Papers by Prof.Dr. İbrahim USLU
PRESTO-II (Prediction of Radiation Effects from Shallow Trench Operations) is a computer code des... more PRESTO-II (Prediction of Radiation Effects from Shallow Trench Operations) is a computer code designed to evaluate possible doses and risks (health effects) from shallow-land burial sites. The model is intended to serve as a non-site-specific screening model for assessing radionuclide transport, ensuing exposure, and health impacts to a static local population for a 1000-year period following the end of disposal operations. Human exposure scenarios include normal releases (including leaching and operational spillage), human intrusion, and limited site farming or reclamation. Pathways and processes of transport from the trench to an individual or population include ground-water transport, overland flow, erosion, surface water dilution, suspension, atmospheric transport and deposition, inhalation, external exposure, and ingestion of contaminated beef, milk, crops, and water. The proposed waste disposal area in Koteyli, Balikesir, Turkey, has been evaluated using the PRESTO-II methodol...
Studies involving proposed waste disposal facilities in Turkey
Transactions of the American Nuclear Society, 1987
The Turkish government is in the process of planning two nuclear reactors in Turkey. The Turkish ... more The Turkish government is in the process of planning two nuclear reactors in Turkey. The Turkish Atomic Energy Authority has been given the task of developing plans for improved control of low-level wastes (LLW) in Turkey. Principal sources of radioactive wastes are hospitals, research institutions, biological research centers, universities, industries, and two research reactors in Turkey. These wastes will be treated in a pilot water treatment facility located in Cekmece Nuclear Research and Training Center, Istanbul. In this temporary waste disposal facility, the wastes will be stored in 200-l concrete containers until the establishment of the permanent waste disposal sites in Turkey in 1990. The PRESTO-II (prediction of radiation effects from shallow trench operations) computer code has been applied for the general probable sites for LLW disposal in Turkey. The model is intended to serve as a non-site-specific screening model for assessing radionuclide transport, ensuring exposur...
Crystal structure and electrical properties of gadolinia doped bismuth oxide nanoceramic powders
Materials Chemistry and Physics, 2012
A novel method of fabrication of gadolinia doped bismuth oxide nanoceramic via the sol–gel techni... more A novel method of fabrication of gadolinia doped bismuth oxide nanoceramic via the sol–gel technique is reported. Their thermal, structural and morphological properties are described by measurements of Differential Thermal Analysis/Thermal Gravimetry, X-ray Powder Diffraction and Scanning Electron Microscopy. The samples have stable high ion conductive face centered cubic δ-phase nanocrystalline structure. The electrical measurements of the nanoceramic powders were carried out in the temperature range of (689–1091 K) using 4-point probe technique. There is a transition between two distinct regions at 720 °C, which can be attributed to the order–disorder transition. This observation is supported by the differential thermal analysis measurements. The experimental results show that the value of conductivity increases with increasing temperature over linear parts characterized by two different activation energies. The conductivity data over whole measured temperature range were fitted t...
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Correlation between thorium concentrations in soil and gamma readings in FUSRAP site in New Jersey
Thorium ores were processed in Wayne and Maywood, New Jersey, between 1916 and 1956. During the c... more Thorium ores were processed in Wayne and Maywood, New Jersey, between 1916 and 1956. During the course of Th processing, the wastes from the operations were pumped into dikes next to the plant. Construction in the area caused the dispersal of waste into adjacent areas. The Department of Energy (DOE) adopted a policy of assigning an independent verification contractor to ensure the effectiveness of remedial action performed within the Formerly Utilized Sites Remedial Action Program (FUSRAP). The Environmental assessment group of Oak Ridge National Laboratory was assigned the responsibility for this task at the Maywood and Wayne, New Jersey sites. The soil samples collected from the area were analyzed to determine the thorium concentration. In this study, a correlation is described between the thorium concentration and the gamma readings of the site. The statistical analysis of the data indicates that this correlation is site-specific and depends on the depth of the radionuclide. Data...
