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Electronic characteristics are difficult to monitor in nanocomposites. Here we describe indirect assessments of these characteristics using THz, Raman and IR spectroscopy. Specifically we seek to gain understanding of the electron mobility in semiconductive and conductive nanostructures for electronic, electrooptic and nonlinear optical purposes.

We present in this paper the experimental results of transport hysteresis in an extremely imbalanced electron double-quantum-well (DQW) structure. The ratio of the top layer density (n_top) to bottom layer density (n_bot) is continuously tuned by applying voltage to a front gate. Under a condition when the top layer is nearly depleted (n_top~3×10¹⁰cm^-2) while the bottom layer remains at n_bot=1.9×10¹¹cm^-2, the hysteresis is absent in the B sweeps as long as the total Landau level filling ν<1 and the 2D electron systems are in the fractional quantum Hall effect regime. Surprisingly, a large hysteresis is observed during the gate sweeps at the same values of B and n_top. We attribute this unexpected hysteresis to the formation of an insulating state, probably a weakly pinned Wigner solid state, in the top layer.

The electrical resistivity, thermal conductivity, and thermopower of α-TiAl alloy samples with Al content from 0 at.% to 10 at.% are measured from room temperature down to liquid helium temperature. It is found that with the increase in Al content the single phonon scattering contribution to the resistivity remains nearly constant, but the multi-phonon scattering contribution monotonously increases. This provides an alternative explanation of resistivity saturation to the shunt-resistor model. The Wiedemann–Franz law holds for the whole temperature range, allowing the separation of the electron and phonon contributions to the thermal conductivity. The data from samples with different doping levels enable us to separate the band and the scattering terms in the thermopower.

We study the nature of tunneling phase time for various quantum mechanical structures such as networks and rings having potential barriers in their arms. We find the generic presence of the Hartman effect, with superluminal velocities as a consequence, in these systems. In quantum networks, it is possible to control the "super arrival" time in one of the arms by changing the parameters on another arm which is spatially separated from it. This is yet another quantum nonlocal effect. Negative time delays (time advancement) and "ultra Hartman effect" with negative saturation times have been observed in some parameter regimes. In the presence and absence of Aharonov-Bohm (AB) flux, quantum rings show the Hartman effect. We obtain the analytical expression for the saturated phase time. In the opaque barrier regime, this is independent of even the AB flux thereby generalizing the Hartman effect. We also briefly discuss the concept of "space collapse or space destroyer" by introducing a free space in between two barriers covering the ring. Further, we show in presence of absorption that the reflection phase time exhibits the Hartman effect in contrast to the transmission phase time.

When the usual operator of the Fröhlich's coupling between electrons and longitudinal optical phonons of semiconductor single quantum dot is used to calculate electronic energy relaxation, a permanent phonon generation in quantum dot is obtained, leading to an artificial effect of permanent heating up of the lattice. The mechanism of the phonon heating is identified here with the influence of the transverse part of the interaction operator. This part is responsible first of all for a tendency to build the polaronic well of an electron in a quantum dot. The effect of overheating is shown to be possibly eliminated to a considerable extent upon removing the transverse part of the interaction with the help of the Lang–Firsov canonical transformation and upon modifying accordingly the longitudinal part of the coupling. The resulting electronic relaxation and optical phonon generation is demonstrated numerically in a relatively simple approximation to electron and phonon self-energy, in which the model of quantum dot is reduced to an electron coupled to a single-LO-phonon mode. It is interesting to see that the removal of the phonon overheating based on the application of the Lang–Firsov canonical transformation has a rather small influence on electronic characteristics calculated with electronic transport equations. In this sense, the long-time limit properties of the electronic subsystem, like the electronic up-conversion and incomplete depopulation effect, calculated earlier, remain nearly untouched.

Zinc oxide (ZnO) thin films were deposited onto glass substrates by d.c. magnetron sputtering. The structural analysis, by X-ray diffraction and atomic force microscopy, indicate that the studied films are polycrystalline and have a wurtzite (hexagonal) structure. The film crystallites are preferentially oriented with (002) planes parallel to the substrates.

