Fabrication of polyaniline/ heterojunction structure using plasma enhanced polymerization technique

The work reports on the fabrication of a p–n heterojunction structure comprised of polyaniline (PANI) and TiO₂ nanoparticles. PANI was deposited by plasma enhanced polymerization on TiO₂ thin film substrates. The structural and the crystalline properties demonstrated the coherence and the substantive interaction of the plasma polymerized PANI molecules with the TiO₂ nanoparticle thin film. The UV–Vis studies of PANI/TiO₂ thin film supported the internalization of PANI with TiO₂ nanoparticles due to π–π^* transition of the phenyl rings with the lone pair electrons () of the nitrogen atom present in the PANI molecules. The I–V characteristics of the PANI/TiO₂ heterojunction structure were obtained in the forward and the reverse biased at applied voltage ranging from −1 V to +1 V with a scan rate of 2 mV/s. The proficient current in the PANI/TiO₂ heterojunction structure was attributed to the well penetration of PANI molecules into the pores of the TiO₂ nanoparticle thin film. The I–V characteristics ensured an efficient charge movement at the junction of PANI/TiO₂ interface and thus, behaved as a typical ohmic system.     

The effect on the annealing temperature of Li doped ZnO thin film for a film bulk acoustic resonator

We investigated the material and electrical properties of Li doped ZnO thin film (ZLO) with variation of the annealing temperature. In the 500 C sample, ZLO film showed well defined (002) c-axis orientation and a full width half-maximum property of 0.25. The electrical properties of ZLO thin films showed the excellent specific resistance of 1.5×10¹¹ Ω cm. Finally, the frequency characteristics of the ZLO thin film FBAR, according to the annealing temperature, showed improvement of the return loss from 24.48 to 30.02 dB at a resonant frequency of 1.17 GHz.     

Interrelation between electronic structure and interatomic distances for compounds

The heat capacity was studied for LaMn₂Si₂, La_0.75Y_0.25Mn₂Si₂, La_0.7Y_0.3Mn₂Si₂, YMn₂Si₂ and LaFe₂Si₂ isostructural intermetallic compounds in the temperature range 1.8–360 K. The electronic, magnetic and lattice contributions to the heat capacity of the compounds were determined and analyzed. The interrelation was found between values of the electronic contribution to the heat capacity (density of states at the Fermi level) and crystal lattice parameters of R(Mn,Fe,Ni)₂Si₂ compounds. The electronic contribution and the density of states at Fermi level increase with increasing lattice parameters of the compounds. The change of interlayer Mn–Mn exchange interactions with change of Y concentration in La_1-xY_xMn₂Si₂ compounds is not accompanied by considerable changes in the electronic contribution to the heat capacity and density of states at the Fermi level. The performed analysis of the magnetic contribution shows that no essential differences exist between the behavior of the heat capacity of the compounds with d_Mn–Mnd_c and with d_Mn–Mn<d_c upon various types of the magnetic phase transitions.     

Transport properties of single crystal

Transport properties of BaNi₂P₂ single crystals prepared by high-pressure synthesis method have been investigated. The temperature dependence of the resistivity is that of a typical metal with the anisotropy ratio ρ/ρ of 6.3 and suggests that electron–phonon interaction dominates the scattering mechanism. We have also found that the Hall effect and the magnetoresistance can be explained by a two-carrier model which is consistent with a multiple-band structure with both hole and electron characters.     

Structural and optical properties of thermally evaporated thin films

Chalcogenide glass Se₅₅Ge₃₀As₁₅ have amorphous structure in both as-deposited and annealed conditions. The optical properties of the as-deposited and annealed films were studied using spectrophotometric measurements of transmittance, T(λ), and reflectance, R(λ), at normal incidence of light in the wavelength range 200–2500 nm. Neither annealing temperature nor film thickness can influence spectral response on refractive index and absorption index of films. The type of electronic transition responsible for optical properties is indirectly allowed transition with energy gap of 1.94 eV and phonon energy of 40 meV. The dispersion of the refractive index is discussed in terms of the single oscillator Wemple–Didomenico (WD) model. The width of band tails of localized states into the gap (ΔE), the single oscillator energy (E_o), the dispersion energy (E_d), the optical dielectric constant (ε_∞), the lattice dielectric constant (ε_L), the plasma frequency (ω_p) and the free charge carrier concentration (N) were estimated.     

