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The sample of pure and malachite green doped Polysulfone in the form of foil was prepared by solution cast technique. For the preparation of pure sample 3 gm of Polysulfone was dissolved in 50 ml of Dimethyl farmamide (DMF) solvent, while for the preparation of doped sample 3 mg, 5 mg and 7 mg Malachite Green was mixed with 3 gm of Polysulfone respectively. For the study of structural characterization of these pure and doped sample, Ultra-Violet Spectroscopy (UV) technique was used. PSF and MG used for the present study were supplied by Glexo Leb. Bombay. The absorption spectra were record by UV-VIS spectrophotometer 2540 in the wavelength range from 200 to 800 nm.The sample of pure and malachite green doped Polysulfone in the form of foil was prepared by solution cast technique. For the preparation of pure sample 3 gm of Polysulfone was dissolved in 50 ml of Dimethyl farmamide (DMF) solvent, while for the preparation of doped sample 3 mg, 5 mg and 7 mg Malachite Green was mixed with 3 gm of Polysulfone respectively. For the study of structural characterization of these pure and doped sample, Ultra-Violet Spectroscopy (UV) technique was used. PSF and MG used for the present study were supplied by Glexo Leb. Bombay. The absorption spectra were record by UV-VIS spectrophotometer 2540 in the wavelength range from 200 to 800 nm.

Polymers are regarded as good dielectrics which are capable of storing the charge in them permanently, when subjected to a field – temperature treatment. The electret state and carrier mobility of polymers can be greatly affected by impregnating the polymer with suitable dopants. The process of doping of organic compound of low molecular weight improves the electrical conductivity of polymer due to formation of charge transfer interaction between acceptor and donor molecule. Spectroscopic techniques are used to illustrate the structural modification in pure polymer with increasing ratio of impurity. In the present investigation, Polysulfone is used as host polymer and malachite Green is used as dopant. The sample of pure and malachite green doped Polysulfone in the form of foil were prepared by isothermal immersion technique. For the preparation of pure sample 4 gm of Polysulfone was dissolved in 50 ml of Dimethyl farmamide (DMF) solvent, while for the preparation of doped sample 10,25, 50 and 100 mg Malachite Green was mixed with 4 gm of Polysulfone respectively. For the study of structural and optical characterization of these pure and doped samples, X-Ray Diffraction Spectroscopy (XRD) and UV-Visible spectroscopy techniques were used. The XRD diffractograms of pure and doped polysulfone shows both sharp as well as diffused peaks respectively correspond to the crystalline regions and amorphous regions of polymer. While considering the variation of intensity with two theta angle, it is observed that for pure sample maximum intensity is observed at 18.280, whereas for doped samples maximum intensity is observed at 18.510, 18.860, 20.360, 20.810 respectively due to the increase in doping ratio. This observation confirms the enhancement in amorphous nature of polysulfone. The UV-Visible spectroscopic study shows that the transmittance decreases as the ratio of doping is increased in pure polysulfone. The reduction in intensity of transmittance of pure sample is clearly apparent in the present case and some new peaks are also observed. This action indicates the development of Charge Transfer Complexes (CTC) between the donor and acceptor molecule, and hence signifies the improvement in electrical properties of Polysulfone polymer.

Electrical conductivity of pure PVC, PMMA and their polyblends samples has been studied in detail as a function of polarizing fields at constant temperatures. Different plots were drawn to investigate the nature of mechanism responsible for conduction. The nature of all the thermograms is nonlinear but similar for all temperatures. The plots have two slopes, i.e., ohmic conduction with slope of curve ≈1 at lower voltage region and a non-ohmic conduction with slope ≈1.9 at higher voltage region are observed. The increase in the conductivity and decrease in the activation energy, suggest that plasticization effect is taking place between the polymers when they are blended. Fowler–Nordheim plots are not consistent and showing negative and positive slopes simultaneously for lower as well as higher values of applied voltage. Theoretical and experimental values of βSR and βPF were calculated and the βexp of pure and polyblend samples is in agreement with theoretically βPF. The βexp value lies close to βPF, this shows that Poole–Frenkel mechanism is also effective. The calculated metal electrode potential barrier at a constant voltage suggests that the dominant charge carrier mechanism is Schottky–Richardson type. Hence in the present case both SR and PF mechanisms are seem to be operative.

