Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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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.Article Citation - WoS: 21Citation - Scopus: 22Structural and Electrical Characterization of the Nickel Silicide Films Formed at 850 °c by Rapid Thermal Annealing of the Ni/Si(1 0 0) Films(Elsevier Ltd., 2010) Utlu, G.; Artunç, N.; Budak, S.; Tarı, SüleymanNickel di-silicide formation induced by RTA process at 850 °C for 60 s in the Ni/Si(1 0 0) systems are investigated as a function of the initial Ni film thickness of 7-89 nm using XRD, RBS, SEM, X-SEM and AFM. Based on the XRD and RBS data, in the silicide films of 400-105 nm, NiSi and NiSi2 silicide phases co-exist, indicating that Ni overlayer is completely transformed to NiSi and NiSi2 silicide phases. SEM reveals that these films consist of large grains for co-existence of NiSi2 and NiSi phases, separated from one another by holes, reflecting that NiSi2 grows as islands in NiSi matrix. These films have low sheet resistance, ranging from 1.89 to 5.44 Ω/□ and good thermal stability. For thicknesses ≤ 80 nm RBS yields more Si-rich silicide phases compared to thicker films, whereas SEM reveals that Si-enriched silicide islands with visible holes grow in Si matrix. As the film thickness decreases from 400 to 35 nm, AFM reveals a ridge-like structure showing a general trend of decreasing average diameter and mean roughness values, while sheet resistance measurements exhibit a dramatic increase ranging from 1.89 to 53.73 Ω/□. This dramatic sheet resistance increase is generated by substantial grain boundary grooving, followed by island formation, resulting in a significant phase transformation from NiSi2-rich to Si-rich silicide phases. © 2010 Elsevier B.V. All rights reserved.Article Citation - WoS: 26Citation - Scopus: 24Effect of Ta Buffer Layer and Thickness on the Structural and Magnetic Properties of Co Thin Films(AVS Science and Technology Society, 2009) Vahaplar, Kadir; Tarı, Süleyman; Tokuç, Hüseyin; Okur, SalihSingle Co and Ta/Co bilayers were grown on Si(100) substrates in a magnetron sputtering system. The effect of Ta buffer layer and the thickness of Co layer on the structural and magnetic properties of the Co layers has been studied. A single Co layer shows a textured structure above thickness of 40 nm according to the x-ray diffraction (XRD) pattern. The magnetic properties of Co layers depend significantly on the thickness of the films. Ta grows as highly textured Β -Ta (tetragonal) phase on Si with a smooth surface. The XRD and atomic force microscopy results show that the Ta buffer layer improves the structural properties dramatically, resulting in a strongly textured and smoother surface morphology. The Ta layer also affects the magnetic properties of Co layers to a large extent, especially inducing an in-plane anisotropy in thin Co films.