The mechanism of electronic transport is explained in terms of Seto's model elaborated for polycrystalline semiconducting films (crystallite boundary trapping theory). Some parameters of used model (impurity concentration, density and energy of the trapping states, etc.) have been calculated. The optical bandgap (E_g0 = 3.28–3.37 eV) was determined from absorption spectra.

Based on nonequilibrium Green's function and first-principles calculations, we investigate the electronic transport properties of 4,4′-biphenyldithiol functionalized molecular junction with different torsion angles between two phenyl rings. Numerical results show that torsion angle plays an important role in the conducting behavior of molecular junction. By changing the torsion angle, molecule can exhibit a switching behavior. Especially, when the molecule is functionalized with NO₂ side group, it will perform a molecular memory effect. Furthermore, effects of different adsorption positions of sulfur atom on molecular memory are also discussed.

The electronic transport through a mesoscopic confining region coupled to two spin-orbit coupling semiconductor leads is studied. We mainly focus on how the transport behaviors are affected by the Rashba spin-orbit interaction (SOI), which has been neglected in the previous theoretical papers but indeed exists in the semiconductor leads from the recent experimental results. By using Landauer–Büttiker formula and the non-equilibrium Green's function method, the linear conductance of this device is obtained. The numerical results exhibit that the conductance are similar for the two cases of the absence and the presence of the SOI. It means that the SOI in the leads does not qualitatively affects the transport behaviors. However, in detail, the peaks of the conductance are widened and enhanced by the SOI. In some specific cases, the widening and the enhancement could be very strong.

The effect of gate voltage on electronic transport properties in single C₆₀ molecular device is investigated by a first-principles method based on density functional theory and nonequilibrium Green's function formalism. The calculated results show that the variation of the equilibrium conductance with gate voltage strongly corresponds with the variation of transmission eigenvalues and depends on the shift of molecular orbitals. The positive gate voltage can enhance the device's electronic transport, while negative gate voltage weaken it, which shows a gate-controlled molecular current switch. More importantly, the negative differential resistance behavior is observed and can be modulated by the gate potential. A detailed explanations for these phenomena are given.

Quantum mechanics manifests in experimental observations in several ways. Hauge et al. (1987) and Leavens et al. (1989) had pointed out that interference effects dominate a physical quantity called injectance. We show that, very paradoxically, the interference related term vanish in a quantum regime making semi-classical formula for injectance exact in this regime. This can have useful implications to experimentalists as semi-classical formulas are much more simple. There are other puzzling facts in this regime like an ensemble of particles that can be transmitted without any time delay or negative time delays.

By applying nonequilibrium Green's function formalism combined with first-principles density functional theory, we investigate the effect of different anchoring groups on the rectifying behavior in diblock molecular junctions. The spatial distributions of molecular orbitals and the influence of transmission coefficients under various external voltage biases on the electronic transport through the molecular device are discussed in detail. The results show that the anchoring groups play a significant role on the electronic transport properties. The rectifying performance in molecular junctions can be manipulated, enhanced, or suppressed by a careful consideration of the effects of the anchoring group and such modifications become crucial in optimizing the electronic transport properties of chemical structures.

The discovery of graphene, a single layer of covalently bonded carbon atoms, has attracted intense interest. Initial studies using mechanically exfoliated graphene unveiled its remarkable electronic, mechanical and thermal properties. There has been a growing need and rapid development in large-area deposition of graphene film and its applications. Chemical vapor deposition on copper has emerged as one of the most promising methods in obtaining large-scale graphene films with quality comparable to exfoliated graphene. In this paper, we review the synthesis and characterizations of graphene grown on copper foil substrates by atmospheric pressure chemical vapor deposition. We also discuss potential applications of such large-scale synthetic graphene.

We have investigated electronic transport of charge carriers in a gapped bilayer graphene superlattice (GBGS), based on transfer matrix method. We have found that conductivity of the system has an oscillatory behavior respect to the gap value. As the gap value is simply changeable by external voltage in bilayer graphene, the conductivity can be controlled by gate voltage. It also has been shown that transmission probability for normal incident angle depends on barrier width in presence of band gap within barrier region. As a result, a GBGS behaves very differently compared to a gapless bilayer graphene superlattice.

