Tunneling-assisted impact ionization fronts in semiconductors

We propose a novel type of ionization front in layered semiconductor structures. The propagation is due to the interplay of band-to-band tunneling and impact ionization. Our numerical simulations show that the front can be triggered when an extremely sharp voltage ramp ($\sim 10 {\rm kV/ns}$) is applied in reverse direction to a Si $p^+-n-n^+-$structure that is connected in series with an external load. The triggering occurs after a delay of 0.7 to 0.8 ns. The maximal electrical field at the front edge exceeds $10^6 {\rm V/cm}$. The front velocity $v_f$ is 40 times faster than the saturated drift velocity $v_s$. The front passes through the $n-$base with a thickness of $100 {\mu m}$ within approximately 30 ps, filling it with dense electron-hole plasma. This passage is accompanied by a voltage drop from 8 kV to dozens of volts. In this way a voltage pulse with a ramp up to $500 {\rm kV/ns}$ can be applied to the load. The possibility to form a kilovolt pulse with such a voltage rise rate sets new frontiers in pulse power electronics.Comment: 12 pages, 6 figure

Tektites: Origin as melts produced by the impact of small projectiles onto dry targets

The formation of tektites in general and layered tektites in particular seems to require a very special kind of cratering event. Evidence for the formation of pools of melt free of unmelted clasts has not been reported for the well-studied terrestrial craters such as Manicouagan or Ries. It is suggested that large amounts of relict-free melt were produced only when a sizeable fraction of the cratered target consisted of dry, high-porosity materials such as aeolian sediments. Since dry, high-porosity target materials are always confined to the outer 100 to 200 m of the Earth, the fraction of melt produced melt is probably higher in small (radius 50 to 500 m) craters than in large (r greater than 1 km) craters. Another reason to infer that the Southeast Asian tektites were produced in a multitude of small craters is the wide distribution of layered tektites. The file spans at least 1200 km, which would require ballistic ejection at velocities greater than 2 km s(-1) if all melt was generated in a single crater. It seems impossible to devise a scenario that would lead to the deposition of primary melt as a crystal-free pool at a distance of 600 km from the crater

Ordered layered organic-inorganic of 4-chlorophenoxyacetate-zinc layered hydroxide nanohybrid

Ordered layered organic‐inorganic nanostructure composed of zinc layered hydroxide‐4‐chlorophenoxy acetate (ZLH‐4CPA) was prepared by reaction of an organic anion, 4‐chlorophenoxy acetate (4CPA) with ZnO under aqueous environment. The concentration of 4CPA was found to be a controlling factor in determining the formation of phase pure, well ordered nanolayered hybrid material. At lower concentration of 4CPA (0.05 M), a mixed phase was observed in which ZnO co‐existed with the nanohybrid. At 0.01 M, a pure phase is obtained with high crystallinity but a well ordered nanolayered structure is lacking. A pure phase, well ordered nanolayered hybrid can be clearly observed at 0.2 M 4CPA. ZnO shows well defined grain structure of various sizes at nanometer scale range. Direct reaction between ZnO and 4CPA under aqueous environment resulted in the formation of 4CPA‐ZLH nanohybrid with flake‐like fibrous structure. On heating at 500° C for 5 h under atmospheric condition, the nanohybrid was transformed back to well defined grain structure, as previously observed for the starting materials, ZnO. This shows that the nanohybrid has “memory effect” property. Well ordered nanolayered hybrid with up to 5 harmonics, from which the average basal spacing of 19.03 Å of the material was deduced, showing long range order of the layer packing

Synthesis, Modification And Characterization Of Layered Hydroxides And Magnetite And Their Nanohybrids With D-Gluconate And Gallate Anions

