Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 36Citation - Scopus: 38Humidity Sensing Properties of Cds Nanoparticles Synthesized by Chemical Bath Deposition Method(American Chemical Society, 2011) Demir, Ramazan; Okur, Salih; Şeker, Mavişe; Zor, MuhsinThin films of CdS nanoparticles were synthesized by the chemical bath deposition (CBD) technique to investigate humidity response characteristics. The morphology and the crystal structure of CdS thin films were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The quartz crystal microbalance (QCM) technique was used to measure the water vapor adsorption and desorption rates of CdS thin films. The dynamic Langmuir model was used to analyze the kinetics of the moisture adsorption and desorption process under relative humidity (RH) between 17 and 85% RH. Our results indicate that CdS thin films have a great affinity to humidity at room temperature.Article Citation - WoS: 3Citation - Scopus: 3Synthesis and Raman Spectroscopic Investigation of a New Self-Assembly Monolayer Material 4-[n Acid for Organic Light-Emitting Devices(John Wiley and Sons Inc., 2011) Kurt, Mustafa; Okur, Salih; Demiç, Şerafettin; Karpagam, J.; Sundaraganesan, N.We have synthesized 4-[N-phenyl-N-(3-methylphenyl)-amino]-benzoic acid (4-[PBA]) and investigated its molecular vibrations by infrared and Raman spectroscopies as well as by calculations based on the density functional theory (DFT) approach. The Fourier transform (FT) Raman, dispersive Raman and FT-IR spectra of 4-[PBA] were recorded in the solid phase. We analyzed the optimized geometric structure and energies of 4-[PBA] in the ground state. Stability of the molecule arising from hyperconjugative interactions and charge delocalization was studied using natural bond orbital analysis. The results show that change in electron density in the δ* and π* antibonding orbitals and E 2 energies confirm the occurrence of intramolecular charge transfer within the molecule. Theoretical calculations were performed at the DFT level using the Gaussian 09 program. Selected experimental bands were assigned and characterized on the basis of the scaled theoretical wavenumbers by their total energy distribution. The good agreement between the experimental and theoretical spectra allowed positive assignment of the observed vibrational absorption bands. Finally, the calculation results were applied to simulate the Raman and IR spectra of the title compound, which show agreement with the observed spectra.Article Citation - WoS: 45Citation - Scopus: 43Analysis of Electronic Parameters and Interface States of Boron Dispersed Triethanolamine/P-si Structure by Afm, I-V, C-V and G/?-v-f Techniques(Elsevier Ltd., 2010) Yakuphanoğlu, Fahrettin; Okur, SalihThe electronic parameters and interface state properties of boron dispersed triethanolamine/p-Si structure have been investigated by atomic force microscopy, I-V, C-V-f and G/ω-V-f techniques. The surface topography and phase image of the TEA-B film deposited onto p-Si substrate were analyzed by atomic force microscopy. The atomic force microscopy results show a homogenous distribution of boron particles in triethanolamine film. The electronic parameters (barrier height, ideality factor and average series resistance) obtained from I-V characteristics of the diode are 0.81 eV, 2.07 and 5.04 kΩ, respectively. The interface state density of the diode was found to be 2.54 × 1010 eV- cm-2 under Vg = 0. The obtained Dit values obtained from C-V and G/ω measurements are in agreement with each other. The profile of series resistance dependent on voltage and frequency confirms the presence of interface states in boron dispersed triethanolamine/p-Si structure. It is evaluated that the boron dispersed triethanolamine controls the electronic parameters and interface properties of conventional Al/p-Si diode. © 2009 Elsevier B.V. All rights reserved.Article Citation - WoS: 36Citation - Scopus: 36High-Mobility Pentacene Phototransistor With Nanostructured Sio2 Gate Dielectric Synthesized by Sol-Gel Method(Elsevier Ltd., 2010) Okur, Salih; Yakuphanoğlu, Fahrettin; Stathatos, E.We have fabricated a pentacene based phototransistor