Electrical conductivity and optical transparency of bacterial cellulose based composite by static and agitated methods

Composites consisting of bacterial cellulose (BC) and ionic conducting polymer (ICP) were prepared. BC was biosynthesized in media at 0, 25, 50 and 100 rpm. ICP was chemically synthesized at different concentrations of ionic salt. The corresponding electrical conductivity of the composites was measured as a function of ionic salt concentration. ICP improved the optical transparency and electrical conductivity of the BC/ICP composites. Morphological images of BC/ICP composites showed that the pore size of the BC pellicle increased while the diameter and density of the BC fibers decreased. The cultivation method was critical in affecting the structure and electrical conductivity of the composites.     

Plasma-aided hydrogenation and Al-doping: Increasing the conductivity and optical transparency of ZnO transparent conducting oxide

Plasma-assisted magnetron sputtering with varying ambient conditions has been utilised to deposit Al-doped ZnO (AZO) transparent conductive thin films directly onto a glass substrate at a low substrate temperature of 400 °C. The effects of hydrogen addition on electrical, optical and structural properties of the deposited AZO films have been investigated using X-ray diffractometry (XRD), scanning electron microscopy (SEM), Hall effect measurements and UV-vis optical transmission spectroscopy. The results indicate that hydrogen addition has a remarkable effect on the film transparency and conductivity with the greatest effects observed with a hydrogen flux of approximately 3 sccm. It has been demonstrated that the conductivity and the average transmittance in the visible range can increase simultaneously contrary to the effects observed by other authors. In addition, hydrogen incorporation further leads to the absorption edge shifting to a shorter wavelength due to the Burstein-Moss effect. These results are of particular relevance to the development of the next generation of optoelectronic and photovoltaic devices based on highly transparent conducting oxides with controllable electronic and optical properties.     

From electromagnetically induced transparency to absorption in planar optical metamaterials

We theoretically investigate the classical analog of electromagnetically induced transparency （EIT） and electromagnetically induced absorption （EIA） in a planar metamaterial at optical frequency, which origi- hates from destructive and constructive interference between dark and radiative elements. The metama- terial consists of two coupled resonators with different geometries. An EIT-like transparent window with low absorption is observed and found to be strongly affected by resonant states of the resonators. The transition between the EIT and EIA is achieved by changing the split width and coupling distance. The absorption is enhanced up to 2.5 times compared with the dipolar case. The excitation of the dark mode is very important for EIT- and EIA-like responses of the proposed metamaterial. The EIT and EIA phenom- ena offer a potential method for manipulating electromagnetic response in metamaterial-based devices.     

Delayed optical images through coupled-resonator-induced transparency

We propagated transverse two-dimensional images encoded on optical pulses through a frequency window of a coupled-image-resonator-induced transparency. The optical images are stored and delayed by 10.6ns, reflecting the tunable dispersion of the coupled resonator. The k-space bandwidth of the amplitude transfer function of the system is discussed in the presence of the off-resonance Fano interference effect between the two resonators.     

Quantum correlations of two optical fields close to electromagnetically induced transparency

We show that three-level atoms excited by two cavity modes in a Lambda configuration close to electromagnetically induced transparency can produce strongly squeezed bright beams or correlated beams which can be used for quantum nondemolition measurements. The input intensity is the experimental "knob" for tuning the system into a squeezer or a quantum nondemolition device. The quantum correlations become ideal at a critical point characterized by the appearance of a switching behavior in the mean fields intensities. Our predictions, based on a realistic fully quantum three-level model including cavity losses and spontaneous emission, allow direct comparison with future experiments.     

Self-induced transparency of very short optical pulses

Solutions to a first order wave equation, appropriate to ultrashort optical pulse theory and to the optical undamped Bloch equations are presented. Detuning is shown to play essential role in the physical interpretation of these solutions. Related cases have been discussed by Courtens and by Lee. It is noted that the rotating wave approximation introduces strong restrictions on the range of validity of possible solutions. Pulses with Lorentzian shapes, while implied by the equations, appear to be without physical significance.     

Unconventional strongly interacting bose-einstein condensates in optical lattices

Feschbach resonances in a non-s-wave channel of two-component bosonic mixtures can induce atomic Bose-Einstein condensates with a nonzero orbital momentum in the optical lattice, if one component is in the Mott insulator state and the other is not. Such non-s-wave condensates break the symmetry of the lattice and, in some cases, time-reversal symmetry. They can be revealed in specific absorption imaging patterns.     

Tabular electrical conductivity for aluminium

A new Sesame-type table for the electrical conductivity of aluminium is described. The table is based on density functional theory calculations and ranges from 10⁻³ to 1 times solid density (2.7 g/cm³), and from 10⁻² to 10³ eV in temperature. The table is compared with other those of simulations and to experiments and is generally in good agreement. The high-temperature, classical limit of the conductivity is recovered for the highest temperatures and lowest densities. The table is critically evaluated, and directions for improvements are discussed.     

