The effects ofmolecularweight and the solvents used for gate dielectric deposition on output and transfer characteristics ofOFETdeviceswith bottomgate contact have been studied. Polyvinylalcohol (PVA)withmolecularweights 30000 and 145000 g/ mol (PVA1 and PVA2, respectively)was used as gate dielectric and deionized-water and dimethylsulfoxide (DMSO) as solvents.This studydemonstratedthat both themolecularweight and solvent affect the output and transfer characteristics of theOFETdevices.Consider-ableimprovement inthresholdvoltagehasbeenachieved for eachmolecularweight in the case ofDMSOused as solvent. The observed clockwise hysteresis fromthe Vgs-Ids curves and their solvent dependence implies that the presence of the polar groups inside the gate dielectric can control device characteristics.

The electrical, optical, and metal-semiconductor contact properties of the polyaniline prepared by emulsion polymerization have been investigated to obtain an organic semiconductor material. The obtained results suggest that the polyaniline (PANI) studied is an organic semiconductor material with optical band gap (E(g) = 2.21 eV) and room electrical conductivity (sigma(25) = 3.12 x 10(-2) S/cm) values. A Schottky diode with configuration Ag/PANI/n-Si was fabricated. The ideality factor and barrier height of Ag/PANI/n-Si diode at room temperature were found to be 4.59 and 0.38 eV, respectively. The obtained diode parameters change with temperature. The Richardson constant A* value for the Ag/PANI/n-Si diode was found to be 3.81 x 10(-4) A/cm(2).K. The Ag/PANI/n-Si diode is a metal-insulator-semiconductor-type device. The standard deviation, which is a measure of the barrier homogeneity, was found to be 0.14, indicating the presence of interface inhomogeneities. It can be concluded that the polyaniline prepared by emulsion polymerization is an organic semiconductor and Ag/PANI/n-Si configuration shows a Schottky contact.

The results of measurements of the dielectric constant of TlGaSe2 in the temperature range of successive phase transitions in various regimes, including the measurements after annealing the sample at a fixed temperature in the incommensurate phase are presented. A noticeable influence of the sample prehistory on the dielectric behavior of TlGaSe2 has been revealed. Peculiarities of the anomalies in the temperature dependence of the dielectric constant corresponding to structural phase transitions at the temperatures of 108K and 115K are discussed. It is suggested that these anomalies can be interpreted as successive lock-in commensurate transitions due to incommensurate structures appearing at 120K and 242K respectively.

The optical absorption spectrum, luminescence and photoconductivity on single crystals PbMg1/3Nb2/3O3 and on ceramics Pb0.91La0.09(Zr0.65Ti0.35)O-3 are investigated in the wide temperature range. The luminescence spectrum correlates with the photoconductivity spectrum. The position of the maximum of the luminescent emission spectrum indicates the origin of the charge carriers emitted from the defect centers. On the basis of the data the properties of the local centers are determined, and the phenomenological approach to the relaxor theory is discussed.

The alternating current (AC) conductivity and dielectric properties of the Co-doped TiO2 were investigated. The temperature dependence of AC conductivity and the parameter s, is reasonably well interpreted by the correlated barrier hopping (CBH) model. The activation energy (E), and the density of states at Fermi level, N(EF) were determined. The dielectric constant decreases with frequency at low frequencies and increases at high frequencies.

The phase transition in carbon nano-balls' doped nematic liquid crystals has been investigated by electrical conductivity-dielectric measurements. The results of electrical conductivity and dielectric constant as a function temperature and frequency indicate that a phase transition, which is of the first order, takes place from nematic state and isotropic state. The phase transition for E7 and E7/C60 samples takes place at 326 and 321 K temperatures, respectively.

The temperature dependences of the dielectric constants of the ferroelectric semiconductors TlInS2 and TlGaSe2 have been studied following their annealing within the incommensurate phase. Unusual memory effects accompanied by both a remarkable inflection of the temperature dependence curves in the incommensurate phase and various shifts of the incommensurate (Ti) and commensurate (Tc) phase transition temperatures have been revealed in both crystals. The observed effects are explained on the basis of a defect density wave model taking into account the interaction of modulation waves with charge carriers localized at impurity states. The thermally activated population of these states during the heating or cooling processes is responsible for the changes of the phase transition temperatures.

