16 results
Search Results
Now showing 1 - 10 of 16
Article Citation - WoS: 2Citation - Scopus: 2Electron-Lattice Interaction Scattering Mobility in Tl2ingase4< Single Crystals(Iop Publishing Ltd, 2008) Qasrawi, A. F.; Gasanly, N. M.In this work, the dark electrical resistivity, charge carrier density and Hall mobility of Tl(2)InGaSe(4) single crystal have been recorded and analyzed to investigate the dominant scattering mechanism in the crystal. The data analyses have shown that this crystal exhibits an extrinsic n-type conduction. The temperature-dependent dark electrical resistivity analysis reflected the existence of two energy levels as 0.396 and 0.512 eV, being dominant above and below 260 K, respectively. The temperature dependence of the carrier density was analyzed by using the single-donor-single-acceptor model. The latter analysis has shown that the above maintained 0.512 eV energy level is a donor impurity level. The compensation ratio for this crystal is determined as 0.96. The Hall mobility of Tl(2)InGaSe(4) is found to be limited by the scattering of electron-acoustic phonon interactions. The calculated theoretical acoustic phonon scattering mobility agrees with the experimental one under the condition that the acoustic deformation potential is 12.5 eV.Article Citation - WoS: 14Citation - Scopus: 13Light Illumination Effect on the Electrical and Photovoltaic Properties of In6s7< Crystals(Iop Publishing Ltd, 2006) Qasrawi, AF; Gasanly, NMThe electrical and photoelectrical properties of In6S7 crystals have been investigated in the temperature regions of 170-300 K and 150-300 K, respectively. The dark electrical analysis revealed the intrinsic type of conduction. The energy band gap obtained from the temperature-dependent dark current is found to be 0.75 eV. It is observed that the photocurrent increases in the temperature range of 150 K up to T-m = 230 K and decreases at T > T-m. Two photoconductivity activation energies of 0.21 and 0.10 eV were determined for the temperature ranges below and above Tm, respectively. The photocurrent (I-ph)-illumination intensity (F) dependence follows the law I-ph alpha F-gamma. The value of. decreases when the temperature is raised to T-m, then it starts increasing. The change in the value. with temperature is attributed to the exchange in role between the recombination and trapping centres in the crystal. The crystals are found to exhibit photovoltaic properties. The photovoltage is recorded as a function of illumination intensity at room temperature. The maximum open-circuit voltage and short-circuit photocurrent density, which are related to an illumination intensity equivalent to one sun, are 0.12 V and 0.38 mA cm(-2), respectively.Conference Object Citation - WoS: 9Citation - Scopus: 11Effect of Lithium Doping on the Properties of Tl-Based Superconductors(Iop Publishing Ltd, 2001) Kayed, TS; Özkan, H; Gasanly, NMThe effects of lithium doping on the formation and properties of the T1-based superconductors have been studied. Lithium atoms up to around 3 mol.% have been added to the oxides of nominal composition Tl1.8Ba2Ca2.2Cu3Ox, and the usual solid-state reaction method has been applied. Lithium additions in the range 0.23-0.29 mol.% increase the fraction of the Tl-2223 phase and significantly improve the critical temperature of the samples. Higher amounts of lithium additions diminish the Tl-2223 phase, reduce the fraction of the Tl-2212 phase, and cause separate non-superconducting phases to be formed.Article Citation - WoS: 8Citation - Scopus: 8Temperature- and Photo-Excitation Effects on the Electrical Properties of Tl4se3< Crystals(Iop Publishing Ltd, 2009) Qasrawi, A. F.; Gasanly, N. M.The extrinsic energy states and the recombination mechanism in the Tl4Se3S chain crystals are being investigated by means of electrical and photoelectrical measurements for the first time. The electrical resistivity is observed to decrease exponentially with increasing temperature. The analysis of this dependence revealed three impurity levels located at 280, 68 and 48 meV. The photocurrent is observed to increase as temperature decreases down to a minimum temperature T-m=200 K. Below