Sait Eren San

Molecular reorientation-based grating diffraction in dye-doped nematic liquid crystals with red pumping source

Abstract We report the results of a grating diffraction experiment in which a blue anthraquinone dye, Disperse blue 14 , is doped to nematic liquid crystal host and the sample is employed as a nonlinear media. The change of refractive index, caused by the photoinduced molecular reorientation, brings about the promising grating diffraction capability of a novel liquid crystal system. This system contains an anthraquinone dye in the absorbance band of red He–Ne laser, which is used as a pumping source. Accessible diffraction efficiency is 20% under optimum circumstances and analyzed results are in consistency with the expectations reinforced by the literature information of the other resembling liquid crystal systems.

Effect of laser illumination on the electro optical characters of dye doped nematic liquid crystals

Electro optical properties of a dye doped nematic liquid crystal system is investigated by concerning the laser induced effects on molecular reorientation. In the scope of this work, various measurements were performed to see the order and tendency of laser heating in a dye doped liquid crystal system including an anthraquinone derivative dye as a doping in E7 coded nematic host. Experimental results exhibit dependency on laser heating in the level of switching voltage of reorientation and analysis of electro optical parameters are investigated by the dependency of dissipation factor in dark and laser induced circumstances for dye doped and no-dye samples. Dielectric anisotropy dependency, which is another feeling of the same effect, is also studied for the mentioned conditions and its dependency is quantitatively estimated by capacitive measurements.

PENTACENE-BASED ORGANIC THIN FILM TRANSISTOR WITH SiO2 GATE DIELECTRIC

An organic thin film transistor (OTFT) based on pentacene was fabricated with SiO2 as the gate dielectric material. We have investigated the effects of the thickness of pentacene layer and the organic semiconductor (OSC) material on OTFT devices at two different thicknesses. Au metal was deposited for gate, source and drain contacts of the device by using thermal evaporation method. Pentacene thin film layer was also prepared with thermal evaporation. Our study has shown that the change in pentacene thickness makes a noteworthy difference on the field effect mobility (μFET), values, threshold voltages (VT) and on/off current ratios (Ion/Ioff). OTFTs exhibited saturation at the order of μFET of 3.92 cm2/Vs and 0.86 cm2/Vs at different thicknesses. Ion/Ioff and VT are also thickness dependent. Ion/Ioff is 1 × 103, 2 × 102 and VT is 15 V, 27 V of 40 nm and 60 nm, respectively. The optimized thickness of the pentacene layer was found as 40 nm. The effect of the OSC layer thickness on the OTFT performance was found to be conspicuous.

Electrical properties of Zn-phthalocyanine and poly (3-hexylthiophene) doped nematic liquid crystal

An E7 coded nematic liquid crystal was doped with zinc phthalocyanine and poly (3-hexylthiophene). A variety of properties including relaxation time, absorption coefficient, and critical frequency of this doped system were investigated using impedance spectroscopy. The doped systems displayed increased absorption coefficients in the range 0.22-0.55 and relaxation times from 5.05 × 10-7 s to 3.59 × 10-6 s with a decrease in the critical frequency from 3.54MHz to 2.048 MHz.

Fabrication and characterization of organic bulk heterojunction based displacement and bend sensitive field effect transistors

In this work, we report the fabrication and characterization of organic bulk heterojunction based displacement and bend sensitive field effect transistors (FETs). Transistors were fabricated in MESFET configuration with top gate and bottom drain-source electrodes using the blend of poly (3-hexylthiophene) (P3HT) and [6, 6]-phenyl C61-butyric acid methylester (PCBM) as active layer on glass and flexible PET substrates. Active (semiconducting) layer showed Schottky type contact with Aluminum gate electrode and Ohmic contact with Silver drain-source electrodes. Surface properties of the active layers were analyzed using Atomic Force Microscope (AFM). Current Voltage (I-V) characteristics of the devices were found similar to p-type mode I-V characteristics of a typical low voltage ambipolar organic field effect transistor. The effect of displacement and compressive bending on the drain to source current of the devices was investigated. It was found that the current increases with the increase of displacement and bending. Realization of such low voltage devices will provide potential for the development of low cost large area flexible sensor arrays and other low power microelectronic devices in future.

Investigation of the effect of gate voltage on the performance of organic bulk hetero-junction based phototransistor

In this work, we have investigated the effect of gate voltage on the performance of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methylester (PCBM) bulk hetero-junction based organic phototransistor. Transistor was fabricated in MESFET configuration with top gate and bottom drain-source electrodes on glass substrate. Active layer showed Schottky type contact with Gate electrode and Ohmic contact with Drain-Source electrodes. Current-Voltage (I-V) characteristics of the device were studied under dark and UV-Vis illumination. Active layer of the device has shown p-type and ambipolar properties under dark and UV-Vis illumination, respectively. Drain to source current of the phototransistor was found dependent on the illumination intensity and gate to source voltage. Photo sensitivity and responsivity values of the device were found to decrease exponentially with the increase of gate voltage. Photo sensitivity and responsivity values of the device were found equal to 11 and 0.024 A/W, respectively, at 90mW/cm2 UV-Vis illumination intensity and 0 gate voltage.