Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Research Project Plazma Nitrürlenmiş Cocrmo Ortopedik Alaşım Malzemesinin Yapısal ve Kompozisyonel Karakterizasyonu(2010) Öztürk, Orhan; Rıvıere, Jean Paul; Pichon, Luc; Okur, SerdalPlazma nitrürleme teknikleri, CoCrMo alaşımlarının yakın yüzey tabakalarını modifiye ederek bu malzemelerin yüzeylerinde aşınma ve korozyona dayanıklı tabakalar oluşturmakta kullanılmaktadır. Bu çalışmada, medikal sınıfı CoCrMo alaşımı, düşük basınç altında (~ 60 mTorr), 60% N2 – 40% H2 gaz karışımında ve 400 ºC de 1, 2, 4, 6 ve 20 saat sürelerince RF plazma nitrürlenmiştir. Plazma nitrürlenmiş tabakaların yapısal ve kompozisyonel karakterizasyonu X-ışınları kırınımı (XRD), taramalı electron mikroskobu (SEM), atomik kuvvet mikroskobu (AFM) ve glow discharge optik emisyon spektroskopisi (GDOES) teknikleri kullanılarak incelenmiştir. Nitrürlenmiş tabakaların sertlik ve aşınma davranışları mikrosertlik ve pin-on-disc testleri kullanılarak incelenmiştir. Deneysel analiz sonuçları, 400 ºC’ deki plazma nitrürleme işlemi sonucunda, yüksek azot içeriğine sahip (~ 30 at.%) genişlemiş östenit fazının (γN) oluştuğunu göstermektedir. Bununla birlikte, uzun nitrürleme sürelerinde (6 ve 20 saat) γN fazında CrN dekompozisyonu ve yüzeye paralel olan γN taneciklerde (200) tercihli yönelmeler oluşmaktadır. Elektrokimyasal ve Ar+ ışınları yöntemiyle dağlanmış nitrürlenmiş malzemelerinin kesit-yüzey mikroskopi analizlerine ve GDOES verilerine göre, nitrürlenmiş tabakaların kalınlıkları yaklaşık olarak 2 ile 10 mikrometre arasında değişmektedir. Kalınlık analizlerine göre, CoCrMo malzemelerinin 400 ºC’ de plazma nitrürlenmesi sonucu, ortalama azot diffüzyon katsayısı yaklaşık olarak 1.5x10-11 cm2/s bulunmuştur. Tüm plazma nitrürlenmiş CoCrMo alaşımlarında önemli sertlik ve aşınma iyileşmeleri gözlenmesine rağmen, en iyi aşınma-korozyon dayanıklılığı yalnızca γN yapısına sahip CoCrMo alaşımlarında gözlenmiştir.Research Project Yüksek Kalite İnce Kataliz Filmler Üzerine Kimyasal Buhar Biriktirme Yöntemleri ile Kontrollü Grafen Büyütülmesi, Karakterizasyonu ve Uygulamaları(2016) Selamet, Yusuf; Öztürk, Orhan; Tarhan, EnverGrafen hem çok hafif hem de çelikten kat kat sağlam bir malzemedir. Aynı zamanda görünür bölgede geçirgendir ve metalik özellik gösterir. Grafen değişik şekillerde kesildiğinde bir bant aralığı oluşur ve bunlardan üstün özellikli devre elemanları üretilebilir. Grafen’de elektronik alanında Si’un yerini alacak potansiyel görülmektedir. Bunlarla tek atom kalınlığında elektronik, nano-boyutlu aygıtlar yapılabilir ve normal yarıiletkenlerin boyutlarının daha da küçülmesini sınırlayan kuantum tünelleme olayından etkilenmezler. Grafen kuantum ve rölativistik fizik ile ilgili birçok deneyleri, milyarlarca dolar harcanarak oluşturulan hızlandırıcılara gerek kalmadan basit laboratuvar ortamında yapma olanağı sunar. Grafen’in içerdiği benzersiz fizik tamamen yeni cihazların tasarımlanmasına yol açabilecek yeniliktedir.Article Citation - WoS: 17Citation - Scopus: 19Bacterial Surface, Biofilm and Virulence Properties of Listeriamonocytogenes Strains Isolated From Smoked Salmon and Fish Food Contact Surfaces(Elsevier, 2021) Sudağıdan, Mert; Özalp, Veli Cengiz; Öztürk, Orhan; Yurt, Mediha Nur Zafer; Yavuz, Orhan; Taşbaşı, Behiye Busra; Uçak, Samet; Mavili, Zehra Seda; Çoban, AyşenBiofilm formation is one of the defense mechanisms of bacteria against disinfectants and antimicrobials. The aim of this study was to determine biofilm-forming L.monocytogenes from fish processing and salmon surfaces. Biofilm formation at 15, 25, 37, and 40 degrees C from 1 to 6-days period, adhesion to glass, polypropylene and stainless-steel surfaces, bacterial surface charge and hydrophobicity was determined. Adhesion behavior of the strains was evaluated using Surface Plasmon Resonance (SPR) technique. Totally 32 L.monocytogenes strains belonging to serogroups IIa (n:17), IIc(n:14) and IVb(n:1) were detected from 1320 swabs and 16 smoked salmons. Biofilm formation tests revealed that 21 strains form biofilm on microplate by increasing