THEORY OF LC BIOMEMBRANE——A PROBE INTO SOFT CONDENSED MATTER PHYSICS

Soft condensed-state physics is a disciplinary frontier of 20th-century physics. An interdiscipline in nature, it involves biology, chemistry and even pure mathematics. Taking the liquid crystal (LC) biomembrane as an example, this article expounds the current development trend of this new and promising branch of contemporary physics.

Effects of substrate temperature and annealing on the anisotropic magnetoresistive property of NiFe films

Ni_(83)Fe_(17) films with a thickness of about 100 nm were deposited onthermal oxidized silicon substrates at ambient temperature, 240, 350, and 410℃ by DC magnetronsputtering. The deposition rate was about 0.11 nm/s. The as-deposited films were annealed at 450,550, and 650℃, respectively, in a vacuum lower than 3 x 10~3 Pa for 1 h. The Ni_(83)Fe_(17) filmsmainly grow with a crystalline orientation of [111] in the direction of the film growth. With theannealing temperature increasing, the [111] orientation enhances. For films deposited at all fourdifferent temperatures, the significant improvement on anisotropic magnetoresistance occurs at theannealing temperature higher than 550℃. But for films deposited at ambient temperatures and 240 ℃,the anisotropic magnetoresistance can only rise to about 1% after 650 ℃ annealing. For filmsdeposited at 350℃ and 410℃, the anisotropic magnetoresistance rises to about 3.8% after 650℃annealing. The atomic force microscopy (AFM) observation shows a significant increase in grain sizeof the film deposited at 350℃ after 650℃ annealing. The decrease in resistivity and the increasein anisotropic magnetoresistance are caused by the decrease in point defects, the increase in grainsize, and the improvement in lattice structure integrity of the films.

Roles of Te and Mn in the two phases of manganite with nominal composition La_(0.6)Sr_(0.1)Te_xMnO_3

Powder samples with nominal composition La0.6Sr0.1TexMnO3 （x = 0.00, 0.05, 0.10, 0.15, 0.20） were prepared using the sol-gel method with thermal treatment up to 1473 K. On the basis of powder X-ray diffraction （XRD）, thermogravimetric and magnetic measurements, it was found that almost all of the Te and a few of the Mn ions were lost from the samples when they were calcined at 1473 K. The reason for the Te loss and a quantitative phase analysis for the samples calcined at 1473 K are discussed in detail.

Research on charge ordering and magnetic properties in La_(0.3)Ca_(0.7)Mn_(1-x)W_xO_3 system

The perovskite manganite sample La0.3Ca0.7Mn1-xWxO3 （x = 0.08, 0.12） was prepared by the solid-state reaction method. The effect of W doping on the Mn site to La0.3Ca0.7MnO3 charge ordering phase and the changing process of magnetic properties were studied through the measurement of the M-T curve, M-H curves, and ESR curves of the sample. The results showed that when x = 0.08, the charge ordering （CO） phase exists in the system, the transition temperature Tco= 275 K, and the system exhibits PM when T 〉 275 K. The system transforms from spin-disordering paramagnetism to spin-ordering antiferromagnetism in the charge ordering state with the temperature decreasing from 275 K to 230 K. The long-range antiferromagnetism forms and AFM/CO states coexist between 230 K and 5 K. There is a little ferromagnetic component in the AFM/CO background in a low temperature range. When x = 0.12, the CO phase in the system has almost melted completely. There is a little remnant of the CO phase below 150 K. The system exhibits paramagnetism when T 〉 150 K and transforms from paramagnetism to ferromagnetism when T〈 150 K.

