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https://hdl.handle.net/20.500.12587/18861

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Can Stable MoS2 Monolayers and Multilayers Be Constituted in the Biphenylene Network?
(Amer Chemical Soc, 2023) Gorkan, Taylan; Demirci, Salih; V. Barth, Johannes; Aktürk, Ethem; Çıracı, Salim
Based on the first-principles calculations, we predict that the well-known 2H-MoS2 monolayer of the trigonal prismatic phase appearing in a hexagonal network can also constitute another stable phase in the biphenylene network (B-MoS2). It consists of the connected octagon, hexagon and square rings and hence maintains the same numbers of neighbors of the constituent atoms, but its bonds between transition metal and chalcogen atoms are deformed to construct a direct but narrow band gap semiconductor with directional electronic conduction and optical properties with strong absorption in the near-infrared region. It has softer mechanical properties and site specific chemical activities of the same kind of constituent atoms. In the same way, vacancies of different chalcogen atoms in the cell attain different defect states in the band gap. This phase can remain stable above the room temperature and has a cohesive energy comparable to all the other 2D phases of the same compound. In fact, transitions from the 2H-phase to the B-phase can be possible. The B-phase can form multilayers and also a metallic 3D layered, van der Waals crystal with weak interlayer coupling. The narrow band gap of the monolayer is reduced in the bilayer but diminishes in multilayers and 3D layered crystals to change the semiconductor to a metal. Even more interesting is that B-MoS2 is versatile for the modulation of the band gap, even for the metal-insulator transition under applied strains.
Sınıf Öğretmeni Adaylarının Fen ve Teknoloji Laboratuvarında Kullanılan Deney Türlerinin Motivasyon ve Kavramalarına Etkisiyle İlgili Görüşleri
(2019) Aydın, Nilgün; Aydın, Abdullah
Fen deneyleri, yapılış şekillerine, amaçlarına ve yapılış zamanına göre üç başlık altında toplanabilir. Bu araştırmanın amacı, sınıf öğretmeni adaylarının fen ve teknoloji laboratuvarı derslerinde kullanılan deney türlerinin motivasyonlarını ve kavramalarını nasıl etkilediğiyle ilgili görüşlerinin belirlenmesidir. Bu amaçla araştırmada olgubilim (fenomenoloji) deseni kullanılmıştır. Çalışma grubunu bir devlet üniversitesinin, Eğitim Fakültesi, Sınıf Öğretmenliği Anabilim Dalı’nda 2017-2018 eğitim-öğretim yılı bahar döneminde 2.sınıfta öğrenim gören 52 öğretmen adayı oluşturmaktadır. Verilerin elde edilmesinde 4 tane açık uçlu sorudan oluşan yarı yapılandırılmış görüşme formu kullanılmıştır. Bulgulara göre çalışma grubundaki öğretmen adaylarının %48,08’i, yapılış şekline göre hem gösteri hem de grup deneylerinin, %17,3’ü tamamen grup deneylerinin, %28,8’i tamamen gösteri deneylerinin, %5,7’si de bireysel deney yapılması yönünde görüş bildirmişlerdir. Öğretmen adaylarının %59,6’sının yapılış amacına göre kapalı uçlu deneyleri, %19,23’ünün açık uçlu deneyleri, %17,3’ünün hem kapalı uçlu hem de açık uçlu deney türünü %3,8’inin de hipotez test etme deneyini tercih ettikleri görülmüştür. Araştırmanın sonuçlarına göre, öğretmen adaylarının farklı deney yapma türlerini tercih ettikleri ve bu tercihleri doğrultusunda deneyler yapıldığında motivasyon ve kavramalarının daha olumlu etkileneceği yönünde görüş bildirdikleri görülmüştür.