this temperature the photocurrent decreases upon temperature lowering. Two photoconductivity activation energies of 10 and 100 meV were determined for the temperature ranges below and above T-m, respectively. The photocurrent (I-ph) versus illumination intensity (F) dependence follows the I-ph proportional to F-gamma law. The value of gamma decreases from similar to 1.0 at 300K to similar to 0.34 at 160K. The change in the value of gamma with temperature is attributed to the exchange of roles between the monomolecular recombination at the surface near room temperature and trapping centers in the crystal, which become dominant as temperature decreases.Article Citation - WoS: 9Citation - Scopus: 13Enhanced Second Harmonic Generation From Coupled Asymmetric Plasmonic Metal Nanostructures(Iop Publishing Ltd, 2015) Yildiz, Bilge Can; Tasgin, Mehmet Emre; Abak, Musa Kurtulus; Coskun, Sahin; Unalan, Husnu Emrah; Bek, AlpanWe experimentally demonstrate that two coupled metal nanostructures (MNSs), a silver nanowire and bipyramid, can produce similar to 30 times enhanced second harmonic generation compared to the particles alone. We develop a simple theoretical model, presenting the path interference effects in the nonlinear response of coupled MNSs. We show that the reason for such an enhancement can be the occurrence of a Fano resonance due to the coupling of the converter MNS to the long-lived mode of the attached MNS.Article Citation - WoS: 4Citation - Scopus: 5Thermal lattice scattering mobility and carrier effective mass in intrinsic Tl2InGaTe4 single crystals(Iop Publishing Ltd, 2007) Qasrawi, A. F.; Gasanly, N. M.Systematic structural, dark electrical resistivity and Hall coefficient measurements have been carried out on n- type Tl2InGaTe4 single crystals. The data from x- ray powder diffraction allowed determination of the tetragonal unit cell lattice parameters. Analysis of the electrical resistivity and carrier concentration, which was recorded in the temperature range 210 - 350 K, reveals the intrinsic type of conduction with an average energy band gap of 0.85 eV. The temperature- dependent Hall mobility was observed to follow the mu alpha T-3/2 law and was analysed assuming the domination of acoustic phonons scattering. The experimental Hall mobility data for Tl2InGaTe4 crystals agrees with the theoretical acoustic phonon scattering mobility data with an acoustic deformation potential of 7.6 eV.Article Citation - WoS: 25Citation - Scopus: 25Temperature Effect on Dark Electrical Conductivity, Hall Coefficient, Space Charge Limited Current and Photoconductivity of Tlgas2 Single Crystals(Iop Publishing Ltd, 2005) Qasrawi, AF; Gasanly, NMThe dark electrical conductivity, Hall coefficient, space charge limited current, and illumination and temperature dependences of the photocurrent of TIGaS2 single crystals in the temperature regions of 100-350, 200-350, 200-290 and 100-350 K, respectively, have been measured and analysed. The Hall coefficient measurements revealed the extrinsic type of conduction with conductivity-type conversion from p- to n-type at a critical temperature of 315 K. The temperature dependence of the dark electrical conductivity exhibits activation behaviour with activation energies (0.360 +/- 0.005) eV and (0.240 +/- 0.005) eV at high and low temperatures, respectively. The space charge limited current analysis has shown that the energy level of (0.240 +/- 0.005) eV is a trapping state with trap density of (2.2-3.9) x 10(12) cm(-3). The data analysis of the photocurrent-temperature dependence has revealed two photoconductivity activation energies of (0.660 +/- 0.005) eV and (0.360 +/- 0.005) eV in the temperature regions of 290-350 K and 220-280 K, respectively. The illumination dependence of photoconductivity is found to exhibit linear and supralinear recombination mechanisms above and below 290 K, respectively.Article Citation - WoS: 11Citation - Scopus: 13Fabrication and Characterization of To/Gase Au) Schottky Diodes(Iop Publishing Ltd, 2006) Qasrawi, AF; Department of Electrical & Electronics EngineeringThe optical properties of amorphous GaSe thin films deposited onto tin oxide (TO) coated glass