Browsing by Author "Raston, CL"

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    Electro-polymerization rates of diazonium salts are dependent on the crystal orientation of the surface
    (Elsevier, 2022-11-15) Rahpeima, S; Le Brun, AP; Raston, CL; Darwish, N
    Electro-polymerization of diazonium salts is widely used for modifying surfaces with thin organic films. Initially this method was primarily applied to carbon, then to metals, and more recently to semiconducting Si. Unlike on other surfaces, electrochemical reduction of diazonium salts on Si, which is one of the most industrially dominant material, is not well understood. Here, we report the electrochemical reduction of diazonium salts on a range of silicon electrodes of different crystal orientations (111, 211, 311, 411, and 100). We show that the kinetics of surface reaction and the reduction potential is Si crystal-facet dependent and is more favorable in the hierarchical order (1 1 1) > (2 1 1) > (3 1 1) > (4 1 1) > (1 0 0), a finding that offers control over the surface chemistry of diazonium salts on Si. The dependence of the surface reaction kinetics on the crystal orientation was found to be directly related to differences in the potential of zero charge (PZC) of each crystal orientation, which in turn controls the adsorption of the diazonium cations prior to reduction. Another consequence of the effect of PZC on the adsorption of diazonium cations, is that molecules terminated by distal diazonium moieties form a compact film in less time and requires less reduction potentials compared to that formed from diazonium molecules terminated by only one diazo moiety. In addition, at higher concentrations of diazonium cations, the mechanism of electrochemical polymerization on the surface becomes PZC-controlled adsorption-dominated inner-sphere electron transfer while at lower concentrations, diffusion-based outer-sphere electron transfer dominates. These findings help understanding the electro-polymerization reaction of diazonium salts on Si en route towards an integrated molecular and Si electronics technology. © 2022 Elsevier Inc
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    Structural and conductivity evolution of fluorite-type Bi2O3-Er2O3-PbO solid electrolytes during long-term annealing
    (Elsevier, 2008-08) Webster, NAS; Ling, CD; Raston, CL; Lincoln, FJ
    Quenched-in fcc fluorite-type materials in the Bi2O3-Er2O3-PbO system were annealed in air at 500 and 600 degrees C for up to 2000 h. Each material experienced a conductivity-lowering structural transformation, thus making them unsuitable for use in SOFCs. For example, the materials (BiO1.5)(0.80)(ErO1.5)(0.20-x)(PbO)(x), x = 0.03, 0.06 and 0.09, underwent a fluorite-type to tetragonal transformation during annealing at 500 degrees C due to (100) oxide-ion vacancy ordering, and the rate of conductivity decay at 500 degrees C increased with increasing Pb2+/Er3+ ratio. © 2008, Elsevier Ltd.
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    Structure and conductivity of new fluorite-type Bi2O3-Er2O3-PbO materials
    (Elsevier, 2007-10) Webster, NAS; Ling, CD; Raston, CL; Lincoln, FJ
    Fluorite-type fcc phases have been synthesised in the system Bi2O3-Er2O3-PbO by solid state reaction, and a partial air-quenchable domain of the fluorite-type phase has been established. Some of these materials display high oxide ion conductivities, notably (BiO1.5)(0.80)(ErO1.5)(0.11)(PbO)(0 09) and (BiO1.5)(0.85)(ErO1.5)(0.12)(PbO)(0.03), which have conductivities of 0.49 and 0.72 S cm(-1) at 750 degrees C, respectively, placing them among the most conductive Bi2O3-based materials. Conductivity was found to increase with increasing Pb2+/Er3+ ratio and decreasing (Er3+ + Pb2+)/Bi3+ ratio. Positional disorder in the oxide ion sublattice was characterised by neutron powder diffraction. At room temperature, the oxide ion sublattice appeared to be completely disordered, with oxide ions only in 32f and 48i sites, and changes in occupancy with increasing Pb2+/Er3+ and (Er3+ + Pb2+)/Bi3+ ratios were not significant. At 700 degrees C, there appeared to be oxide ions in 8c sites for the material (BiO1.5)(0.80)(ErO1.5)(0.11)(PbO)(0 09), with a correspondingly smaller occupancy of the 32f sites, whilst the occupancy of the 48i sites had not changed significantly. © 2007, Elsevier Ltd.
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    Vortex fluidic induced mass transfer across immiscible phases
    (Royal Society of Chemistry, 2022-01-31) Jellicoe, M; Igder, A; Chuah, C; Jones, DB; Luo, X; Stubbs, KA; Crawley, EM; Pye, SJ; Joseph, N; Vimalananthan, K; Gardner, Z; Harvey, DP; Chen, XJ; Salvemini, F; He, S; Zhang, W; Chalker, JM; Quinton, JS; Tang, YH; Raston, CL
    Mixing immiscible liquids typically requires the use of auxiliary substances including phase transfer catalysts, microgels, surfactants, complex polymers and nano-particles and/or micromixers. Centrifugally separated immiscible liquids of different densities in a 45° tilted rotating tube offer scope for avoiding their use. Micron to submicron size topological flow regimes in the thin films induce high inter-phase mass transfer depending on the nature of the two liquids. A hemispherical base tube creates a Coriolis force as a ‘spinning top’ (ST) topological fluid flow in the less dense liquid which penetrates the denser layer of liquid, delivering liquid from the upper layer through the lower layer to the surface of the tube with the thickness of the layers determined using neutron imaging. Similarly, double helical (DH) topological flow in the less dense liquid, arising from Faraday wave eddy currents twisted by Coriolis forces, impact through the less dense liquid onto the surface of the tube. The lateral dimensions of these topological flows have been determined using ‘molecular drilling’ impacting on a thin layer of polysulfone on the surface of the tube and self-assembly of nanoparticles at the interface of the two liquids. At high rotation speeds, DH flow also occurs in the denser layer, with a critical rotational speed reached resulting in rapid phase demixing of preformed emulsions of two immiscible liquids. ST flow is perturbed relative to double helical flow by changing the shape of the base of the tube while maintaining high mass transfer between phases as demonstrated by circumventing the need for phase transfer catalysts. The findings presented here have implications for overcoming mass transfer limitations at interfaces of liquids, and provide new methods for extractions and separation science, and avoiding the formation of emulsions. © 2022 The Author(s). Published by the Royal Society of Chemistry. Open Access CC BY.