Physical Properties of Martensitic Phase Transformations in Fe - 18.79%Mn-4.53%Ni Alloys
(2016) Türk, Dilek; Yağcı, Nermin Kahveci
Bu çalışmada, Fe-%18,79Mn-%4,53Ni alaşımında termal etki ile oluşturulan martensitik faz dönüşümlerinin kristalografik ve manyetik özellikleri araştırıldı. Taramalı Elektron Mikroskobu (SEM) ile termal etkili martensitelerin mikroyapıları incelendi. Mikroyapı incelemelerinde, termal etkili martensite yapı miktarının uygulanan sıcaklık derecelerinin artması ile arttığı gözlendi. Austenite faz içerisinde oluşan termal etkili martensite fazın hacim yüzdeleri Mössbauer Spektrometresi tekniği yoluyla belirlendi. X-ışını tekniği ile örgü parametrelerinde meydana gelen değişimler tespit edildi
Hydroxyapatite-based nanoparticles as a coating material for the dentine surface: An antibacterial and toxicological effect
(ELSEVIER SCI LTD, 2020) Erdem, Umit; Dogan, Mustafa; Metin, Aysegul U.; Baglar, Serdar; Turkoz, Mustafa B.; Turk, Mustafa; Nezir, Saffet
In this study, nano sized hydroxyapatite (nHAp) and Ag(I) doped hydroxyapatite (Ag-nHAp) particles were synthesized by the precipitation method and used as a coating material for remineralization on caries-affected dentine samples. Characterization studies of both the synthesized hydroxyapatite-based particles and the coated dentine samples were performed using instrumental techniques such as SEM and FFIR, and then toxicity and antibacterial properties were also evaluated. It was observed that dentine samples were effectively coated by both nHAp and Ag center dot nHAp particles which have no toxic effects. Furthermore, the costing of nano-hydroxyapatite on dentine samples positively contributed to the viability of L929 fibroblast cells and also provided an antibacterial effect against to bacteria such as S. mutants, C. albicans and E. coli bacteria that are most frequently caused caries in the teeth. While all type of bacteria was eliminated by the nHAp coated dentine samples at 24th, Ag-nHAp coated dentine samples removed to all bacteria type at 1st.
Temperature, strain and charge mediated multiple and dynamical phase changes of selenium and tellurium
(ROYAL SOC CHEMISTRY, 2020) Demirci, Salih; Gürel, Hikmet Hakan; Jahangirov, Seymur; Çıracı, Salim
Semiconducting selenium and tellurium in their 3D bulk trigonal structures consist of parallel and weakly interacting helical chains of atoms and display a number of peculiarities. We predict that thermal excitations, 2D compressive strain and excess charge of positive and negative polarity mediate metal-insulator transitions by transforming these semiconductors into different metallic crystal structures. When heated to high temperature, or compressed, or charged positively, they change into a simple cubic structure with metallic bands, which is very rare among elemental crystals. When charged negatively, they transform first into body-centered tetragonal and subsequently into the body-centered orthorhombic structures with increasing negative charging. These two new structures stabilized by excess electrons also have overlapping metallic bands and quasi 2D and 1D substructures of lower dimensionality. Since the external charging of crystals can be achieved through their surfaces, the effects of charging on 2D structures of selenium and tellurium are also investigated. Similar structural transformations have been mediated also in 2D nanosheets and free-standing monolayers of these elements. These phase changes assisted by phonons are dynamical, reversible and tunable; the resulting metal-insulator transitions can occur within very short time intervals and may offer important device applications.
Electronic, Elastic, Vibrational and Thermodynamic Properties of HfIrX (X = As, Sb and Bi) Compounds: Insights from DFT-Based Computer Simulation
(SPRINGER, 2020) Arikan, Nihat; Dikici Yildiz, Gokcen; Yildiz, Yasin Gokturk; Iyigor, Ahmet
Ab-initio calculations were performed to reveal and thoroughly understand the structural, electronic, elastic, thermodynamic and vibrational properties of HfIrX (X = As, Sb and Bi) compounds in the C1(b) phase. Basic physical characteristics, such as bulk modulus, pressure derivative of bulk modulus, anisotropy factor, shear modulus, Poisson's ratio, Cauchy pressure, elastic constants and Young's modulus were obtained and some of them were compared with those in the literature. Electronic band structure, the density of states and phonon dispersion curves were obtained and compared with current theoretical calculations. It was concluded according to current band structure calculations that the HfIrAs and HfIrBi compounds showed semimetal characteristics, while the HfIrSb compound behaves as a semiconductor. It was determined based on phonon calculations that all three compounds were dynamically stable. Various thermodynamic properties, such as heat capacity, thermal expansion coefficient values and Gruneisen parameter were calculated under constant volume and constant pressure by using Gibbs2 code within the Quasi-harmonic approach, and these results are discussed.