Thermally stimulated discharge current (TSDC) studies were carried out on pure poly(methyl methacrylate), poly(vinyl chloride) and polyblends (of various weight ratios, 100:0, 90:10, 80:20 and 70:30) as a function of polarizing fields at constant temperature, to study the polarization and relaxation phenomena in them. For PVC and different blends a peak around 140–180 °C and for PMMA two peaks at around 95 and 165 °C were observed. No regular variation in peak position for PMMA and blends was observed. The various TSDC parameters i.e. activation energy, charge released and relaxation times were calculated. In the blend samples it is suggested that the chains are so entangled that in the total polarization the dipolar contribution is less and the observed polarization seems to be mainly due to the formation of induced dipoles and an increase in free volume and mobility of charge carriers due to a plasticization effect.

Dental, oral and maxillofacial region are very sensitive so low radiation imaging technique like Cone Beam Computed Tomography (CBCT) is useful for investigation of diseases. But due to low radiation, quality of images is not fine they have noise and low contrast in visual impression. So for dentistry diagnostic purpose it is important to pre-process the CBCT image. This paper focuses on improvement of contrast, brightness and noise reduction of dental CBCT images by using Bi Histogram Equalization technique with bent activation function and adaptive median filter for noise reduction. The output image has been analyzed and evaluated using peak value ratio in term of Signal versus Noise (PSNR) and matrix of Structure in term of Similarity Index (SSIM). From the experimental results, it has been found that the adaptive median and Bi histogram with bent activation function has a better noise and enhancement capability as compare to convectional histogram method.

Dielectric properties of polymer blend of polyvinylidenefluoride (PVDF) and polysulfone (PSF) of different wt. % have been studied to understand the molecular motion and their relaxation behavior in the frequency range of 100 Hz to 10 kHz at different temperatures between 30 and 190 °C. The dielectric constant of the blend decreased with frequency and increased with the increasing temperature and PSF content in the blend. The magnitude of dielectric loss also increased with increase in temperature and PSF content. The observed characteristic has been consistently explained in terms of dipolar motions and the plasticization effect brought about by blending of PSF with PVDF. At constant frequency and temperature, the blend follows a linear relationship between logarithm of their dielectric constant and different ratios of blend. The appearance of a peak for each concentration in dielectric loss suggests the presence of relaxing dipoles in the blend. In addition of PSF with PVDF, the peak shifts toward higher frequency side suggesting the speed up the relaxation process. AC dielectric data is also combined with thermally stimulated depolarization current (TSDC) data which is generally studied for low-frequency dielectric properties of polymers blends so as to produce the results in a wide frequency range. The glass transition temperature ( T g ) of the blend was studied by differential scanning calorimetric technique (DSC), the T g was compared and correlated with TSDC peak. The blend samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) to study the formation of blend and micro structural properties of the materials. The shifting of peak toward lower diffraction angle side confirms the reduction in particle size with increasing amorphous content in the blend.

The TSDC and transient currents measurement have been carried out on pure poly(vinyl chloride), poly(methyl methacrylate) and polyblends of various weight ratios as a function of electric fields at constant poling temperature. For PVC and different blend samples single peak in the temperature range 100–170 °C has been observed in TSDC thermograms, however, for PMMA samples two peaks were observed at around 90 and 165 °C. The various TSDC parameters i.e. activation energy, charge released and relaxation times have been calculated. Results suggest that dipolar and space charge mechanism are dominant for observed current.

