameter, and on the distance between the center of the beam and the diameter of the cell, but that the nature and magnitude of these errors render them essentially undetectable in practical analytical work.     

Microscopic cross section for ion-molecule reactions with polar molecules

Using Kapitsa's method of separating rapidly varying processes from slower translational motions, a microscopic capture cross section for gas phase ion-molecule reactions is derived (centrifugal barrier approximation), leading to rate coefficients lying between the values of Langevin's theory and those of the locked dipole approximation (LD).

---

, , - ( ), , , , LD-.

     

Absorption cross section and photolysis of OIO

Pulsed laser photolysis combined with transient absorption spectroscopy and resonance fluorescence was used to examine the photolysis of OIO at a number of wavelengths corresponding to absorption bands in its visible spectrum between approximately 530 and 570 nm. Photolysis at 532 nm was found to result in substantial depopulation of the absorbing ground state, enabling an estimate for the absorption cross section of OIO at 610.2 nm of (6 +/- 2) x 10(-18) cm2 molecule(-1) to be obtained. No evidence was found for I atom formation following photolysis of OIO at 532, 562.3, 567.9 and 573.8 nm, enabling an upper limit to the I atom quantum yield of < 0.05 (560-580 nm) and < 0.24 (532 nm) to be established.     

Photoabsorption cross section of H2S

The photoabsorption cross sections for H₂S were measured in the 47–102 nm region using synchrotron radiation. The absorption cross section in the range of λ > 90 nm showed many small peaks assigned to the 5a₁ → 6sa₁ Rydberg transition. and in the 77–90 nm region the 2b₂ → nda₁ (n = 4.5) Rydberg series were observed. At the energies of 18.2. 19.5 and 21.1 eV, small broad peaks were recognized and tentatively assigned to the vertical ionization potentials of the 1⁴A₂, ⁴B₁ and 2⁴A₂ electronic states of the H₂S⁺ ion, respectively, by comparing with the recent ab initio calculations for the H₂S⁺ energy diagram.     

Suggestion for a new two-photon cross section

We suggest a new two-photon (TP) absorption cross section which is independent of the wavelength of the two laser beams. The different wavelengths may cause changes in the regular cross section by orders of magnitude in the same absorbing molecule. This effect is not due to the resonance term, but to the number of modes.     

Photoionization cross section calculated by dynamical theory

A new theoretical method to calculate the photoionization cross sections of complex molecules and solids is derived in the framework of the dynamical theory by using the Green's function method. The approximations applicable to treat the photoionization by x-rays are also discussed.     

The photoionization cross section for diatomic CH

Many body perturbation theory is used to calculate an approximate Hartree-Fock photoionization cross section for CH. the results show a large increase at threshold compared to that obtained from unperturbed atomic matrix elements. At higher energies the cross section approaches the atomic value.     

Synthesis of InP nanotubes

Indium phosphide (InP) nanotubes have been synthesized via the vapor-liquid-solid (VLS) growth mechanism. The nanotubes are crystalline and have the (bulk) zinc blende structure and therefore represent a new class of tube materials. The tubes show photoluminescence, which is considerably blue-shifted with respect to bulk emission, indicating that the optical properties are not dominated by defect states. They are formed at higher temperatures than those at which nanowires are fabricated. A simple model for the formation of the nanotubes is presented. The wall thickness can be controlled by the synthesis temperature and is in the range of 2-20 nm.     

Actinide targets for neutron cross section measurements

The Advanced Fuel Cycle Initiative (AFCI) and the Generation IV Reactor Initiative have demonstrated a lack of detailed neutron cross sections for certain “minor” actinides. For some closed-fuel-cycle reactor designs more than 50% of reactivity will, at some point, be derived from “minor” actinides that currently have poorly known or in some cases not measured (n,γ) and (n,f) cross sections. Using a combination of resurrected techniques and new developments, we have made a series of targets including highly enriched ²³⁹Pu, ²⁴⁰Pu, and ²⁴²Pu. Thus far, we have electrodeposited these actinide targets. The chemical purification and electodeposition techniques will be described.     

Classical S-matrix theory of viscomagnetic production cross section

The semiclassical theory of Marcus and Miller is applied to obtain an expression for the production cross section in the shear viscosity Senftleben-Beenakker effect, whose exact expression has been recently obtained by Liu et al. The result involves a multi-dimensional integral over a function of the orientation angles between the initial orbital angular momentum and the final rotational angular momentum, and in principle can be evaluated by a Monte Carlo procedure through the computation of classical trajectories.     

Synthesis of PNIPAM-co-MBAA copolymer nanotubes with composite control

We report the preparation of copolymer, poly(N-isopropylacrylamide)-co-(N,N'-methylenebisacrylamide) (PNIPAM-co-MBAA) nanotubes with different composite ratios through surface-initiated atom transfer radical polymerization using a porous anodic aluminum oxide membrane as a template. It is found that the tubular wall strongly depends on the monomer concentration. The composite-induced changes in dimension and shape of nanotubes, especially the wall thickness, were studied by scanning electron microscopy, transmission electron microscopy, atom force microscopy, FT-IR, and gel permeation chromatography. The PNIPAM-co-MBAA nanotubes exhibit a high flexibility and stability.     

Synthesis of alumina nanotubes using carbon nanotubes as templates

Alumina nanotubes have been fabricated using carbon nanotubes (CNTs) as templates at 1473 K. The Al₂O₃ nanotubes are polycrystals. They are less than 100 nm in outer diameter and tens of nanometer in inner diameter, which is close to the outer diameters of the templates. Under certain conditions, AlN and Al₂O₃ nanowires can also be fabricated in this reaction system. Discussions on the growth mechanisms of these nanotubes and nanowires are presented.