Intersection Magnetization and Temperature Revealed by FCC-FCT Phase Transformation in the FePd Binary Alloy System
(SPRINGER, 2020) Yildiz, Gokcen Dikici
This study investigated the fcc-fct phase transformation effect on the magnetic properties of the FePd alloy system by means of the effective field theory (EFT) developed by Kaneyoshi (1993). We determined the thermal magnetization loop and magnetic hysteresis loop of fcc-FePd and fct-FePd for both the ferromagnetic (FM) and antiferromagnetic (AFM) case. We found that the FM fcc-FePd and fct-FePd have a single thermal magnetization area, whereas AFM fcc-FePd and fct-FePd have binary thermal magnetization area. In the AFM case, the magnetization curves for fcc-FePd and fct-FePd had an intersection temperature point (Ti = 1.33 at H = 0). At Ti, the magnetization value of the fcc-FePd and fct-FePd was almost the same (Mi = 0.59) and we call this magnetization the intersection magnetization. However, the magnetic hysteresis loop area of the fcc-FePd was higher than that of the fct-FePd for both the FM and AFM case. Fcc-fct phase transformation has a strong effect on the FM and AFM properties of the FePd binary alloy system.
Monolayer diboron dinitride: Direct band-gap semiconductor with high absorption in the visible range
(AMER PHYSICAL SOC, 2020) Demirci, Salih; Rad, Soheil Ershad; Kazak, Sahmurat; Nezir, Saffet; Jahangirov, Seymur
We predict a two-dimensional monolayer polymorph of boron nitride in an orthorhombic structure (o-B2N2) using first-principles calculations. Structural optimization, phonon dispersion, and molecular dynamics calculations show that o-B2N2 is thermally and dynamically stable. o-B2N2 is a semiconductor with a direct band gap of 1.70 eV according to calculations based on hybrid functionals. The structure has high optical absorption in the visible range in the armchair direction while low absorption in the zigzag direction. This anisotropy is also present in electronic and mechanical properties. The in-plane stiffness of o-B2N2 is very close to that of hexagonal boron nitride. The diatomic building blocks of this structure hint at its possible synthesis from precursors having B-B and N-N bonds.
Focusing-free impedimetric differentiation of red blood cells and leukemia cells: A system optimization
(ELSEVIER SCIENCE SA, 2020) Bilican, Ismail; Guler, Mustafa Tahsin; Serhatlioglu, Murat; Kirindi, Talip; Elbuken, Caglar
A focusing-free microfluidic impedimetric cell detection system is developed. The effect of the channel dimensions, solution conductivity, excitation voltage, and particle size on impedimetric signal outputs were optimized to increase the sensitivity of the system. Conventional microfabrication techniques were adapted to obtain low height, resealable microchannels. The geometry optimization was performed by a combination of analytical, numerical and experimental approaches. The results demonstrate that reliable impedimetric particle differentiation can be achieved without any labeling or particle focusing. The system parameters were studied and rule-of-thumb design criteria were provided. Finally, using the developed system, red blood cells and leukemia cells were experimentally detected and differentiated. Thanks to its simplicity, the focusing-free cell differentiation system may find applications in several cellular diagnostic uses.