Thermally stimulated depolarization current (TSDC) have been undertaken on solution grown foil samples of polyvinylidenefluoride (PVDF)-polysulfone (PSF) blends as a function of the polarizing temperature, applied field, and polysulfone weight percentage in the blend. The TSDC thermograms of pure PVDF and PSF shows two peaks whereas the blend composition of the two polymers shows a single peak at around 170–190°C. The magnitude of the TSDC peak current increases and the peak current position shifted toward the lower temperature side as the polysulfone weight percentage in the blends was increased. The peak temperature of blend samples is higher than the dipolar peak (β peak) of PVDF samples and does not vary with change in polarizing field. This indicates that this peak may be due to dipoles. At the same time, the peak shifts towards higher temperatures with increase in polarizing temperature, which shows the behavior of space charge peak. This contradiction may be explained on the basis of induced dipole...

The temperature and electric field dependence of dielectric relaxation have been investigated in amorphous polysulfone (PSF) samples using thermally stimulated discharge current (TSDC) and AC dielectric measurement. All measurements were performed on solution grown thin films of thickness 50 μm. The nature of relaxation mechanisms in amorphous PSF is discussed on the basis of TSDC and dielectric measurement results. The comparative studies of dielectric properties with TSDC indicated a strong resemblance between the two techniques. Polysulfone (PSF) films are characterized by two TSDC peaks, i.e. β peak at 348 K and α peak at 470 K. The depolarization current for the β peak increases linearly with poling field. The peak obtained at lower temperature (i.e. β peak) is associated with dipolar relaxation and the other one obtained at high temperature (i.e. α peak), which appears due to the α relaxation.

A commercial mode locked cavity dumped Nd:YAG dye laser operating at 10 Hz repetition rate is modified to produce a high contrast (>5000:1) single laser pulse while maintaining the energy stability and high beam quality. A trigger generator biases the cavity dumping photodiode, which is triggered externally by a pulse from the microprocessor-based control unit controlling a ∼2 J/200 ps laser chain. In the laser chain, the high contrast (>5000:1) is achieved by an external pulse selector based on single Pockel's cell to select a single laser pulse of high contrast, which is a prerequisite for experimental study of the equation of state. Laser-induced shock velocity measurement in thin aluminum, gold on aluminum, and copper on aluminum foil targets using this modified laser system are also presented. The equation of state of Al, Au, and Cu obtained using an impedance matching technique are in agreement with the reported results of SESAME and simulation results.

In the present paper charging and discharging transient currents in polyvinyl formal (PVF) were measured as a function of temperatures (40–80°C), poling fields (90 ×103−9.0 × 104 V/cm) and electrode combinations (Al-Al, Au-Al, Zn-Al, Bi-Al, Cu-Al and Ag-Al). The current-time characteristics have different values of slope lying between 0.42–0.56 and 1.42–1.63. The polarization is considered to be due to dipolar reorientation associated with structural motions and space charge relaxations due to trapping of injected charge carriers in energetically distributed traps.

An appreciable electric current is observed in a system consisting of a polyvinyl formal (PVF) film in a sandwich configuration, in the temperature range 30–110°C. The maximum value of the current during first heating is found to be of the order of 10−10 A and its thermograms exhibit one transition (i.e. current peak) at around 60°C. The position of the current peak in thermal spectrum shifts with the heating rate. A temperature dependence of the open circuit voltage is also observed. The activation energy of the process responsible for the current is determined. The magnitude of the current is more in the case of dissimilar electrode systems. It is proposed that the electric current arising from unpolarized metal-polymer-metal system is a water activated phenomenon, which is influenced by the transitional changes of the polymer.

The charge-transport behaviour in pure and chloranil (Chl) doped ethyl cellulose (EC) system has been studied by measuring the dependence of current on field, temperature, electrode material and dopant concentration. The role of doping molecular concentration in the polymer matrix and modification in the conduction characteristics are studied. Lowering of the activation energy due to doping was observed. The current was found to increase with an increase in the chloranil concentration. An explanation for this has been attempted on the basis of formation of molecular aggregates between chloranil molecules and ethoxy groups of ethyl cellulose. It is suggested that chloranil occupies interstitial positions between the polymer chains and assists in carrier transportation by reducing the hopping barriers. The current-voltage characteristics of different samples are analyzed using space charge limited current theory and quantitative information about the transport parameters is derived. The values of effective drift mobility and trapped charge carrier concentration which result in the build up of space charge have been calculated.