substrates are presented for the purpose of using this material for the fabrication of metal-semiconductor devices. Specifically, the room temperature direct allowed and forbidden transition energy band gaps of glass/TO and glass/TO/GaSe films are estimated and found to exhibit values of 3.95 and 1.95 eV, respectively. The temperature dependence of the energy band gap of the glass/TO/GaSe is also studied in the temperature range of 295 - 450 K by means of optical transmittance and reflectance spectra. This study allowed the identification of the rate of change of the band gap with temperature as -5.0 x 10(-4) eV K-1 and the 0 K energy band gap as 2.1 eV. The above reported optical parameters of the glass/TO/GaSe structure seem to be suitable for semiconductor device production such as solar cell converters, metal - insulator - semiconductor (MIS), metal-oxide-semiconductor (MOS), MOSFET, etc devices. As an application, we have used the glass/TO/GaSe substrate for fabricating Schottky diodes using Ag and Au point contacts. The diodes are characterized by measuring the current (I) - voltage (V) characteristics at room temperature. The I - V curves exhibit rectifying properties. The I-V data analysis in the Schottky region (below 1.0 V) revealed barrier heights of 0.60 and 0.73 eV for Ag and Au point contacts, respectively.Article Citation - WoS: 25Citation - Scopus: 24Preparation of Electrospun Pcl-Based Scaffolds by Mono/Multi-functionalized Go(Iop Publishing Ltd, 2019) Basar, Ahmet Ozan; Sadhu, Veera; Sasmazel, Hilal TurkogluIn the present study, sythetic biodegradable polymer poly(epsilon-caprolactone) (PCL) and graphene oxide (GO) were combined together to prepare 3D, composite tissue scaffolds (PCL/GO scaffolds) by using electrospinning technique. Also, the influence of Gly-Arg-Gly-Asp-Ser-Pro (GRGDSP) and/or thiophene (Th) modified GO on the composite PCL/GO mats (PCL/GO, PCL/GO-GRGDSP, PCL/ GO-Th, PCL/GO-GRGDSP-Th) was further investigated. Characteristic examinations of the scaffolds were carried out by scanning electron microscope (SEM), contact angle (CA) measurements, x-ray photoelectron spectroscopy, TGA, electrical conductivity tests, phosphate buffer saline absorption and shrinkage tests and mechanical tests. All of the scaffolds were exhibited suitable bead free and uniform morphology according to SEM images. With the addition of GO, better hydrophilicity and a slight CA decrease (similar to 5 degrees) for the PCL/GO scaffolds were observed. Mechanical properties were reinforced drastically with the addition and well-dispersion of GO into PCL matrix. The incorporation of PCL and GO exhibited enhanced electrical conductivity and the highest value was found for PCL/GO-GRGDSP-Th (2%) as 15.06 mu S cm(-1). The MG-63 osteoblast cell culture studies (MTT assay, ALP activity, Alizarin-Red staining, fluorescence and SEM analyses) showed that PCL/GO-GRGDSP-Th (1%) scaffolds exhibited the highest biocompatibility performance (1.87 fold MTT absorbance value comparing with neat PCL) due to the advanced properties of GO and the biological interfaces.Article Citation - WoS: 11Citation - Scopus: 11Dispersive Optical Constants and Temperature-Dependent Band Gap of Cadmium-Doped Indium Selenide Thin Films(Iop Publishing Ltd, 2005) Qasrawi, AF; Department of Electrical & Electronics EngineeringPolycrystalline cadmium-doped indium selenide thin films were obtained by the thermal co-evaporation of alpha-In2Se3 crystals and Cd onto glass substrates kept at a temperature of 200 degrees C. The temperature dependence of the optical band gap in the temperature region of 300-450 K and the room temperature refractive index, n(lambda), of these films have been investigated. The absorption edge shifts to lower energy as temperature increases. The fundamental absorption edge corresponds to a direct energy gap that exhibits a temperature coefficient of -6.14 x 10(-4) eV K-1. The room temperature n(lambda) which was calculated from the transmittance data allowed the identification of the oscillator strength and energy, static and lattice dielectric constants and static refractive index as 20.06 and 3.07 eV, 7.43 and 10.52 and 2.74, respectively.
