Barry J. Wood

Uptake and localisation of lead in the root system of Brassica juncea

The uptake and distribution of Pb sequestered by hydroponically grown (14days growth) Brassica juncea (3days exposure; Pb activities 3.2, 32 and 217microM) was investigated. Lead uptake was restricted largely to root tissue. Examination using scanning transmission electron microscopy-energy dispersive spectroscopy revealed substantial and predominantly intracellular uptake at the root tip. Endocytosis of Pb at the plasma membrane was not observed. A membrane transport protein may therefore be involved. In contrast, endocytosis of Pb into a subset of vacuoles was observed, resulting in the formation of dense Pb aggregates. Sparse and predominantly extracellular uptake occurred at some distance from the root tip. X-ray photoelectron spectroscopy confirmed that the Pb concentration was greater in root tips. Heavy metal rhizofiltration using B. juncea might therefore be improved by breeding plants with profusely branching roots. Uptake enhancement using genetic engineering techniques would benefit from investigation of plasma membrane transport mechanisms.

Vertically aligned nanorod-like rutile TiO2 single crystal nanowire bundles with superior electron transport and photoelectrocatalytic properties

In this work, vertically aligned nanorod-like rutile TiO2 single crystal nanowire bundles were directly grown onto FTO conducting substrates via a facile, one-pot hydrothermal method. The fabricated nanorod-like rutile TiO2 single crystal nanowire bundles display a diameter range of 150–200 nm and a mean length of 0.9 μm. The nanorod-like bundles assemble by individual single crystal nanowires of 5–7 nm in diameter. The photoanode made of vertically aligned nanorod-like rutile TiO2 single crystal nanowire bundles shows excellent photoelectrocatalytic activity towards water oxidation, which is almost 3 times higher than that of the photoanode made of vertically aligned anatase TiO2 nanotube film of similar thickness. The high photoelectrocatalytic activity of the photoanode made of the nanorod-like rutile TiO2 single crystal nanowire bundles is mainly due to the superior photoelectron transfer property, which has been manifested by the inherent resistance (R0) of the rutile TiO2 film via a simple photoelectrochemical method. Using this approach, the calculated R0 values are 52.1 Ω and 71.0 Ω for the photoanodes made of vertically aligned nanorod-like rutile TiO2 single crystal nanowire bundles and the vertically aligned anatase TiO2 nanotubes, respectively. The lower R0 of the rutile TiO2 photoanode means a superior photoelectron transfer property. XPS valence-band spectra analysis indicates that the nanorod-like rutile TiO2 film has almost identical valence band position (1.95 eV) when compared to the anatase TiO2 nanotube film, meaning a similar oxidation capability, further confirming the superior photoelectron transport property of the nanorod-like rutile TiO2 single crystal nanowire bundles.

Photoelectrochemical Characterization of Hydrogenated TiO2 Nanotubes as Photoanodes for Sensing Applications

In this work, hydrogenated TiO2 nanotubes (H-TNTs) electrodes were successfully fabricated via the anodization of a titanium sheet followed by a hydrogenation process. Oxygen vacancies were induced in the crystalline structure of TiO2 nanotubes (TNTs) as shallow donors that enhance the electronic conductivity of the TNTs. This improvement in the electronic conductivity and photoelectrocatalytic (PEC) performance was confirmed and evaluated by a photoelectrochemical characterization. Most importantly, the H-TNTs electrode was able to degrade potassium hydrogen phthalate (strong adsorbent) and glucose (weak adsorbent) indiscriminately. The corresponding photocurrents at the H-TNTs were 2-fold greater than that of the TNTs samples for the same concentrations of the organic compounds. This suggests that the H-TNTs electrode can be a promising sensor for the PEC determination of individual organic compounds or as an aggregative parameter of organic compounds (e.g., chemical oxygen demand).

Directly hydrothermal growth of single crystal Nb3O7(OH) nanorod film for high performance dye-sensitized solar cells.

Hydrothermal growth of high crystallinity Nb(3) O(7) (OH) single crystal nanorod film onto FTO substrate is directly used as the photoanode for DSSCs without calcination. The resultant DSSCs possess an impressive overall efficiency of 6.77%, the highest among all reported DSSCs assembled by niobium oxide-based photoanodes.

Synthesis and surface modification of birefringent vaterite microspheres

This paper reports on the synthesis of birefringent vaterite microspheres with narrow size distribution using a seeded growth method. In a post-treatment the microspheres were stabilized and functionalized through coating with a combination of organosilica and silica. The coating vastly enhanced the stability of the vaterite microspheres in biological buffers and allowed the attachment of biomolecules such as DNA or proteins. As an example, streptavidin was attached to the surface of the functionalized microspheres. These results pave the way for the use of birefringent vaterite particles for the micromanipulation of single biological molecules such as DNA or specific proteins in an optical trap capable of exerting and measuring torques. The stabilized birefringent microspheres may also find use for biosensor and biological screening applications.