We have numerically investigated electronic transport properties in single-walled carbon nanotubes (SWCNTs) doped with boron (B) and nitrogen (N) substitutional impurities. Our calculations are performed by the ab initio density functional theory (DFT) and the nonequilibrium Green's function (NEGF) approach. We show that the electronic transmissions are moderated after the doping on both metallic and semiconducting CNTs. In B and N codoping nanotubes, depending on the arrangements of B and N substitutions, electronic and transport properties have been also modified. Calculating from electronic transmissions under bias, I–V characteristics of doped CNTs are demonstrated. In our simulations, we find that the substituting impurities in the semiconducting CNT raise the conductivity regardless of p- or n-type doping, whereas the conductivity of metallic CNTs is reduced by doping.

In a comparative framework, an ensemble Monte Carlo was used to elaborate the electron transport characteristics in two different silicon carbide (SiC) polytypes 3C-SiC and 4H-SiC. The simulation was performed using three-valley band structure model. These valleys are spherical and nonparabolic. The aim of this work is to forward the trajectory of 20,000 electrons under high-flied (from 50 kV to 600 kV) and high-temperature (from 200 K to 700 K). We note that this model has already been used in other studies of many Zincblende or Wurtzite semiconductors. The obtained results, compared with results found in many previous studies, show a notable drift velocity overshoot. This last appears in subpicoseconds transient regime and this overshoot is directly attached to the applied electric field and lattice temperature.

In this paper, we have studied the electronic transport behavior of the system formed by the Al₂N₂ cluster and the Al(100)-3 × 3 electrodes by using the first principle based on nonequilibrium Green’s function (NEGF). The total energies and the equilibrium conductances of the system are calculated at different distances between the clusters and the electrodes, and the results show that the equilibrium conductance is 0.1335 G₀ and the total energy is the lowest at d = 2.8 Å (d means the distance between the Al₂N₂ cluster and the electrodes). When d increases, the equilibrium conductance decreases. In the bias voltage range of [−1 V, 1 V], the system has the electrical characteristics similar to the metal when the d is 2.0, 2.4, 2.8, 3.2 and 3.5 Å.

We discuss the temperature independent resistivity of s–p impurities and rare earth impurities diluted in noble hosts, using a T-matrix formulation. We take into account translational symmetry breaking and therefore a nonlocal charge potential is obtained. The effect of volume difference between impurity and host elements is also considered in the calculation. In the case of "magnetic" impurities (i.e. almost all rare earth impurities) we calculate the spin disorder resistivity, obtaining a charge potential renormalized De Gennes–Friedel spin disorder resistivity. Our numerical results describe the available experimental data quite well.

We investigate the electronic transport properties of molecular devices constructed by porphyrin modulated with central metal ions by applying the elastic scattering Greens function theory approach in combination with the hybrid density functional theory. The effect of the porphyrin center metal ions and the twisting of the middle benzene rings on the electronic transport properties of the molecular devices is considered in detail. The results show that the the center metal ions can enhance the coupling of the molecule and electrode, while the twisting of the middle benzene rings is of a opposite effect.

Applying the elastic scattering Green's function theory in combination with the frontier molecular orbital theory for describing the surface-molecule coupling and hybrid density-function theory for geometrical and electronic structure calculations, we successfully reproduce the current–voltage properties of the 4,4-biphenyldithiol molecular junction, which has been measured using a lock-in technique by Lee et al.¹ We also analyze the conductance characteristics of different dimensional electrodes in contact with the molecular device, and we think that the one-dimensional formula is consistent with the experiment, and that the interaction between neighboring molecules will decrease the molecular orbital energies and draw the conductance peak positions closer to experimental results.

We have investigated the magnetic and electrical properties of multiferroic BiFe_1-xMo_xO₃ ceramics (BFMO, x = 0.0%, 0.2%, 0.5% and 0.8%) prepared by the sol–gel method. The phase structure of BFMO samples were confirmed by X-ray diffraction. It was found that the substitution of Mo is responsible for the increasing of the magnetization in BFMO ceramics. Moreover, both dielectric and polarization-electric field properties suggest that the Mo doping could improve the dielectric and ferroelectric properties in BFMO ceramic.