The PRESTO-II (Prediction of Radiation Effects from Shallow Trench Operations) computer code has ... more The PRESTO-II (Prediction of Radiation Effects from Shallow Trench Operations) computer code has been applied for the following sites; Koteyli, Balikesir and Kozakli, Nevsehir in Turkey. This site selection was based partially on the need to consider a variety of hydrologic and climatic situations, and partially on the availability of data. The results obtained for the operational low-level waste disposal site at Barnwell, South Carolina, are presented for comparison. 6 refs., 2 figs., 1 tab.
Synthesis and characterization of boron-doped bismuth oxide-erbium oxide fiber derived nanocomposite precursor
In this study, boron doped and undoped Bi2O3-Er2O3 nanocomposite fibers were produced via electro... more In this study, boron doped and undoped Bi2O3-Er2O3 nanocomposite fibers were produced via electrospinning technique. Obtained fibers were turned into ceramics via calcination process. Obtained nanocomposite fibers and ceramics were characterized by Fourier transform infrared, x-ray diffraction, and scanning electron microscopy techniques. X-ray diffraction results show that boron undoped Bi2O3-Er2O3 ceramic consisted of face-centered cubic Bi2O3-Er2O3 phase. However, boron doped Bi2O3-Er2O3 ceramic consisted of orthorhombic phase. Crystallite sizes of the ceramics were evaluated using Scherrer’s equation. Crystallite sizes of boron doped and undoped ceramics were calculated as 50 and 17 nm, respectively. The average fiber diameters for boron doped and undoped poly vinyl alcohol/Bi-Er acetate nanofibers were calculated as 79 nm and 96 nm, respectively. The Brunauer Emmett teller results show that boron undoped and doped Bi2O3-Er2O3 nanocrystalline powder ceramic structures sintered a...
High Thermoelectric Performance Of Unsintered NaCo2O4 Nanocrystal
Sodium cobaltite (NaCo2O4) nano crystalline thermoelectric materials were obtained using electros... more Sodium cobaltite (NaCo2O4) nano crystalline thermoelectric materials were obtained using electrospinning technique. Electrospunnanofibers was calcined at 800 oC and sintered at 850 oC in open air atmopshere. We have investigated the microstructure and thermoelectric properties of the sintered and unsintered samples for analysis sintering effect. The calcined sodium cobaltite crystal structures were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Products molded by cold pressing method, and one of the pellets were sintered at 850 oC by conventional sintering, the other not subjected to the sintering process. Thermoelectric properties of the both materials were measured by PPMS system in the temperature range 10-300 K. The dimensionless figure of merit (ZT) values at 300 K is 4×10−5and 9×10−5 for sintered and unsintered samples respectively. Although conventional sintered technique increase thermoelectric power and thermal conductivity approximately % 50 but it 4-fold decreased electrical conductivity.
Metal oxide ceramic thin films are widely used in the electronics industry and chemical industry ... more Metal oxide ceramic thin films are widely used in the electronics industry and chemical industry as electro catalyst and as selective catalysts for oxidation. In the literature the preparation of metal oxide ceramic films has been accomplished by physical vapor deposition, chemical vapor deposition and chemical solution deposition techniques. Various metal oxide fibers were obtained by high temperature calcinations. Large surface area and high aspect ratio of metal oxide fibers may have significant industrial importance especially for catalysis and filtration applications but conventional metal oxide fiber synthesis techniques of wet, dry, melt, and gel spinning, are capable of producing polymer fibers with diameters down to the micrometer range. Electrospinning is a process capable of producing polymer fibers with nanoscale diameters [1-5] .
