We demonstrate GaInN multiple quantum well (MQW) light-emitting diodes (LEDs) having ternary GaInN quantum barriers (QBs) instead of conventional binary GaN QBs for a reduced polarization mismatch between QWs and QBs ...
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Plasma at atmospheric pressure is very power tool for modification of tapioca starch as it leaves no additional chemical agent into the modified starch. Atmospheric plasma consists of energetic particles such as ions,...
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Plasma at atmospheric pressure is very power tool for modification of tapioca starch as it leaves no additional chemical agent into the modified starch. Atmospheric plasma consists of energetic particles such as ions, electrons, excited atom as well as electromagnetic radiation such as ultraviolet and visible light. In this study, tapioca starch samples were prepared as tablet of 16 mm in diameter and about 1 mm in thickness and were then stored in desiccators under two different relative humidity environments (RH), 10% and 78%, by storing in lithium iodide and sodium chloride salt saturated atmosphere respectively. These samples were brought to be treated by glow-discharge argon plasma at atmospheric temperature of plasma power 40 watt for 30 minutes. Starch samples were then characterized by X-ray diffractometry (XRD) and differential scanning calorimetry (DSC). It was found that the structure of starch is A-type and the crystallinity of starch is decreasing after plasma treatment. It is believed that an amorphous region is increasing from water molecules in the granules, which is a consequence of cross linking on starch. Also, the gelatinization and enthalpy is increasing after plasma treatment. It is believed that cross linking can stabilized the molecular structure of the starch granules causing gelatinization to occur at relatively high temperature. Other characterization methods for example FTIR, SEM, contact angle were applied in addition to XRD and DSC for comparison between before and after plasma treatment. Treatments with RF plasma at low pressure or with UV+Ozone were also carried out for comparison. If applicable, polyethylene and polypropylene were studied to compare effect of plasma treatment.
We theoretically studied how the electric field effect can modify thermoelectric properties of intrinsic, n-type and p-type bismuth telluride nanowires with the growth direction [110]. The electronic structure and the...
We theoretically studied how the electric field effect can modify thermoelectric properties of intrinsic, n-type and p-type bismuth telluride nanowires with the growth direction [110]. The electronic structure and the wave functions were calculated by solving self-consistently the system of the Schrödinger and Poisson equations using the spectral method. The Poisson equation was solved in terms of the Newton-Raphson method using the predictor-corrector approach. The electron-electron exchange-correlation interaction was taken into account in our analysis. In the temperature range from 77 to 500 K, the dependences of the Seebeck coefficient, thermal conductivity, electron (hole) concentration, and thermoelectric figure of merit on the nanowire thickness, gate voltage, and excess hole (electron) concentration were investigated in the constant relaxation-time approximation. The results of our calculations indicate that the external perpendicular electric field can increase the Seebeck coefficient of the bismuth telluride nanowires with thicknesses of 7–15 nm by nearly a factor of 2 and enhance ZT by an order of magnitude. At room temperature, ZT can reach a value as high as 3.4 under the action of the external perpendicular electric field for realistic widths of the nanowires. The obtained results may open up a way for a drastic enhancement of the thermoelectric figure of merit in a wide temperature range.
This paper describes the influence of ballast resistor and field screening on the electron field emission behavior of nano-diamond emitter arrays fabricated on micropatterned silicon pillars. Arrays of 50 × 50 si...
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This paper describes the influence of ballast resistor and field screening on the electron field emission behavior of nano-diamond emitter arrays fabricated on micropatterned silicon pillars. Arrays of 50 × 50 silicon pillars with different ballast resistances, pillar separations, capped with nano-diamond, have been fabricated on different silicon substrates as cathode for field emission testing. The goal of this study is to evaluate the fabrication method and electron emission characteristics in this configuration for field emission applications. The electron field emission results have been compared to observe the effect of the ballast resistive behavior and array spacing of micropatterned silicon pillars on the nano-diamond field emission behaviors.
