Thermally stimulated currents in lithium-sodium disilicate glasses

Thermally stimulated polarization and depolarization currents were measured for thin films of lithium-sodium disilicate glasses. As reported previously two thermally stimulated depolarization current peaks were found. The low-temperature peak was attributed to conduction polarization of alkali ions, while the high-temperature was attributed to localized motion of non-bridging oxygens in the alkali-depleted region near the anode rather than to space charge or interfacial polarization, as proposed earlier. Although the high-temperature peak was dominant under medium polarizing conditions, it was swept away irreversibly by biasing at extremely high electric field.     

Thermally stimulated discharge currents in corona-charged aramid paper

Thermally stimulated discharge (TSD) currents were measured in corona-charged aramid paper to study the mechanisms of charge storage and its subsequent release from the bulk of the material. Studies were carried out on paper thicknesses of 76 and 127 m using a point-plane gap in air at atmospheric pressure. TSD currents were measured over a temperature range of 0–200 °C and the influence of various parameters, such as the poling voltage, rate of heating and effect of electrode materials, were investigated. Corona-charged aramid paper with positive polarity voltage showed that the TSD current is of either polarity depending upon the temperature range. Three distinct peaks were observed, one in the low-temperature range, 20–25 °C, and the other two peaks at higher temperatures. The low-temperature peak was considered to be due to an abnormal TSD current, whereas the currents at higher temperatures were normal TSD currents. Activation energies were determined using the low-temperature tail of the TSD curves and were found to be dependent on extrinsic parameters such as the thickness of the sample. The activation energy for aluminium electrodes was observed to be in the range of 0.5–2.0 eV. The TSD currents for the low-temperature peak was considered to be electronic. It is postulated that the charge carriers are generated within the material by the intense electric field due to corona.     

Thermally stimulated discharge currents in iodine-doped polystyrene films

Studies were made of the thermally stimulated discharge (TSD) current in iodine-doped polystyrene (PS) films (20 μm thick) as a function of the iodine concentration and the temperature of polarization. Unpolarized doped films were observed to give TSD currents. This is attributed to the formation of charge transfer complexes (CTCs) between iodine and the main molecular chain of PS. Doping PS with iodine lowers the temperáture at which the current peak occurs and enhances the peak current. An increase in the temperature of polarization increases the TSD current and shifts its maximum to a higher temperature while an increase in the concentration of iodine lowers the activation energy of the discharge process. The thermally assisted detrapping of carriers is suggested as a possible mechanism.     

Thermally stimulated currents in pyrex and soda-lime glasses

Thermally stimulated current studies of commercially available soda-lime and pyrex glasses were made within the temperature range 170–700 K. Three different polarization peaks were found and compared with the peaks for alkali-rich glasses. The data were interpreted in terms of the heterogeneous distribution of alkali ions and structural rearrangement of the silicon network near the electrodes.     

Thermally stimulated currents of Lanthanum metaniobate ceramics

A series of LaNb₃O₉ samples was prepared at 1325-1360 °C by the solid state reaction. The structures, temperature dependence of thermally stimulated currents and impedances were investigated. The samples show single phase of LaNb₃O₉ by XRD analysis. The SEM analysis exhibits that the grain size increases and the porosity factor decreases with increasing sintering temperature. The stimulated current decreases with increasing sintering temperature and a large current of ∼ 110 µA without applied voltage was observed in the LaNb₃O₉ sample sintered at 1325 °C. The polarization-electric field and temperature dependence of impedance results suggest that the temperature dependence of current does not originate from pyroelectric effect, but from the release of thermally stimulated current.     

Thermally stimulated currents in n-InS single crystals

Thermally stimulated current measurements are carried out on as-grown n-InS single crystals in the temperature range of 10-125 K. Experimental evidence is found for four trapping centers present in InS. They are located at 20, 35, 60 and 130 meV. The trap parameters have been determined by various methods of analysis, and they agree well with each other.     

Thermally stimulated discharge currents in polyvinyl pyrrolidone polymer films

Polyvinyl pyrrolidone films of thickness 17.6 μm were grown by the isothermal solution growth technique. Thermally stimulated discharge currents were studied on these films as a function of polarizing field strength and polarizing temperature, at a constant heating rate of 0.14 Ks⁻¹. In all these studies only one TSDC peak was observed and the temperature corresponding to this peak was found to show weak but definite dependence on the polarizing field strength and polarizing temperature. The activation energies and relaxation parameters and charge associated with this peak were evaluated. The origin of TSDC was attributed to the space charge process.     

