Charge transport in monolayer poly（3-hexylthiophene） thin-film transistors

It is found that ultrathin poly（3-hexylthiophene） （P3HT） film with a 2.5 nm-thick layer exhibits a higher mobility of 5.0× 10-2 cm2/V-s than its bulk counterpart. The crystalline structure of the as-fabricated ultrathin P3HT layer is verified by atomic force microscopy as well as grazing incidence X-ray diffraction. Transient measurements of the as-fabricated transistors reveal the influence of the interface traps on charge transport. These results are explained by the trap energy level distribution at the interface manipulated by layers of polymer film.     

Charge transport across the metal–polymer film boundary

Thin polyaniline films were fabricated by thermal vacuum evaporation from a Knudsen effusion cell. The conducting properties of films synthesized under different evaporation conditions were studied. The enhancement of the emission capacity of a wolfram tip coated with a polyaniline film of a nanometer thickness was demonstrated experimentally. A model of the discovered effect was proposed. The obtained Fowler–Nordheim current–voltage characteristics were used to estimate the change in the electronic work function occurring when a thin film is deposited on the tip surface. The effective temperature of electrons emitted from the polyaniline film was determined based on the results of analysis of energy distributions, and the specific features of charge transport in the metal–polyaniline–vacuum system were examined. A model of energy bands of the metal–polymer film contact was also constructed.     

Dipole relaxation and proton transport in polycrystalline γ-cyclodextrin hydrate: A dielectric spectroscopy study

The polycrystalline γ-cyclodextrin hydrate (γ-CD·12.2H₂O) has been investigated via dielectric spectroscopy over a frequency range of 0-100 kHz and the temperature ranges of 108.0-298.5 K (cooling) and 109.0-433.0 K (heating). At T < 250.0 K, the electrical properties of the sample accept a great contribution from the flip-flop proton orientational disorder and a much lesser one from the positional fluctuations of the water molecules. Moreover, a strong synergy is observed between the stability of the γ-CD molecules and the dynamic disorder of the infinite flip-flop chains. This type of disorder disappears upon cooling (T_trans = 186.7 K) and reappears upon heating (T_trans = 194.5 K). At T > 250.0 K, the dielectric permittivity ε′ and loss ε″ increase abruptly due to the proton dc-conductance of γ-CD·12.2H₂O which has been interpreted in terms of a theoretical model (Pnevmatikos, 1988) being consistent with the generation of ionic defects and their combination with the dipole reorientations in a collective motion of soliton-type. The influence of the simultaneous dehydration process on this charge transport mechanism relies on the very sensitive balance between the diffusive motion of water molecules (exchange between symmetry related positions) and their removal from the crystal lattice. The Arrhenius semiconductive behavior of the ac-conductivity in the ranges of 257.1-313.2 K (E_a = 0.42 eV) and 331.2-385.1 K (E_a = 0.39 eV) implies the dominance of water diffusion which conserves the structural integrity of the endless hydrogen-bonded chains and the proton transfer along them. The limited decrease of the ac-conductivity from 313.2 to 331.2 K along with its rapid decrease above 385.1 K, indicates that the removal of the water molecules rules out their diffusive motion. The Cole-Cole diagrams (ε″ vs. ε′) make clear that during the heating process the grain boundary polarization gradually becomes more significant than the grain interior one. In the range of 348.0-385.1 K, the constrictive grain boundary resistances are totally eliminated allowing the extensive proton transport through the grains of the polycrystalline specimen.     

Analyzing Affect of Image Charge in Space Charge Effect

There is an increasing requirement of high injection current and highly charged ion beams for accelerators at many laboratories, such as CERN, GSI, GANIL and IMP, with the development of super-conducting ECR source in recent.years. In this case, the space charge effect becomes a major concern when the beam current is as high as tens of mA. In fact, the faradic field induced by the image charges will be come into the metallic surfaces while the beams are transported in a vacuum tube or in between two plates. In order to ensure studying the space charge effect in reason, it is necessary to investigate the effect from such a field.     

