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Öğe Characterization of Langmuir-Blodgett films of a calix[8]arene and sensing properties towards volatile organic vapors(Elsevier Science Sa, 2010) Capan, R.; Ozbek, Z.; Goktas, H.; Sen, S.; Ince, F. G.; Ozel, M. E.; Stanciu, G. A.Within this article, we report the characterization and organic vapor sensing properties of Langmuir-Blodgett (LB) thin films of calix[8]arenes. Surface pressure-area isotherms show that very stable monolayers are formed at the air-water interface. The LB film could be deposited onto different substrates which allowed the films to be characterized by UV, quartz crystal microbalance (QCM), surface plasmon resonance (SPR) and atomic force microscopy (AFM). The results indicate that good quality, uniform LB films can be prepared with transfer ratios of over 0.95. QCM results showed that the deposited mass of calix[8]arene monolayer onto a quartz crystal decreased from 693 to 204 ng as the number of layers is increased. AFM studies showed a smooth, and void free surface morphology with a rms value of 1.202 nm. The sensing abilities of this LB film towards the development of room temperature organic vapor sensing devices are also studied. Responses of the LB films to various vapors are fast, large, and reversible. It was found that the obtained LB film is significantly more sensitive to chloroform than other vapors. It can be concluded that this molecule could have a potential application in the research area of room temperature vapor sensing devices. (C) 2010 Elsevier B.V. All rights reserved.Öğe Effect of an azo dye (DR1) on the dielectric parameters of a nematic liquid crystal system(Elsevier, 2007) Ozder, S.; Okutan, M.; Koysal, O.; Goktas, H.; San, S. E.The dielectric parameters and relaxation properties of azo dye (DR1) doped E7 and pure E7 liquid crystal (LC) have been investigated in a wide frequency range of 10k-10MHz through the dielectric spectroscopy method at room temperature. Dielectric anisotropy (Delta epsilon) property of the LC changes from the positive type to negative type and dielectric anisotropy values decrease with doping of DR1. The relaxation frequency f(r) of E7 and E7/DR1 LC was calculated by means of Cole-Cole plots. Influence of bias voltage on the dielectric parameters has also been investigated. (c) 2006 Elsevier B.V. All rights reserved.Öğe Optical parameters of calix[4]arene films and their response to volatile organic vapors(Elsevier Science Sa, 2011) Ozbek, Z.; Capan, R.; Goktas, H.; Sen, S.; Ince, F. G.; Ozel, M. E.; Davis, F.The Langmuir-Blodgett (LB) technique was employed to produce thin LB films using an amphiphilic calix-4-resorcinarene onto different substrates such as quartz, gold coated glass and quartz crystals. The characteristics of the calix LB films are assessed by UV-visible, quartz crystal microbalance (QCM) and surface plasmon resonance (SPR) measurements. UV-vis and QCM measurements indicated that this material deposited very well onto the solid substrates with a transfer ratio of >0.95. Using SPR data, the thickness and refractive index of this LB film are determined to be 1.14 nm/deposited layer and 1.6 respectively. The sensing application of calixarene LB films towards volatile organic vapors such as chloroform, benzene, toluene and ethanol vapors is studied by the SPR technique. The response of this LB film to saturated chloroform vapor is much larger than for the other vapors. The response is fast and fully recoverable. It can be proposed that this sensing material deposited onto gold coated glass substrates has a good sensitivity and selectivity for chloroform vapor. This material may also find potential applications in the development of room temperature organic vapor sensing devices. (C) 2011 Elsevier B.V. All rights reserved.Öğe Plasma Polymerized Calixarene Thin Films and their Sensing Properties to Chloroform Vapors(Taylor & Francis Ltd, 2010) Ince, F. G.; Goktas, H.; Ozbek, Z.; Capan, R.; Davis, F.The production of calixarene thin films via double discharge plasma technique and their sensitivity towards chloroform vapor are presented here in. The calixarene thin film is fabricated for the first time by plasma polymerized technique. Each experiment carried out at room temperature, at 0.6 mbar operating pressure, 2.0 kV DC and 19 kV pulsed voltages. From the UV-vis spectra it is observed that the polyconjugated structure is established and the thin films highly possess the characteristic bands of the oligomer. The SPR results revealed that the films thickness is at the order of several nm and the refractive index range from 2.2 to 2.8. The QCM results show that the thin films are highly sensitive with a fast and reversible adsorption to chloroform. The typical response time was of a few seconds.