Dielectric capacities and losses were measured, in the temperature (50–170°C) and frequency (01–100 kHz range), for undoped and acrylic acid (AA) doped ethyl cellulose (EC) films (thickness about 20 μm) with progressive increase in the concentration of dopant in the polymer matrix. The variation of capacity with temperature is attributed to thermal expansion in the lower temperature region to the orientation of dipolar molecules in the neighbourhood of glass transition temperature (T g) and random thermal motion of molecules aboveT g. The dielectric losses exhibit a broad peak. Doping with AA is found to affect the magnitude and position of the peak. AA is found to have a two-fold action. Firstly, it enhances the chain mobility and secondly, it increases the dielectric loss by forming charge transfer complexes.

Thermally stimulated depolarization current (TSDC) studies have been performed on solution grown cellulose acetate films doped with different concentrations of acrylic acid (AA) prepared at the poling temperatures (40–75°C) with poling fields (10–50 kV/cm). The TSDC spectra of pure and AA doped CA films reveal two relaxation peaks at 80°C and 180 ±2°C, having activation energies centred around 0.25 and 0.55 eV. The phenomena of the existence of these current maxima have been analyzed and discussed in terms of the molecular motion of the polar side groups and release of the remaining part of the frozen dipoles by their cooperative motion with adjoining segments of the main polymer chain. The peak currents, released charge and activation energies associated with the peaks are affected by AA doping. The effect of doping with acrylic acid on the discharge current indicates the formation of molecular aggregates

Infrared-to-visible wave-length conversion in the Yb3+−Er3+ doped phosphors system has been described by a simple three level model based on two ions mechanism. The excitation in the range of 900–1000 nm of an IR-photon is first absorbed by Yb3+ ion as a sensitizer attributed to the resonant energy transition in Er3+ ion from 4I3/2 → 4S15/2 and 1F9/2 → 4I15/2, respectively for green and red emission. The essential energy transfer processes in this system i.e. upconversion from 4I11/2 and 1I13/2, cross-relaxation from 4S3/2 and 1F9/2 are taken into account. The limitations of the rate-equation approach are examined with a focus on the underlying dynamics of this rare-earth system.

Current-voltage (I–V) characteristics of pure polyvinyl formal (PVF) were investigated at different fields, range 5–100 kV/cm, as a function of temperature, range 313–363 K. It was observed that while at low fields (up to 25 kV/cm), the conduction was Ohm’s law-dependent at high fields (beyond 25 kV/cm), the conduction was Poole-Frenkel (P-F) mechanism-dependent. An attempt was made to identify the nature of the current by comparing its observed dependence on temperature, electric field and electrode materials with their respective characteristic features of the existing theories of electrical conduction. The current showed a strong dependence on temperature. To identify the possible mechanism of conduction, current versus square root of field characteristics were drawn with aluminium, silver, copper and gold as upper electrodes and Al as the lower electrodes. The observed characteristic suggested that the charge carriers were generated by the field-assisted lowering of coulombic barriers at the traps, and were subsequently conducted through the bulk of the material by a hopping process between the localized states by a Jonscher-Ansari-modified P-F mechanism. The calculated value of the modified P-F barrier was ⋍ 1·94×10−19 J (1·21 eV).

Mechanisms of charge generation and its persistence in one and both-side vacuum-aluminized ethyl cellulose (EC):polymethyl methacrylate (PMMA) blend thermoelectrets, prepared under different fields (10, 25, 50 and 100 kV/cm) and temperatures (40, 60, 80 and 100°C), have been analysed using short- and open-circuit thermally stimulated depolarization current (TSDC) technique. The TSDCs were recorded by reheating the samples at a linear heating rate of 4°C/min. The TSDC thermograms of polyblends containing EC:PMMA in different weight ratio are, in general, characterized with two peaks in lower and higher temperature regions. However, the polarity of the peaks was found to be just opposite in short- and open-circuit TSDC measurements. Moreover, results on 97:3, 93:7 and 90:10 EC:PMMA polyblends indicated that the current increases with concentration of PMMA. The results indicate the existence of heterocharge due to dipole orientation and ionic charge drift together with the injection of charge carriers from electrodes with their subsequent localization in surface and bulk traps. Further, the chances of charge trapping in polyblends, at the interfaces are greater than in the individual polymers.

