Disorder dominated microwave conductance spectra of doped silicon nanowire arrays

Conductance spectra of doped silicon nanowire (SiNW) arrays were measured from 0.5 to 50 GHz at temperatures between 4 and 293 K. For arrays consisting of 11 to >10(4) SiNWs, the conductance was found to increase with frequency as f(s), with 0.25 < s < 0.45, consistent with behavior found universally in disordered systems. A possible cause is disorder from Si/SiO x interface states dominating the conductance due to the high surface-to-volume ratio of the nanowires.

The mechanisms of conduction in proteins

Theoretical calculations have already shown that the electronic properties of biopolymers may be described in terms of conduction and valence energy bands in which electrons are delocalized to a significant degree. Because these bands are separated by a large energy gap, it is concluded that electronic conduction in such systems must be by 'holes' in the valence band. The mechanism of this conduction is discussed with special reference to dry proteins where the charge-transfer role of appropriate acceptor molecules and the modulating influence of amino acid residues will encourage localized and delocalized hole production at the valence band edge. It is suggested that there are close similarities, which have shown up in measurements, in the electrical behaviour of proteins and other non-biological semi-crystalline solids. The significance of such long-range conduction and attendant polarization is considered briefly in the light of evidence for the existence of proteins in cell membranes and in the skeleton of the cytoplasm

pH Sensitivity of Novel PANI/PVB/PS3 Composite Films

This paper reports on the results from the investigation into the pH sensitivity ofnovel PANI/PVB/PS3 composite films. The conductimetric sensing mode was chosen as itis one of the most promising alternatives to the mainstream pH-sensing methods and it is theleast investigated due to the popularity of other approaches. The films were deposited usingboth screen-printing and a drop-coating method. It was found that the best response to pHwas obtained from the screen-printed thick films, which demonstrated a change inconductance by as much as three orders of magnitude over the pH range pH2-pH11. Thedevices exhibited a stable response over 96 hours of operation. Several films were immersedin buffer solutions of different pH values for 96 hours and these were then investigated usingXPS. The resulting N 1s spectra for the various films confirmed that the change inconductance was due to deprotonation of the PANI polymer backbone. SEM andProfilometry were also undertaken and showed that no considerable changes in themorphology of the films took place and that the films did not swell or contract due toexposure to test solutions.

TSDC spectroscopy of relaxational and interfacial phenomena

Applications of thermally stimulated depolarisation current (TSDC) technique to a variety of systems with different dispersion phases such as disperse and porous metal oxides, polymers, liquid crystals, amorphous and crystalline solids, composites, solid solutions, biomacromolecules, cells, tissues, etc. in gaseous or liquid dispersion media are analysed. The effects of dipolar, direct current (dc) and space charge relaxations are linked to the temperature dependent mobility of molecules, their fragments, protons, anions, and electrons and depend on thermal treatment, temperature and field intensity of polarisation, heating rate on depolarisation or cooling rate on polarisation. Features of the relaxation mechanisms are affected not only by the mentioned factors but also by morphological, structural and chemical characteristics of materials. The interfacial phenomena, especially the role of interfacial water, received significant attention on analysis of the TSDC data. Comparison of the data of TSDC and dielectric relaxation spectroscopy (DRS), differential scanning calorimetry (DSC), 1H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial water, adsorption/desorption of nitrogen, water and dissolved organics demonstrates high sensitivity and information content of the TSDC technique, allowing a deeper understanding of interfacial phenomena.

Use of dielectric relaxation for measurements of surface energy variations during adsorption of water on mordenite

This paper tries to assess simply and quantitatively the link between classical adsorption theories and dielectric spectroscopy, in order to demonstrate that dielectric spectroscopy can be used as a tool of determination of surface energy variations due to movements of charge carriers at the surface of solids. A simple theory is developed to analyze hops of cations at the surface of mordenite, which are detected by complex impedance spectroscopy during adsorption of water. An energy of extraction of the cation can be determined from measurements and its dependence on the quantity of water molecules adsorbed is shown and qualitatively and quantitatively explained, using relationships developed in order to interpret adsorption phenomena generally. The agreement with other determinations of the adsorption energies and solid surface energy is correct.

Simple model for ac ionic conduction in solids

We present a model for the ac conduction in ionically conducting solids that takes into account, in a simple way, the interaction between carriers. The Coulomb force forms an "ionic atmosphere" that exerts a restoring force on a central ion, whose motion corresponds to an overdamped oscillator. We consider the effect of the relaxation of the ionic atmosphere by introducing an additional equation for the displacement of the potential toward the particle position. The general behavior of the ac conductivity can be understood in terms of two types of motions: motion of the bound ion at high frequencies determined by microscopic friction, and a much slower motion coupled to the surrounding carriers relaxation at low frequencies.

Coulomb "Blockade" of nuclear spin relaxation in quantum dots

We study the mechanism of nuclear spin relaxation in quantum dots due to the electron exchange with the 2D gas. We show that the nuclear spin relaxation rate 1/T(1) is dramatically affected by the Coulomb blockade (CB) and can be controlled by gate voltage. In the case of strong spin-orbit (SO) coupling the relaxation rate is maximal in the CB valleys, whereas for the weak SO coupling the maximum of 1/T(1) is near the CB peaks.

Ionic conduction in glass: new information on the interrelation between the "Jonscher behavior" and the "nearly constant-loss behavior" from broadband conductivity spectra

We analyze broadband ac conductivity spectra of various ion conducting glasses with regard to the composition dependence of the "Jonscher behavior" and of the "nearly constant-loss behavior." In the temperature range of our experiments (173 K< or =T< or =573 K), both types of behavior are closely related, indicating that both arise from ion hopping. However, the "nearly constant-loss behavior" observed at temperatures below 100 K seems to be caused by other dynamic processes.

Voltage-modulated millimeter-wave spectroscopy on a polymer diode: mesoscopic charge transport in conjugated polymers

We present a new technique to determine the carrier mobility mu in semiconducting, undoped, conjugated polymers in the millimeter-wave frequency range, 10-500 GHz. This method probes charge conduction on mesoscopic length scales, a regime inaccessible to other transport experiments. The experiment is based on the detection of millimeter-wave absorption of field-induced charge in polymer diodes, and is applied to poly( p-phenylene vinylene). We demonstrate that locally mu can be as high as 10(-4) m(2)/V s, and deduce the typical hopping parameters in the mesoscopic high- mu regions in the material.