Phase transitions in the quantum Hall liquid in a quantum wire

Two scenarios for the collapse of the ν=1 quantum Hall liquid (QHL) state, with the effective quantum wire (QW) width defined by the Fermi vector k_F, are studied. Here, ν for the QW is defined as the filling factor of Landau levels (LL) at the center of the QW. In the first one there is no electron redistribution at critical magnetic field , where the Fermi energy, E_F, coincides with the bottom of the empty upper spin-split LL. For the ν=1 state is unstable due to exchange-correlation effects and lateral confinement. In the second scenario, a transition to the ν=2 state occurs, with much smaller width, at . The latter scenario is analyzed in the Hartree–Fock approximation (HFA). Here the Hartree contribution to the total energy affects drastically due to strong electron redistribution in the QW. In both scenarios, the exchange-enhanced g-factor is suppressed at B_cr. The critical fields, activation energy, and optical g-factor obtained in the first scenario are very close to the measured ones.     

Cold nuclear matter effects on production: Intrinsic and extrinsic transverse momentum effects

Cold nuclear matter effects on J/ψ production in proton–nucleus and nucleus–nucleus collisions are evaluated taking into account the specific J/ψ-production kinematics at the partonic level, the shadowing of the initial parton distributions and the absorption in the nuclear matter. We consider two different parton processes for the -pair production: one with collinear gluons and a recoiling gluon in the final state and the other with initial gluons carrying intrinsic transverse momentum. Our results are compared to RHIC observables. The smaller values of the nuclear modification factor R_AA in the forward rapidity region (with respect to the mid rapidity region) are partially explained, therefore potentially reducing the need for recombination effects.     

Dramatic change of optical properties at a quantum critical point in the heavy fermion system

Optical properties of have been studied via infrared spectroscopy. For x>0.3, a hump in the optical conductivity σ₁ is observed at about 0.2 eV, resulting from strong hybridization between conduction electrons and Ce 4-f electronic states. For x0.3, in contrast, no such hump is observed. The low frequency plasmon indicating the existence of heavy particles is also observed below coherence temperature T^* for x>0.3.     

Quantum transport in a mesoscopic ring: Evidence of an OR gate

We explore the OR gate response in a mesoscopic ring threaded by a magnetic flux . The ring is symmetrically attached to two semi-infinite one-dimensional metallic electrodes, and two gate voltages, V_a and V_b, are applied in one arm of the ring; these are treated as the two inputs of the OR gate. All the calculations are based on the tight-binding model and the Green’s function method, which numerically compute the conductance–energy and current–voltage characteristics as functions of the gate voltages, ring-to-electrode coupling strengths and magnetic flux. Our theoretical study shows that, for =₀/2 (₀=ch/e, the elementary flux-quantum), a high output current (1) (in the logical sense) appears if one or both the inputs to the gate are high (1), while if neither input is high (1), a low output current (0) appears. It clearly demonstrates the OR gate behavior, and this aspect may be utilized in designing an electronic logic gate.     

First-principles study of fundamental properties and electronic structure of alloys

We have performed first-principles calculations using full-potential augmented-plane-wave method to investigate the fundamental properties of the Cd_1–xZn_xTe alloys. The composition dependence of the lattice constant and the bulk modulus have been estimated from total energy calculations. By means of the analytical fitting the band structures in the vicinity of the Brillouin center a complete set of effective electron- and hole-masses have also been derived. In order to further understand the effects of the chemical bonding on the above macroscopic properties we then studied the relaxation behaviors and the changes of the electronic states upon alloying for x=0.25 system. The results presented here yield a general understanding of the fundamental properties for the Cd_1–xZn_xTe crystals studies.     

Effect of the -doping on the electron transport in a structure modulated by the magnetic barriers

The effect of the δ-doping on the electron transport has been theoretically studied in a structure modulated by the magnetic barriers. The results show that the transmission probability and the electron conductance can be dramatically suppressed by the weight of the δ-doping. However, the spin-injection efficiencies are obviously enhanced. In addition, the transmission probability and the spin-polarization both show a periodic profile with the increase of L₂. These interesting features will be more helpful for developing new types of devices.     

Integrable structure of melting crystal model with two -parameters

This paper explores integrable structures of a generalized melting crystal model that has two q-parameters q₁,q₂. This model, like the ordinary one with a single q-parameter, is formulated as a model of random plane partitions (or, equivalently, random 3D Young diagrams). The Boltzmann weight contains an infinite number of external potentials that depend on the shape of the diagonal slice of plane partitions. The partition function is thereby a function of an infinite number of coupling constants t₁,t₂,… and an extra one Q. There is a compact expression of this partition function in the language of a 2D complex free fermion system, from which one can see the presence of a quantum torus algebra behind this model. The partition function turns out to be a tau function (times a simple factor) of two integrable structures simultaneously. The first integrable structure is the bigraded Toda hierarchy, which determines the dependence on t₁,t₂,…. This integrable structure emerges when the q-parameters q₁,q₂ take special values. The second integrable structure is a q-difference analogue of the 1D Toda equation. The partition function satisfies thisq-difference equation with respect to Q. Unlike the bigraded Toda hierarchy, this integrable structure exists for any values of q₁,q₂.     