Fabrication of ZnO-based thick film varistors with high potential gradient

ZnO-based thick film varistors have been fabricated by Y203 doping and low-temperature sintering, of which the sample with the best electrical properties has a high potential gradient value of 3159.4 V/mm. The effects of Y2O3 doping concentration and sintering temperature on the potential gradient of the samples were systematically investigated. The results show that the sample with the best electrical properties can be obtained by doping 0.08 mol% Y2O3 and sintering at 725℃. Under these optimum preparation conditions, the leakage current and the nonlinear coefficient are found to be 36.4 gA and 13.1. The sample with the best electrical properties has a grain size of 1.290um, a single grain boundary voltage of 4.08 V, a barrier height of 0.81 eV, and a depletion layer width of 10.2 nm, which are determined by thermionic emission. Small grain size with good grain boundary characteristics is beneficial to improve the electrical properties of varistors and promote the potential gradient.

Thermal expansion anomaly and spontaneous magnetostriction of Tb_2Fe_(15)Cr_2 compound

The structural and magnetic properties of Tb2Fe15CF2 compound were investigated by means of X-ray diffraction and magnetization measurements. Tb2Fe15Cr2 compound has a hexagonal Th2Ni17-type structure. Negative thermal expansion was found in Tb2Fe15Cr2 compound from 372 to 452 K by X-ray dilatometry. The coefficient of the average thermal expansion is α^- =-3.14×10^-5 K^-1. The magnetostrictive deformations from 292 to 450 K were calculated. The result showed that the spontaneous volume magnetostrictive deformation ms remains nearly constant with increasing temperature up to 360 K, but decreases with the further increase of temperature. The spontaneous linear magnetostrictive deformation λc along the c axis decreases with increasing temperature. The spontaneous linear magnetostrictive deformation, λa, in the basal-plane increases with increasing temperature up to 360 K, but decreases with further increasing temperature.

Spontaneous volume magnetostriction of Dy_2AlFe_(12)Mn_4 compound

The structure and magnetic properties of Dy2AlFe12Mn4 compound have been investigated by means of X-ray diffraction and magnetization measurements. The Dy2AlFe12Mn4 compound has a hexagonal Th2Ni17-type structure. Negative thermal expansion was found in Dy2AlFe12Mn4 compound from 229 to 280 K by X-ray dilatometry. The coefficient of the average thermal expansion is α^- =-3.8×10^-5 K^-1. The magnetostrictive deformations from 105 to 270 K have been calculated by means of the differences between the experimental values of the lattice parameters and the corresponding values extrapolated from the paramagnetic range. The result shows that the spontaneous volume magnetostrictive deformation ωs decreases from 6.2 × 10^-3 to near zero with the temperature increasing from 105 to 270 K, the spontaneous linear magnetostrictive deformation λc along the c axis is much larger than the spontaneous linear magnetostrictive deformation λa in basal-plane at the same temperature except close to 249 K.

Magnetic and electric characteristics and abnormality of low-temperature resistivity in La_(0.67–x)Er_xSr_(0.33)MnO_3(0.00≤x≤0.20) system

M-T curves, ρ-T curves, and MR-T curves of La0.67-xErxSr0.33MnO3(x=0.00, 0.10, 0.20) system were studied by experiments. The experiments showed that: with increasing the doping amount, the magnetic structure of the system transformed from long-range ferromagnetic ordering to spin-cluster glass state, and M-T curves bent up in the extremely low temperature range; the resistivity of the system increased with increasing doping amount and exhibited the minimum phenomenon of low-temperature resistivity. The variation of the magnetic and electric properties came from the extra magnetic coupling induced by the doping and from the Kondo effect induced by the lattice distortion and local magnetic moments which was similar to that induced by the scattering of magnetic impurities on electron spins. © 2009 The Chinese Society of Rare Earths.

Site Selective Excitation and Energy Transfer in LiKGdF_5 Crystal Co-doped with Er^(3+) and Tb (3+)

Crystals of LiKGdF 5∶Er 3+, Tb 3+ grown by the hydrothermal synthesis technique with concentrations of 2% and 0.4% were analysed. By using site selective excitation measured at low temperature, luminescence and excitation spectra from Er 3+ and Tb 3+ ions embedded in LiKGdF 5 were clearly separated. The lifetimes of the emitting levels 4S 3/2 of Er 3+ and 5D 4 of Tb 3+ were also determined. Following the site selective spectroscopy study, the dominant energy transfer process from Tb 3+ to Er 3+ in the crystal was then investigated via transient experiments.

