Spatial Distribution Of Holes Research Articles

A Novel Thermomechanical Processing Route to Fabricate ODS Ferritic Stainless Steel Interconnects and Their Oxidation Behavior

Oxide dispersion-strengthened AISI 430 alloy was fabricated using a novel thermomechanical processing route for potential application as interconnect in solid oxide fuel cells. The process can be termed as reverse friction deposition wherein the final product is formed by curling up as a seamless tube on the surface of the parent rod which is used as a consumable tool in a friction stir welding machine. The oxide dispersion alloy is obtained by incorporating 8 mol% yttria-stabilized zirconia powder in drilled holes in the rod. The number and spatial distribution of holes were optimized for a sound product and uniform distribution of the particles. The oxidation behavior of the formed tube was remarkably different from that of the parent rod. The dispersion of zirconia particles on the outer surface of the tube retards Cr diffusion owing to their grain boundary pinning effect which also refines the Fe2O3 crystal size. (Cr, Mn)O4 spinel, which is known to be electrically conductive, formed in the inner surface of the tube. The tube thus can be used as an interconnect in tubular solid oxide fuel cells and potentially prevent Cr poisoning of the cathode.

Electron-hole interactions in coupled InAs-GaSb quantum dots based on nanowire crystal phase templates

We report growth and characterization of a coupled quantum dot structure that utilizes nanowire templates for selective epitaxy of radial heterostructures. The starting point is a zinc blende InAs nanowire with thin segments of wurtzite structure. These segments have dual roles: they act as tunnel barriers for electron transport in the InAs core, and they also locally suppress growth of a GaSb shell, resulting in coaxial InAs-GaSb quantum dots with integrated electrical probes. The parallel quantum dot structure hosts spatially separated electrons and holes that interact due to the type-II broken gap of InAs-GaSb heterojunctions. The Coulomb blockade in the electron and hole transport is studied, and periodic interactions of electrons and holes are observed and can be reproduced by modeling. Distorted Coulomb diamonds indicate voltage-induced ground-state transitions, possibly a result of changes in the spatial distribution of holes in the thin GaSb shell.

Habitat engineering by decadal-scale bioturbation around shipwrecks on the Great Barrier Reef mid-shelf

Conspicuous, systematic patterns of holes in soft sediment around wreck sites on the Great Barrier Reef mid-shelf are documented. Multibeam bathymetry data show concentric 'halos of holes' extending hundreds of meters around the wrecks. These halos at 5 wreck sites between 16 and 111 yr old consist of hundreds of tightly spaced depressions with diameters of up to 10 m. Seafloor imagery clearly indicates a biogenic origin of the holes. The halos of the 2 youngest wrecks (<25 yr) have fewer holes than older wrecks, suggesting a relationship between wreck age and excavation activity. Conversely, the size of a wreck does not appear to control the sediment turnover activity. Holes are comparatively long-lived, and some of them are actively maintained by bioturbation activity. The spatial distribution of holes is consistent with resource depletion by a central-place forager, albeit on yearly to decadal time scales. Tow-camera data show that some holes support diverse sessile faunal assemblages of sponges, soft corals, and hard corals in an otherwise flat seafloor devoid of sessile fauna. The (to date unknown) bioturbator(s) are thus allogenic habitat engineers. The systematic occurrence of halos around wrecks suggests that 'the ecosystem wreck' extends beyond the spatial confines of the hull of a wreck to the seafloor, by a distance 10-fold greater than the size of a wreck itself. This has implications for the evaluation of ecological effects of artificial reefs such as wrecks and offshore wind farms on decadal time scales.

A Comparison of Various Surface Finishes and the Effects on the Early Stages of Pore Formation during High Field Etching of SiC

The effects of initial surface morphology on the early stages of porous SiC formation under highly biased photoelectrochemical etching conditions are discussed. We etched both Si-face and C-face polished n-type 6H SiC with different surface finishes prepared either by mechanical polishing or by chemical mechanical polishing at NOVASiC. For both Si-face and C-face porous SiC samples, a variety of surface and cross sectional porous morphologies, due to different surface finishes, are observed. The proposed explanation is based on the spatial distribution of holes at the interface of the SiC and electrolyte inside the semiconductor.

Local structural distortions and Mn random distributions in (Ga,Mn)As: A first-principles study

The effect of random distribution of Mn atoms on the electronic and magnetic properties of ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ with $x=0.0625$ is studied with Vienna ab initio simulation package. We use a $2\ifmmode\times\else\texttimes\fi{}2\ifmmode\times\else\texttimes\fi{}2$ supercell, in which 64 atoms are included, and two Mn atoms substitute Ga positions. Five different Mn-Mn configurations are considered. Local structural relaxations show that the bond lengths of Mn-As are smaller than those of the nearby Ga-As. The total-energy calculation indicates that because of the inhomogeneous spatial distribution of holes, the ferromagnetic interaction between two Mn ions strongly depends on the direction along the two Mn ions. The inhomogeneous distribution of Mn atoms makes the holes stay in slightly stronger localized states. The value of magnetic moments and their spatial distributions are slightly affected by random distribution of Mn atoms.

Holes in finite electron systems with strong correlation

The ground-state properties of several finite two-dimensional clusters were numerically investigated within the Hubbard model. In particular the spatial distribution of holes (with respect to the half-filled band case) is studied in detail. It is found that in systems with frustrated sites the holes prefer to occupy these sites for large U, and repel each other. This effect can be used to stabilise the antiferromagnetic order in the clusters by introducing coupling to additional sites.

A Reappraisal of Certain Aspects of Transistor Theory

ABSTRACT In the usual analyses of transistor action various assumptions are frequently made; for example, that space charge neutrality exists in the base region, that pn junctions are depleted of mobile carriers, that minority carrier densities next to reverse biased junctions arc near zero, etc. It is shown that none of these assumptions is strictly valid. A now examination of the problem, in which those assumptions are put in better perspective, leads to: (a) a complete, partially numerical, analysis of abrupt pn junctions in equilibrium showing the spatial distribution of holes, electrons and field; (6) a qualitative discussion of these distributions when current is flowing; (c) a revised expression for the small signal capacitance of abrupt pn junctions; (d) a now space-charge-neutral solution for the complex current gain of transistors (this is compared with Shockley's solution). Finally a preliminary numerical solution of the carrier and field distribution in a collector junction, under conditions o...