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Öğe Capacitive solvent sensing with interdigitated microelectrodes(Springer, 2016) Bilican, Ismail; Guler, Mustafa Tahsin; Gulener, Neset; Yuksel, Mustafa; Agan, SedatWe were able to quantify dielectric properties of solvents such as DI water, isopropyl alcohol, and acetone using interdigitated microelectrodes (IMEs). IMEs were fabricated using conventional micro fabrication techniques. The fabricated IMEs were dipped into the solution, and the dielectric property of the medium was measured. A range of frequencies and excitation voltages were swept in order to determine the operation region that yields the highest signal to noise ratio. Measurements were performed at 1 MHz and 100 mV which resulted in best signal to noise ratio. We applied a simple analytical model for the calculation of the capacitance and measured the capacitance value using a simple parallel capacitor and resistor model which resulted in perfect agreement with theoretical results. The presented sensor provides a simple and accurate method to determine solvent type which may have possible future applications.Öğe Elasto-Optical Properties of Thin Polymer Films by Prism Coupling Technique(American Institute of Physics Inc., 2004) Ay, Ferudun; Agan, Sedat; Kocabaş, Aşkın; Aydınlı, AtillaReliable measurement of stress dependent refractive index of thin polymer films has been achieved. The effect of the applied stress on the refractive index and birefringence of the films was investigated. The out-of-plane elastic moduli of the thin polymer films were deduced by using the same prism coupling setup. Three dimensional finite element method (FEM) analysis was used to obtain the principal stresses for each polymer film and combining them with the stress dependent refractive index measurements, the elasto-optic coefficients of the polymer films were determined, for the first time. © 2004 American Institute of Physics.Öğe Influence of Mo and Co on the magnetic properties and martensitic transformation characteristics of a Fe-Mn alloy(Elsevier Science Sa, 2009) Sarı Uğur; Kirindi, T.; Yüksel, Mustafa; Agan, SedatThe effects of the Mo and Co on the magnetic properties and the characteristics of martensitic transformation of the Fe-Mn alloy have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimeter (DSC), and Mossbauer spectroscopy. Experiments reveal that two types of thermal-induced martensites, epsilon(h.c.p.) and alpha'(b.c.c.) martensites, form in the as-quenched alloys and these transformations have athermal characters. The Mo or Co (5 wt%) addition to the Fe-13%Mn alloy does not change coexistence of epsilon and alpha' martensites between 10-15 wt%Mn content. However, it stabilizes the parent phase leading to the depression of the transformation temperatures. In addition, Mossbauer spectra of the alloys reveal a paramagnetic character with a singlet for the gamma(fc.c.) austenite and epsilon martensite phases and a ferromagnetic character with a broad sextet for alpha' martensite phase. The volume fractions of the phases change and the amount of alpha' martensite increases significantly with the Mo or Co addition. Third element addition also influences internal magnetic field and particularly, the addition of the Mo considerably decreases the internal magnetic field in the Fe-Mn alloy. (C) 2008 Elsevier B.V. All rights reserved.Öğe Magnetic Transitions and The Magnetic Characteristics of The Martensitic Transformations in A Fe-Mn-Co Alloy(Gazi Univ, 2012) Yuksel, Mustafa; Agan, SedatIn this study, the magnetic transitions and the magnetic characteristics of the thermally induced martensitic transformations in Fe-13.2% Mn-5.3%Co alloy have been investigated. The microstructure analysis of difusionless phase transformations forming in the alloy were performed by scanning electron microscopy (SEM), and the magnetic properties were revealed by Mossbauer spectroscopy and AC susceptibility. SEM observations reveal that two types of thermal-induced martensites, epsilon (h.c.p.) and alpha' (b.c.c.) martensites, form in the austenite grains of the alloy. Mossbauer spectra at room temperature reveal a paramagnetic character with a singlet for the gamma (f.c.c.) austenite and epsilon martensite phases and a ferromagnetic character with a broad sextet for alpha' martensite phase. In addition, measurement of the AC susceptibility of the alloy shows that the magnetic transition from the paramagnetic order to magnetic disordered occurs below room temperature at 258 K.Öğe Plasma enhanced chemical vapor deposition of low loss as-grown germanosilicate layers for optical waveguides(2004) Ay, Feridun; Agan, Sedat; Aydinli, AtillaWe report on systematic growth and characterization of low-loss germanosilicate layers for use in optical waveguides. Plasma enhanced chemical vapor deposition (PECVD) technique was used to grow the films using silane, germane and nitrous oxide as precursor gases. Chemical composition was monitored by Fourier transform infrared (FTIR) spectroscopy. N-H bond concentration of the films decreased from 0.43 ×1022 cm -3 down to below 0.06x 1022 cm-3, by a factor of seven as the GeH4 flow rate increased from 0 to 70 seem. A simultaneous decrease of O-H related bonds was also observed by a factor of 10 in the same germane flow range. The measured TE loss rates at ?=632.8 nm were found to increase from are 0.20 ± 0.02 to 6.46 ± 0.04 dB/cm as the germane flow rate increased from 5 to 50 seem, respectively. In contrast, the propagation loss values for TE polarization at ?