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    Assessment of fetal antioxidant and oxidant status during different anesthesia techniques for elective cesarean sections
    (Medknow Publications & Media Pvt Ltd, 2015) Karabayirli, Safinaz; Keskin, Esra Aktepe; Kaya, Ahmet; Koca, Cemile; Erel, Ozcan; Demircioglu, Ruveyda Irem; Muslu, Bunyamin
    Background: We aimed to investigate the effects of general, spinal and epidural anesthesia on fetal total antioxidant status (TAS) and total oxidant status (TOS), and oxidative stress index (OSI) during elective cesarean section in this study. Materials and Methods: Forty-seven parturients scheduled for elective cesarean section were randomly allocated into three groups: Group spinal (n = 15), group epidural (n = 17), and group general (n = 15), This prospective randomized study was performed in Faculty of Medicine, Turgut Ozal University, Turkey. After the baby was delivered; TAS, TOS levels, and arterial blood gases parameters were analyzed in an umbilical arterial blood sample. OSI values are calculated by a ratio of TOS to the TAS. Results: The levels of TAS and TOS in umbilical arterial blood sample were not statistically different among three. However, OSI values were significantly different among the three groups (P = 0.042). Median OSI values is 24 (interquartile range [IQR], 2-37) in group spinal, 19 (IQR, 4-44) in group epidural, and 8 (IQR, 4-36) in group general. There was no significant difference in OSI values in the comparison of group spinal with group general and group epidural, but it was significantly lower in group general when compared with group epidural with Bonferroni correction (P = 0.017). Umbilical cord arterial blood gas values (pH, PaCO2 , PaO2 , SaO(2) , HCO3 , and CtO(2) ), glucose, lactate, and hemoglobin levels were similar in three groups. Conclusion: General anesthesia may be more favorable than epidural in those undergoing cesarean section when fetal oxidative status gains importance.
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    Capacitance/Conductance-Voltage-Frequency Characteristics of Au/PVC+TCNQ/p-Si Structures in Wide Frequency Range
    (Ieee-Inst Electrical Electronics Engineers Inc, 2014) Kaya, Ahmet; Tecimer, Huseyin; Vural, Ozkan; Tasdemir, Ibrahim Hudai; Altindal, Semsettin
    The energy dependence of the interface states (N-ss) and relaxation time (tau) and capture cross section (sigma(p)) of N-ss in (Au/PVC+TCNQ/p-Si) heterojunction were investigated using high-low frequency capacitance (C-HF-C-LF) and conductance method, which contains many capacitance/conductance [C/(G/omega)-V] plots. The C value of the heterojunction increases with decreasing frequency as almost exponentially due to the existence of N-ss between metal and semiconductor. The N-ss and tau values have been obtained in the (0.053-E-v)-(0.785-E-v)-eV energy range by considering the voltage-dependent surface potential obtained from the lowest measurable frequency C-V curve at 1 kHz. The magnitude of N-ss ranges from 3.88x10(12) eV(-1)cm(-2) to 3.24 x 10(12) eV(-1)cm(-2). In the same energy range, the value of tau ranges from 5.73x10(-5) to 1.58x10(-4) s and shows almost an exponential increase with increasing bias from the top of the valance band edge toward the midgap of semiconductor. The obtained N-ss values from C-HF-C-LF and conductance methods are in good agreement with each other for the heterojunction. As a result, the mean value of N-ss was found on the order of 10(12) eV(-1)cm(-2) and this value is very suitable for an electronic device.
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    Electrical and dielectric properties and intersection behavior of G/?-V plots for Al/Co-PVA/p-Si (MPS) structures at temperatures below room temperature
    (Korean Physical Soc, 2014) Yucedag, Ibrahim; Kaya, Ahmet; Altindal, Semsettin; Uslu, Ibrahim
    Both the electrical and the dielectric properties of the Al/Co-doped polyvinyl alcohol/p-Si metal-polymer-semiconductor (MPS) structure have been studied using temperature-dependent admittance-voltage (C/G-V) measurements at temperatures below room temperature at 300 kHz. The C-V plot indicates two peaks for each temperature corresponding to inversion and accumulation regions, respectively. The first peak was attributed to a particular distribution of interface traps (D (it) ), and the second was attributed to the series resistance (R (s) ) and interfacial polymer layer. G/omega-V plots show almost U-shape behavior for all temperatures and a crossing at almost 3 V. Such behavior of the G/omega-V plots may be attributed to the lack of free charge at low temperatures. After this intersection point, while the value of the capacitance (C) starts decreasing, the G/omega continues to increase. The temperature-dependent real and imaginary parts of the dielectric constant (epsilon', epsilon aEuro(3)) and of the electric modulus (M', MaEuro(3)), as well as the ac electrical conductivity (sigma (ac) ), of structure were obtained using C and G data before and after the intersection point (at 2 and 6 V), respectively. Experimental results show that the epsilon', epsilon aEuro(3), loss tangent (tan delta), sigma (ac) , M', and MaEuro(3) values were strong functions of the temperature and the applied bias voltage. In addition, G/omega-T and epsilon aEuro(3)-T plots show two different behaviors, one before and the other after the intersection point.
