Laure Bourgeois

Large-scale synthesis and HRTEM analysis of single-walled B- and N-doped carbon nanotube bundles

Bundles of B- and N-doped single-walled carbon nanotubes (SWNTs) containing up to ∼10 at% B and up to ∼2 at% N were synthesized at high yields under thermo–chemical treatment of pure C SWNT bundles and B2O3 in a flowing nitrogen atmosphere. The bundles were characterized by means of high-resolution transmission electron microscopy and electron energy loss spectroscopy. The effects of synthesis temperature (1503–1773 K) and time (30–240 min) on the B and N contents and yield of the SWNT bundles were determined. The maximum yield of the B- and N-doped SWNT bundles was obtained under synthesis at 1553 K over 30 min. Atomic structure and morphology of individual SWNTs in the bundles, in particular, packing of doped SWNTs, helicity distribution, encapsulation of fullerene-like clusters, diameter and shell number variations were studied. The synthesized SWNTs in the bundles were stacked in a honeycomb array with the uniform inter-tube spacing of ∼0.3 nm. No preferable orientation for the graphene-like tubular shells was found, i.e. both zigzag and armchair edges were observed with approximately equal proportions. Frequently, diameter increase took place for the outer tubes in a bundle and for isolated SWNTs. C-based or BN-based fullerene-like encapsulates were observed in individual SWNTs. Carbon oxidation by the B2O3 vapor and B and N substitution for C is thought to underlie the doping of C SWNTs. The substitution reaction temperature–time limits with respect to the morphological stability of B- and N-doped SWNT bundles are finally elucidated.

Ending Aging in Super Glassy Polymer Membranes

Aging in super glassy polymers such as poly(trimethylsilylpropyne) (PTMSP), poly(4-methyl-2-pentyne) (PMP), and polymers with intrinsic microporosity (PIM-1) reduces gas permeabilities and limits their application as gas-separation membranes. While super glassy polymers are initially very porous, and ultra-permeable, they quickly pack into a denser phase becoming less porous and permeable. This age-old problem has been solved by adding an ultraporous additive that maintains the low density, porous, initial stage of super glassy polymers through absorbing a portion of the polymer chains within its pores thereby holding the chains in their open position. This result is the first time that aging in super glassy polymers is inhibited whilst maintaining enhanced CO2 permeability for one year and improving CO2/N2 selectivity. This approach could allow super glassy polymers to be revisited for commercial application in gas separations.

Insights into the structure of BN nanotubes

The following features of multiwalled BN nanotubes were discovered using a field emission high-resolution analytical transmission electron microscope: (i) coexistence of hexagonal and rhombohedral stacking in nanotube shell assembly; (ii) flattening of nanotube cross section, which makes possible clear atomic resolution of the core structure in a three-shelled nanotube; and (iii) change in chirality of tubular layers from armchair to zigzag arrangement in a 30° double-walled nanotube kink, as revealed by atomically resolved images of tube wall segments.

Modification of mesoporous TiO2 electrodes by surface treatment with titanium(IV), indium(III) and zirconium(IV) oxide precursors: preparation, characterization and photovoltaic performance in dye-sensitized nanocrystalline solar cells

Post-treatment of titanium dioxide (TiO2) films for use in dye-sensitized solar cells has been carried out with titanium(IV), indium(III) and zirconium(IV) oxide precursor solutions. The nanostructured electrodes were characterized using nitrogen gas sorption (NGS), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), energy dispersive x-ray spectroscopy (EDX), field emission scanning electron microscopy (FEGSEM) and high resolution transmission electron microscopy (HRTEM). The change in the nanostructure was quantified and the thicknesses of the core?shell coatings determined. An evaluation of the dependence of thickness by HRTEM concluded that one coating step of either the indium or zirconium precursor gave thicknesses of 0.5?nm, with EDX and XPS confirming the presence of either In or Zr at the TiO2 electrode surface, respectively. These working electrodes were then used to fabricate dye-sensitized nanocrystalline solar cells (DSSCs) whose performance was tested under AM1.5G 100?mW?cm?2 illumination. TiCl4 post-treatment was found to improve the photovoltaic efficiencies from 3.6% to 5.3%. Single coatings of either In2O3 or ZrO2 on the TiO2 working electrode resulted in an increased efficiency from 3.6% up to 5.0%. Thinner coatings gave the highest solar cell efficiency. The drop in performance was mainly due to a decrease in short circuit current density (Jsc) with the greater shell thicknesses. ZrO2-coated TiO2 electrodes subjected to microwave heat treatment using a 2.45?GHz microwave produced the highest efficiencies (5.6%) largely due to an increase in short circuit current from 11.4 to 13.3?mA?cm?2.

