Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Research Project Süperiletkenlerdeki Josephson girdap akısının terahertz ışıması(2008) Özyüzer, Lütfi; Okur, Salih; Tarı, Süleyman; Şimşek, Yılmaz; Ulucan, Savaş; Özdemir, Mehtap; Köseoğlu, Hasan[No Abstract Available]Research Project Magnetron sputtering yöntemiyle büyütülen manyetik tünel eklemleri' nin yapısal, elektronik ve manyetik özelliklerinin incelenmesi(2009) Tarı, Süleyman; Özyüzer, Lütfi; Selamet, Yusuf; Vahaplar, Kadir; Tokuç, Hüseyin; Alagöz, Serhat HüseyinElektronun spin özelliğini kullanarak yeni elektronik aygıtların yapılması son zamanlarda çok yoğun araştırma konusu olmuştur. Bu aygıtlara spinin kontrol edilmesinden dolayı spintronik aygıtlar denmektedir. İki ferromanyetik katman arasına konulan bir yalıtkan bariyerden oluşan yapıya manyetik tünel eklemi denir. Elektronun bu katmanlardan yüzeye dik olarak geçisi quantum mekaniksel tünelleme olayı sayesindedir. Manyetik alan altında göstereceği direnç ferromanyetik katmanların birbirlerine göre manyetik yönelimlerine bağlıdır. Bu dirence tünel manyetik direnç (TMR) denir ve yüksek TMR değeri elde edilmesi spintronik aygıtların daha küçük ve yoğun yapılabilmesine yol açar. Bununla birlikte hızlı bilgi iletimi için FM/Y ara yüzeyinde direnç-alan çarpımının (RA) küçültülerek (~1Ω(μm)2 ) yüksek sinyal-gürültü oranı elde eldilmesi gerekmektedir. Bunun için iki yöntem kullanılmaktadır: yalıtkan filmin kalınlığını inceltmek (~1nm) veya arayüzeyde oluşan bariyer yüksekliğini küçültmek. İkinci yöntemde, küçük bant aralığına sahip yalıtkanların kullanılması gerekir. Yalıtkan olarak Ta2O5 kullanılması yenidir. Ta2O5 bant aralığı ~3.5eV’ tur ve FM/Ta2O5 arayüzeyinde ~ 0.4 eV bariyer yüksekliği verir. Bu projede Farklı FM katmanlar ve bariyerler kullanılarak MTJ’ ler büyütülmüşlerdir. Öncelikle Ta2O5 olmak üzere Al2O3, MgO bariyer olarak kulanılmıştır. MTJ’ ler iki farklı yöntem ile elde edilmiş ve manyetik direnç ölçümleri yapılmıştır. Spin kutuplanmış elektronların geçişini kontrol eden ve FM katmanlarının yönelimlerinin değiştirilmesi için gerekli olan farklı Hc değerlerine sahip FM filmler kullanılmıştır. Sürekli olarak büyütülen filmlerin yapısal, ve manyetik özellikleri çalışılmıştır. Elektriksel ölçümlerden oluşturulan bazı MTJ yapılarda, %3.5 dolayında TMR değeri bulunmuştur. Fotoelektron spektroskopisi analizlerinden ferromanyetik katmanların oksitlendiği görülmüş, ayrıca manyetik analizlerden ferromanyetik/(yalıtkan, metal) arayüzeylerde manyetik ölü katmanların varlığı tespit edilmiştir.Article Citation - WoS: 38Citation - Scopus: 40Influences of Deposition Time and Ph on Magnetic Nife Nanowires Fabrication(Elsevier, 2009) Atalay, Funda E.; Kaya, Harun; Atalay, Selcuk; Tarı, SüleymanIn this work, NiFe nanowires were grown into highly ordered porous anodic alumina oxide (AAO) templates by dc electrodeposition at various deposition times and pH values. During the deposition process some electrochemical bath parameters such as ion content, deposition voltage, and temperature of solution were kept constant. The morphological properties of the nanowire arrays were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the chemical composition was determined by examination of the energy dispersive X-ray (EDX) spectra, and the magnetic behavior of the arrays was determined by vibrating sample magnetometer (VSM). (C) 2008 Elsevier B.V. All rights reserved.Article Citation - WoS: 4The Synthesis of Ferromagnetic La0.75ca0.25mno3 Nanowires by a Sol-Gel Method(National Institute of Optoelectronics, 2010) Atalay, Funda E.; Yağmur, V.; Atalay, Selçuk; Kaya, Harun; Tarı, Süleyman; Avşar, D.In this study, densely packed La0.75Ca0.25MnO3 (LCMO) nanowires were synthesized within a porous anodic aluminum oxide (AAO) template by means of a sol-gel method using nitrate as raw material and ethylene glycol as the chelating agent. It was observed from measurements of hysteresis curves that the magnetic behavior of the LCMO nanowire arrays was strongly dependent on the pH of the solution. As it has been reported that bulk polycrystalline La0.75Ca0.25MnO3 samples have a Curie temperature of 224 K [1], it is interesting to find that nanowires produced at pH 3 show ferromagnetic properties at room temperatureArticle Citation - WoS: 24Citation - Scopus: 24The Effect of Back Electrode on the Formation of Electrodeposited Conife Magnetic Nanotubes and Nanowires(Elsevier, 2010) Atalay, Funda E.; Kaya, Harun; Yağmur, Vedat; Tarı, Süleyman; Atalay, Selçuk; Avşar, DuyguThe electrodeposition of cobalt + nickel + iron alloy nanostructures in aqueous sulfate solution has been studied using vitreous templates placed on highly ordered porous anodic alumina oxide (AAO). During the deposition process some electrochemical bath parameters such as ion content, deposition voltage, pH and temperature of solution were kept constant. The morphological properties of the nanostructures were studied by scanning electron microscopy (SEM) and the chemical composition was determined by examination of the energy dispersive X-ray (EDX) spectra. The magnetic behaviour of the arrays was determined with a vibrating sample magnetometer (VSM). Voltammetric and galvanostatic results indicate that the back electrodes placed on AAO plays the main