Silver–titanium dioxide nanocomposites as effective antimicrobial and antibiofilm agents

Recent studies have revealed the existence of liver cancer stem cells (CSCs). Therefore, there is an urgent need for new and effective treatment strategies specific to liver CSCs. In this work, the poly(d,l-lactide-coglycolide) nanoparticles containing paclitaxel were prepared by emulsification-solvent evaporation method. The nanoparticles decorated with anti-CD133 antibody, termed targeted nanoparticles, were prepared by carbodiimide chemistry for liver CSCs. The physicochemical characteristics of the nanoparticles (i.e., encapsulation efficiency, particle size distribution, morphology, and in vitro release) were investigated. Cellular uptake and accumulation in tumor tissue of nanoparticles were observed. To assess anti-tumor activity of nanoparticles in vitro and in vivo, cell survival assay and tumor regression study were carried out using liver cancer cell lines (Huh7 and HepG2) and their xenografts. Particle size of targeted nanoparticles was 429.26 ± 41.53 nm with zeta potential of ?11.2 mV. Targeted nanoparticles possessed spherical morphology and high encapsulation efficiency (87.53 ± 5.9 %). The accumulation of targeted nanoparticles depends on dual effects of passive and active targeting. Drug-loaded nanoparticles showed cytotoxicity on the tumor cells in vitro and in vivo. Targeted nanoparticles resulted in significant improvement in therapeutic response through selectively eliminating CD133 positive subpopulation. These results suggested that the novel nanoparticles could be a promising candidate with excellent therapeutic efficacy for targeting liver CSCs.     

Effect of the “inversion” of a scattering medium in layers of close-packed titanium dioxide nanoparticles

The features of the behavior of the diffuse transmission of layers of close-packed titanium dioxide nanoparticles in the visible and near infrared spectral ranges with an increase in the volume fraction f of the particles in a layer have been analyzed. It has been found that an increase in f for layers of small particles (about 25 nm) with a relatively low volume fraction (0.20–0.25) is accompanied by the expected decrease in diffuse transmission. At the same time, an increase in f for layers of large particles (about 100 nm) with a volume fraction of 0.45–0.50 results in a strong increase in transmission. The described phenomenon has been interpreted in terms of the concepts of inverse scattering systems, where the main scattering centers are air nanocavities in a TiO₂ matrix rather than TiO₂ particles in an air matrix.     

Crystal structure and electrical transport properties of polycrystalline TbMn1−xFexO3

Polycrystalline TbMn_1−xFe_xO₃ (x=0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) were synthesized by solid sintering method. The Rietveld refinement results based on the X-ray powder diffraction (XRD) data showed that all samples were identified as orthorhombic perovskite structure with space group Pbnm (62). The lattice parameters a and c increased, while the b decreased with increasing of Fe content, indicating the crystal unit cell shrinks in the ab-plane and extends along c-axis with increasing concentration of Fe. Temperature dependent resistance (R–T) was also measured. The transition temperature of TbMn_1−xFe_xO₃ samples increased monotonically with increase of x. The activation energy of TbMn_1−xFe_xO₃ decreased with increasing Fe content (x≤0.5) and increased with increasing Fe content when x>0.5, meaning that the TbMn_0.5Fe_0.5O₃ has the lowest activation energy. These results implied that the transition temperature and conductivity could be controlled by impuring different elements, especially to obtained better performance as for the semiconductor materials working at broad temperature.     