Investigation of the Mechanical, Electronic and Phonon Properties of X2ScAl (X = Ir, Os, and Pt) Heusler Compounds
(KOREAN PHYSICAL SOC, 2020) Arikan, Nihat; Ocak, Hamza Yasar; Yildiz, Gokcen Dikici; Yildiz, Yasin Gokturk; Unal, Rahmi
In the present study, the second-order elastic constants and the electronic band structures of the X2ScAl (x= Ir, Os, and Pt) compounds crystallized in the L2(1)phase were calculated separately by using theab-initiodensity functional theory. According to the results for the second-order elastic constants, these compounds met the Born mechanical stability criteria. Also, according to the Pugh criteria, they were found to have a ductile structure and to show anisotropic behavior. The microhardneses of the compounds were between 2 and 14 GPa, and the highest hardness was found in the Ir2ScAl (14.290 GPa) compound. In addition, the energy band structures of these compounds were calculated, and the crystals were found to have a metallic bond structure. All the computed data were compared with previously calculated results obtained with different methods. According to the findings obtained in the present study, in terms of its mechanical and electronic behaviors, Ir2ScAl was found to have better physical properties than Os2ScAl and Pt2ScAl. The phonon dispersion curves and their corresponding total and projected densities of states were investigated for the first time by using a linear-response approach in the context of density functional perturbation theory. The frequencies of the optical phonon modes of all compounds at the Gamma point were 4.767, 7.504 and 9.271 THz for Ir2ScAl, 2.761, 7.985 and 9.184 THz for Os2ScAl and 2.012, 5.6952 and 8.118 THz for Pt2ScAl. The heat capacityC(v)at constant volume versus temperature was calculated using a quasi-harmonic approach and the results are discussed.
Crystal structure, Hirshfeld surface analysis and DFT studies of (E)-4-methyl-2-{[(4-methylphenyl)-imino]methyl}phenol
(INT UNION CRYSTALLOGRAPHY, 2020) Yagci, Nermin Kahveci; Faizi, Md Serajul Haque; Aydin, Alev Sema; Dege, Necmi; Dogan, Onur Erman; Agar, Erbil; Mashrai, Ashraf
In the title compound, C15H15NO, the configuration of the C=N bond of the Schiff base is E, and an intramolecular O-H center dot center dot center dot N hydrogen bond is observed, forming an intramolecular S(6) ring motif. The phenol ring is inclined by 45.73 (2)degrees from the plane of the aniline ring. In the crystal, molecules are linked along the b axis by O-H center dot center dot center dot N and C-H center dot center dot center dot O hydrogen bonds, forming polymeric chains. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the packing arrangement are from H center dot center dot center dot H (56.9%) and H center dot center dot center dot C/C center dot center dot center dot H (31.2%) interactions. The density functional theory (DFT) optimized structure at the B3LYP/ 6-311 G(d,p) level is compared with the experimentally determined molecular structure, and the HOMO-LUMO energy gap is provided. The crystal studied was refined as an inversion twin.
Two dimensional ruthenium carbide: structural and electronic features
(ROYAL SOC CHEMISTRY, 2020) Görkan, Taylan; Demirci, Salih; Jahangirov, S.; Gokoglu, Gökhan; Aktürk, Ethem
The design and realization of novel 2D materials and their functionalities have been a focus of research inspired by the successful synthesis of graphene and many other 2D materials. In this study, in view of first principles calculations, we predict a novel 2D material ruthenium carbide (RuC) in graphene-like honeycomb hexagonal lattice with planar geometry. Phonon dispersion spectra display a dynamically stable structure. Comprehensive molecular dynamics calculations confirm the stability of the structure up to high temperatures as approximate to 1000 K. The system is a narrow gap semiconductor with a band gap of 53 meV (345 meV) due to GGA-PBE (HSE) calculations. Band gap exhibits significant changes by applied strain. Elastic and optical properties of the system are examined in monolayer form. RuC/RuC bilayer, RuC/graphene and RuC/h-BN heterostructures are also investigated. By calculating the phonon dispersion it is verified that RuC bilayer is the most stable in AA type-stacking configuration where Ru and C atoms of both layers have identical lateral coordinates. The effects of atomic substitutions on electronic band structures, acting as p-type and n-type doping, are revealed. A novel 3D RuCLi structure is also predicted to be stable and the isolation of its monolayer forms are discussed. Ruthenium carbide, as a 2D material which is dynamically and thermally stable, holds promise for applications in nanoelectronics.
New empirical formula for calculating (n, p) reaction cross-sections at 14.5 MeV neutrons
(WORLD SCIENTIFIC PUBL CO PTE LTD, 2020) Akrawy, Dashty T.; Ahmed, Ali H.; Tel, Eyüp; Aydın, Abdullah; Sihver, L.