A four-arm Nd:phosphate glass laser system is being built and is being tested. Major design features include Nd:phosphate glass rods up to a diameter of 80 mm and a disc amplifier system of diameter 100 mm. The system has a sequentially-relayed and spatially-filtered architecture. Since this project is a technology demonstrator, the main aim of this project has been to develop indigenously Nd:phosphate glass rods and discs and the dielectric coated optics for this laser. A program has also been taken up for large diameter deuterated KDP pockels cells and harmonic converters.

Depolarization current characteristics of solution grown pure ethyl cellulose (EC) films of about 20µm thickness have been studied as a function of electrode materials at constant poling field (5 × 104 V/cm) and poling temperature 40°C. Thermally stimulated current (TSC) thermograms of EC consists of two well resolved peaks (located at 60°C and 140°C) for Al-Al system, which are attributed to the deorientation of strongly attached ethoxy groups of glycosidal units and diffusion of space charges either at electrodes or due to their thermal release at higher temperatures from the defect levels. For dissimilar electrode combinations (Al-Ag/Cu/Au/Sn/Pb), an indication of peak of lower magnitude at around (50–70°C) alongwith a higher temperature peak (140–155°C), have been observed. TSC parameters are found to change with the choice of electrode material. The dependence of dark current at 40°C in metal-ethyl cellulose-metal systems on applied voltage in the range (2·0–5·0) × 104V/cm has also been studied. The results of current-voltage measurement on EC have been interpreted to show that the Schottky-Richardson mechanism is the controlling transport mechanism. Zero field current density extrapolated fromI-E 1/2 plots are found to vary with metal work function.

A detailed study of electrical conduction mechanism in bimetallized ferrocene-doped polyvinyl pyrrolidone films was carried out. The measurements were carried out on films of about 20 μm thick, in the field range of (2.0–8.0) x 104 V/cm at temperatures ranging from 363 to 423 K. An investigation of the effect of impurity such as ferrocene in the polymer matrix was undertaken. Lowering of activation energy and increase in current due to doping were observed. The results showed that the charge carriers were generated by field-assisted lowering of coulombic barriers at the traps and were conducted through the bulk of the material by a hopping process between the localized states by a Jonscher-Ansari modified Poole-Frenkel mechanism. The dependence of current and activation energy on the ferrocene concentration is explained on the basis of charge transfer type of interaction between dopant and polymeric material.

A study of the spontaneous response currents from the metal-iodine doped polyvinyl pyrrolidone-metal (MPM) systems, on thermal stimulation at a constant rate, has been made with similar (Al-Al, Ag-Ag and Au-Au) and dissimilar (Al-Cu/Ag/Ni/PbZn) electrode systems. Thermograms of spontaneous current emission of iodine-doped PVP films exhibit two maxima around 90 ± 10°C and 130–160°C in the first heating run, whereas with the second heating run a single peak is found around 140–170°C. The magnitude and direction of current depend on the choice and combination of electrode materials. The position of the current peak in the thermal spectrum shifts with different heating run. A temperature dependence of open-circuit voltage (OCV) is also reported and it was found that OCV varied linearly with the difference in electrode work functions. The active centres of PVP are the carbonyl group of double-bond tertiary nitrogen atom (> N-C=O), and thus the charge transfer complexes are formed with iodine in PVP. The spontaneously-generated current is discussed in terms of weak complex formation with the water molecules and the liberation of different types of charges.

The electrical transport behaviour of ferrocene mixed poly (methyl methacrylate) (PMMA) films (≈ 20 µm in thickness) deposited by the isothermal immersion technique has been studied in the temperature range of 333–373 K and field from (2·0–4·0)×104 V/cm. It has been found that at higher fields and temperatures, the observed conduction behaviour could be consistently described by the Richardson-Schottky emission. The increase in current due to doping has been attributed to the formation of charge transfer complexes. The dopant molecules act as an additional trapping centre and provide a link between polymer molecules in amorphous region leading to the formation of charge transfer complex.

