Growth of Anodic Oxides on n-InP Studied by Electrochemical Methods and Surface Analyses
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Growth, formation, and stability of anodic oxides obtained on were investigated by coupling electrochemical methods and X-ray photoelectron spectroscopy (XPS) analyses. Photocurrent transients and capacitance measurements performed before and after the semiconductor surface oxidation exhibit new electrical interfacial properties, whereas XPS analysis gives access to chemical composition and estimation of oxide layer thickness. In this work, using a galvanostatic method, oxidation of the surface has been studied at pH 9 for two current densities: 0.2 and . Using transient photocurrent and Mott–Schottky behavior as in situ probes, we have pointed out several steps for the oxidation process, correlated to a gradual oxide coverage which is evidenced by XPS characterization. The current density chosen to perform the oxidation governs the resulting chemical composition, texture, and electrical properties of the oxide. For low current density, the anodic mechanism varies progressively from a pure semiconductor oxidation process to a solvent oxidation contribution. For high current density, this trend disappears whereas semiconductor oxidation continues to take place.Keywords:
Photocurrent
This chapter contains sections titled: Photocurrent Generation and Switching in Neat Semiconductors Photocurrent Switching in MIM Organic Devices Photocurrent Switching in Semiconducting Composites Photocurrent Switching in Surface-Modified Semiconductors References
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In aluminium reduction cells, the profile of a new carbon anode changes with time before reaching a steady state shape, since the anode consumption rate, depending on the current density normal to anode surfaces, varies from one region to another. In this paper, a two-dimension model based on Laplace equation and Tafel equation was built up to calculate the secondary current distribution, and the shift of anode shape with time was simulated with arbitrary Lagrangian-Eulerian method. The time it takes to reach the steady shape for the anode increases with the enlargement of the width of the channels between the anodes or between the anode and the sidewall. This time can be shortened by making a sloped bottom or cutting off the lower corners of the new anode. Forming two slots in the bottom surface increases the anodic current density at the underside of the anode, but leads to the enlargement of the current at the side of the anode.
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Photoelectrochemical cell
Photoelectrochemistry
Quantum yield
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Switching of photocurrent direction in semiconducting systems upon changes of the electrode potential or incident light wavelength was realized by a series of photoelectrodes covered with titania modified with pentacyanoferrate complexes, [Fe(CN)5L]n- (L = NH3, thiodiethanol, thiodipropanol). These materials were characterized by optical spectroscopy and electrochemistry. The structure of the surface complexes was modeled using simple quantum-chemical models. The electrodes described in this paper enable control of the photocurrent direction by two stimuli: Changing the wavelength or the photoelectrode potential easily switches the direction of photocurrent. The materials are different from those of similar characteristics studied by other authors: They are not composites comprising of two types of semiconductors but rather engineered uniform materials. The photocurrent switching phenomenon is an intrinsic feature resulting from a specific electronic structure of the surface-modified semiconductor.
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The cusped field thruster is a new electric propulsion device that is expected to have a non-uniform radial current density at the anode. To further study the anode current density distribution, a multi-annulus anode is designed to directly measure the anode current density for the first time. The anode current density decreases sharply at larger radii; the magnitude of collected current density at the center is far higher compared with the outer annuli. The anode current density non-uniformity does not demonstrate a significant change with varying working conditions.
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In this paper, anode current density distribution in high-current vacuum arcs have been investigated experimentally based on the split anode and cup-shaped axial magnetic field (AMF) cathode configuration system. The anode surface was divided into four areas by split: one central area with a diameter of 18mm, and three symmetrical peripheral fan-shaped areas with the internal and external diameters of 22 mm and 60 mm, respectively. The contacts material was CuCr25 and the arc current varied from 6kA to 14kA (rms). The currents of the four areas on the anode contact were measured by four Rogowski Coils outside of the vacuum chamber, and the anode current density of each areas was determined by the area and current of regions. From the experimental results, the peak anode current density of central area on the anode surface increased from 14.4 A/mm 2 to 37.7 A/mm 2 , accompanied with the arc mode from the intense arc mode (14kA) from the diffuse arc mode (7.6kA). Moreover, the current density distribution became more non-uniform as the current increased, and the current density of the central area was much larger than that of other peripheral regions on the anode surface.
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We present a comparison of two electrospun anode materials characterized with Shewanella oneidensis MR-1 under steady state conditions. The achievable anodic current densities of microbial fuel cells in a half-cell setup operated with S. oneidensis are very responsive to the anode morphology. Two electrospun anode materials were investigated which mainly differ in fiber diameter resulting in an approximately four-fold fiber surface area difference. The electrospun material with 126 nm fibers yields current density of (56 ± 14) µA cm -2 (normalized to the projected anode area) at -0.2 V vs. SCE and performs more than a factor of three better than the material with 848 nm fibers with a current density of (16 ± 14) µA cm -2 . The volumetric current density of the 126 nm fiber material (3378 ± 830) µA cm -3 is more than a factor of three higher than the carbon nanotube based material
Shewanella oneidensis
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Exchange current density
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The objective of this paper is to determine the radial distribution of the anode current in the high current vacuum arcs under the axial magnetic field(AMF). Based on the specially experimental geometry of a split anode and a butt-type cathode, the currents of the every four divided areas at the anode were measured. In this experiment, four types of the split anode contacts were selected, with the diameters of the central area of 10 mm, 14 mm, 20 mm and 20 mm, respectively. The contact material was CuCr25 (25% Cr). The arc current I ranged from 6 to 14 kA (rms) at 50 Hz. The opening velocity was 2.4 m/s. An external applied uniform AMF was 74 mT. The appearance of the vacuum arcs was recorded by a high-speed charge-coupled device video camera. The experimental results quantitatively reveal the radial distribution of the anode current by the four types split-anode contacts. In our experiments, the current density in the four types split-anode under different geometry was quantitatively measured, which was closely related to the anode current distribution in radial direction. The current density of central area decreased evidently with the increasing of the diameter of the anode central area, which quantitatively indicated that the anode current density concentrated in the central area. The current density of anode central area with the smaller diameter had a higher increasing rate with the increasing of the arc current.
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