Papers by Keyword: Charge Density

Abstract: In this work, some properties of the InAs/InGaAs quantum well (QW) were calculated, such as the wave functions and the charge density of the 2D free electron gas (2DEG) by solving the Poisson- Schroedinger equation. The thinner capping layer gives charge densities forming inside the QW that are higher than the thicker values. The optimal thickness of the capping layer can be 10 nm due to the most stable charge density and fully symmetrical wave functions. Our result indicates that higher charge densities can be found with higher Si-delta doping concentrations. However, the distance of the Si-delta doping also affects the charge population. The charge density linearly decreases with a higher Si-delta doping spacer; the thickness was chosen as 7nm. We performed the growth with different concentrations of Si with optimal thicknesses and compared them with the calculated values. There is good agreement between the simulations and experiments with the lower Si-doping concentrations.

Abstract: In the present study, we have computed the electronic band structure and electronic charge density of the alloy (Be, Cd)Se in the zinc-blende structure; using the local Empirical Pseudopotential Method (EPM), which takes into account the disorder effect into the Virtual Crystal Approximation (VCA) by introducing an effective potential disorder. The obtained results show a reasonable agreement with the available experimental data. Detailed plots of the valence charge distribution along the [111] direction and in the (110) plane are also presented and discussed.

Abstract: The electronic structures, densities of states and Fermi surfaces of ErX (X = Cu, Ag and Au) intermetallic compounds are studied using full potential linear augmented plane wave (FP-LAPW) method within generalized gradient approximation (GGA) for the exchange-correlation functional. The total energies are computed as a function of volume and fitted to the Birch equation of state. The ground state properties such as equilibrium lattice constants (a₀), bulk modulus (B) and pressure derivative of bulk modulus (B') and density of states at the Fermi level N (E_F) are calculated. The states at the Fermi level (E_F) are dominated by Er ‘d’ states with significant contribution of ‘p’ and ‘d’ states of X. We have also plotted charge density and Fermi surface to study the bonding properties of ErX compounds.

Abstract: The centre Au-doped armchair graphene nanoribbons (AGNRs) are investigated using the local density approximation based on density function theory. The charge density, electronic energy band and project density of states of centre Au-doped AGNRs are calculated. Our results indicate the charge density is transferred between C and Au atoms and mainly located on the Au atoms. The centre Au-doped AGNRs are an indirect band gap semiconductor with an energy gap of 1.046 eV. The Fermi level is located on valence band so that the AGNRs of doping Au become into degenerate semiconductor. The project density of states is calculated to reveal localization and hybridization between C-2p and Au-6s, 5d electronic states. The localization and hybridization are much stronger in the valence band. The hybridization between C-2p and Au-6p electronic states are strongly in the conduction band.

Abstract: For passive RDX, fluent software was applied to simulate the cook-off for explosive of different charge density at heating rates of 1, 5, 10k/min to improve thermal safety in the ammunition storage, transport and battle. The results show that the heating rate has great effect on ignition time and position for passive RDX. Charge density also has great influence on ignition time but no influence on ignition position. The ignition time decreases and ignition position moves from the center to the two ends of the cylinder edge with the increase of the heating rate. The ignition time increases with the increase of charge density under the same condition. Therefore, increasing the charge density can effectively improve the thermal safety of ammunition.

Abstract: Based on a one-dimensional model of dielectric charging for capacitive RF MEMS switches, the accumulated charge density and actuation voltage shift were simulated. The results illustrate that rougher surface can reduce dielectric charging, so the dielectric layer should be fabricated much rougher during deposition process. But the capacitance ratio of switch will be decreased with rougher surface, which can cause a reduction of switch performance. Thus the dielectric surface roughness should be balanced in reliability and isolation.

Abstract: The reaction of the xylan-type hemicellulose with 2,3-epoxypropyltrimethylammonium chloride and acrylamide in ethanol-water-alkali slurry yielded water-soluble, cationic etherified xylan-type hemicellulose derivatives. The degree of substitution (DS) value reaches up to 0.40 by adjusting the mass ratios (NaOH/hemicellulose, total etherifying agents/hemicellulose and 2,3-epoxypropyltrimethylammonium chloride/acrylamide), the reaction temperature and the reaction time in a one-step synthesis. The etherified hemicellulose was characterized by infrared spectroscopic analysis (FT-IR), Zeta potential analysis, charge density analysis and thermogravimetric analysis (TGA). It is found that Zeta potential is promoted from-30.50mv to +35.81mv and charge density is promoted from-0.50mmol/g to +0.88mmol/g during etherification under the conditions used. The thermal stability of the etherified hemicellulose is lower than that of the unmodified xylan-type hemicellulose polymers.

Abstract: Perforating parameters, such as charge density, charge quantity and shooting density, are the important factors that affect the strength security of perforation string. Finding out the relationship between this two and understanding the regularity has the guiding significance to avoid the perforating accidents. Based on the research about the strength security of perforation string at the moment of perforating, taking a perforated completion gas well as an example, by changing the perforating parameters and conducting the contrastive analysis and research, then gets the regularity understanding about the influence of the perforating parameters on the strength security of perforation string:When the charge density is more than 1.9g/m3, the amplification of peak pressure will slow down ,and the influence of charge density will decrease; When the charge quantity is more than 40 gram, the amplification of the peak pressure on the packer and the peak stress of tubing will slow down ,and the influence of charge quantity will decrease; When the shooting density is more than 20 hole/m, the amplification of peak will slow down, and the influence of shooting density will decrease.

Abstract: A series of dodecyl sulfate (DS-) intercalated Zn/Fe layered double hydroxides (DS-Zn/Fe-LDHs) were prepared by co-precipitation method from the electroplating wastewater containing high concentration of zinc (Zn2+). In addition, the influences of their charge density on the interlayer structure of LDHs were investigated by XRD and FT-IR. The removal rate of Zn2+ in the electroplating wastewater was reached 99.9%. The charge density decreased with the increasing of the ratio of Zn/Fe. The results showed that with the increase of the charge density, the interlamellar spacing of organic-LDH increased. The synthesis product was applied in the sorption of organic contaminant ( nitrobenzene ) and the sorption mechanism was partition. The synthetic DS-Zn/Fe LDHs were good sorbents for organic contaminant.

Abstract: An effort has been made to understand the charge density distribution of the Si and Ge based diluted magnetic semiconductors. A theoretical analysis has been done on the variation of charge densities when the semiconductors Si and Ge are doped with the transition metal atoms of V, Mn and Co with different concentrations of x (0.02, 0.04, 0.06, 0.08, and 0.10), in Si_1-xM_x and Ge_1-xM_x. Two dimensional electron density contour maps have been plotted for all the compositions studied in this work. The theoretical mid bond densities were found out for the compounds which can be taken as the reference values for comparison of the experimental values of the same compositions.