Transient currents, measured with pure and iodine doped polyvinyl formal (PVF) films as a function of poling field (15–100 kV/cm) and temperature (30–95°C), have been found to follow Curie-von Schweidler law characterized with two slopes in short and long time regions. The isochronals (i.e. current/temperature plots at constant times) have been found to give rise to a peak located at 75°C. The order of current has been found to increase with increase in poling field, temperature and iodine mixing. The comparative studies of the isochronals with the thermally stimulated discharge current (TSDC) indicated the strong resemblance between the two studies. It is suggested that both the dipolar orientation due to molecular mechanism of motions with the side chains and space charge due to trapping of injected charge carriers in energetically distributed traps may be responsible for the observed currents. The dependence of current and activation energy on iodine mixing is explained on the basis of a charge transfer type of interaction.

This paper describes the method for investigating the electrical properties of high solids via the study of thermal relaxation effects and offers an alternative scheme to the conventional bridge methods or the current voltage temperature measurements. For standard TSD experiment, this is comparable to a dielectric loss measurement, the low equivalent frequency and high sensitivity (ability to detect dipole concentration). The activation energies found by initial rise method are 0.31 ± 0.02 eV for pure and 0.43 ± 0.03 eV for malachite green sensitized PVK thermoelectrets. The peak current charges and activation energy associated with the peaks are affected by concentration of malachite green and have been explained in terms of formation of charge transfer complexes and molecular aggregates. The microscopic origin of a given current spectrum is explained by comparing the predictions of the general theories regarding the main polarization processes with the experimental data.

Thermally stimulated current (TSC) characteristics are investigated in thermally charged 20 μm thick vacuum aluminized polymethyl methacrylate doped with various concentrations of malachite green. The dopant is found to form acceptor-donor charge transfer complexes with the host material. The increased mobility of charge carriers is observed to have considerable effect on peak characteristics. The appearance of an anomalous peak at around 125 ± 5 °C in doped samples is attributed to the formation of a hetero space charge near the electrodes.

The transient currents measured in discharge mode with cellulose acetate (CA): polyvinyl acetate (PVAc) blend films (≈ 20µm thick) as a function of charging field [(1.5–4.5)×104 V/cm], temperatures (323–373 K) and polymer weight ratio (90:10 and 75:25) have been found to follow Curie-von Schweidler law, characterized with two slopes in short and long time regions. Isochronals characteristics (i.e. current/temperature plots at constant times) constructed from these data seemed to reveal a broad peak observed at 363 K. Values of activation energy increase with PAVc content and also with time of observation. Space charge due to trapping of injected charge carriers in energetically distributed traps and induced dipoles created because of the piling up of charge carriers at the phase boundary of heterogeneous structure of blend are considered to account for the observed currents.

The electrical conduction behavior of malachite green doped PVK thermoelectrets has been carried out in the temperature range 40 °C to 70 °C with four different polarizing fields for samples of constant thickness about 40 μm.The observed linear I‐V characteristics show two regions of conduction with a slope of 0.68–0.88 at lower and 1.87–2.05 at higher fields. The results on pure and malachite green doped PVK samples are interpreted to show that the low field steady state conduction is ohmic in nature and in high fields the charge carriers are generated by field assisted lowering of coulombic barriers at the traps and are conducted through the bulk of the material between the localized states by a Poole Frenkel mechanism.

This paper describes the results of SEM, EDX, UV‐vis and TSDC study of malachite green doped PVK thermelectrets. TSDC study has been carried out in the temperature range 300 °C to 1500 °C with four different polarizing fields. One peak was observed at 110±10 °C which shifts toward high temperature with the increase in polarizing field. The activation energy found by initial rise method are 0.27±0.02 eV for pure and 0.40±0.03 eV for malachite green doped PVK thermoelectrets. Spectroscopic study concluded that impregnation of malachite green in polymer matrix forms charge transfer complexes.

