Guven Cankaya | Ankara Yildirim Beyazit University (original) (raw)

Papers by Guven Cankaya

IEEE Conference Proceedings, 2016

The goal of this work was to provide ideas to analyze the electrical properties of biomimetic gro... more The goal of this work was to provide ideas to analyze the electrical properties of biomimetic growth chitin nanofibers that was studied for frequencies between 100 Hz and 1 MHz. Dielectric measurements were performed using a HIOKI “3532-50 LCR HiTESTER” and the special built probe system that was used for determining thickness of the material sample at the same time. Specimens were prepared in a plate form. After sample testing, the frequency dependences of the capacitance, conductance, dielectric constant, and loss coefficient graphs, and the voltage dependences of the capacitance graph were plotted for material.

Journal for Manufacturing Science and Production, Sep 1, 1999

The Schottky barrier height (SBH), b, and ideality factor, η ,of Au/n-GaAs Schottky diodes (SDs) ... more The Schottky barrier height (SBH), b, and ideality factor, η ,of Au/n-GaAs Schottky diodes (SDs) have been measured using current-voltage ( I -V) and capacitance-voltage (C-V) techniques under the hydrostatic pressure. The calculated value was 0.80 eV (0.93) eV when using I-V {C-V) technique with an ideality factor of 1.061 at atmospheric pressure. The φπ increased to 0.91 eV (1.0 eV) with an ideality factor of 1.037 after hydrostatic pressure 6 kbar. The discrepancy between I-V and C-V measurements was attributed to different nature of the I-V and C-V measurement techniques.

Physica B-condensed Matter, 2010

The interface state density obtained from current-voltage (I-V) characteristics of Cd/n-type GaAs... more The interface state density obtained from current-voltage (I-V) characteristics of Cd/n-type GaAs Schottky barrier diodes (SBDs) at room temperature under hydrostatic pressure was investigated. SBD parameters such as ideality factor (n), series resistance (R s), and barrier height (f b), were obtained from I-V measurements using Cheung's method. The diode parameters, such as ideality factor, series resistance, and barrier heights, were found in the range of 1.464-1.474, 0.995-4.359 kO and 0.739-0.777 eV, respectively, with sweeping pressure. The diode shows non-ideal I-V behaviors with an ideality factor greater than unity. Additionally, the energy distribution of interface state density was determined from the forward bias I-V characteristics by taking into account the bias dependence of the effective barrier height. The results have shown that the presence of the interfacial native oxide layer between the metal and the semiconductor seriously affects interface state density under hydrostatic pressure.

High Temperature Materials and Processes, Jun 1, 2002

The stage-I work-hardening behavior of Cd single crystals from stress-strain curve measurements h... more The stage-I work-hardening behavior of Cd single crystals from stress-strain curve measurements has been investigated as a function of temperature and strain-rate. The results show that the temperature and the strain-rate introduce opposite effects on the work-hardening behavior. The stress was found to be approximately linear on the square root of strain for both low and high strain values at different temperatures. There is an inflexion point at intermediate strains. This inflexion point moves to higher strain values with increasing temperature.

Materials Technology, Jul 1, 2012

Zirconium oxide (ZrO 2) thin films were prepared by the sol-gel dip coating technique, in combina... more Zirconium oxide (ZrO 2) thin films were prepared by the sol-gel dip coating technique, in combination with annealing at different temperatures in air atmosphere, with the final goal of studying the water wettability of the surface. The annealing effects on the structural and optical properties of the ZrO 2 films were investigated to check the characteristics of the material. X-ray diffraction (XRD) patterns of ZrO 2 annealed at 450 • C and 550 • C show the formation of tetragonal phase, with layers constituted by nanoparticles with average particle size of 21 nm and 25 nm, respectively. Fourier-transform infrared spectroscopy (FT-IR) spectra revealed the presence of vibrational modes associated to ZrO 2. Photoluminescence (PL) and ultraviolet-visible spectroscopy (UV-Vis) spectroscopy was used for optical properties. All deposited ZrO 2 thin films presented a high optical transparency, with an average transmittance above 70% in the visible range (400-700 nm). The hydrophilic properties of ZrO 2 films were characterized by means of the measurements of the contact angle. When the sample was annealed at 550 • C, the hydrophilicity reached the best behavior, which was explained as an effect of the structural and morphological change of the films.