Brittle–ductile transitions in polycrystalline tungsten

The strain rate dependence of the brittle-to-ductile transition (BDT) temperature was investigated in notched and un-notched miniature bars made of high-purity polycrystalline tungsten and in notched bars of less-pure sintered material. The activation energy, E _BDT, for the process controlling the BDT in pure tungsten was equal to 1.0 eV both in un-notched and notched specimens, though the brittle–ductile transition temperature, T _BDT, was ≈ 40 K lower at each strain rate for the un-notched samples, indicating that the activation energy, E _BDT, is a materials parameter, independent of geometrical factors. The experimental data obtained from pure tungsten are described well by a two-dimensional dislocation-dynamics model of crack-tip plasticity, which is also discussed. For sintered tungsten, E _BDT was found to be 1.45 eV; T _BDT at a given strain rate was higher than in the pure tungsten by ≈ 90 K, suggesting that the BDT in tungsten is very sensitive to impurity levels.     

Charge transport in activated carbon electrodes: the behaviour of three electrolytes vis-à-vis their specific conductance

In this study, the electrochemical performances of different aqueous electrolytes (6 M KOH, 2 M KCl and 0.5 M K₂SO₄) in activated carbon electrodes are evaluated with regard to their use in electrochemical double layer capacitor (EDLC). The results from cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS) were analysed. The lowest value of equivalent series resistance (ESR) and the highest values of specific capacitance and coulombic efficiency were observed, when KOH was the electrolyte. The impedance spectroscopy plots were fitted to an equivalent circuit of ladder type to evaluate the resistances to ion transport at different levels of hierarchies in the pore network. Also, the quality of the double layer capacitance at lower hierarchy that primarily contributes to the overall capacitance of the device was evaluated from the leakage resistance in the equivalent circuit. The fitted circuit parameters were further reviewed vis-à-vis the specific conductance of chosen electrolyte, and the number of successive charge–discharge cycles prior to the EIS measurements.     

Magnetic-octupole order in neptunium dioxide?

The phase transition occurring at 25 K in NpO2, discovered almost 50 years ago, is the most long-lasting mystery in the physics of actinide compounds. Theories based on magnetic or electric-quadrupole order lead inevitably to fundamental, qualitative inconsistencies with observations. We show that the phenomenology of NpO2 can be understood if the order parameter is assumed to be a magnetic octupole of gamma(2) ( xyz) symmetry. NpO2 is the first compound for which indications of an octupolar phase transition have been found.     

Phase transformation of nanostructured titanium dioxide thin films grown by sol–gel method

Nanostructured TiO₂ thin films were deposited on quartz glass at room temperature by sol–gel dip coating method. The effects of annealing temperature between 200^∘C to 1100^∘C were investigated on the structural, morphological, and optical properties of these films. The X-ray diffraction results showed that nanostructured TiO₂ thin film annealed at between 200^∘C to 600^∘C was amorphous transformed into the anatase phase at 700^∘C, and further into rutile phase at 1000^∘C. The crystallite size of TiO₂ thin films was increased with increasing annealing temperature. From atomic force microscopy images it was confirmed that the microstructure of annealed thin films changed from column to nubbly. Besides, surface roughness of the thin films increases from 1.82 to 5.20 nm, and at the same time, average grain size as well grows up from about 39 to 313 nm with increase of the annealing temperature. The transmittance of the thin films annealed at 1000 and 1100^∘C was reduced significantly in the wavelength range of about 300–700 nm due to the change of crystallite phase. Refractive index and optical high dielectric constant of the n-TiO₂ thin films were increased with increasing annealing temperature, and the film thickness and the optical band gap of nanostructured TiO₂ thin films were decreased.     

Dose–dependent biodistribution of prenatal exposure to rutile-type titanium dioxide nanoparticles on mouse testis

Au@TiO₂/graphene (Gr) composite with visible-light response was fabricated. The prepared samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscope, and diffuse reflection spectroscopy, respectively. The results indicated that metallic Au nanoparticles with round shape and about 10 nm in size were loaded on TiO₂ particles uniformly, and Au@TiO₂ was grafted on Gr shaped in thin and big sheets. Photocatalytic degradation of 2,4-dichlorophenol (2,4-DCP) was conducted under the visible-light irradiation (>420 nm) in order to evaluate the activity of photocatalysts. The light absorption spectrum of TiO₂ was extended to visible-light region by loading Au nanoparticles with plasmonic effect and 2,4-DCP could be degraded with Au@TiO₂ and Au@TiO₂/Gr by photocatalysis under visible light. Compared to that with Au@TiO₂, the elimination rate of 2,4-DCP was increased with Au@TiO₂/Gr. This enhanced photocatalytic performance was attributed to the concentration effect due to the improved adsorption performance introduced by Gr.     