Preparation and Characterization of Polyvinyl Alcohol Based Copolymers as Wound Dressing Fibers
International Journal of Polymeric Materials, Jul 23, 2015
Evaluation of Electric and Dielectric Properties of Metal–Semiconductor Structures With 2% GC-Doped-(Ca3Co4Ga0.001O<italic>x</italic>) Interlayer
IEEE Transactions on Electron Devices
Electrical and dielectric properties of Au/n-Si metal–semiconductor structures with high dielectr... more Electrical and dielectric properties of Au/n-Si metal–semiconductor structures with high dielectric have been examined by capacitance/conductance–voltage (<inline-formula> <tex-math notation="LaTeX">${C}/{G}$ </tex-math></inline-formula>–<inline-formula> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula>) measurements in the frequency range of 5–500 kHz at room temperature. Voltage-dependent profiles of interface states (<inline-formula> <tex-math notation="LaTeX">${N}_{\text {ss}}$ </tex-math></inline-formula>) and resistance (<inline-formula> <tex-math notation="LaTeX">${R}_{i}$ </tex-math></inline-formula>) were extracted from the C and G data using the low–high-frequency capacitance and Nicollian–Brews methods, respectively. The real and imaginary components of the complex dielectric constant (<inline-formula> <tex-math notation="LaTeX">$\varepsilon ^\prime $ </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">$\varepsilon ^{\prime \prime }$ </tex-math></inline-formula>), electric modulus (<inline-formula> <tex-math notation="LaTeX">${M}^\prime $ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">${M}^{\prime \prime }$ </tex-math></inline-formula>), and ac conductivity (<inline-formula> <tex-math notation="LaTeX">$\sigma _{\mathsf {ac}}$ </tex-math></inline-formula>) were calculated from the <inline-formula> <tex-math notation="LaTeX">${C}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">${G}$ </tex-math></inline-formula> data. All parameters have a strong relation with frequency and voltage, especially at low frequencies due to Maxwell–Wagner relaxation and <inline-formula> <tex-math notation="LaTeX">${N}_{\mathsf {ss}}$ </tex-math></inline-formula>. The observed peaks in the <inline-formula> <tex-math notation="LaTeX">${N}_{\mathsf {ss}}$ </tex-math></inline-formula>–<inline-formula> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">${R}_{i}$ </tex-math></inline-formula>–<inline-formula> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> plots can be ascribed by the special distribution of <inline-formula> <tex-math notation="LaTeX">${N}_{\mathsf {ss}}$ </tex-math></inline-formula> at M/S interface. These results confirmed that [2% graphene cobalt-doped (Ca<sub>3</sub>CO<sub>4</sub>Ga<sub>0.001</sub>O<sub><italic>x</italic></sub>)] interlayer has high-dielectric constant and can be used an interlayer instead of the traditional SiO<sub>2</sub> at M/S interface to increase their capacitance or more charges/energy storage and reduce both the values of <inline-formula> <tex-math notation="LaTeX">${N}_{\mathsf {ss}}$ </tex-math></inline-formula> and series resistance (<inline-formula> <tex-math notation="LaTeX">${R}_{s}$ </tex-math></inline-formula>). The values of <inline-formula> <tex-math notation="LaTeX">$\sigma $ </tex-math></inline-formula> are almost constant at lower–intermediate frequencies, but they start to increase at high frequencies that are corresponding to the dc and ac conductivity, respectively.
Investigation of the effect of different Bi2O3–x:PVA (x = Sm, Sn, Mo) thin insulator interface-layer materials on diode parameters
Journal of Materials Science: Materials in Electronics
The synthesis of boron undoped and doped indium stabilized bismuth oxide nanoceramic powders via ... more The synthesis of boron undoped and doped indium stabilized bismuth oxide nanoceramic powders via the polymeric precursor technique were described. The physical properties of the precursor polymer solutions (pH, surface tension, viscosity and conductivity) were measured. The morphological and structural characteristics of the nanoceramic powders were investigated by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The lattice constant, average particle size, microstrain and dislocation density of the samples were calculated. The results show that the average particle size decreased while both the microstrain and the dislocation density values increased in the boron doped indium stabilized bismuth oxide. The structure proposed from FTIR spectra is mainly based on BiO 6 and BiO 3 units.