Semiconductor Science and Technology, Dec 21, 2005

ABSTRACT Schottky barrier diodes (SBDs) on p-type GaTe have been fabricated by Cd metallization a... more ABSTRACT Schottky barrier diodes (SBDs) on p-type GaTe have been fabricated by Cd metallization and characterized by current–voltage (I–V) and capacitance–voltage (C–V) techniques as a function of hydrostatic pressure (0.0–7.0 kbar). The evaluation of the experimental data reveals a decrease of barrier height (Φb), ideality factor (n) and series resistance (Rs) with an increase in the hydrostatic pressure. The zero-bias barrier height, ideality factor and series resistance values for the Cd/p-GaTe SBD by I–V measurements have been in the range of 0.743–0.682 eV, 1.246–1.219 and 30.5–16.4 Ω for the 0.0–7.0 kbar pressure interval, respectively. C–V measurements at 1.0 MHz have resulted in higher barrier heights than those obtained from I–V measurements. The discrepancy between Schottky barrier heights (SBHs) obtained from I–V and C–V measurements is explained by the introduction of a spatial distribution of SBHs due to barrier height inhomogeneities that prevail in the metal/GaTe interface. The change of barrier height values (Φb(0) − Φb(P)) obtained from the I–V and C–V techniques turns out to have a mean linear pressure coefficient of −8.77 ± 0.10 meV kbar−1 (=−87.7 ± 1.0 eV GPa−1), approximately equal to that found for the band gap of GaTe. We have concluded that the variation of the barrier height due to the applied pressure should follow precisely the variation of the semiconductor band gap, accepting that the Fermi level is a reference level which is pinned to the conduction-band minimum (CBM) as a function of the pressure.

Semiconductor Science and Technology, Dec 24, 2002

ABSTRACT The current–voltage (I–V) characteristics of Cd/p-GaTe Schottky barrier diodes were meas... more ABSTRACT The current–voltage (I–V) characteristics of Cd/p-GaTe Schottky barrier diodes were measured in the temperature range 90–330 K. The apparent barrier height and the ideality factor derived by using thermionic emission (TE) theory were found to be strongly temperature dependent. Evaluating forward I–V data reveals a decrease of zero-bias barrier height (Φb0) but an increase of ideality factor (n) with decrease in temperature, and these changes are more pronounced below 150 K. The conventional Richardson plot exhibits nonlinearity below 150 K with the linear portion corresponding to an activation energy of 0.52 eV. The value of effective Richardson constant (A*) turns out to be 6.74 × 10−2 A K−2 cm−2 against the theoretical value of 119.4 A K−2 cm−2. It is demonstrated that the findings cannot be explained on the basis of tunnelling and image force lowering effects. Also, the concept of the flat-band barrier height (Φfb) fails to account for the temperature dependence of the diode parameters. Finally, it is demonstrated that these anomalies result due to the barrier height inhomogeneities prevailing at the metal–semiconductor interface. The inhomogeneities are considered to have Gaussian distribution with a mean barrier height of = 0.886 eV and a standard deviation of σs0 = 0.091 eV at zero bias. Furthermore, the mean barrier height and the Richardson constant values were obtained as 0.875 eV and 62.2 A K−2 cm−2, respectively, by means of the modified Richardson plot, ln(J0/T2) − (q2σ2s0/2k2T2) versus 1000/T. Hence, it has been concluded that the temperature dependence of the I–V characteristics of the Schottky barrier on p-type GaTe can be successfully explained on the basis of TE mechanism with Gaussian distribution of the barrier heights.

Social Science Research Network, 2023

Zeitschrift für Naturforschung, Apr 1, 2008

Au/n-GaAs Schottky barrier diodes (SBDs) have been fabricated. The effect of indentation on Schot... more Au/n-GaAs Schottky barrier diodes (SBDs) have been fabricated. The effect of indentation on Schottky diode parameters such as Schottky barrier height (φ b) and ideality factor (n) was studied by current-voltage (I-V) measurements. The method used for indentation was the Vickers microhardness test at room temperature. The experimental results showed that the I-V characteristics move to lower currents due to an increase of φ b with increasing indentation weight, while contacts showed a nonideal diode behaviour.