Öğe Spectroscopic investigation of a double discharge pulsed electron beam generator(Taylor & Francis Inc, 2008) Goktas, H.; Kacar, E.; Demir, A.The wide range of applications of the plasma-based electron beam generator make it necessary to diagnose the device with a noninterfering method. The results of experimental and modeling studies of neutral helium and hydrogen beta spectral lines emitted from the double discharge pulsed electron beam generator are presented in this paper. Neutral helium lines emitted from the plasma in the pressure range 0.1-0.4torr are studied and compared with results of the collisional radiative model. The duration of the electron beam is shorter than 100 ns, and the peak current intensity is of order amperes. The full width at half maximum of the H spectral line is used for the determination of the plasma electron density, found as 3.16 x 10(21) m(-3) at 0.3 torr, and good agreement is obtained by comparing with the full computer simulation method.Öğe Spectroscopic measurements of electron temperature and electron density in electron beam plasma generator based on collisional radiative model(Taylor & Francis Inc, 2007) Goktas, H.; Demir, A.; Kacar, E.; Hegazy, H.; Turan, R.; Oke, G.; Seyhan, A.The current work describes a spectroscopic method for determining the electron temperature and electron density in an electron beam generator using argon spectral lines based on a collisional radiative model. Neutral and first-ionized Ar lines emitted from the electron beam generator are studied experimentally. A collisional radiative code was developed to simulate the Ar (I) and Ar (II) spectral emission and to compare the results with the experimental data for electron density and temperature determination. At lines and excited level densities were calculated by solving rate equations using the Gauss elimination method. The argon spectrum is recorded experimentally by superposing two discharges, namely a low pressure DC glow discharge and a high current pulsed discharge. Spectral lines between 350 nm and 950 nm were recorded using an integrated signal technique on a charge-coupled device. Electron temperature is determined by the relative intensity ratio method of two spectral lines. The relative intensity ratios of each peak are compared in a specific pressure range at various values, and good correlation is reported.Öğe The molecular structure of plasma polymerized thiophene and pyrrole thin films produced by double discharge technique(Elsevier Science Sa, 2009) Goktas, H.; Ince, F. G.; Iscan, A.; Yildiz, I.; Kurt, M.; İsmet, KayaProduction of polythiophene (PTH) and polypyrrole (PPY) thin films via double discharge plasma system has been studied. The double discharge system is a superposition of an ordinary low-pressure dc glow discharge and a high-current pulsed one. The glass substrates were located simultaneously at three different positions in the reactor and the thin films were synthesized at constant plasma parameters to evaluate the influence of the position on the molecular structure. And, the as-grown and iodine doped thin films were investigated to find out the correlation between molecular structure variation of the iodine-film interactions, too. The PTH (C4H4S) and PPY (C4H5N) monomers without using any carrier gases have been used as plasma precursors, each at 1 mbar operating pressure. The thin films were compared by using Fourier transform infrared (FTIR), X-ray photoelectron (XPS), and UV-visible absorption spectroscopy. It is found that the thin films obtained at the pulsed plasma region where the gas phase polymerization is dominated resemble to conventional polymeric structure. The XPS depth profiles revealed that while the stoichiometry of the monomer was almost preserved with the successive depth of PTH samples, but at the PPY one was not preserved. Moreover, the atomic concentration of oxygen and nitrogen observed at the surface of the films significantly drops down beneath the surface which indicates that they could be employed as anti-corrosive materials. It is found that chemical bonding with iodine take place after doping and the value of the optical band gap of polymers (E-g) are reduced proportionally with doping time. (C) 2009 Elsevier B.V. All rights reserved.