role in obtaining nanowire or nanotube structured material. (C) 2009 Elsevier B. V. All rights reserved.Article Citation - WoS: 2Citation - Scopus: 2Scanning Probe Oxidation Lithography on Ta Thin Films(American Scientific Publishers, 2008) Okur, Salih; Büyükköse, Serkan; Tarı, SüleymanA Semi-Contact Scanning Probe Lithography Technique (SC-SPL) has been applied to create nano-oxide patterns on Ta thin films grown by DC magnetron sputtering method on SiO 2/Si substrates. The height and linewidth profiles of nano-oxide lines created by a conductive AFM tip on Ta film surfaces were measured as a function of applied voltage, oxidation time, humidity, and tip apex curvature. The AFM surface measurements show that the height of the oxides increases linearly with increasing voltage; but there was no oxide growth, when less than 4 V was applied even at 85% relative humidity. Electrical measurements were performed and the resistivities of the TaO x layer and Ta film were obtained as 5.76 × 10 8 and 1.4 × 10 5 Ohm-cm, respectively.Article Citation - WoS: 35Citation - Scopus: 37Modification of Ito Surface Using Aromatic Small Molecules With Carboxylic Acid Groups for Oled Applications(Elsevier Ltd., 2011) Havare, Ali Kemal; Can, Mustafa; Demiç, Şerafettin; Okur, Salih; Kuş, Mahmut; Aydın, Hasan; Yağmurcukardeş, Nesli; Tarı, Süleyman4-[(3-Methylphenyl)(phenyl)amino]benzoic acid (MPPBA) was synthesized in order to facilitate the hole-injection in Organic Light Emitting Diodes (OLED). MPPBA was applied to form self-assembled monolayer (SAM) on indium tin oxide (ITO) anode to align energy-level at the interface between organic semiconductor material (TPD) and inorganic anode (ITO) in OLED devices. The modified surface was characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). KPFM was used to measure the surface potential and work function between the tip and the ITO surface modified by SAM technique using MPPBA. The OLED devices (ITO/MPPBA/TPD/Alq3/Al) fabricated with SAM-modified ITO substrates showed lower turn-on voltages and enhanced diode current compare to the OLED devices fabricated with bare ITO substrates.Article Citation - WoS: 8Citation - Scopus: 8An Interface Study of Crystalline Fe/Ge Multilayers Grown by Molecular Beam Epitaxy(Elsevier Ltd., 2011) Tarı, SüleymanFe/Ge multilayers were grown on single crystal Ge(0 0 1) substrates by molecular beam epitaxy. The structural, electronic and magnetic properties of Fe/Ge have been studied. The analysis shows that Fe grows in a layer-by-layer epitaxial growth mode on Ge(0 0 1) substrates at 150 ◦C and no intermixing has been observed. Growth of a crystalline Ge film at 150 ◦C on a single crystal Fe film has been observed. At this temperature Ge films grow by means of the island growth mode according to reflection of high energy electron diffraction patterns. Fe layers of 36nm thickness, deposited at 150 ◦C on Ge(0 0 1) substrates, show two magnetization reversal values indicating the growth of Fe in two different crystal orientations. 36nm thick Fe and Ge layers grown at 150 ◦C in Ge/Fe/Ge/Fe/Ge(0 0 1) sequence shows ferromagnetic behavior, however, the same structure grown at 200 ◦C shows paramagnetic behavior.Article Effect of Ta Buffer Layer and Tao X Barrier Thickness on the Evolution of the Structural and Magnetic Properties of the Fe/Tao X /Co Trilayers(Springer Verlag, 2010) Tokuç, Hüseyin; Tarı, SüleymanFe/TaO x /Co trilayers were grown on Si(100)/SiO2 substrates and on tantalum buffer layers by a high vacuum magnetron sputtering system. The effects of both Ta buffer layer and tantalum-oxide barrier layer thickness on the structural and magnetic properties and the coupling of the ferromagnetic layers have been studied. It was observed that Ta improves the structural properties of the Fe layer resulting in an increased coercive field. For a barrier thickness of 4 nm a weak decoupling starts to appear between the ferromagnetic layers and a clear step formation is observed with increasing thickness. The minor hysteresis loops predict an interlayer coupling for thin barriers. The annealing of trilayers up to 250°C shows an increased coercivity for only the Fe layer. Annealing further at 400°C has the opposite effect of decreasing the coercivity, indicating intermixing at the interfaces of the Fe. The refractive index of the insulator barrier shows that the barrier layer is not totally in the form of tantalum-pentoxide. © 2009 Springer-Verlag.Article Citation - WoS: 2Citation - Scopus: 2Znte/Gaas(2 1 1)b Heterojunction Valence Band Discontinuity Measured by X-Ray Photoelectron Spectroscopy(Elsevier Ltd., 2011) Wang, X. J.; Tarı, Süleyman; Sporken, R.; Sivananthan, S.Thin ZnTe layers were grown by molecular beam epitaxy on single crystal GaAs(2 1 1)B substrates. Reflection high energy electron diffraction monitored the deoxidation of substrate and entire growth process. Valence band offset was calculated with X-ray photoelectron spectroscopy. Also interface formation of the ZnTe/GaAs was studied. Analysis shows that interface is abrupt and calculated valance band offset is 0.25±0.1 eV and indicates type I alignment. The experimental result agrees well with the theoretical predictions involving interface dipole effect as well as electron affinity rule.