The temperature dependences of the dielectric constants of the ferroelectric semiconductors TlInS2 and TlGaSe2 have been studied following their annealing within the incommensurate phase. Unusual memory effects accompanied by both a remarkable inflection of the temperature dependence curves in the incommensurate phase and various shifts of the incommensurate (T-i) and commensurate (T-c) phase transition temperatures have been revealed in both crystals. The observed effects are explained on the basis of a defect density wave model taking into account the interaction of modulation waves with charge carriers localized at impurity states. The thermally activated population of these states during the heating or cooling processes is responsible for the changes of the phase transition temperatures.

Some renal stones were investigated by electron paramagnetic resonance of their untreated, UV-photolyzed and gamma-irradiated states. Powder X-ray diffraction technique indicated that the renal stones were made mainly from CaC2O4, MgC2O4, MgCO3 and NH4MgPO4·6H2O. Before radiation treatment, the renal stones yielded a signal that could be attributed to a C˙2O4- radical. UV-photolysis seems to slightly increase the intensity of this signal, but does not produce any new centres. Gamma-irradiation initially gives –CH2C˙(CH3)–R and C˙O2- radicals, and while the intensity of the –CH2C˙(CH3)–R signal decreases, the intensity of the C˙O2- signal increases as time elapses.

Electronic and interface state distribution properties of Ag/p-Si Schottky diode have been investigated. The diode indicates non-ideal current–voltage behavior with an ideality factor greater than unity. The capacitance–voltage (C–V) characteristic is linear in reverse bias indicating rectification behavior and charge density within depletion layer is uniform. From I–V and C–V characteristics, junction parameters such as diode ideality factor and barrier height were found as 1.66 and ϕB(I–V)=0.84eV (ϕB(C–V)=0.90eV), respectively. The interface state density Nss and relaxation time τ of the Schottky diode were determined by means of Schottky capacitance spectroscopy method. The results show the presence of thin interfacial layer between the metal and semiconductor.

In this study diamond-like carbon based functionally graded Ti/TixCy/DLC films were deposited by the hybrid technique of magnetron sputtering and DC plasma-enhanced chemical vapor deposition. The coating parameters investigated are; substrate bias (60-200 V), sputtering power (1.0-1.1 kW) and plasma booster current (1.7-2.5 A). The mechanical properties were investigated by calotest and scratch adhesion tests. The elemental depth profiling and the morphology of the coatings were examined by secondary ion mass spectrometer (SIMS) and electron probe micro analyzer (EPMA) which revealed that a functionally graded structure was successfully formed.

Natural alunite and kaolin minerals obtained from West Anatolia were investigated by electron paramagnetic resonance (EPR) in natural and γ-irradiated states at room temperature and at 113 K. The paramagnetic centres at ambient temperature in natural alunite were attributed to the ĊH2OH, , , and [AlO4]0 radicals. In natural kaolin, the paramagnetic centres were attributed to the , , and [AlO4]0 radicals. The γ-irradiation does not produce any detectable effects on these radicals. At 113 K, the lines for ĊH2OH could not be observed well, probably due to the anisotropic behaviour of the hyperfine interaction of the methylene protons, but the lines for [AlO4]0 centres were found to be perfectly observable at above 20 mW microwave power in both alunite and kaolin powders before and after γ-irradiation. The EPR parameters of the observed paramagnetic centres were reported.

c-axis-oriented zinc-oxide (ZnO) thin films were prepared on microscope glass substrates by sol–gel deposition. A homogeneous and stable solution was prepared by dissolving zinc-acetate 2-hydrate (ZnAc) in 2-propanol and diethanolamine. Crystalline ZnO thin films were obtained following an annealing process at temperatures between 450°C and 550°C for 1 h. Increasing annealing temperature increased the grain size and the c-axis orientation. The X-ray diffraction analysis revealed single-phase ZnO with hexagonal zincite structure. The absorption edge analysis revealed that the optical band-gap energy for the films were between 3.26 and 3.28 eV and electronic transition was direct transition type.