time and temperature. Although all strains strongly formed biofilm on glass surfaces, two strains slightly adhered polypropylene surfaces. High surface roughness of stainless-steel FeCrNi alloy (Ra = 4.15 nm) and CoCrMo alloy (Ra = 10.75 nm) increased biofilm formation of L.monocytogenes on stainless-steel surfaces. Zeta potential results showed that non-biofilm formers were more negatively charged after 6-days and hydrophobicity couldn't give a distinct distribution among biofilm formers and non-formers. SPR analysis method was evaluated to distinguish biofilm formers to adhere SPR gold chip surfaces. PCR results revealed that all strains were positive for hylA, iap, actA, plcA, plcB, fri, flaA, inlA, inlB, inlC, inlJ, and lmo1386 genes. Additionally, all strains were susceptible to penicillin, ampicillin, meropenem, erythromycin and trimethoprim-sulfamethoxazole. Biofilm-forming, virulence properties of L. monocytogenes strains isolated from fish processing surfaces and smoked salmons were evaluated and SPR was used to differentiate biofilm formers as a sensitive technique for biofilm studies.Article Citation - WoS: 4Citation - Scopus: 5Identifying Threading Dislocations in Cdte Films by Reciprocal Space Mapping and Defect Decoration Etching(American Institute of Physics, 2018) Polat, Mustafa; Bilgilisoy, Elif; Arı, Ozan; Öztürk, Orhan; Selamet, YusufWe study threading dislocation (TD) density of high-quality cadmium telluride (CdTe) layers grown on a (211) oriented GaAs substrate by molecular beam epitaxy. High-resolution X-ray diffraction was performed to calculate the density of screw-type TDs by measuring the broadening of the asymmetrical (511) Bragg reflections of CdTe epilayers. In addition, total TD densities were determined by the Everson-etching method and were compared with screw TDs. Our results show that the total TD densities in CdTe films were dominated by those with screw character. The screw component TDs are estimated to account for more than 90% of the total TD density. CdTe layers grown at a thickness of less than 3.0 μm typically exhibit the screw TD densities in the 106 cm-2 and 107 cm-2 range. It can be noted that as the nucleation temperature increases, i.e., ≥222 °C, both the area density of TDs with the screw component of the CdTe films and the total TD density are roughly four times larger than those of the epilayer grown at the nucleation temperature of 215 °C. Furthermore, we discuss the influence of the II/VI flux ratio on the density of threading dislocations. The contribution of screw TDs to the total TD density showed a significant decrease in roughly 30% in the case of a high II/VI flux ratio. We further examine the reciprocal space maps in the vicinity of the (422) reflections.Article Citation - WoS: 10Citation - Scopus: 10The Influence of Plasma-Based Nitriding and Oxidizing Treatments on the Mechanical and Corrosion Properties of Cocrmo Biomedical Alloy(Springer Verlag, 2018) Noli, Fotini; Pichon, Luc; Öztürk, OrhanPlasma-based nitriding and/or oxidizing treatments were applied to CoCrMo alloy to improve its surface mechanical properties and corrosion resistance for biomedical applications. Three treatments were performed. A set of CoCrMo samples has been subjected to nitriding at moderate temperatures (~ 400 °C). A second set of CoCrMo samples was oxidized at 395 °C in pure O2. The last set of CoCrMo samples was nitrided and subsequently oxidized under the experimental conditions of previous sets (double treatment). The microstructure and morphology of the layers formed on the CoCrMo alloy were investigated by X-ray diffraction, Atomic Force Microscopy, and Scanning Electron Microscopy. In addition, nitrogen and oxygen profiles were determined by Glow Discharge Optical Emission Spectroscopy, Rutherford Backscattering Spectroscopy, Energy-Dispersive X-ray, and Nuclear Reaction Analysis. Significant improvement of the Vickers hardness of the CoCrMo samples after plasma nitriding was observed due to the supersaturated nitrogen solution and the formation of an expanded FCC γN phase and CrN