Microwave, x-ray, and radio-frequency radiation sources require a cathode emitting electrons into vacuum. Thermionic B-type dispenser cathodes consist of BaxOz coatings on tungsten (W), where the surface coatings lowe...
Microwave, x-ray, and radio-frequency radiation sources require a cathode emitting electrons into vacuum. Thermionic B-type dispenser cathodes consist of BaxOz coatings on tungsten (W), where the surface coatings lower the W work function and enhance electron emission. The new and promising class of scandate cathodes modifies the B-type surface through inclusion of Sc, and their superior emissive properties are also believed to stem from the formation of a low work function surface alloy. In order to better understand these cathode systems, density-functional theory (DFT)-based ab initio modeling is used to explore the stability and work function of BaxScyOz on W(001) monolayer-type surface structures. It is demonstrated how surface depolarization effects can be calculated easily using ab initio calculations and fitted to an analytic depolarization equation. This approach enables the rapid extraction of the complete depolarization curve (work function versus coverage relation) from relatively few DFT calculations, useful for understanding and characterizing the emitting properties of novel cathode materials. It is generally believed that the B-type cathode has some concentration of Ba-O dimers on the W surface, although their structure is not known. Calculations suggest that tilted Ba-O dimers are the stable dimer surface configuration and can explain the observed work function reduction corresponding to various dimer coverages. Tilted Ba-O dimers represent a new surface coating structure not previously proposed for the activated B-type cathode. The thermodynamically stable phase of Ba and O on the W surface was identified to be the Ba0.25O configuration, possessing a significantly lower Φ value than any of the Ba-O dimer configurations investigated. The identification of a more stable Ba0.25O phase implies that if Ba-O dimers cover the surface of emitting B-type cathodes, then a nonequilibrium steady state must dominate the emitting surface. The identification of a
Photonic crystal cavities with tunable surface area via multiple-hole defects were investigated for increased resonance wavelength shifts upon exposure to variable-index analytes. Sensitivity was improved by 10% compa...
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Photonic crystal cavities with tunable surface area via multiple-hole defects were investigated for increased resonance wavelength shins upon exposure to variable-index analytes. Sensitivity was improved by 10% compar...
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We have formulated the problem of generating dense packings of nonoverlapping, nontiling nonspherical particles within an adaptive fundamental cell subject to periodic boundary conditions as an optimization problem ca...
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We have formulated the problem of generating dense packings of nonoverlapping, nontiling nonspherical particles within an adaptive fundamental cell subject to periodic boundary conditions as an optimization problem called the adaptive-shrinking cell (ASC) formulation [S. Torquato and Y. Jiao, Phys. Rev. E 80, 041104 (2009)]. Because the objective function and impenetrability constraints can be exactly linearized for sphere packings with a size distribution in d-dimensional Euclidean space Rd, it is most suitable and natural to solve the corresponding ASC optimization problem using sequential-linear-programming (SLP) techniques. We implement an SLP solution to produce robustly a wide spectrum of jammed sphere packings in Rd for d=2, 3, 4, 5, and 6 with a diversity of disorder and densities up to the respective maximal densities. A novel feature of this deterministic algorithm is that it can produce a broad range of inherent structures (locally maximally dense and mechanically stable packings), besides the usual disordered ones (such as the maximally random jammed state), with very small computational cost compared to that of the best known packing algorithms by tuning the radius of the influence sphere. For example, in three dimensions, we show that it can produce with high probability a variety of strictly jammed packings with a packing density anywhere in the wide range [0.6, 0.7408…], where π/18=0.7408… corresponds to the density of the densest packing. We also apply the algorithm to generate various disordered packings as well as the maximally dense packings for d=2, 4, 5, and 6. Our jammed sphere packings are characterized and compared to the corresponding packings generated by the well-known Lubachevsky-Stillinger (LS) molecular-dynamics packing algorithm. Compared to the LS procedure, our SLP protocol is able to ensure that the final packings are truly jammed, produces disordered jammed packings with anomalously low densities, and is appreciably more robust an
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