Bulletin of Materials Science, 2018
Three different thicknesses (50, 150 and 500 nm) Zn-doped polyvinyl alcohol (PVA) was deposited o... more Three different thicknesses (50, 150 and 500 nm) Zn-doped polyvinyl alcohol (PVA) was deposited on n-4H-SiC wafer as interlayer by electrospinning method and so, Au/(Zn-doped PVA)/n-4H-SiC metal–polymer–semiconductor structures were fabricated. The thickness effect of Zn-doped PVA on the dielectric constant (ε), dielectric loss (ε), loss-tangent (tan δ), real and imaginary parts of electric modulus (M and M) and ac electrical conductivity (σ ac) of them were analysed and compared using experimental capacitance (C) and conductance (G/ω) data in the frequency range of 1–500 kHz at room temperature. According to these results, the values of ε and ε decrease with increasing frequency almost exponentially, σ ac increases especially, at high frequencies. The M and M values were obtained from the ε and ε data and the M and M vs. f plots were drawn for these structures. While the values of ε , ε and tan δ increase with increasing interlayer thickness, the values of M and M decrease with increasing interlayer thickness. The double logarithmic σ ac vs. f plots for each structure have two distinct linear regimes with different slopes, which correspond to low and high frequencies, respectively, and it is prominent that there exist two different conduction mechanisms. Obtained results were found as a strong function of frequency and interlayer thickness.
Journal of Electronic Materials, 2018
The aim of this study is to improve the electrical property of Ag/n-Si metal–semiconductor (MS) s... more The aim of this study is to improve the electrical property of Ag/n-Si metal–semiconductor (MS) structure by growing an Ru-doped PVP interlayer between Ag and n-Si using electrospinning technique. To illustrate the utility of the Ru-doped PVP interface layer, current–voltage (I–V) characteristics of Ag/n-Si (MS) and Ag/Ru-doped PVP/n-Si metal–polymer–semiconductor (MPS) structures was carried out. In addition, the main electrical parameters of the fabricated Ag/Ru-doped PVP/n-Si structures were investigated as a function of frequency and electric field using impedance spectroscopy method (ISM). The capacitance–voltage (C–V) plot showed an anomalous peak in the depletion region due to the special density distribution of interface traps/states (Dit/Nss) and interlayer. Both the values of series resistance (Rs) and Nss were drawn as a function of voltage and frequency between 0.5 kHz and 5 MHz at room temperature and they had a peak behavior in the depletion region. Some important parameters of the sample such as the donor concentration atoms (ND), Fermi energy (E F ), thickness of the depletion region (WD), barrier height (Φ B0 ) and R s were determined from the C−2 versus V plot for each frequency. The values of N D , W D , Φ B0 and R s were changed from 1 × 1015 cm−3, 9.61 × 10−5 cm, 0.94 eV and 19,055 Ω (at 0.5 kHz) to 0.13 × 1015 cm−3, 27.4 × 10−4 cm, 1.04 eV and 70 Ω (at 5 MHz), respectively. As a result of the experiments, it is observed that the change in electrical parameters becomes more effective at lower frequencies due to the Nss and their relaxation time (τ), dipole and surface polarizations.
Journal of Materials Science: Materials in Electronics, 2018
The frequency and voltage dependence of the capacitance–voltage (C–V) and conductance–voltage (G/... more The frequency and voltage dependence of the capacitance–voltage (C–V) and conductance–voltage (G/ω–V) characteristics of the Al/(%7 Zn-doped PVA)/p-Si (MPS) structure were investigated in the wide range of frequency and voltage. Frequency and voltage dependence of C and G/ω shows that these parameters are functions of frequency and voltage. The C–V plot has an anomalous peak and an intersection/crossing point around 1.4 V after which C becomes negative. This negative capaci-tance (NC) phenomena was attributed to the surface states (N ss), series resistance (R s) and minority carrier injection. The intensity of NC decreases with increasing frequency and the minimum value of C corresponds to the maximum value of G/ω at strong accumulation region. Whereas the C–V plots have only one peak at low frequencies, they have two peaks at high frequencies due to the special density distribution of N ss and their relaxation time. In addition, the changes in the C and G/ω were attributed to the increase in the polarization and the increased number of carriers in the structure. Impedance method was used for calculation of R s whereas N ss was obtained using two methods; (i) the high–low frequency capacitance and (ii) Hill-Coleman method as a function of voltage and frequency, respectively. The Fermi energy level (E F), the concentration of doping acceptor atoms (N A) and barrier height (Φ B) values were obtained from reverse bias C −2 vs V plots for each frequency.