Formation of organic-inorganic nanohybrid material of D-gluconate in the lamellae of zinc-aluminum-layered double hydroxide was accomplished by both spontaneous self-assembly (direct method) and ion-exchange methods. PXRD together with CHNS and FTIR analyses showed that the hybridization of D-gluconate with pure phase and good crystallinity was successfully accomplished using both direct and indirect methods. This work showed that a food additive, such as D-gluconate can be hybridized into an inorganic host for the formation of a new nanohybrid compound which can be used to regulate the release of acidity in the food industry. A new organo-mineral nanohybrid material, in which the organic moiety was hybridized into the inorganic interlamellae, was prepared using gallate anion (GA), an anti-carcinogenic, anti-mutagenic, and anti-microbial agent as a guest, and Zn-Al-layered double hydroxide, as an inorganic layered host using the ion-exchange technique. The release of the anion from the interlamellae of the nanohybrid was found to be of controlled manner, governed by the first order kinetic and it was also concentration-dependent. Zinc hydroxide nitrate, a brucite-like layered material, was synthesized using pH controlled method. Poly (vinyl alcohol) and poly (ethylene glycol) were used at various percentages as size decreasing agents during the synthesis of zinc layered hydroxide. SEM images, PXRD, TGA and surface area analyses showed the decrease of size and thickness of the resultant zinc layered hydroxides. When zinc layered hydroxides were heat-treated at 500 °C, the sizes of obtained nano zinc oxides were depended on the size of the parent material, zinc layered hydroxide nitrate. The memory effect of calcined zinc layered hydroxide nitrate, with gallate anion solutions, was studied. The brucite-like material, zinc layered hydroxide nitrate was heat-treated at 150-800 ºC. XRD analysis showed the growth of the calcined materials, nano sized zinc oxides in both thickness and diameter occurring simultaneously with increasing calcination temperature. The rehydration behavior of the calcined material was investigated by placing the material in a solution containing gallate anions. The best result for brucite-like phase reconstruction was obtained for a sample heated at 500 ºC and treated with 0.1 M anion. XRD analysis showed the formation of a layered structure material after rehydration process. Brucite-like materials, undoped and doped zinc layered hydroxide nitrate with (2 % molar in mother liquor) Fe3+, Co2+ and Ni2+ were synthesized. Their organic-inorganic nanohybrid materials with gallate anion as a guest, and the undoped and doped zinc hydroxide materials,as inorganic layered hosts, were prepared by the ion-exchange method. The nanohybrid materials were heat-treated at various temperatures, 400-700 ºC. XRD, TGA/DTG and FTIR results showed that incorporation of the doping agents within the zinc layered hydroxide has enhanced thermal stability of the nanohybrid materials in the thermal decomposition pathway. FESEM images have illustrated porous carbon materials obtained from the heating of the nanohybrids at 600 and 700 ºC after the acid washing process. Magnetite nanoparticles with narrow size distribution was prepared by using poly (vinyl pyrrolidone) as a stabilizing agent during the synthesis. Immobilization of gallate anion (GA), onto the surface of magnetite nanoparticles was accomplished by adsorption technique that was found to be efficient for the hybridization process in the formation of the core-shell nanohybrid. FTIR and CHNS results indicated that the GA was actually adsorbed onto the surface of the magnetite nanoparticles. Also, size analysis showed successive size increases of the particles after the adsorption process. The release of the anion from the surface of the nanohybrid was found to be controllable by the selection of the release media. This study showed that the formation of organic-inorganic nanohybrid materials of D-gluconate and gallate anions as organic guests and zinc-aluminum-layered double hydroxide, zinc layered hydroxide nitrate and also magnetite nanoparticles as hosts can be successfully accomplished

Lamella Structure of Zinc Aluminum Layered Double Hydroxide as Molecular Containers for the Preparation of Mesoporous Carbon

Open lamella systems such as layered double hydroxides (LDHs) can be used to generate new nanostructured materials of layered organic-inorganic nanohybrid type. The inorganic Zn-Al-layered double hydroxide (ZAL) was used as a matrix, hosting an active agent or a guest, toluene-4-sulphonate (TSA), 2,4-dichlorophenoxyacetic acids (24D), naphthaleneacetic acid (NAA) anthraquinone-2,6-disulphonate (AQDS) and dodecylsulfate sodium salt (SDS). They were prepared by spontaneous self-assembly method from an aqueous solution for the formation of a new layered organic-inorganic hybrid nanocomposite material. The Zn to Al ratio at R=4 and the various concentrations of anion organics at pH 10 was found suitable to give well-ordered nanolayered organic-inorganic hybrid structure. PXRD and FTIR analyses show that the inorganic-organic structure of LDH expanded from 8.8 Å to accommodate the anion organics for the formation of the nanocomposite. Nanocomposites were then calcined under N2 gas at different temperatures, 500 °C, 700 °C, and 1000 °C for the formation of the carbon products. In order to remove the carbonaceous products from the template matrix, the carbonized nanocomposite was treated with 2 M nitric acid. Powder X-ray diffraction pattern of the carbons showed that they are of amorphous type. The surface area and porosity studies show that the resulting materials are of mesoporous carbon with high BET surface area and high percentage of micropore content. No significant difference in the surface morphology of ZAL and its nanocomposites was observed under a scanning electron microscope. Both of them afforded non-uniform irregular agglomerates of compact and non-porous structure of plate-like morphology. The morphology of carbons showed agglomerates of compact and porous granular structure

Rateless Codes with Progressive Recovery for Layered Multimedia Delivery

This paper proposes a novel approach, based on unequal error protection, to enhance rateless codes with progressive recovery for layered multimedia delivery. With a parallel encoding structure, the proposed Progressive Rateless codes (PRC) assign unequal redundancy to each layer in accordance with their importance. Each output symbol contains information from all layers, and thus the stream layers can be recovered progressively at the expected received ratios of output symbols. Furthermore, the dependency between layers is naturally considered. The performance of the PRC is evaluated and compared with some related UEP approaches. Results show that our PRC approach provides better recovery performance with lower overhead both theoretically and numerically