Graeme Auchterlonie

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.

Oxygen vacancy ordering in heavily rare-earth-doped ceria

25 at. % Rare-earth (RE)-doped ceria samples (RE=Sm, Dy, Y, and Yb) were examined using transmission electron microscopy and electron energy loss spectroscopy, from which the oxygen vacancy ordering in nanosized domains was confirmed. The relationships of the dopant type, oxygen vacancy ordering, and ionic conductivity of doped ceria were established. It is found that the ordering of oxygen vacancies depends strongly on the dopant type, and the development of nanosized domains with a higher degree of ordering can lead to a more dramatic decrease of ionic conductivity in doped ceria. (c) 2006 American Institute of Physics.

Ion‐assisted deposition of mixed TiO2‐SiO2 films

Mixed thin films of TiO2 and SiO2 were produced by coevaporation from separate electron‐beam sources and simultaneous bombardment of the growing film with oxygen ions. The optical properties of the films were determined during growth by in situ ellipsometry and the surface composition of the deposited films studied by in situ ion scattering spectroscopy, ex situ x‐ray photoelectron spectroscopy, and energy filtered electron diffraction. The correlation between the optical and surface characterization is presented. There is evidence of local variations in the relative concentrations of TiO2 and SiO2. The position of the Si 2p binding energy depends on the TiO2 content in the film, indicating the possible formation of an intimate mixture.

Influence of nano-structural feature on electrolytic properties in Y2O3 doped CeO2 system

Abstract Doped ceria (CeO2) compounds are fluorite type oxides which show oxide ionic conductivity higher than yttria stabilized zirconia, in oxidizing atmosphere. As a consequence of this, considerable interest has been shown in application of these materials for ‘low temperature operation (500–650 8C)’ of solid oxide fuel cells (SOFCs). In this study, YxCe12xO22d (x ¼ 0:05; 0:1; 0:15; 0:2 and 0.25) fine powders were prepared using a carbonate co-precipitation method. The relationship between electrolytic properties and nano-structural features in the sintered bodies was examined. The micro-structures of Y0.05Ce0.95O1.975, Y0.15Ce0.85O1.925 and Y0.25Ce0.75O1.875 as representative three specimens have been investigated in more detail with transmission electron microscopy (TEM). The big diffuse scattering was observed in the background of electron diffraction pattern recorded from Y0.15Ce0.85O1.925 and Y0.25Ce0.75O1.875 sintered bodies. This means that the coherent micro-domain with ordered structure is in the micro-structure. While Y0.25Ce0.75O1.875 sintered body with low conductivity and high activation energy has big micro-domains, the micro-domain size in Y0.15Ce0.85O1.925 with high conductivity and low activation energy was much smaller than that of Y0.25Ce0.75O1.875. TEM observation gives us message that the size of coherent micro-domain with ordered structure would closely relate to the electrolytic properties such as conductivity and activation energy in the specimens. It was concluded that a control of micro-domain size in nano-scale in Y2O3 doped CeO2 system was a key for development of high quality solid electrolyte in fuel cell application.

Phase Separation Induced by Au Catalysts in Ternary InGaAs Nanowires

We report a novel phase separation phenomenon observed in the growth of ternary In(x)Ga(1-x)As nanowires by metalorganic chemical vapor deposition. A spontaneous formation of core-shell nanowires is investigated by cross-sectional transmission electron microscopy, revealing the compositional complexity within the ternary nanowires. It has been found that for In(x)Ga(1-x)As nanowires high precursor flow rates generate ternary In(x)Ga(1-x)As cores with In-rich shells, while low precursor flow rates produce binary GaAs cores with ternary In(x)Ga(1-x)As shells. First-principle calculations combined with thermodynamic considerations suggest that this phenomenon is due to competitive alloying of different group-III elements with Au catalysts, and variations in elemental concentrations of group-III materials in the catalyst under different precursor flow rates. This study shows that precursor flow rates are critical factors for manipulating Au catalysts to produce nanowires of desired composition.

The effect of trace elements on the sintering of an Al-Zn-Mg-Cu alloy

Trace elements can have a significant effect on the processing and properties of aluminium alloys, including sintered alloys. As little as 0.07 wt% (100 ppm) lead, tin or indium promotes sintering in an Al-Zn-Mg-Cu alloy produced from mixed elemental powders. This is a liquid phase sintering system and thin liquid films form uniformly throughout the alloy in the presence of the trace elements, but liquid pools develop in their absence. Analytical transmission electron microscopy indicates that the trace elements are confined to the interparticle and grain boundary regions. The sintering enhancement is attributed to the segregation of the microalloying addition to the liquid-vapour interface. Because the microalloying elements have a low surface tension, they lower the effective surface tension of the liquid. This reduces the wetting angle and extends the spreading of the liquid through the matrix. An improvement in sintering results

Direct evidence of dopant segregation in Gd-doped ceria

Microstructures and segregations of dopants and associated oxygen vacancies in gadolinium-doped ceria (GDC) have been characterized by high-resolution transmission electron microscopy (HRTEM) and scanning TEM (STEM). Diffuse scattering was detected in 25 at. % GDC (25GDC) in comparison to 10GDC, which is ascribed to nanodomain formation in 25GDC. HRTEM, dark-field, and STEM Z-contrast imaging investigations all provide direct evidence for dopant segregation in doped ceria. It is illustrated that dopant cations cannot only segregate in grain interior forming larger nanodomains but also at grain boundary forming smaller ones. Detailed analyses about nanodomain formation and related dopant segregation behaviors are then elucidated.

Microstructural aspects of oxygen ion conduction in solids

The microstructure of solid electrolyte ceramics plays a key role in defining the level of ionic conduction of the material. The polycrystalline nature and the metastable state of most practically useful materials require that the conducting ion must negotiate a series of interfacial features during the conducting process. These features may either enhance or impede the conducting ions and include such things as precipitates, microdomains, various zone configurations and the ubiquitous grain boundaries. By combining the technique of impedance spectroscopy with extensive microstructural analysis, it has been shown that it is possible to develop a comprehensive picture of how some of these features influence the conductivity and to use this knowledge to improve the materials design. A number of examples to illustrate this approach will be discussed, including some recent results on the effect of Al2O3 additions to zirconia ceramics - work that began in Professor Steeles group almost 20 years ago

Evidence of Intragranular Segregation of Dopant Cations in Heavily Yttrium-Doped Ceria

The intragranular segregation of dopant cations in 25 atom % yttrium- doped ceria was explored by energy filtering transmission electron microscopy. Through the comparison between samples sintered at different temperatures, the correlation between the intragranular segregation of dopant cations and the formation of nanosized domains in heavily doped ceria is clearly shown. It is suggested that the segregation can lead to the domain formation, and the oxygen vacancies may also segregate into the domains with the dopant cations. (c) 2006 The Electrochemical Society.

Evolution of InAs branches in InAs/GaAs nanowire heterostructures

The Australian Research Council is acknowledged for the financial support of this project. One of the authors M.P. acknowledges the support of an International Postgraduate Research Scholarship.