Studies on the electrical conductivity, optical absorption and x-ray diffraction in bismuth thin film

Spectroscopically pure bismuth is evaporated onto glass substrates at different substrate temperature using a Hind Hivac coating plant. The electrical conductivity of bismuth thin films, prepared at different substrate temperatures is measured and thermal activation energy is evaluated. From the recorded optical absorption spectrum in the ultraviolet and visible regions optical band gapE _g is determined. X-ray diffractograms are recorded and lattice parameters are determined.     

Graphene oxide with improved electrical conductivity for supercapacitor electrodes

Predominant few-layer graphene (FLG) sheets of high electrical conductivity have been synthesized by a multi-step intercalation and reduction method. The electrical conductivity of the as-synthesized FLG is measured to be ∼3.2 × 10⁴ S m⁻¹, comparable to that of pristine graphite. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman analysis reveal that the as-synthesized FLG sheets have large areas with single and double layers. The specific capacitance of 180 F g⁻¹ is obtained for the FLG in a 1 M Na₂SO₄ aqueous electrolyte by integrating the cyclic voltammogram. The good capacitive behavior of the FLG is very promising for the application for next-generation high-performance electrochemical supercapacitors.     

Effect of conductivity on a self-induced transparency 0π pulse with a complicated structure

The theory of optical self-induced transparency is developed for a 0π pulse with a complicated internal structure in an absorbing medium. It is shown that, in the process of propagation through the medium, the effects of conductivity lead to a change in the wave parameters. Explicit analytic expressions describing the double breather under these conditions are presented.     

Enhancement of electrical conductivity in MgO due to lithium impurities

The electrical conductivity of lithium-doped MgO crystals at room temperature is shown to be enhanced by the thermal creation of stable [Li]⁰ defects by oxidation at elevated temperatures. The current-voltage curves are found to be nonlinear at low voltages. The enhancement in conductivity is attributed to localized regions of high [Li]⁰ concentration in which the holes at the [Li]⁰ sites are thermally ionized into the valence band, causing these regions to be semiconducting.     

Far-infrared to visible optical conductivity of single-wall carbon nanotubes

The reflectance of unoriented single-wall carbon nanotube films has been measured over a wide wavelength range (far-IR–UV). The results are consistent with the film being a mixture of conducting (armchair), small bandgap (n≡m, mod 3) and semiconducting nanotubes. The optical conductivity shows peaks corresponding to transitions between density-of-states peaks of these tubes, at energy locations consistent with 1.4 nm diameter tubes. In addition optical absorption spectroscopy of aligned single-wall carbon nanotubes shows that the optical transitions are well-aligned along the tube axis. This behavior is consistent with polarized resonant Raman and electronic structure calculations.     

Precise measurement of optical frequency with the help of electromagnetically induced transparency

We have studied electromagnetically induced transparency (EIT) spectra in a frequency span as wide as 300 MHz. This tunability of EIT spectra provides an opportunity to utilize the sub-natural spectra in measuring unknown laser frequency very accurately. EIT is observed when control and probe laser frequency detunings are equal. This correlation has been used to identify and measure unknown probe frequency with a very high degree of accuracy, subject to the condition that control laser frequency is known.     

Transport and optical conductivity in

We present the results of a dc transport and optical investigation of WO₃ and Na_xWO₃ with x =0.01. Upon Na-doping we find a (Drude) metallic component in the optical conductivity, while the transport data display a crossover from an activated to a variable range hopping regime around 210 K. We suggest the possible formation of polarons (and bipolarons) and speculate that superconductivity could be induced, provided the dc percolation threshold is achieved. Received 28 March 2000     

Anisotropy of graphite optical conductivity

The graphite conductivity is evaluated for frequencies between 0.1 eV, the energy of the order of the electronhole overlap, and 1.5 eV, the electron nearest hopping energy. The in-plane conductivity per single atomic sheet is close to the universal graphene conductivity e ²/4ħ and, however, contains a singularity conditioned by peculiarities of the electron dispersion. The conductivity is less in the c direction by the factor of the order of 0.01 governed by electron hopping in this direction.     

The electrical conductivity of chloride melts

The interrelationship between electrical conductivity, molar volume and enthalpy of mixing was studied for molten chlorides and their mixtures. The dependence of electrical conductivity and activation energy on the molar volume is different for various groups of salts. The dependence of specific conductivity on molar volume obtained for molten alkali chlorides was found to be similar to other chloride salts. The specific conductivity of binary mixtures that lack strong chemical interactions between the components can also be described by the proposed empirical equation. The enthalpy of mixing should be taken into consideration for these chemical interactions.