by employing a modified nanostructured SiO2 gate dielectric. The photosensing properties of the pentacene thin film transistor fabricated on n-Si substrate with nanostructured SiO2 as gate dielectric have been investigated. The photocurrent of the transistor increases with an increase in illumination intensity. This suggests that the pentacene thin film transistor behaves as a phototransistor with p-channel characteristics. The photosensitivity and responsivity values of the transistor are 630.4 and 0.10 A/W, respectively at the off state under AM 1.5 light illumination. The field effect mobility of the pentacene phototransistor was also found to be 2.96 cm2/Vs. The nanostructured surface of the gate possibly is the cause of the high-mobility value of the phototransistor due to light scattering from the increased surface area. Crown Copyright © 2009.Article Citation - WoS: 12Citation - Scopus: 15Local Oxidation Nanolithography on Hf Thin Films Using Atomic Force Microscopy (afm)(IOP Publishing Ltd., 2009) Büyükköse, Serkan; Okur, Salih; Özyüzer, Gülnur AygünWell controlled Hf oxide patterns have been grown on a flat Hf thin film surface produced by the dc magnetron sputtering method on Si and SiOx substrates. These patterns have been created by using the technique of semi-contact scanning probe lithography (SC-SPL). The thickness and width of the oxide patterns have been measured as a function of applied voltage, duration and relative humidity. There is a threshold voltage even at 87% humidity, due to insufficient energy required to start the oxide growth process for a measurable oxide protrusion. Electrical characterization was also performed via the I-V curves of Hf and HfOx structures, and the resistivity of HfO x was found to be 4.284 × 109 Ω cm. In addition to the I-V curves, electric force microscopy and spreading surface resistance images of Hf and HfOx were obtained.Article Citation - WoS: 38Citation - Scopus: 42Layered Clay/Epoxy Nanocomposites: Thermomechanical, Flame Retardancy, and Optical Properties(John Wiley and Sons Inc., 2008) Kaya, Elçin; Tanoğlu, Metin; Okur, SalihIn this study, layered clay/polymer nano-composites were developed based on epoxy resins and montmorillonite as the nanoplatelet reinforcement. Clay particles were treated with hexadecyltrimethylammonium chloride (HTCA) through an ion exchange reaction. In this way, Na+ interlay er cations of the clay is exchanged with onium cation of the surfactant that turns the hydrophilic clays (MMT) to organophilic (OMMT) characteristics. Thermal analysis results revealed that the glass transition temperature (Tg) and the dynamic mechanical properties including the storage and loss modulus of the neat epoxy resin increases by the incorporation of clay particles. It was also found that flame resistance of the polymer is improved by the addition of the clay particles.Article Citation - WoS: 43Citation - Scopus: 45Electrical and Interface Properties of Au/Dna Organic-On Structures(Elsevier Ltd., 2009) Okur, Salih; Yakuphanoğlu, Fahrettin; Özsöz, Mehmet; Kadayıfçılar, Pınar KaraThe effect of the thickness and coverage rate of a DNA film on the electrical and interface properties of Au/DNA/n-Si organic-on-inorganic structures has been investigated. The thin film properties of the DNA deposited on n-Si wafer were characterized by atomic force microscopy. The effect of the thickness and coverage rate of the DNA layer was investigated by evaluating electrical parameters, such as the barrier height, ideality factor, series resistance, and interface state density. The thickness and coverage rate of the DNA layer significantly affects the electrical properties of the Au/DNA/n-Si organic-on-inorganic structures. The interface state density properties of the Au/DNA/n-Si diodes were determined by conductance technique. The results show that the interface state density decreases with decrease in both film thickness and coverage rate of the DNA in an acetate buffer, modifying the electronic parameters of the Au/DNA/n-Si diodes.Article Citation - WoS: 12Citation - Scopus: 12Modification of Metal/Semiconductor Junctions by Self-Assembled Monolayer Organic