Ambiversion of

An analysis including most recent Belle data on X(3872) is performed, using coupled channel Flatté formula. A third sheet pole close to but below D⁰D^*0 threshold is found, besides the bound state/virtual state pole discussed in previous literature. The co-existence of two poles near the D⁰D^*0 threshold indicates that the X(3872) may be of ordinary 2³P₁ state origin, distorted by strong coupled channel effects. The latter manifests itself as a molecular bound state (or a virtual state).     

Optical intersubband transitions in double Si -doped GaAs under an applied magnetic field

For different applied magnetic fields, the intersubband transitions of double Si δ-doped GaAs structures is theoretically investigated for a uniform donor distribution. The electronic structure has been calculated by solving the Schrödinger and Poisson equations self-consistently. It is found that the intersubband optical absorption and mobility are sensitive to the applied magnetic field: for all allowed intersubband transitions the intersubband absorption spectra show blueshifts. The results open the possibility to design devices for use as optical filters controlled by an applied magnetic field, depending on the δ-doped structure. It is hoped that these results will provide important improvement in device applications, for a suitable choice of magnetic field.     

Effect of the -function potential on the electron transport in a magnetic nanostructure

In this paper, the spin-dependent electron transport is studied in detail in a magnetic nanostructure with a δ-function potential. It is shown that the large spin-polarization can be achieved in such a device, and the degree of the spin-polarization strongly depends on the height of the δ-function potential. It is also shown that the conductance-polarization apparently has the bigger oscillatory magnitudes with the height of δ-function potential increasing. These interesting features will be more helpful for developing new types of devices.     

Spectral flow invariants and twisted cyclic theory for the Haar state on

In [A.L. Carey, J. Phillips, A. Rennie, Twisted cyclic theory and an index theory for the gauge invariant KMS state on Cuntz algebras. arXiv:0801.4605], we presented a K-theoretic approach to finding invariants of algebras with no non-trivial traces. This paper presents a new example that is more typical of the generic situation. This is the case of an algebra that admits only non-faithful traces, namely SU_q(2) and also KMS states. Our main results are index theorems (which calculate spectral flow), one using ordinary cyclic cohomology and the other using twisted cyclic cohomology, where the twisting comes from the generator of the modular group of the Haar state. In contrast to the Cuntz algebras studied in [A.L. Carey, J. Phillips, A. Rennie, Twisted cyclic theory and an index theory for the gauge invariant KMS state on Cuntz algebras. arXiv:0801.4605], the computations are considerably more complex and interesting, because there are non-trivial ‘eta’ contributions to this index.     

Performance of Nd:YLF laser by using crystal electrooptic Q-switch

The polarization rotating coefficient and the laser-damage threshold of La₃Ga₅SiO₁₄ crystal at 1064 nm are measured, which are 1.1 deg/mm and , respectively. The working principle and the design method of electrooptic Q-switch based on La₃Ga₅SiO₁₄ crystal, which has the optical activity, are reported. The performance of Nd:YLF laser with the electrooptic Q-switch of La₃Ga₅SiO₁₄ crystal was studied. The output pulses with an energy of 379 mJ, a duration of 8.7 ns and repetition of 10 Hz are achieved.     

-Factor tuning of 2D electrons in double-gated Si/SiGe quantum wells

We report on the design and first experiments of Si/SiGe heterostructures that allow gate-operated shifting of a 2D electron gas between two channels with different Landé g-factors. This allows gate-operated moving of electrons in and out of resonance in an electron spin resonance (ESR) experiment, which can act as a building block of a proposed solid-state quantum computer. We use MBE-grown modulation-doped quantum-wells (QWs) on SiGe pseudosubstrates with up to 30% Ge and low-temperature electron mobilities up to . A double QW structure with two different Ge contents separated by a thin barrier was optimized for this purpose with self-consistent simulations. The band structure simulations show that by applying gate voltages one can completely shift the wave function from one well to the other. First experiments on pure Si channels show the working of the gate setup. Both carrier density and mobility can be increased by using the back gate which corresponds to shifting the wave function in the channel.     

Solutions of the reflection equation for the vertex model

We investigate the possible regular solutions of the boundary Yang–Baxter equation for the fundamental U_q[G₂] vertex model. We find four distinct classes of reflection matrices such that half of them are diagonal while the other half are non-diagonal. The latter are parameterized by two continuous parameters but only one solution has all entries non-null. The non-diagonal solutions do not reduce to diagonal ones at any special limit of the free-parameters.