An empirical formula to calculate the (n, p) reaction cross-sections for 14.5 MeV neutrons for 183 target nuclei in the range 44 <= A <= 212 is presented. Evaluated cross-section data from TENDL nuclear data library were used to test and benchmark the formula. In this new formula, the nonelastic cross-section term is replaced by the atomic number Z, while the asymmetry parameter-dependent exponential term has been retained. The calculated results are presented in comparison with the seven previously published formulae. We show that the new formula is significantly in better agreement with the measured values compared to previously published formulae.
A new formulae study for the (n,2p) reaction cross-section systematics at 14-15 MeV
(PERGAMON-ELSEVIER SCIENCE LTD, 2020) Kavun, Yusuf; Aydin, Abdullah; Tel, Eyyüp
The cross-section calculation systematics for nuclear reactions have great importance in describing the particleinduced excitation of nuclei. In this study, for 14-15 MeV of incident neutron energy, it has been suggested new empirical formulae to describe the (n, 2p) reactions cross sections. The new empirical formulae have been obtained for 29 <= A <= 159, 29 <= A <= 103 and 133
Crystal structure, Hirshfeld surface analysis and DFT studies of (E)-4-methyl-2-{[(2-methyl-3-nitrophenyl)imino]methyl}phenol
(INT UNION CRYSTALLOGRAPHY, 2020) Cinar, Emine Berrin; Faizi, Md Serajul Haque; Yagci, Nermin Kahveci; Dogan, Onur Erman; Aydin, Alev Sema; Agar, Erbil; Dege, Necmi
The title compound, C15H14N2O3, was prepared by condensation of 2-hydroxy-5-methyl-benzaldehyde and 2-methyl-3-nitro-phenylamine in ethanol. The configuration of the C=N bond is E. An intramolecular O-H center dot center dot center dot N hydrogen bond is present, forming an S(6) ring motif and inducing the phenol ring and the Schiff base to be nearly coplanar [C- C-N-C torsion angle of 178.53 (13)degrees]. In the crystal, molecules are linked by C-H center dot center dot center dot O interactions, forming chains along the b-axis direction. The Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from H center dot center dot center dot H (37.2%), C center dot center dot center dot H (30.7%) and O center dot center dot center dot H (24.9%) interactions. The gas phase density functional theory (DFT) optimized structure at the B3LYP/ 6-311 G(d,p) level is compared to the experimentally determined molecular structure in the solid state. The HOMO-LUMO behaviour was elucidated to determine the energy gap.
Nuclear structure properties of even-even chromium isotopes and the effect of deformation on calculated electron capture cross sections
(ELSEVIER, 2020) Nabi, Jameel-Un; Boyukata, Mahmut; Ullah, Asim; Riaz, Muhammad
In this study, we investigate the role of the nuclear deformation on the calculated electron capture cross section (ECC) of even-even chromium (Cr) isotopes. We first determined the nuclear structure properties of these nuclei within the interacting boson model-1 (IBM-1). The energy spectra and E2 transition probabilities were calculated by fitting the parameters in the model formalism. The analysis of the potential energy surface were also performed to predict the geometric shape of the Cr nuclei by plotting their contour plot in the plane of (beta, gamma ) deformation parameters. Later, we calculated the ECC within the proton-neutron quasiparticle random phase approximation (pn-QRPA) model. In particular we studied how the calculated ECC changed with different values of nuclear deformation parameter. The calculated Gamow-Teller (GT) strength distributions were widely spread among the daughter states. The total GT strength decreased with increasing value of the beta parameter. The computed ECC values, however, increased with increase in the beta value of the Cr isotopes. (c) 2020 Elsevier B.V. All rights reserved.