Films(Elsevier Ltd., 2009) Yakuphanoğlu, Fahrettin; Okur, Salih; Özgener, HüseyinTwo new metal/molecule/semiconductor contacts, Au/n-Si/TDA/Au and Au/p-Si/ODM/Au, were fabricated to understand effect of organic compounds, tridecylamine and octadecylmercaptan self-assembled monolayer (SAM) films, on electrical charge transport properties of the metal/semiconductor junctions. The morphology of the organic monolayers deposited on Si substrates was investigated by atomic force microscopy. The molecular coverage of ODM deposited on p-Si is poorer than that of TDA on n-Si substrate. The ideality factors of the p-Si/ODM and n-Si/TDA diodes were found to be 1.66 and 1.48, respectively. The electrical results show that the tridecylamine monolayer passivated junction has a lower ideality factor. The ideality factor indicates clear dependence on two different type functional groups R-SH (Thiol) and R-NH2 (Amin) groups and it increases with different functional groups of organic molecule. The barrier height φb value of the n-Si/TDA diode is smaller than that of p-Si/ODM diode, as a result of chain length of the SAM organic molecules. The interface state density Dit values of the diodes were determined using conductance technique. The n-Si/TDA diode has the smaller interface state density according to p-Si/ODM diode. We have evaluated that the organic molecules control the electronic parameters of metal/semiconductor diodes and thus, organic modification helps to get one step closer towards to new organic assisted silicon based microelectronic devices.Conference Object Citation - WoS: 6Citation - Scopus: 9Sub-Bandgap Optical Absorption Spectroscopy of Hydrogenated Microcrystalline Silicon Thin Films Prepared Using Hot-Wire Cvd (cat-Cvd) Process(Elsevier Ltd., 2006) Göktaş, Oktay; Işık, Nebile; Okur, Salih; Güneş, Mehmet; Carius, Reinhard; Klomfaß, Josef; Finger, FriedhelmHydrogenated microcrystalline silicon (μc-Si:H) thin films with different silane concentration (SC) have been prepared using the HW-CVD technique. Dual beam photoconductivity (DBP), photothermal deflection spectroscopy (PDS), and transmission measurements have been used to investigate the optical properties of the μc-Si:H films. Two different sub-bandgap absorption, α(hν), methods have been applied and analyzed to obtain a better insight into the electronic states involved. A good agreement has been obtained in the absorption spectrum obtained from the PDS and DBP measurements at energies above the bandgap. Differences between PDS and DBP spectra exist below the bandgap energy where DBP spectra always give lower α(hν) values and show a dependence on the SC. For some films, differences exist in the α(hν) spectra when the DBP measurements are carried out through the film and substrate side. In addition, for some films, there remains fringe pattern left on the spectrum after the calculation of the fringe-free absorption spectrum, which indicates structural inhomogeneities present throughout the film.Conference Object Citation - WoS: 8Citation - Scopus: 9Diffusion Length Measurements of Microcrystalline Silicon Thin Films Prepared by Hot-wire/Catalytic Chemical Vapor Deposition (hwcvd)(Elsevier Ltd., 2006) Okur, Salih; Güneş, Mehmet; Finger, Friedhelm; Carius, ReinhardHydrogenated microcrystalline silicon (μc-Si:H) films prepared by using the hot-wire/catalytic chemical vapor deposition (HWCVD) technique at low substrate temperatures between 185 °C and 220 °C with different silane concentrations (SC) were investigated using steady-state photocarrier grating (SSPG) and the steady-state photoconductivity methods (SSPC). Crystalline volume fractions (IC RS) obtained from Raman spectroscopy change from 0.22 to 0.77. The diffusion length (LD) is measured at generation rates between G = 1019 and 1021 cm- 3 s- 1. LD changes from 27 nm to 270 nm, with maximum values around SC = 5%. The dependence of LD on SC is similar to that observed for similar quality microcrystalline silicon films prepared using the VHF-PECVD technique. The grating quality factor, γ0, drops from about 0.9 to 0.5 after transition to the microcrystalline regime as indication of scattering from surface patterns.