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    Electrical and dielectric properties of Al/p-Si and Al/perylene/p-Si type diodes in a wide frequency range
    (Iop Publishing Ltd, 2014) Kaya, Ahmet; Zeyrek, Sedat; San, Sait Eren; Altindal, Smsettin
    The perylene (C20H12) layer effect on the electrical and dielectric properties of Al/p-Si (MS) and Al/perylene/p-Si (MPS) diodes have been investigated and compared in the frequency range of 0.7 kHz-2 MHz. Experimental results show that C-V characteristics give an anomalous peak for two structures at low frequencies due to interface states (N-ss) and series resistance (R-s). The increases in C and G/omega at low frequencies confirm that the charges at interface can easily follow an ac signal and yield excess capacitance and conductance. The frequency-dependent dielectric constant (epsilon') and dielectric loss (epsilon '') are subtracted using C and G/omega data at 1.5 V. The epsilon' and epsilon '' values are found to be strongly dependent on frequency and voltage, and their large values at low frequencies can be attributed to the excess polarization coming from charges at traps. Plots of ln(sigma(ac))-ln(omega) for two structures have two linear regions, with slopes of 0.369 and 1.166 for MS, and of 0.077 and 1.061 for MPS, respectively. From the C-2-V characteristics, the doping acceptor atom concentration (N-A) and barrier height (Phi(B)) for Schottky barrier diodes (SBDs) of MS and MPS types are also obtained to be 1.484 X 10(15) and 1.303 x 10(15) cm(-3), and 1.10 and 1.13 eV, respectively.
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    Electronic transport of Au/(Ca1.9Pr0.1Co4Ox)/n-Si structures analysed over a wide temperature range
    (Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2015) Alialy, Sahar; Kaya, Ahmet; Marıl, Elif; Altındal, Şemsettin; Uslu, Ibrahim
    The barrier height (BH) of the Au/(Ca1.9Pr0.1Co4Ox)/n-Si structure was evaluated in the temperature range of 120-360 K using current-voltage (I-V) measurements. The zero-bias BH (?Bo) and ideality factor (n) values deduced from standard thermionic emission theory were found to be 0.35 eV and 6.30 at 120 K and 0.83 eV and 5.1 at 360 K, respectively. Because such changes in ?Bo were not in agreement with the negative temperature coefficient (?) of the Si band gap, effects of tunnelling and BH inhomogeneity were added to the analysis of junction current. With this modification, the value of ?Bef. was found to decrease with temperature at a rate of -2.4 × 10-4 eVK-1 in approximate agreement with the known ? of the Si band gap. Attempts to model the inhomogeneous BH with a single Gaussian distribution were also successful, rendering a mean value of BH(?Bo) of 0.997 eV and a standard deviation (?o) of 0.12 eV. Similar conclusions were drawn from additional analyses, employing the modified Richardson plots. Our results suggest that the analysis of electronic transport at this and possibly other MIS junctions should include both the effect of tunnelling and that of BH inhomogeneity. © 2020 Elsevier B.V., All rights reserved.