-1550 nm were found to decrease from 0.32 ± 0.03 down to 0.14 ± 0.06 dB/cm for the same samples leading to the lowest values reported so far in the literature, eliminating the need for high temperature annealing as is usually done for these materials to be used in waveguide devices.Öğe SiGe Nanocrystal Formation In Pecvd Grown SiOX/Si/Ge/Si/SiOX Multilayers(World Scientific Publ Co Pte Ltd, 2009) Agan, Sedat; Aydınlı, AtillaWe have studied alternating germanium-silicon-silicon oxide layers of 41 nm thickness grown on Si substrates by plasma enhanced chemically vapor deposition. The compositions of the grown films were determined by X-ray photoelectron spectroscopy. The films were annealed at temperatures varying from 700 to 950 degrees C for 7.5 minutes under nitrogen atmosphere. High resolution cross section TEM images, electron diffraction and electron energy-loss spectroscopy as well as energy-dispersive X-ray analysis (EDAX) confirm presence of Ge nanocrystals in each layer. The effect of annealing on the Ge nanocrystal formation in multilayers was investigated by Raman spectroscopy and TEM.Öğe A simple approach for the fabrication of 3D microelectrodes for impedimetric sensing(Iop Publishing Ltd, 2015) Guler, Mustafa Tahsin; Bilican, Ismail; Agan, Sedat; Elbuken, CaglarIn this paper, we present a very simple method to fabricate three-dimensional (3D) microelectrodes integrated with microfluidic devices. We form the electrodes by etching a microwire placed across a microchannel. For precise control of the electrode spacing, we employ a hydrodynamic focusing microfluidic device and control the width of the etching solution stream. The focused widths of the etchant solution and the etching time determine the gap formed between the electrodes. Using the same microfluidic device, we can fabricate integrated 3D electrodes with different electrode gaps. We have demonstrated the functionality of these electrodes using an impedimetric particle counting setup. Using 3D microelectrodes with a diameter of 25 mu m, we have detected 6 mu m-diameter polystyrene beads in a buffer solution as well as erythrocytes in a PBS solution. We study the effect of electrode spacing on the signal-to-noise ratio of the impedance signal and we demonstrate that the smaller the electrode spacing the higher the signal obtained from a single microparticle. The sample stream is introduced to the system using the same hydrodynamic focusing device, which ensures the alignment of the sample in between the electrodes. Utilising a 3D hydrodynamic focusing approach, we force all the particles to go through the sensing region of the electrodes. This fabrication scheme not only provides a very low-cost and easy method for rapid prototyping, but which can also be used for applications requiring 3D electric field focused through a narrow section of the microchannel.Öğe Stress effects in prism coupling measurements of thin polymer films(Springer Heidelberg, 2005) Agan, Sedat; Ay, Feridun; Kocabaş, A.; Aydınlı, A.Due to the increasingly important role of some polymers in optical waveguide technologies, precise measurement of their optical properties has become important. Typically, prism coupling to slab waveguides made of materials of interest is used to measure the relevant optical parameters. However, such measurements are often complicated by the softness of the polymer films when stress is applied to the prism to couple light into the waveguides. In this work, we have investigated the optical properties of three different polymers, polystyrene (PS), polymethyl-methacrylate (PMMA), and benzocyclobutane (BCB). For the first time, the dependence of the refractive index, film thickness, and birefringence on applied stress in these thin polymer films was determined by means of the prism coupling technique. Both symmetric trapezoid shaped and right-angle prisms were used to couple the light into the waveguides. It was found that trapezoid shaped prism coupling gives better results in these thin polymer films. The refractive index of PMMA was found to be in the range of 1.4869 up to 1.4876 for both TE and TM polarizations under the applied force, which causes a small decrease in the film thickness of up to 0.06 mum. PMMA waveguide films were found not to be birefringent. In contrast, both BCB and PS films exhibit birefringence albeit of opposing signs.Öğe TEM studies of ge nanocrystal formation in PECVD grown SiO2 : Ge/SiO2 multilayers(Iop Publishing Ltd, 2006) Agan, Sedat; Dana, Aykutlu; Aydınlı, A.We investigate the effect of annealing on the Ge nanocrystal formation in multilayered germanosilicate-oxide films grown on Si substrates by plasma enhanced chemical vapour deposition (PECVD). The multilayered samples were annealed at temperatures ranging from 750 to 900 degrees C for 5 min under nitrogen atmosphere. The onset of formation of Ge nanocrystals, at 750 degrees C, can be observed via high resolution TEM micrographs. The diameters of Ge nanocrystals were observed to be between 5 and 14 nm. As the annealing temperature is raised to 850 degrees C, a second layer of Ge nanocrystals forms next to the original precipitation band, positioning itself closer to the substrate SiO2 interface. High resolution cross section TEM images, electron diffraction and electron energy-loss spectroscopy as well as energy-dispersive x-ray analysis (EDAX) data all indicate that Ge nanocrystals are present in each layer.
