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161.
162.
O.J. Guy G. Pope I. Blackwood K.S. Teng L. Chen W.Y. Lee S.P. Wilks P.A. Mawby 《Surface science》2004,573(2):253-263
The use of a silicon interface pre-treatment to produce low resistance Ohmic nickel contacts to 4H-SiC, circumventing the need for contact post annealing, is reported. The effects of two different SiC pre-metal deposition surface preparation techniques: RCA cleaning (control sample) and a silicon interlayer pre-treatment (SIP), are discussed. Electrical characterization of contacts on treated surfaces, using circular transfer length measurements (CTLM), revealed that contacts to RCA cleaned samples were Schottky in nature, unless annealed at temperatures greater than 700 °C. In contrast, contacts formed on SIP SiC surfaces exhibited Ohmic behaviour directly after fabrication, without the need for post metallisation annealing. Average contact resistances as low as 1.3E−05 Ω cm2 have been recorded for SIP samples. This fabrication process has distinct technological advantages compared to standard techniques for forming Ohmic contacts to SiC. To consolidate our findings the chemical and electrical nature of the SIP nickel-SiC interface, as it was sequentially formed and annealed, was examined using X-ray photoelectron spectroscopy (XPS). Based on these results, a model is proposed to explain the as-deposited Ohmic contact nature of the SIP sample. 相似文献
163.
Rapid prototyping methods such as additive manufacturing (three dimensional printing) and laser scribing have attracted much attention for manufacturing next-generation electrochemical energy storage devices because of their simplicity, low cost, medium throughput, and ability to prepare electrodes with unique form factors and multiple functionalities, such as stretchability, flexibility, and wearability. Of the wide array of potential active materials that can be used for energy storage, two dimensional materials such as graphene, MXenes, and MoS2 have exceptionally high conductive surface areas and are attractive candidates for printing thick, high loading supercapacitors and batteries. In this brief review, we highlight recent progress and major challenges which must be overcome to make these manufacturing approaches and the resulting printed devices commercially viable. 相似文献
164.
Chemical-shift-selective imaging at microscopic resolution has been applied to the study of various plant materials including orange peel, grape berries and both dried and undried fruits of fennel. It is shown that selective imaging of aromatics and carbohydrates as well as water and oil can be performed with in-plane resolution down to 13 microns and slice thicknesses of 1 mm or less, at a field strength of 4.7 Tesla. The noninvasive nature of the method gives it advantages over established methods of plant histochemistry which involve sectioning and staining to reveal different chemical constituents. 相似文献
165.
The role of susceptibility effects in the production of artifacts in chemical shift images generated by the selective excitation technique is discussed. The effects are demonstrated in images of phantom samples of agarose gels containing small air bubbles. The artifacts can lead to erroneous interpretations, in which the resonances to be resolved exhibit a relatively small chemical shift separation, such as that between water and soluble carbohydrates (sugars). 相似文献
166.
Jones JE Amoroso AJ Dorin IM Parigi G Ward BD Buurma NJ Pope SJ 《Chemical communications (Cambridge, England)》2011,47(12):3374-3376
UV-visible titrations, (1)H NMRD experiments and molecular docking studies show that emissive anthraquinone appended dimetallic lanthanide complexes bind to DNA. The strength of binding and the observed relaxivity behaviour depend on the nature of the substituted anthraquinone core. 相似文献
167.
Jones JE Kariuki BM Ward BD Pope SJ 《Dalton transactions (Cambridge, England : 2003)》2011,40(14):3498-3509
The syntheses of four new ligands based upon 3-picolyl functionalised amino anthraquinone (AQ) chromophores are described via a one-pot reductive amination procedure giving the desired ligands L1-L4 (L1, 1-(3-picolylamino)anthracene-9,10-dione; L2, 1-hydroxy-4-(3-picolylamino)anthracene-9,10-dione; L3, 1,4-bis(3-picolylamino)anthracene-9,10-dione; L4, 1,5-bis(3-picolylamino)anthracene-9,10-dione). Each ligand was characterised in solution via(1)H and (13)C{(1)H} NMR, with three examples giving single crystal X-ray diffraction data. The structures confirmed the proposed formulations and also revealed the presence of intramolecular H-bonding between the quinone and secondary amine units. The electronic characteristics of the ligands were investigated using a combined experimental/theoretical approach, revealing that in each case absorption in the visible region constitutes significant charge transfer (CT) character, originating from N-(amine)-to-quinone transitions, and is solvent sensitive. Density functional theory (DFT) calculations also suggest that the position of amino-substitution at the AQ core influences the wavelength of the lowest energy feature, by modulation of the HOMO, rather than the LUMO energy. The coordination chemistry of the ligands was probed through reaction with fac-[Re(CO)(3)(di-imine)(MeCN)](BF(4)) where di-imine = 1,10-phenanthroline (phen) and 2,9-dimethyl-1,10-phenanthroline (dmp). Combined structural and spectroscopic studies confirmed that the ligands coordinate to Re(i) exclusively via the pyridyl units, however in the case of L3 only monometallic complexes were isolated. The optical properties of the complexes are dominated by AQ-centred (>425 nm) absorptions superimposed upon (1)MLCT features, as well as diimine-based intra-ligand (<350 nm) transitions. The luminescence properties of the complexes generally display dual emission, which was dependent upon the wavelength of sensitisation, with short-lived AQ fluorescence superimposed upon long-lived (3)MLCT phosphorescence. 相似文献
168.
Certain supergravity theories admit a remarkable consistent dimensional reduction in which the internal space is a sphere. Examples include type IIB supergravity reduced on S5, and eleven-dimensional supergravity reduced on S4 or S7. Consistency means that any solution of the dimensionally-reduced theory lifts to give a solution in the higher dimension. Although supersymmetry seems to play a role in the consistency of these reductions, it cannot be the whole story since consistent sphere reductions of non-supersymmetric theories are also known, such as the reduction of the effective action of the bosonic string in any dimension D on either a 3-sphere or a (D−3)-sphere, retaining the gauge bosons of SO(4) or SO(D−2) respectively. We show that although there is no supersymmetry, there is nevertheless a natural Killing spinor equation for the D-dimensional bosonic string. A projection of the full integrability condition for these Killing spinors gives rise to the bosonic equations of motion (just as happens in the supergravity examples). Thus it appears that by extending the notion of supersymmetry to “pseudo-supersymmetry” in this way, one may be able to obtain a broader understanding of a relation between Killing spinors and consistent sphere reductions. 相似文献
169.
170.
Propagation speed of combustion and invasion waves in stochastic simulations with competitive mixing
We consider the propagation speeds of steady waves simulated by particles with stochastic motions, properties and mixing (Pope particles). Conventional conservative mixing is replaced by competitive mixing simulating invasion processes or conditions in turbulent premixed flames under the flamelet regime. The effects of finite correlation times for particle velocity are considered and wave propagation speeds are determined for different limiting regimes. The results are validated by stochastic simulations. If the correlation time is short, the model corresponds to the KPP–Fisher equation, which is conventionally used to simulate invasion processes. If the parameters of the simulations are properly selected, the model under consideration is shown to be consistent with existing experimental evidence for propagation speeds of turbulent premixed flames. 相似文献