Advanced Materials Research Vol. 981

Abstract: We present the design and characterization of a three-dimension metamaterial consisted of a Jerusalem cross unit cell on the each side of cube lattice substrate for terahertz frequencies. The retrieved effective medium parameters from scattering data prove that the three-dimension metamaterial has a negative permeability and permittivity in wide frequencies range of 1.47-1.73 THz. We demonstrate that the three-dimension can be regarded as a polarization insensitive absorber with an absorptivity of 46% at 1.49 THz. Such designed materials may find numerous applications ranging from the active element in a thermal detector to terahertz stealth technology.

Abstract: In this report, the micro structure of PI/ TiO₂ films with different components prepared by in-situ polymerization method is researched by XRD, TEM, synchrotron radiation SAXS. Its micro structure characteristics include nano-particles distribution, PI molecule chains spacing and interface layer thickness. The experimental result shows that after doping, particle radius is almost 10nm, and cluster of nano-particles became more serious with increase of components, however, the spacing of PI molecule chains decreases 5.238 Å-4.625 Å. The scattering curves occurs negative deflection in Debye theory, it shows that there are interface layers with thicknesses in the range 0.7nm-2.1nm between nano-particles and composite matrix. Through analyzing the three kinds of micro structure change, it shows that when the component is 15 wt.%, the micro-structure of composite film is the optimal.

Abstract: Through the theoretical deviation based on charge decay theory a trap level distribution function relative to the isothermal discharge current is given in this paper. Based on that, the effect of AlN(treated)-MMT nanoparticles with different contents of 1wt%, 3wt%, 5wt% on surface trap level distribution is researched. The experimental results show that the trap level density is significantly increased compared with traditional IDC and TSC methods. Trap level density and the number of trap charges increase due to the doping AlN (treated)-MMT nanoparticles, and increase with doping contents. The maximum trap energy level density of AlN(treated)-MMT film with 5wt% is 9.14×10²⁴/(eV·m³) , which is 3.3 times compared with the PI film corresponding to the trap level in the range of 1.0~1.1eV. The trap level density is affected by the interface trap effect caused by the AlN(treated)-MMT nanoparticles and different contents.

Abstract: In this paper, the code of Particle-In-Cell/Monte Carlo Collision (PIC/MCC) for oxygen microwave breakdown is developed. This code is based on the three dimensional particle-in-cell platform CHIPIC, and with a module for increasing the charge of each super-particle. With this PIC/MCC code, the multiplication rate of the electron density and the delay time in oxygen breakdown at atmospheric conditions are researched. The results show: the multiplication rate of the electron density is periodic, and its period is the half of the electric field period; the breakdown delay time in the gas breakdown increases while the frequency of electric field or the gas pressure increases.

Abstract: With the method of vacuum dc sputtering and vacuum evaporation,the green light double organic light-emitting devices (OLED) of ITO/CuPc/Alq3 / Al structure were prepared, the electrical characteristics and electroluminescent properties of the device were measured. Devices show good luminous performance, light intensity reaches 600000 cps, when the wavelength of luminescence spectrum is 510 nm, luminance is 2641I/a.u.

Abstract: Through solving an extended Fick’s diffusion equation for the solidification front of a paraboloid of revolution, a generalized Ivantsov function is obtained. The relaxation effect of nonequilibrium liquid diffusion is taken into account. The solute profile in the interfacial region and in the bulk liquid during steady-state dendritic solidification is uniquely determined. It is concluded that the consideration of the relaxation effect and the diffuse interface of finite thickness which decreases with increasing of velocities are necessary for achieving the good model predictions.

Abstract: Al-5Ti-1C master alloy refiner was prepared by melt reaction method, and its refining efficiency was examined by purity aluminum in the paper. The microstructures under different process conditions were studied by OM, SEM and XRD. The results shown that the grains were finer, TiAl₃ and TiC phases were uniformly distributed at 900¡æ, held time for 15min. The refining efficiency was best at addition of 0.4% (wt.%) refiner and held time for 10min.

Abstract: In order to take good advantage of polysilicon nanofilm, optimized technical characteristics of the polysilicon nanofilm are very necessary to investigated. In this paper, the polysilicon nanofilms were prepared under different technical parameters, including thickness and doping concentration, which are very important for preparation of the nanofilm. The experimental results of piezoresistive and temperature characteristics show that the optimized technical characteristics are followed, the thickness is about 90nm, and the doping concentration is about 4.1×10¹⁹cm^-3 or between 2.0×10²⁰cm^-3 and 4.1×10²⁰cm^-3 from different point of view. The investigations of optimized technical characteristics are very useful for application of the polysilicon nanofilm to piezoresistive sensor.

Abstract: The CdSe/ZnS core/shell quantum dots (QDs) were synthesized and characterized with absorption spectrometry, photoluminescence (PL) spectrometry and transmission electron microscopy. PL quenching of colloidal CdSe/ZnS QDs in the presence of charge transferring material was studied by means of steady-state and time-resolved PL spectroscopy. With increasing charge transferring materials concentration in the CdSe/ZnS QDs solution, the PL intensity and lifetime of CdSe/ZnS QDs decrease gradually. The quenching efficiency of CdSe/ZnS QDs decrease with increasing the oxidation potential of charge transferring materials. Based on the analysis, there are two pathways in the PL quenching process: static quenching and dynamic quenching. The dynamic quenching is correlated with hole transfer from QDs to the charge transferring materials.

Abstract: The effect of organic charge transferring material (CTM) on fluorescence of CdSe/ZnS and CdSe/CdS/ZnS core/shell quantum dots (QDs) are investigated by spectral methods. With the increase of organic molecular concentration, CTM can greatly quench the fluorescence of QDs and shorten the fluorescence lifetime of QDs. In the process of interacting with CTM, the efficiency of fluorescence quenching for CdSe/ZnS is significantly higher than that for CdSe/CdS/ZnS. The results of experiment show that the shell structure of QDs plays the major role in photoluminescence (PL) quenching. The mechanism of PL quenching of QDs is also analyzed.