precipitates. In the case of the oxidized samples, Vickers hardness improvement was minimal. The corrosion behavior of the samples was investigated in simulated body fluid (0.9 pct NaCl solution at 37 °C) using electrochemical techniques (potentiodynamic polarization and cyclic voltammetry). The concentration of metal ions released from the CoCrMo surfaces was determined by Instrumental Neutron Activation Analysis. The experimental results clearly indicate that the CoCrMo surface subjected to the double surface treatment consisting in plasma nitriding and plasma oxidizing exhibited lower deterioration and better resistance to corrosion compared to the nitrided, oxidized, and untreated samples. This enhancement is believed to be due to the formation of a thicker and more stable layer.Article Citation - WoS: 13Citation - Scopus: 16Reciprocal Space Mapping Study of Cdte Epilayer Grown by Molecular Beam Epitaxy on (2 1 1)b Gaas Substrate(IOP Publishing Ltd., 2017) Polat, Mustafa; Arı, Ozan; Öztürk, Orhan; Selamet, YusufWe examine high quality, single crystal CdTe epilayer grown by molecular beam epitaxy (MBE) on (2 1 1)B GaAs substrate using both positions and full width at half maximums (FWHMs) of reciprocal lattice points (RLPs). Our results demonstrate that reciprocal space mapping (RSM) is an effective way to study the structural characteristics of the high-index oriented epitaxial thin films having a large lattice mismatch with the substrate. The measurement method is defined first, and then the influence of shear strain ( xz) on the position of the (5 1 1) node of epilayer is clarified. It is concluded that the lattice tilting is likely to be related with the lattice mismatch. Nondestructive measurement of the dislocation density is achieved by applying the mosaic crystal model. The screw dislocation density, estimated to be 7.56×107 cm2, was calculated utilizing the broadened peakwidths of the asymmetric RLP of the epilayer lattice.Article Citation - WoS: 7Citation - Scopus: 7Mfm Imaging of Expanded Austenite Formed on 304 Ss and Cocrmo Alloys(Elsevier Ltd., 2014) Öztürk, Orhan; Fidan, Mehmet; Mändl, StephanNew data related to the magnetic nature of the expanded austenite layers on CoCrMo and austenitic stainless steel by nitrogen plasma immersion ion implantation (PIII) are presented. Implantations were performed in the temperature range between 300 and 550°C for a fixed processing time of 1h. Magnetic properties, nitrogen distribution, implanted layer phases, and surface topography were studied with a combination of experimental techniques involving magnetic force microscopy, SIMS, XRD, SEM and AFM. As a function of the processing temperature, phase evolution stage for both alloys follows the same trend: (1) initial stage of the expanded phase formation, γN; (2) its full development; and (3) its decomposition into CrN precipitates and the Cr-depleted matrix, fcc γ-(Co, Mo) for CoCrMo and bcc α-(Fe, Ni) for 304 SS. MFM imaging reveals distinct, stripe-like ferromagnetic domains for the fully developed expanded austenite layers both on CoCrMo and 304 SS alloys. Weak domain structures are observed for the CoCrMo samples treated at low and high processing temperatures. The images also provide strong evidence for grain orientation dependence of magnetic properties. The ferromagnetic state for the γN phase observed here is mainly linked to large lattice expansions due to high N content.Article Citation - WoS: 2Citation - Scopus: 3Use of Combination of Accelerator-Based Ion-Beam Analysis Techniques To the Investigation of the Corrosion Behavior of Cocrmo Alloy(Elsevier Ltd., 2014) Noli, F.; Misaelides, P.; Lagoyannis, A.; Pichon, L.; Öztürk, OrhanNuclear Reaction Analysis - NRA in combination with d-RBS (Ed: 1.35 MeV) was applied in order to investigate the corrosion behavior of CoCrMo alloy. The corrosion resistance of the alloy was compared to that of modified CoCrMo samples by several techniques as plasma nitriding and oxidizing at moderate temperature (∼400 °C). Electrochemical techniques in simulated body fluid 0.9% NaCl (37 °C) were applied in order to accelerate the corrosion process. The nitrogen depth distribution before and after the corrosion was determined using the 14N(d,α)12C and the 14N(d,p)15N nuclear reactions whereas the oxygen by the 16O(d,p)17O. The surface morphology and microstructure was investigated using microscopy techniques. It was found that surface treatments produce thick nitrided layers (5-6 μm) consisting of a supersaturated nitrogen solution (nitrogen concentration is ∼30 at.