Li doped zinc oxide thin films were deposited on glass substrates by a sol-gel technique. Acetates of zinc and lithium were used as metal sources. A homogeneous and stable solution was prepared by dissolving acetates in the solution of 2-propanol and ethanolamine. ZnO:Li thin films were obtained after preheating the spin coated films at 250degreesC for I minute after each coating. A post annealing between 450-600degreesC was applied after the deposition of the last layers. XRD analysis revealed ZnO with zincite structure (Card no: 36-1451) in all films. The thickness of the films was measured as 75 nm per layer. The optical band gap of the films increased as doping concentration of Li increased and decreased as the post-annealing temperature increased.

In this study diamond-like carbon based functionally graded Ti/Ti xCy/DLC films were deposited by the hybrid technique of magnetron sputtering and DC plasma-enhanced chemical vapor deposition. The coating parameters investigated are; substrate bias (60-200 V), sputtering power (1.0-1.1 kW) and plasma booster current (1.7-2.5 A). The mechanical properties were investigated by calotest and scratch adhesion tests. The elemental depth profiling and the morphology of the coatings were examined by secondary ion mass spectrometer (SIMS) and electron probe micro analyzer (EPMA) which revealed that a functionally graded structure was successfully formed.

Indium tin oxide (ITO), a transparent conductive oxide, is a wide band gap compound semiconductor with a cubic bixbyte structure. Sn-doped indium oxide (10) thin films (In:Sn=90:10) were deposited on microscope glass substrates by a sot-gel spin coating technique. The precursor solution was prepared by mixing indium (111) nitrate pentahydrate (In(NO3)(3)(.)5H(2)O) and tin (IV) chloride bis(2,4-pentanedionate) (SnCl2(C5H7O2)(2) dissolved in acetic acid and acetone mixture. Crystalline ITO thin films were obtained after an annealing process at temperatures between 450degreesC-550degreesC for one hour. The microstructure and optical properties of ITO films were investigated as function of annealing temperature. XRD analysis revealed single phase In2O3 (JCPDS 06-0416). The optical transmittance of the films in the visible range was more than %80. The direct optical band gap of ITO films was measured between 3.7-3.9 eV.

The results of measurements of the time dependences of the dielectric constant of TlGaSe2 in the commensurate ferroelectric phase are presented. From the result of the observation of the decay of e at different stabilized temperatures below the commensurate phase transition temperature after cooling from the incommensurate phase, the presence of two different characteristic relaxation time constants with the same temperature behaviour has been revealed. This peculiarity is considered as a result of a coexistence of two polar sublattices in the temperature range below 110 K. According to these results, the previously reported dielectric anomaly at about 103 K is considered as a final lock-in phase transition accompanied by the forming of the antiferroelectric state in TlGaSe2. (C) 2004 Elsevier Ltd. All rights reserved.

Cu0.95Me0.05Ox (Me=V, Mn, Li, La) thin films were prepared by a sol-gel-like method on microscope glass substrates. Precursor solutions were prepared by dissolving copper acetate in isopropyl alcohol. Diethanolamine and ethyleneglycol were used to enhance the solubility of copper acetate and to strengthen the adhesion between the films and the glass substrates. The doping type (Me) substantially affected the microstructure and the transparency of the films. All films showed good transparency in near IR region (<75%) while only Mn doped films showed considerable transparency in UV region (<45%). The optical band gaps of the films were between 1.64 (Me=La)-1.84 (Me=Mn) eV.

The results of measurements of the dielectric constant of TlGaSe2 in temperature range of successive phase transitions are presented. An anomaly in the temperature dependence of the real part of dielectric constant in TlGaSe2 has been observed at about 242K in addition to anomalies at 115, 108, and also near 65K as reported in previous publications. The presence of temperature hysteresis effects in temperature interval between 115 and 242K allowed making a conclusion about possible existence of an incommensurate phase in the mentioned temperature range. A model of succession of the structural phase transitions in TlGaSe2 has been suggested.

Copper(II) oxide thin films were prepared by a sol–gel-like method on microscope glass substrates. Precursor solutions were prepared by dissolving copper acetate in isopropyl alcohol. Various stabilizers and additives were used to enhance the solubility of copper acetate and to strengthen the adhesion between the films and the glass substrates. It was observed that the films crystallized to CuO with tenorite structure after heat treatment at 600°C for 30min. The general appearances of the films were uniform and brownish black in color. The microstructures of the films were substantially affected by the chemistry of the precursor solutions. The optical band gaps of the films were between 1.6 and 1.75eV.