Nano Hybrids and Composites, 2018
In this study nickel and boron doped sodium cobalt oxide-nanocrystalline thermoelectric ceramic p... more In this study nickel and boron doped sodium cobalt oxide-nanocrystalline thermoelectric ceramic powders were synthesized using electrospinning techniques and then consolidated into bulk ceramics. The differences in the microstructure and thermoelectric properties of the samples as a result of doping effect have been investigated. The crystalline structures of the powders and nanofibers were characterized using X-ray diffraction and scanning electron microscopy and BET Analysis before and after the calcination process at different temperatures. Nanofibers prepared by the use of electrospinning technique, have a diameter of approximately 300 nm, and the diameter of the grains of calcined powders was observed to range between 150 to 500 nanometers. Thermoelectric properties of the bulk ceramics were measured by physical properties measurement system (Lot-Oriel PPMS) in a temperature range of 15–300 K. The calculated values of dimensionless figure of merit at 300 K are , , and for sintered powders from undoped, Ni and B doped powders, respectively.
In order to interpret the electrical characteristics of fabricated Au/ZnO/n-Si structures as a fu... more In order to interpret the electrical characteristics of fabricated Au/ZnO/n-Si structures as a function of frequency and voltage well, their capacitance– voltage (C–V) and conductance–voltage (G/x–V) measurements were carried out in a wide range of frequencies (0.7 kHz–2 MHz) and voltages (± 6 V) by 50 mV steps at room temperature. Both the C–V and G/x–V plots have reverse, depletion, and accumulation regions such as a metal–insulator/oxide semiconductor (MIS or MOS) structures. The values of doped-donor atoms (N D), Fermi energy level (E F), barrier height (U B), and series resistance (R s) of the structure were obtained as a function of frequency and voltage. While the value of N D decreases with increasing frequency almost as exponentially, the value of depletion width (W D) increases. The values of C and G/x increase with decreasing frequency because the surface states (N ss) are able to follow the alternating current (AC) signal, resulting in excess capacitance (C ex) and conductance (G ex /x), which depends on their relaxation time and the frequency of the AC signal. The voltage-dependent profiles of N ss were obtained from both the high–low frequency capacitance and Hill-Colleman methods. The other important parameter R s of the structure was also obtained from the Nicollian and Brews methods as a function of voltage.
Au/graphene oxide (GO)-doped PrBaCoO nanoceramic/n-Si capacitors were fabricated and their admitt... more Au/graphene oxide (GO)-doped PrBaCoO nanoceramic/n-Si capacitors were fabricated and their admittance measurements were carried out between 1 kHz and 1 MHz at room temperature. Experimental results showed that the capacitance (C) and conductance (G/w) values are strong functions of frequency and applied bias voltage. C–V plot revealed two distinctive peaks at low frequencies which are located at about 0 and 2 V, such that the first peak disappears towards high frequencies. The energy density distribution profile of the interface/surface states (D it / N ss) and their relaxation time (s) and capture cross section (r p) of the sample were obtained by using the admittance method. In addition, the voltage-dependent profile of N ss and resistance were obtained by using low–high frequency capacitance and Nicollian-Brews method, respectively, and they also reveal two distinctive peaks, respectively. Two peaks' behavior in the forward bias C–V, N ss –V and R i –V plots confirmed the existence of two different localized regions of N ss between Si and interfacial layer. The series resistance (R s) of the device decreased with increasing frequency from 175 X at 1 kHz to 72 X at 1 MHz. As a result, the mean value of D it was found about 5 9 10 13 eV-1 cm-2 which is reasonable for an electronic device.
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Papers by Prof.Dr. İbrahim USLU