%) in the matrix (expanded phase γN) and a thin oxygen solution (0.3 μm). The samples subjected to plasma nitridation and oxidation exhibited the lowest deterioration and better resistance to corrosion compared to the single nitrided or single oxidized and the untreated material. This could be attributed to the modified surface region with the high nitrogen content and the presence of oxygen.Article Citation - WoS: 11Citation - Scopus: 13Magnetic Layer Formation on Plasma Nitrided Cocrmo Alloy(Elsevier Ltd., 2011) Öztürk, Orhan; Okur, Salih; Pichon, L.; Liedke, M. O.; Riviere, Jean PaulIn this study structural and magnetic character of the expanded austenite phase (γN) layer formed on a medical grade CoCrMo alloy by a low-pressure Radio-Frequency plasma nitriding process was investigated. The formation of the expanded austenite phase is facilitated at a substrate temperature near 400°C for 1, 2, 4, 6 and 20h under a gas mixture of 60% N2-40% H2. The magnetic state of the γN layers was determined by a surface sensitive technique, magneto-optic Kerr effect (MOKE), and with a scanning probe microscope in magnetic force mode (MFM). Strong evidence for the ferromagnetic nature of the γN-(Co,Cr,Mo) phase is provided by the observation of stripe domain structures and the hysteresis loops. The ferromagnetic state for the γN phase observed here is mainly linked to large lattice expansions (~10%) due to high N contents (~30at.%). As an interstitial impurity, nitrogen dilates the host lattice i.e. the Co-Co (or Fe-Fe) distance is increased, which strongly influences the magnetic interactions. An analogy between the magnetic properties of the expanded phases, γN-(Fe,Cr,Ni) and γN-(Co,Cr,Mo), formed in austenitic stainless steel alloys and the CoCrMo alloy of this study is made, and it is suggested that the ferromagnetic states for the γN-(Co,Cr,Mo) and γN-(Fe,Cr,Ni) phases may be correlated with the volume dependence of the magnetic properties of fcc-Co/Co4N and fcc-Fe/Fe4N, respectively.Article Citation - WoS: 26Citation - Scopus: 24Cocrmo Alloy Treated by Floating Potential Plasma Assisted Nitriding and Plasma Based Ion Implantation: Influence of the Hydrogen Content and of the Ion Energy on the Nitrogen Incorporation(Elsevier Ltd., 2010) Pichon, L.; Okur, Salih; Öztürk, Orhan; Rivière, J. P.; Drouet, M.Nitriding was performed on a medical grade CoCrMo alloy at 400°C in N2 or N2-H2 atmosphere at a working pressure of 0.84Pa for 2h. Various surface treatment techniques were used to incorporate nitrogen into the CoCrMo alloy: without any plasma assistance, by floating potential radio-frequency plasma assisted nitriding (FPPAN), by plasma based ion implantation (PBII) with several high voltage accelerations (up to 20kV). Without plasma activation, no nitrogen is incorporated in the CoCrMo. On the contrary, all the plasma or PBII treated samples show the formation of a nitrogen-rich f.c.c. γN phase. The layer nitrided over few microns has a nitrogen composition ranging from 30at.% to about 20at.% near the nitrided layer-substrate interface, with an enhanced surface microhardness. Hydrogen is found to enhance the nitriding efficiency. Without hydrogen, a high voltage polarization provides a supplementary amount of implanted nitrogen available for further diffusion and the sputtering of the surface passive oxide. So, with limited high voltages, thicker layers with higher amounts of nitrogen can be achieved by PBII compared to plasma nitriding. However, with higher voltages, the sputtering becomes too important and the nitride layer is thinner. © 2010 Elsevier B.V.