Thermally stimulated discharge currents from pyrene-doped polystyrene films

Pyrene was mixed with polystyrene (PS) in different molar concentrations in the range 0.2–12 mol.% and thermally stimulated discharge (TSD) current spectra of the doped PS films were studied for various dopant concentrations, polarizing fields and forming temperatures. Unpolarized films were observed to give a peak at 95°C. The TSD current peak in the main relaxation region of PS shifts to the lower temperature side of the spectrum with increasing concentration of the dopant. The strong dependence of space charge polarization on the dopant concentration and the forming temperature is assigned to an increase in the conductivity of the polymer.     

Dielectric breakdown in monomolecular layers

This paper describes the different phenomena encountered in the breakdown of very thin insulating films made of 1 to 9 Langmuir monomolecular layers. Three steps are observed in the breakdown process: bubble formation, a sharp current increase and the breakdown proper; a mechanism is proposed for each of these phenomena. Values of breakdown voltages and fields are given for monomolecular layers of various molecules between aluminium electrodes. The respective roles of the oxide and of the organic layers are discussed.     

Energy transfer in dye monomolecular layers

In monolayers the planar array of highly polarizable and adjoining dye molecules is favourable to singlet energy transfer. We give some evidences of energy transfer between sensitizers and acceptors in the plane of the layers. The radius of the excitonic cross section of the acceptor is about 60 Å.     

Thermally stimulated currents in a-Se99.5Bi0.5 thin films

The present paper reports on thermally stimulated current measurements in a-Se_99.5Bi_0.5 thin films at different heating rates (β₁ = 2.17 K/min, β₂ = 2.85 K/min, β₃ = 5.00 K/min). A well-defined TSC peak at a particular temperature has been observed which shifts toward higher temperatures (T₁ = 362 K, T₂ = 372 K, T₃ = 392 K) on increasing the heating rate (β). Using three different approaches the trap depth has been calculated giving good agreement with each other. The average value of trap depth is 0.29 eV. Trap density has also been calculated to be 6.62 × 10¹⁹ cm⁻³.     

The trap parameters in polycrystalline tetracene layers from measurements of thermally stimulated currents and space charge limited currents

The trap parameters in thin polycrystalline tetracene films are investigated. The thermally stimulated current technique determining parameters of shallow traps and a differential method of analysis of steady-state isothermal current-voltage characteristics for estimating energies and density of deep traps are used.     

Frictional properties of monomolecular layers of silane compounds

The frictional performance of ultrathin films was evaluated, especially in monomolecular layers of silane compounds. The monolayer of γ-(N,N- dioctadecylsuccinylamino)propyltriethoxysilane is one of the candidates for the best lubricating film. The film exhibited a low coefficient of kinetic friction, μ_k < 0.1, and 10⁵ transits without stick-slip. From X-ray photoelectron spectroscopy and Fourier transform IR analysis, both the adhesion between the molecules of the lubricant and the surface of the substrate and the cohesion between the molecules of the lubricant are extremely strong.     

Thermally induced switching in thin p-quaterphenyl layers

The influence of temperature on the electrical conductivity of p-quaterphenyl layers has been investigated. The current-voltage and current-temperature characteristics are presented.The switching effect that occurs with changes in temperature has been confirmed in the thin p-quaterphenyl films investigated.     

Thermally induced directed currents in hard rod systems

We study the non equilibrium statistical properties of a one dimensional hard-rod fluid undergoing collisions and subject to a spatially non uniform Gaussian heat-bath and periodic potential. The system is able to sustain finite currents when the spatially inhomogeneous heat-bath and the periodic potential profile display an appropriate relative phase shift, ${\phi}$ . By comparison with the collisionless limit, we determine the conditions for the most efficient transport among inelastic, elastic and non interacting rods. We show that the situation is complex as, depending on shape of the temperature profile, the current of one system may outperform the others.     

Thermally stimulated polarization current in sodium germanate glass

The electrical conductivity of XNa₂O·(100–X)GeO₂ glasses where X is 0.19 and 27.5 mol%, was studied by means of the technique of thermally stimulated polarization current. The compositional dependence of the parameter ₀ T/n ^1/3, where ₀ is the preexponential facor for conductivity and n is the nominal concentration of sodium ions, suggests that these glasses contain some sort of inhomogeneities. This suggestion is supported by the phase diagram.