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    Frequency and voltage-dependent electrical and dielectric properties of Al/Co-doped PVA/p-Si structures at room temperature
    (Iop Publishing Ltd, 2014) Yucedag, Ibrahim; Kaya, Ahmet; Altindal, Semsettin; Uslu, Ibrahim
    In order to investigate of cobalt-doped interfacial polyvinyl alcohol (PVA) layer and interface trap (D-it) effects, Al/pSi Schottky barrier diodes (SBDs) are fabricated, and their electrical and dielectric properties are investigated at room temperature. The forward and reverse admittance measurements are carried out in the frequency and voltage ranges of 30 kHz-300 kHz and -5 V-6 V, respectively. C-V or epsilon '-V plots exhibit two distinct peaks corresponding to inversion and accumulation regions. The first peak is attributed to the existence of Dit, the other to the series resistance (R-s), and interfacial layer. Both the real and imaginary parts of dielectric constant (epsilon ' and epsilon '') and electric modulus (M ' and M ''), loss tangent (tan delta), and AC electrical conductivity (sigma(ac)) are investigated, each as a function of frequency and applied bias voltage. Each of the M ' versus V and M '' versus V plots shows a peak and the magnitude of peak increases with the increasing of frequency. Especially due to the Dit and interfacial PVA layer, both capacitance (C) and conductance (G/w) values are strongly affected, which consequently contributes to deviation from both the electrical and dielectric properties of Al/Co-doped PVA/p-Si (MPS) type SBD. In addition, the voltage-dependent profile of Dit is obtained from the low-high frequency capacitance (CLF-CHF) method.
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    Investigation of negative dielectric constant in Au/1 % graphene (GP) doped-Ca1.9Pr0.1Co4Ox/n-Si structures at forward biases using impedance spectroscopy analysis
    (Springer New York LLC barbara.b.bertram@gsk.com, 2015) Çetinkaya, Hayriye Gokcen; Alialy, Sahar; Altındal, Şemsettin; Kaya, Ahmet; Uslu, Ibrahim
    The dielectric properties of Au/(1 % graphene doped-Ca1.9Pr0.1Co4Ox)/n-Si structures were investigated by the impedance spectroscopy method including capacitance–voltage (C–V) and conductance–voltage (G/?–V) measurements in the frequency range of 10–2 MHz at room temperature. The experimental results show that the real and imaginary parts of dielectric constant (??, ???) and electric modulus (M? and M??), and ac electrical conductivity (?ac) are a strong functions of frequency and voltage, both. Negative dielectric constant behavior was observed at sufficiently high forward bias voltages at low frequencies and it was attributed to the interfacial polarization, interface traps and series resistance. ?? decreases with increasing frequency at sufficiently high biases whereas ??? increases. Since interfacial polarization and interface states, both, can follow the ac external signal easily at low frequencies, there occurs a contribution to the measured capacitance and conductance. The negative values of ?? correspond to maximum value of ???. Such contrary behavior in the ?? and ??? appears as an abnormality when compared to the conventional behavior metal–semiconductor structures with and without interfacial layer. Experimental results confirmed that the dielectric properties of these structures are quite sensitive to the frequency and applied bias voltage, both, especially at low frequencies and high voltages because of density distribution of interface states and interfacial polarization. © 2016 Elsevier B.V., All rights reserved.
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    On the anomalous peak in the forward bias capacitance and conduction mechanism in the Au/n-4H SiC (MS) Schottky diodes (SDs) in the temperature range of 140-400 K
    (World Scientific Publ Co Pte Ltd, 2015) Kaya, Ahmet
    The temperature and voltage dependence profile of the surface states (N-ss), series resistance (R-s) and electrical conductivity (sigma(ac)) have been investigated in temperature and voltage ranges of 140-400 K and (-5 V)-(6 V), respectively, The value of barrier height (BIT) decreases with increasing temperature as Phi(B)(T) = (1.02- 4 x 10(-4)center dot T) eV. These values of negative temperature coefficient (-4 x 10(-4) eV center dot K-1) is in good agreement with the a of band gap of SiC (-3.1 x 10(-4) eV K-1). Capacitance-voltage (C-17) plots for all temperatures show an anomalous peak in the accumulation region because of the effect of series resistance (R-s) and N-ss. The effect of R-s and N-ss on the C and conductance (G) are found noticeable high especially at low temperatures. The decrease in C values also corresponds to an increase in G/w values in the accumulation region. In addition, Ln(sigma(ac)) versus q/kT plots have two straight lines with different slopes which are corresponding to below and above room temperatures for various forward biases which are an evident two valid possible conduction mechanisms. The values of activation (E-alpha) were obtained from the slope of these plots and they changed from 6.3 rneV to 4.7 meV below room temperatures and 42.5 rneV to 34.4 meV for above room temperatures, respectively.