Alternative screening method for analyzing the water samples through an electrical microfluidics chip with classical microbiological assay comparison of P. aeruginosa
(ELSEVIER, 2020) Bilican, Ismail; Bahadir, Tolga; Bilgin, Kemal; Guler, Mustafa Tahsin
Pseudomonas aeruginosa is a pathogenic bacterium in fresh water supplies that creates a risk for public health. Microbiological analysis of drinking water samples is time consuming and requires qualified personnel. Here we offer a screening system for rapid analysis of spring water that has the potential to be turned into a point-of-need system by means of simple mechanism. The test, which takes 1 h to complete, electrically interrogates the particles through a microfluidic chip suspended in the water sample. We tested the platform using water samples with micro beads and water samples spiked with P. aeruginosa at various concentrations. The mono disperse micro beads were used to evaluate the performance of the system. The results were verified by the gold standard membrane filtration method, which yielded a positive test result only for the P. aeruginosa spiked samples. Detection of 0-11 k bacteria in 30 mu L samples was successfully completed in 1 h and compared with a conventional microbiological method. The presented method is a good candidate for a rapid, on-site, screening test that can result in a significant reduction in cost and analysis time compared to microbiological analyses routinely used in practice.
Definition and detection of simulation noise via imaginary simulated particles in comparison with an electrical microfluidic chip noise
(SPRINGER HEIDELBERG, 2020) Guler, M. Tahsin
Real problems in science and engineering generally do not have an analytical solution, which invariably leads to the application of numerical methods to analyze the problem. The numerical solutions to the same problem give different results due to variations in discretization, which are defined as simulation noise in this study. Microfluidics impedance flow cytometry is employed to demonstrate and compare experimental and simulated noise. For measurement of the simulation noise, an object is assigned with the same electrical parameters as the medium and moved along the electrode region through a microchannel. Since the object is no different to the medium in terms of material properties, forwarding of the object through the electrodes doesn't have any physical effect, but just reorders the meshing. However, the impedance, which is the calculated output parameter of the simulation, fluctuates due to the reordering of the meshes and is defined as the simulation noise. By employing the imaginary object method, noise can be measured for every Finite element method (FEM) simulation even if the problem has a different physical background.
Assessment of PMMA and polystyrene based microfluidic chips fabricated using CO2 laser machining
(ELSEVIER, 2020) Bilican, Ismail; Guler, Mustafa Tahsin
Laser machining could be an alternative way for the fabrication of microchannels. In this study, laser machining of polymethylmethacrylate (PMMA) and polystyrene (PS) substrates were characterized in detail. A fabrication method preventing leakage at PS microchannel inlets was developed. The effect of laser parameters (power, speed and frequency) on engraving was analyzed by scanning electron microscopy. Laser ablation mechanism of both materials was explained through thermal analysis and material properties. Defocusing the laser beam was also analyzed as an additional parameter affecting the channel profile. Two parameters affecting the resolution were analyzed which are the minimum channel size that can be achieved by the laser beam and x-y stage of the laser engraver for straight and complex microchannel geometries. The hydrophilicity of the surface before and after laser machining was tested with contact angle measurements. The capabilities/limitations of machining were revealed through some complex channel structures. Finally, a passive micromixer and a droplet generator microfluidic devices were manufactured and tested, and promising results were obtained.
Magnetic properties of the Martensitic transformations with twinned and detwinned
(Elsevier Science Bv, 2019) Sarli, Numan; Yildiz, Gokcen Dikici; Yildiz, Yasin Gokturk; Yagci, Nermin Kahveci
The effects of the Austenite (A), twinned Martensite (TM) and detwinned Martensite (DTM) structural transformations on the ferromagnetic properties are investegated by means of the effective field theory developed by Kaneyoshi. We find that the critical Curie temperature of the A, TM and DTM is obtained as T-c(A) < T-c(DTM)< T-c(TM) for H = 0. Thermal magnetization loops are obtained for H not equal 0. The area of the thermal magnetization loops of the A-TM is wider than those of the A-DTM. Paramagnetic Austenite has a phase transition from paramagnetic (PM) phase to ferromagnetic (FM) phase at T-c(TM) and T-c(DTM). The temperature of the As (Austenite start), TMf (twinned Martensite finish) and DTM f (detwinned Martensite finish) increase as the external magnetic field (H) increases. The magnetizations of the A, TM and DTM are the same at low temperature (T < A(s)). The coercive field points are obtained as H-c(A) < H-c(DTM)< H-c(TM). The shearing angle plays very important role in the structural transformations and their ferromagnetic properties, especially in TM.

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