Philosophical Magazine, Feb 19, 2014

ABSTRACT This paper describes a simple, low-temperature and cost-effective liquid-phase method to... more ABSTRACT This paper describes a simple, low-temperature and cost-effective liquid-phase method to synthesize homogenous plate-like CuO nanostructures and their sensitivity to humidity. Scanning electron microscopy illustrated that the synthesized CuO nanoplates have thicknesses of ~100 nm. X-ray diffraction measurements showed that the CuO nanostructures have high crystallinity with monoclinic crystal structure preferentially in [Inline formula] and [Inline formula] directions. From the temperature-dependant dark electrical resistivity measurements, the ionization energies of the impurity levels and thermal band gap energies of the films are found as 0.30, 0.32 and 1.37, 1.39 for as-synthesized and annealed films, respectively. Gas sensing characteristics of the films were investigated for different concentrations of humidity, isopropyl alcohol, methanol, ethanol, chloroform and acetone vapours. It was found that the sensor is sensitive to humidity but not to the other volatile organic compounds.

Physica status solidi, Jun 1, 2000

The experimental results have shown that the I±V characteristics of the diode shift to lower curr... more The experimental results have shown that the I±V characteristics of the diode shift to lower current values due to an increase of the Schottky barrier height with increasing hydrostatic pressure and the quality of the diode improves. It has been seen that the I±V characteristics after removal of the hydrostatic pressure have coincided with that at 1 kbar. Furthermore, the time-dependence of I±V characteristics of the Au/n-GaAs Schottky diodes 15, 30 and 45 days after the pressure has been removed have also coincided with that at 1 kbar. After the pressure treatments, this behavior of our diodes has been ascribed to the removal of fabrication-induced lateral inhomogeneities of the barrier height.

Semiconductor Science and Technology, Mar 16, 2011

Multiwalled carbon nanotube (MWCNT) deposited on a pair of predetermined aluminum electrodes trea... more Multiwalled carbon nanotube (MWCNT) deposited on a pair of predetermined aluminum electrodes treated with the (3-Aminopropyl)-triethoxysilane (APTES) self-assembled monolayers (SAMs). The MWCNT bridges electrodes and forms electrode/MWCNT/electrode circuit on silicon with 500 nm silicon dioxide. Then the Metal (Ti/Au) pads were fabricated on MWCNT to bury the MWCNT into metal electrodes. The electrical properties of MWCNT-based circuits before and after the fabrication of metal pads were characterized. Results indicate that metal pads on MWCNT improved the electrical properties MWCNT-based circuit largely.

In radiation therapy, bolus is a material which has properties equivalent to tissue when irradiat... more In radiation therapy, bolus is a material which has properties equivalent to tissue when irradiated. It is widely used in practice to reduce or alter dosing for targeted radiation therapy. As an alternative to commercial bolus materials used in radiotherapy by using 3D modeling and printing technologies, the desired geometry, different material properties, to show that the patient can be produced specific and cheap. Thus, an alternative method for bolus material is to introduce the medical literature. In this study, boluses of the same geometry produced with 10 different materials and commercial bolus were measured in Linac device. The new generation boluses produced from ABS, Bronzefill, HIPS, PetG, PLA, PLAflex, PolyFlex TM, PP, STH and TPU materials were interpreted by comparing the values with the commercial bolus. According to the results, the new generation boluses are very promising.In the treatment planning phase, it will be a great advantage that the new generation bolus, which will be designed by scanning the patient's area to be treated with 3D scanner, will be produced with the materials of the desired characteristics with the support of 3D printer technology and will be compatible with the individual, radiotherapy area and the elements facilitating treatment planning.In addition, due to the surface roughness of the commercial bolus and errors caused by the air gaps formed between the patient's skin and the constant thickness geometry of the commercial bolus are some of the problems encountered during treatment. Since the new generation bolus is produced using 3D printing technology, it can be designed in any desired complex geometry and becomes advantageous over the commercial bolus

International Journal of Electronics, Oct 1, 2000

ABSTRACT

Frontiers in Energy Research, Jul 28, 2023

and Sonmezoglu S (2023), Impact of tellurium as an anion dopant on the photovoltaic performance o... more and Sonmezoglu S (2023), Impact of tellurium as an anion dopant on the photovoltaic performance of wide-bandgap Cu(In,Ga)Se 2 thin-film solar cells with rubidium fluoride post-deposition treatment.

International Journal of Energy and Power Engineering, 2019

This publication investigates to present all new scientific and industrial works all rolled into ... more This publication investigates to present all new scientific and industrial works all rolled into one with more effective and predictability aspect in chalcopyrite Photovoltaics (PVs). The paper suggests that comprehensive and fine-tuned directions supporting a large portfolio of solar energy materials could be extended to most efficiency, which mostly depend on the growth techniques especially usage rates in substituents and their characteristic/specific properties. There is an indispensable source of solar energy. If this were the case, new energy materials could well become a competitive alternative in many applications within the next few years. This publication builds upon past analyses of chalcopyrites contained in the word Energy outlook as efficient alternative materials. It aims at offering an updated picture of current technology trends/demands/markets, as well as new analyses on how solar energy technologies/materials for capturing the purposed efficiency and durableness can be used in the various energy consuming/developing sectors, now and in the future. In this work we have tried to summarize the all significant studies about Chalcopyrite solar cells from the past to the present and also tried to introduce Te doped CuInGaSeTe compound which is a new member of the family that we produced.