The mechanism of charge production and its persistence in pure and malachite green mixed ethyl cellulose (EC) films have been analyzed using short circuit thermally stimulated discharge current (TSDC) in conjunction with that of transient discharging current as a function of similar and dissimilar electrode metals, polarizing fields, and polarizing temperatures. The TSDC thermograms of EC were characterized by two peaks at 343 and 423 K in the case of similar electrodes. With dissimilar electrodes, however, a broad peak was observed between 413-433 K. Transient currents, have been found to follow the Curie-von-Schweidler law, characterized with different slopes in short and long time regions and having different values of decay constant. The corresponding energies are found to increase with measurement time of the discharge current. The conductivity of the films is increased on doping with malachite green. A close scrutiny of the observed results suggest that a dipolar mechanism coupled with space charge formation due to accumulation of charge carriers near the electrodes and subsequent trapping of such carriers in the bulk may be considered as the dominant mechanism responsible for discharging currents. The effect of doping with malachite green on the discharge current indicates the formation of molecular aggregates.

The electrical transport behaviour of ferrocene mixed polymethylmethacrylate (PMMA) films (approximately 20 microns in thickness) deposited by the isothermal immersion technique has been studied in the temperature range of 333-373 K and field from (2.0-4.0)/spl times/10/sup 4/ volts/cm. It has been found that at higher fields and temperatures, the observed conduction behaviour could be consistently described by the Richardson-Schottky emission. Increase in current due to doping has been attributed the formation of charge transfer complexes. The dopant molecules acts as an additional trapping centre and provide a link between polymer molecules in the amorphous region leading to the formation of a charge transfer complex.

The study has been made on 60 /spl mu/m thick solution grown single and two-layer pure and iodine (I/sub 2/) doped polystyrene (PS) specimens. For two-layer samples, I/sub 2/-doped layer was solution grown on previously obtained undoped layer on glass substrate. The samples were vacuum aluminized over central circular area of 3.6 cm diameter on one surface, and then were thermally polarized at different temperatures (T/sub p/) (i.e. 20, 75 and 100/spl deg/C) with 100 kV/cm polarizing field. Initial charge density has been found to be of 10/sup -8/ Coul/cm/sup 2/. The symbols (+) and (-) mean that positive and negative voltage were applied to the doped-layer side. For undoped and two-layer (+) the charge has always been found to be heterocharge. However, two-layer (-) are characterized with homocharge, when poled with high values of field and temperature.

Thermally stimulated currents (TSCs) in short- and open-circuit configuration for thermally poled ethyl cellulose (EC) foil samples have been found to be characterized with two prominent peaks located around 70 and 100 degrees C. Various characteristics of these thermograms along with currents of opposite polarity in short- and open-circuit, and the appearance of anomalous current in the low temperature region of short-circuit TSC thermograms have been considered to be indicative of intense charge trapping in surface and bulk traps and of the injection of carriers from electrodes under strong field at the near-surface region created by heterocharges. >

Mechanisms of charge production and its persistence in one and both side vacuum-aluminized EC:PMMA blend foil thermoelectrets, prepared under different field and temperature conditions, have been analyzed using the short- and open-circuit thermally stimulated current (TSC) techniques. The results indicate the existence of heterocharge due to dipole orientation and ionic charge drift together with the injection of charge carriers from electrodes with their subsequent localization in surface and bulk traps. Various characteristics of both types of thermograms indicated the injection of charge carriers from electrodes during short-circuit TSC under high electric field created at the interface by the strong heterocharge. >

Short-circuit thermally stimulated current (TSC) measurements have been made on thermally polarized foils. The results indicated that the electret state of these samples is due to dipolar orientation and charge trapping. Iodine doping has been found to form a charge transfer complex and hence to modify the electret state of the samples significantly. Higher concentration of doping and charging at higher temperatures has been found to favor charge carrier trapping in energetically deeper traps. An anomalous peak observed in strongly doped samples polarized at higher temperatures is considered to be due to detrapping of carriers from such deeper traps. >