Giant Low-Field Magnetoresistance in Polycrystalline La_(2/3)Ca_(1/3)Mn_(1-x)Cu_x O_3 Sintered at 1100 ℃

The La_(2/3)Ca_(1/3)Mn_(1- x )Cu_ x O_3 (0≤ x <6%) samples were prepared by sol-gel method. Transport properties, conductive mechanism and low-field magnetoresistance ( MR _0) were investigated. It is found that conductive mechanism is described by Mott′s variable-range hopping and the MR _0 near the insulator-metal transition temperature ( T _p) increases from 2% to 80% with x from 0 to 4% for a low field of 0.3 T. The experiment also shows that the intergrain magnetoresistance is largely improved. The results indicate that a proper amount of Cu doping can substantially improve magnetoresistance effects.

New Discrete Element Models for Three-Dimensional Impact Problems

Two 3-D numerical models of the discrete element method （DEM） for impact problems are proposed. The models can calculate not only the impact problems of continuum and non-continuum, but also the transient process from continuum to non-continuum. The stress wave propagation in a concrete block and a dynamic splitting process of a marble disc under impact loading are numerically simulated with the proposed models. By comparing the numerical results with the corresponding results obtained by the finite element method （FEM） and the experiments, it is proved that the models are reliable for three-dimensional impact problems.

Simulation of Light Intensification Induced by Defects of Polished Fused Silica

Light intensity distribution in the vicinity of inclusions and etched cracks in polished fused silica at wavelength scale are simulated by using the finite-difference time-domain algorithm. Light intensity enhancement factor as functions of diameter and refractive index of inclusions are investigated, more than 10 times that of incident beam is obtained in the simulation. We model the etched crack in close proximity to a real structure, which is characterized by AFM. We find that the peak light intensity of the crack is a function of its cross sectional breadth depth ratio, providing good hints for the effective processing of fused silica samples to improve the damage threshold.

Long-Lasting Phosphorescence Properties of Pyrochlore La2Ti2O7：Pr^3＋ Phosphor

The La2Ti2O7：Pr^3＋, which emits red color luminescence upon UV light excitation, is prepared by the conventional high-temperature solid-state method and its luminescent properties are systematically investigated. X-ray diffraction, photoluminescence, afterglow emission spectra and long-lasting phosphorescence （LLP） decay curves are used to characterize this phosphor. After irradiation by a 290-nm UV light for 3 rain, the Pr^3＋-doped La2Ti2O7 phosphor emits intense red emitting afterglow from the ^1D2 →^ 3H4 transitions, and its afterglow can be seen with the naked eye in the dark clearly for more than 1 h after removal of the excitation source. The afterglow decay curve of the Pr^3＋-doped La2Ti2O7 phosphor contains a fast decay component and another slow decay one. The possible mechanism of this red light emitting LLP phosphor is also discussed based on the experimental results.

Coupled THz Waveguide Utilizing Surface Plasmon Polaritons on Thin Dielectric Slab Sandwiched between Two Corrugated Metallic Claddings

We present a comprehensive experimental study of terahertz （THz） wave propagation utilizing surface plasmon polaritons （SPPs） on the interfaces of a thin dielectric core layer sandwiched between two corrugated metallic claddings. THz wave impinges on the structured surfaces at normal incidence. Long-lasting oscillation propagation features are observed in the temporal waveform after traveling through the periodic arrays. The enhanced THz transmission can be achieved due to the coupling between incident waves to SPPs at the bottom and top interfaces. The finite element method is used to simulate the field distribution and the transmission mode in the waveguide. The hybrid waveguide with low absorption has great potential applications in THz integrated devices.