Charge Splitting in πNΔ Form Factor

Physics of Atomic Nuclei - Experimental data on πN scattering in the elastic energy region w ≤ 1.45 GeV are analyzed within the K-matrix approach with effective lagrangians. The charge...     

Anomaly in the Charge Radii and Nuclear Structure

The axially deformed relativistic mean field theory is applied to study the isotope shift of charge distributions of odd-Z Pr isotope chain. The nuclear structure associated with the shell and the isotope effect is investigated. The mechanism of the kink in the isotope shift at the neutron magic number N = 82 is revealed to be dependent on the neutron energy level structure at the Fermi energy, demonstrating that the spin-orbit coupling interaction and p-n attraction are well described by the relativistic mean field theory.     

Solid-state NMR and EPR analysis of carbon-doped titanium dioxide photocatalysts (TiO2−xCx)

Carbon-doped TiO₂ have received attention recently because of their potential for environmental photocatalysis and solar hydrogen conversion applications. Three different carbon-doped TiO₂ nanoparticle materials were synthesized via sol–gel and hydrothermal procedures, and analyzed by ¹³C solid-state nuclear magnetic resonance (SSNMR) and other methods to characterize the environment of the doping species. UV/vis spectra and powder X-ray diffraction (XRD) patterns showed that the synthesized materials absorbed visible light and their crystal structures corresponded to anatase. ¹³C SSNMR analyses of TiO_2?xC_x displayed signals corresponding to carbonate-type or sp²-type carbon species. Variable contact CP-MAS and dipolar dephasing analyses gave evidence for the presence and proximity of H atoms near these carbonate species. Electron paramagnetic resonance (EPR) spectroscopy showed that the thermally oxidized TiO_2?xC_x displayed a complex mixture of point defects, electron and hole trapping centers, all attributable to the incorporation of carbon, while the XPS data ruled out the presence of carbide species.     

Monopole Charge Domain in High-Gain Gallium Arsenide Photoconductive Switches

Considering that semi-insulating gallium arsenide photoconductive switches can be triggered into the high gain mode and no reliable theories can account for the observed transient characteristics,we propose the monopole charge domain model to explain the peculiar switching phenomena occurring in the high gain mode and we discuss the requirements for the lock-on switching.During operation on this mode,the applied field across the switch and the lock-on field are all larger than the Gunn threshold field.Our developed monopole charge domain is based on the transferred-electron effect,but the domain is only composed of large numbers of electrons piled up due to the negative differential mobility.Using the model and taking the physical mechanism of the avalanche impact ionization and recombination radiation into consideration,we interpret the typical phenomena of the lock-on effect,such as the time delay between the beginning of optical illumination and turning-on of the switch,and the conduction mechanism of the sustaining phase.under different conditions of bias field intensity and incident light energy,the time delay of the switching is calculated.The results show that the physical mechanisms of impact ionization and recombination radiation occurring in the monopole charge domain are responsible for the lock-on switching.     

Spin-dependent transport in α-MnS single crystals

The electrical resistivity of single crystal α-MnS in crystallographic directions [111] and [100] was found to be anisotropic in the temperature interval 77–300 K. The change in activation energy below the Néel temperature was determined. Magnetoresistance was revealed, and reversal of its sign in the (111) plane above the Néel point was found. The experimental data are analyzed in terms of the s-d model, with the manganese ion holes interacting with localized spins assumed to be free carriers.