Imogolite: An aluminosilicate nanotube material

Abstract The analogy between carbon nanotubes and synthetic imogolite, an aluminosicate of stoichiometry (OH)3Al2O3SiOH, having a tubular structure of external diameter 2.4 nm and internal diameter 0.9 nm, is examined. High-resolution transmission electron microscopy, image matching and electron diffraction are used to examine the tube structure. Some interesting new results are obtained, concerning the various states of aggregation of the imogolite tubes, ranging from randomly oriented single tubes to essentially close-packed arrays. Both longitudinal and cross-sectional images were obtained. Some possible applications of imogolite as new materials are discussed. The various imogolite textures pose challenging problems for solid-state physicists, concerning for example the transport and optical properties of such fibre bundles.

Direct Electrodeposition of Porous Gold Nanowire Arrays for Biosensing Applications

Nanochannel alumina templates are used as templates for fabrication of porous gold nanowire arrays by a direct electrodeposition method. After modification with glucose oxidase, a porous gold nanowire-array electrode is shown to be an excellent electrochemical biosensor for the detection of glucose. The picture shows an SEM image of a nanowire array after removal of the alumina template by acid dissolution. We report the fabrication of porous gold nanowire arrays by means of a one-step electrodeposition method utilizing nanochannel alumina templates. The microstructure of gold nanowires depends strongly on the current density. The formation of porous gold nanowires is attributed to disperse crystallization under conditions of low nucleation rate. Interfacial electron transport through the porous gold nanowires is studied by electrochemical impedance spectroscopy. Cyclic voltammetric studies on the porous gold nanowire arrays reveal a low-potential electrocatalytic response towards hydrogen peroxide. The properties of the glucose oxidase modified porous gold nanowire array electrode are elucidated and compared with those of nonporous enzyme electrodes. The glucose oxidase modified porous gold nanowire-array electrode is shown to be an excellent electrochemical biosensor for the detection of glucose.

The crystal structure of the equilibrium Φ phase in Mg–Zn–Al casting alloys

Abstract The crystal structure of the equilibrium intermetallic Φ phase formed in a Mg–Zn–Al casting alloy has been characterised using transmission electron microscopy. Electron diffraction patterns recorded from particles of the Φ phase in the casting alloy can be well indexed according to a primitive orthorhombic unit cell, with lattice parameters a =0.90 nm, b =1.70 nm, and c =1.97 nm. Examination of the whole pattern symmetry of principal zone axis diffraction patterns indicates a space group of Pbcm . A model for the decoration of the unit cell of the Φ phase is proposed, in which the Mg 5 (Zn,Al) 12 Friauf polyhedron is the key structural unit. The Zn and Al atoms are all in icosahedral coordination, but their icosahedral shells are distorted due to the presence of Mg atoms. A total of 84 Mg atoms and 68 Zn/Al atoms can be accommodated in the orthorhombic unit cell, resulting in a formula of Mg 21 (Zn,Al) 17 that is consistent with the composition obtained experimentally. Computer simulations of electron diffraction patterns provide very good agreement with experimental observations.

Nanostructured photoelectrochemical solar cell for nitrogen reduction using plasmon-enhanced black silicon.

Ammonia (NH3) is one of the most widely produced chemicals worldwide. It has application in the production of many important chemicals, particularly fertilizers. It is also, potentially, an important energy storage intermediate and clean energy carrier. Ammonia production, however, mostly uses fossil fuels and currently accounts for more than 1.6% of global CO2 emissions (0.57  Gt in 2015). Here we describe a solar-driven nanostructured photoelectrochemical cell based on plasmon-enhanced black silicon for the conversion of atmospheric N2 to ammonia producing yields of 13.3 mg m−2 h−1 under 2 suns illumination. The yield increases with pressure; the highest observed in this work was 60 mg m−2 h−1 at 7 atm. In the presence of sulfite as a reactant, the process also offers a direct solar energy route to ammonium sulfate, a fertilizer of economic importance. Although the yields are currently not sufficient for practical application, there is much scope for improvement in the active materials in this cell.

Tubes of rhombohedral boron nitride

The structure of boron nitride bamboo-like tubular whiskers grown from boron nitride powder is investigated by high-resolution transmission electron microscopy. Despite the relatively small size of the tubes (20-200 nm in diameter), they all exhibit rhombohedral-like ordering in their layer stacking. The tubular sheets also tend to have their [100] direction parallel to the fibre axis. Particles of iron alloys are commonly found encapsulated inside or at the end of the filaments. It is suggested that iron plays an active role in the growth of the fibres.

Boron nitride cones: structure determination by transmission electron microscopy

A form of turbostratic boron nitride containing a large percentage of micrometre-size conically shaped particles was investigated by transmission electron microscopy. Electron diffraction patterns revealed the presence of correlations between adjacent boron nitride layers. The diffraction patterns were also used to determine the cone apex angle of many cone-like objects. The apex angles exhibited a broad distribution from 84 to 130 degrees with an ill defined peak in the 92-95 degrees region. These results could be accounted for by a structure model in which conical boron nitride layers are helically wound about a disclination axis, according to overlap angles that correspond to high densities of coincidental lattice sites between successive layers. The clustering of the apex angles near 93 degrees was attributed to the formation of a square ring during the nucleation stage. This appears to be specific to the boron nitride system.