CuInSe2 Films Prepared by a Plasma-Assisted Selenization Process in Different Working Pressures

The effects of working pressure on the composition, structure and surface morphology properties of CuInSe2 （CIS） films selenized with a plasma-assisted selenization process is investigated. Higher selenium content, better crystalline quality and much more regular surface particles compared to the others are found in the CIS film with 40 Pa working pressure. A Cu（In,Ga）Se2 device fabricated with the optimized plasma-assisted selenization process is demonstrated to be better than our previous result. After discussion, the reason for these phenomena is attributed to the compromise of electron temperature and plasma density.

Numerical Study on Light Localization in Impedance-Matched Meta-Material Random Systems

We investigate the localization properties of light propagating in two-dimensional systems with impedance-matched meta-material scatterers which are randomly positioned. Numerically, the localization length ξ versus the index of meta-material is obtained first. We find that, unlike traditional random systems, the localization length of such meta-material random systems does not depend on the total scattering cross section of scatterers, but on the back-scattering cross-section of scatterers. Furthermore, our analysis shows that there are “back-scattering paths of single scattere” in such meta-material systems, which can cause a strong localization effect. Such back-scattering paths inside single scatterers can be thought of as the supplement to the traditional back-scattering paths of multiple scatterers.

Molecular Dynamics Simulations of Thermal Properties of Solid Uranium Dioxide

Molecular dynamics simulations are performed with the recently developed empirical interaction potential by Morelon et al. Thermodynamics properties of solid UO2 that have been assessed include melt point, density, enthalpy, heat capacity, lattice parameter variation with temperature, mean-square-displacement and diffusion coefficients of oxygen ion. The results are compared with the data in literature and it is suggested that the rigid ionic potential provides perfect results below the superionic range. The data showing thermodynamics properties will become unacceptable when the temperature is higher than 2500 K. Compared with the previous empirical potentials, the empirical potential developed by Morelon et al. improves the agreement of these data with the recommend ones.

Interaction between B-Doped C60 Fullerene and Glycine Amino Acid from First-Principles Simulation

The possibility of formation of complexes between glycine and boron doped C60 （C59B） fullerene is investigated and compared with that of C60 fullerene by using the density functional theory calculations. It has been found that the binding of glycine to C59B generated the most stable complexes via its carbonyl oxygen active site, with a binding energy of-37.89 kcal/mol, while the glycine molecule prefers to bind to the pure C60 cage via its amino nitrogen active site, consistent with the recent experimental and theoretical studies. We have also tested the stability of the most stable Gly-C59B complex with ab initio molecular dynamics simulation, carried out at room temperature. These indicate that the B-doped C60 fullerenes seem to be more suitable materials for bindings to proteins than pure C60 fullerenes.

Effect of Poly（Ether Urethane） Introduction on the Performance of Polymer Electrolyte for All-Solid-State Dye-Sensitized Solar Cells

The introduction of poly（ether urethane） （PEUR） into polymer electrolyte based on poly（ethylene oxide）, LiI and I2, has significantly increased the ionic conductivity by nearly two orders of magnitudes. An increment of I3- diffusion coefficient is also observed. All-solid-state dye-sensitized solar cells are constructed using the polymer electrolytes. It was found that PEUR incorporation has a beneficial effect on the enhancement of open circuit voltage VOC by shifting the band edge of TiO2 to a negative value. Scanningelectron microscope images indicate the perfect interfacial contact between the TiO2 electrode and the blend electrolyte.

Derivative of Electron Density in Non-Equilibrium Green＇s Function Technique and Its Application to Boost Performance of Convergence

The non-equilibrium Green＇s function （NEGF） technique provides a solid foundation for the development of quantum mechanical simulators. However, the convergence is always of great concern. We present a general analytical formalism to acquire the accurate derivative of electron density with respect to electrical potential in the framework of NEGF. This formalism not only provides physical insight on non-local quantum phenomena in device simulation, but also can be used to set up a new scheme in solving the Poisson equation to boost the performance of convergence when the NEGF and Poisson equations are solved self-consistently. This method is illustrated by a simple one-dimensional example of an N＋＋ N＋ N＋＋ resistor. The total simulation time and iteration number are largely reduced.