Turkish Journal of Medical Sciences, Oct 21, 2021

Introduction Burning is one of the most devastating diseases that can cause physical and social r... more Introduction Burning is one of the most devastating diseases that can cause physical and social restriction [1]. There are 6.5 million patients suffering from this problem in the US alone [2]. The annual cost of dealing with these complications for the US is approximately 50 billion USD [2]. Although the magnitude of the effort against these difficulties are tremendously high, the biggest concern of physicians is that the patients do not adapt to splints during their treatment processes and especially during their physiotherapy, and they raise issues that will reduce their quality of life [2,3]. For this reason, investigators are trying to make splints more feasible by using technology, and new products are emerging [3-7]. The main purpose in these pursuits is to obtain a user-friendly, safe, compatible, and cost-effective product [2,4,7,8]. Three-dimensional (3D) printers have been used to produce therapeutic devices like prostheses and orthoses for about 20 years [4,5]. Among these, there are devices Background/aim: We evaluated the feasibility of producing splints with 3D printer technology to prevent contractures in burned children in our clinical prospective study. Materials and methods: After approvals, children with burns greater than 2nd degree were included in the study. Age, sex, burn percentages, printing time, filament types, number of filament trials, splint suitability, patient and doctor comments, preclinical trials' significances and financial impact were evaluated statistically. Results: Seventy-six trials were conducted on 18 patients. Fourteen of the patients were male and 4 are female. Average ages of boys and girls were 5 and 3, respectively. Burn percentage was 36.9 ± 13. Polylactic acid (PLAFlex), polyurethane (PolyFlex), semiflexible copolyester (nGenFlex), and thermoplastic polyurethane (TPU) were the main filaments that were used in the study. Printing time differed from 4 to 29 h according to body regions. Splints were suitable for 81.25% in upper extremity, for 66.7% in lower extremity, and for 100% in mouth. Burn percentage was significantly correlated with total number of filament (p = 0.049). Other statistical evaluations were insignificant. Conclusion: The 3D printer seems to be useful in children with burns. However, difficulties caused by some reasons like production must be overcome. By increasing clinical experience, this emerging custom-made technology may become standard, and documented problems can be solved.

Physica Scripta, 2002

Forward bias capacitance-voltage characteristics and interface state density of Au/n-GaAs Schottk... more Forward bias capacitance-voltage characteristics and interface state density of Au/n-GaAs Schottky diode were investigated by capacitance technique under hydrostatic pressure. It is shown that the capacitance-voltage characteristics are in£uenced due to the change of ionised additional donor-like defect centres. The interface state density decreases with the increase of energy from the edge of the valence band. In addition, it has been found that the hydrostatic pressure seriously a¡ects the interface state density.

Zeitschrift für Naturforschung, Nov 1, 2004

We investigated Schottky barrier diodes of 9 metals (Mn, Cd, Al, Bi, Pb, Sn, Sb, Fe, and Ni) havi... more We investigated Schottky barrier diodes of 9 metals (Mn, Cd, Al, Bi, Pb, Sn, Sb, Fe, and Ni) having different metal work functions to p-type Si using current-voltage characteristics. Most Schottky contacts show good characteristics with an ideality factor range from 1.057 to 1.831. Based on our measurements for p-type Si, the barrier heights and metal work functions show a linear relationship of current-voltage characteristics at room temperature with a slope (S = φ b /φ m) of 0.162, even though the Fermi level is partially pinned. From this linear dependency, the density of interface states was determined to be about 4.5 • 10 13 1/eV per cm 2 , and the average pinning position of the Fermi level as 0.661 eV below the conduction band.

Journal of the mechanical behavior of materials, Jun 1, 1998

The stress-strain curves of white tin single crystals have been determined as a function of cryst... more The stress-strain curves of white tin single crystals have been determined as a function of crystal diameter and orientation at room temperature. The stress-strain curves, especially for thinner crystals, are characterized by a remarkable decrease in stress after yielding followed by a gradual increase in the stress with strain due to work hardening. On the other hand, the easy glide region was found to be a function of both crystal diameter and orientation.