Graphitized silicon carbide microbeams: wafer-level, self-aligned graphene on silicon wafers

Currently proven methods that are used to obtain devices with high-quality graphene on silicon wafers involve the transfer of graphene flakes from a growth substrate, resulting in fundamental limitations for large-scale device fabrication. Moreover, the complex three-dimensional structures of interest for microelectromechanical and nanoelectromechanical systems are hardly compatible with such transfer processes. Here, we introduce a methodology for obtaining thousands of microbeams, made of graphitized silicon carbide on silicon, through a site-selective and wafer-scale approach. A Ni-Cu alloy catalyst mediates a self-aligned graphitization on prepatterned SiC microstructures at a temperature that is compatible with silicon technologies. The graphene nanocoating leads to a dramatically enhanced electrical conductivity, which elevates this approach to an ideal method for the replacement of conductive metal films in silicon carbide-based MEMS and NEMS devices.

Implications of specimen preparation and of surface contamination for the measurement of the grain boundary carbon concentration of steels using x‐ray microanalysis in an UHV FESTEM

The purpose of the present investigation was to gain an understanding of the nature of the carbon contamination on the surface of standard steel transmission electron spectroscopy (TEM) specimens, the effect of exposure of a clean specimen to normal laboratory air, and the efficacy of plasma-cleaning treatments. This knowledge is a necessary prerequisite to the development of appropriate specimen preparation and/or specimen cleaning methods. X-ray photoelectron spectroscopy in combination with argon ion beam profiling was used to characterize the specimen surfaces of X65 steel and 316 stainless steel. The only clean carbon-free surface obtained was that during argon etching of the sample in the surface analysis chamber. Any exposure of a previously cleaned sample to laboratory air resulted in a rapid carbon (hydrocarbon) contamination of the sample surface and the development of surface oxidation, Plasma cleaning with subsequent exposure of the specimen to the laboratory air also resulted in a carbon-contaminated surface. This suggests that procedures of preparation of TEM specimens of steels outside an ultrahigh vacuum chamber are unlikely to result in the lowering of contamination rates on specimens to levels where measurements for carbon in the grain boundaries are possible. What is needed is a cleaning system as an integral part of the specimen insertion system into the field-emission scanning transmission electron microscope. This cleaning could be carried out by argon ion etching. Copyright (C) 2000 John Wiley & Sons, Ltd.

Single-Crystalline 3C-SiC anodically Bonded onto Glass: An Excellent Platform for High-Temperature Electronics and Bioapplications

Single-crystal cubic silicon carbide has attracted great attention for MEMS and electronic devices. However, current leakage at the SiC/Si junction at high temperatures and visible-light absorption of the Si substrate are main obstacles hindering the use of the platform in a broad range of applications. To solve these bottlenecks, we present a new platform of single crystal SiC on an electrically insulating and transparent substrate using an anodic bonding process. The SiC thin film was prepared on a 150 mm Si with a surface roughness of 7 nm using LPCVD. The SiC/Si wafer was bonded to a glass substrate and then the Si layer was completely removed through wafer polishing and wet etching. The bonded SiC/glass samples show a sharp bonding interface of less than 15 nm characterized using deep profile X-ray photoelectron spectroscopy, a strong bonding strength of approximately 20 MPa measured from the pulling test, and relatively high optical transparency in the visible range. The transferred SiC film also exhibited good conductivity and a relatively high temperature coefficient of resistance varying from -12 000 to -20 000 ppm/K, which is desirable for thermal sensors. The biocompatibility of SiC/glass was also confirmed through mouse 3T3 fibroblasts cell-culturing experiments. Taking advantage of the superior electrical properties and biocompatibility of SiC, the developed SiC-on-glass platform offers unprecedented potentials for high-temperature electronics as well as bioapplications.

Functional molecular wires

The properties of self-assembled molecules may be tuned by sequentially coupling components on a gold surface, the molecular electronics toolbox of chemically reactive building blocks yielding molecular wires with diode-like current-voltage (I-V) characteristics. The bias for rectification in each case is dependent upon the sequence of electron-donating and electron-accepting moieties and similar behaviour has been achieved for four different contacting techniques.

Controlled interfaces in low‐temperature‐cured phenolic composites

The surface chemistry and interfacial adhesion of silane-treated E-glass fibers and low-power, oxygen or water plasma-treated ultrahigh-modulus polyethylene (UHMPE) fibers with acid-catalyzed, low-temperature-cured phenolic resins have been measured by X-ray photoelectron spectroscopy, (XPS) and static secondary ion mass spectrometry (SIMS), fiber bundle pullout and flexural and interlaminar shear strength properties of unidirectional composites. The most effective treatment for E-glass involved an epoxy silane rather than an amino silane owing to the protonation by the acid catalyst of the amine as well as the loss of reactive sites by the formation of carbon dioxide adducts stable at the conditions of cure. Scanning electron microscope examination of the cured phenolic resin showed phase-separated water domains; the diameter of these domains decreased towards the fiber surface in a chopped-strand mat composite owing to the lowering of the surface tension produced by the dissolution of the binder by the phenolic resin. Both water and oxygen-plasma treatments of UHMPE increased the fiber bundle pullout force by the same amount and this was attributed to direct chemical bonding to hydroxyl (and possibly epoxy) groups detected by XPS, SSIMS and derivatization. The best composite properties were obtained when oxygen plasma-treated UHMPE was used and this was attributed to the slower restructuring and higher total oxygen content enabling efficient wet-out of the fibers by the resin.