Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Applications of Transparent Conductive Indium Tin Oxide Films in Automotive and Vitrifications Industries(Izmir Institute of Technology, 2009) Tuna, Öcal; Selamet, Yusuf; Selamet, Yusuf; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyDue to its unique electrical and optical properties, highly doped n-type Indium tin oxide used for various applications such as smart glass, LCDs, OLEDs, solar cells and car windows. In this study Indium Tin Oxide (ITO) thin films were grown by both DC and RF magnetron sputtering techniques. To know deposition rate of ITO, system was calibrated for both DCMS and RFMS and then ITO were grown on glass substrate with the thickness of 70 nm and 40 nm by changing substrate temperature. The effect of substrate temperature, film thickness and sputtering method on structural, electrical and optical properties were investigated. Wan der Pauw method was used for electrical characterization and to use this method properly, we patterned ITO thin films by photolithography and Ion beam etching techniques. The results show that substrate temperature and film thickness substantially affects the film properties, especially crystallization and resistivity. The thin films grown at the lower than 150 oC showed amorphous structure. However, crystallization was detected with the further increase of substrate temperature. Substrate temperature and film thickness increment were lead to increase band gap of ITO which can be explained by BMS. Band gap of ITO was calculated to be about 3.64 eV at the substrate temperature of 150 oC, and it widened with substrate temperature increment. From electrical measurements the resistivity at room temperature was obtained 1.28*10 and 1.29*10 cm, for DC and RF sputtered films, respectively. We also measured temperature dependence resistivity and the Hall coefficient of the films, and we calculated carrier concentration and Hall mobility.Master Thesis Electrical Surface Modification and Characterization of Metallic Thin Films Using Scanning Probe Microscope (spm) Nanolithography Method(Izmir Institute of Technology, 2009) Büyükköse, Serkan; Okur, Salih; Okur, Salih; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThis thesis focuses on local oxidation of metallic thin films using atomic force microscopy (AFM). The primary aim of this thesis is to investigate the growth kinetics of oxide forms of these metallic materials and characterize the resulted oxide structures. In this study, tantalum, hafnium and zirconium thin films were used to be oxidized via AFM. During this work, metallic thin films were grown on Si and SiOx substrates with DC magnetron sputtering method. Thin films were characterized via x-ray diffraction, scanning electron microscopy and atomic force microscopy. Oxidation experiments were performed under different environmental conditions to explore the effect of influential parameters; such as bias voltage, oxidation time and relative humidity, and line shape oxide structures were created on metallic films. Dimensional analysis of created oxide structures was carried out measuring height and line-width of oxide lines as a function of applied voltage, oxidation time and relative humidity. In addition to the dimensional analysis, electrical characterization of metal-oxides was performed via AFM electrical characterization methods which are two terminal I-V measurements, electric force microscopy and spreading resistance measurements. At the end of the thesis, the capability of this method to create lateral metal-oxide-metal junction was shown oxidizing a tantalum stripe and performing in-situ resistance measurement. Patterning of tantalum stripes was accomplished by standard photolithography process and lift-off technique.Master Thesis Grawth and Electrical Characterization of High Purity Carbon Nanotubes(Izmir Institute of Technology, 2009) Kır, Serap; Selamet, Yusuf; Selamet, Yusuf; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThis thesis work is focused on growing high purity vertically aligned Carbon nanotubes by ethylene gas thermal chemical vapor deposition method on very thin Cobalt and Iron catalyst thin films deposited on to Si/SiO2/Al2O3 substrates by DC magnetron sputtering. In this study, the effective parameters were changed to grow aligned CNTs. Hence, the vertically aligned CNTs were performed and also the ideal parameters were determined for this kind of growth mechanism. The effect of support layer was examined for three different hydrocarbon gas ratios. SiO2 and Al2O3 were used as support layers between metal catalyst thin films and Si substrate. Two kinds of samples were compared; one of them had only Al2O3 and the other one includes both Al2O3 and SiO2 layers. As a result, the sample that had both oxide layers gave better results for density of CNTs on the surface of samples. Moreover, types of catalyst material effect also were examined on growth of CNTs for three different temperatures. For this aim, the performance of Fe and Co catalyst thin films was compared. According to our results, Fe was more reactive with ethylene gas than Co catalysts and also, the density of CNTs was increased by using Fe as a catalyst material. Hydrogen pretreatment time was performed for another significant effect. Seven different time parameter which were 0, 5, 10, 15, 20, 25, 30 minutes, were examined. The density and diameters of catalysts particles were compared for these different treatment times. Finally, the electrical characterization of CNTs was performed. The resistance of CNTs was measured by using two point contact technique. Moreover, the interaction between resistance of CNTs and humidity was examined.Master Thesis Fabrication and Characterizarion of Superconductor Ybco Josephson Junctions(Izmir Institute of Technology, 2008) Algül, Berrin Pınar; Abukay, Doğan; Abukay, Doğan; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyA well-controlled, high-yield Josephson junction production process forms the basis of superconducting electronic device and circuit technology. In order to use the Josephson junctions effectively and fabricate them reproducibly, their structural and electrical characterization should be performed.This study concentrates on the fabrication and characterization of high temperature bicrystal grain boundary Josephson junctions fabricated onto 24-dand 30-degree SrTiO3 bicrystal substrates using high quality YBa2Cu3O7-. (YBCO) thin-films.200 nm thick YBCO thin films were deposited using a dc Inverted Cylindrical Magnetron Sputtering technique by investigating the thin film deposition conditions in order to obtain device quality films. The superconducting properties of the thin films were determined by electrical characterizations, consisting of resistance versus temperature and magnetic susceptibility versus temperature measurements. Structural properties were analyzed by Atomic Force Microscope, Scanning Electron Microscope and X-Ray Diffraction.Prepared thin film samples were patterned as bicrystal grain boundary Josephson junctions by standard photolithography and chemical etching processes. The current-voltage characteristics of the Josephson junctions were performed at 77 K under zero and non-zero applied field in magnetically shielded environment. The critical current values (Ic), normal resistance (Rn) and IcRn product of the output signals were determined, and the values were discussed as function of the film growth conditions. The optimization of the Josephson junctions was performed in order to improve both the signal performance and the stability of our devices against thermal cycling.Master Thesis Pixel Array Application of High Temperature Superconducting Ybco Transition Edge Infrared Bolometers(Izmir Institute of Technology, 2009) Pekerten, Barış; Abukay, Doğan; Abukay, Doğan; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyIn this thesis, we patterned pregrown epitaxial YBCO thin films on MgO, LAO and STO substrates into meander shaped high-Tc superconducting transition edge monolithic bolometers. We set up and automatized the electrical characterization processes of the bolometers. We also measured the bolometric response of the meanders to red and nearinfrared light and fit them to theoretical models in literature. We compared the single pixel bolometric responses to literature and found that our results are similar to or better than the results for similar devices in the literature.We also patterned staring arrays (focal plane arrays) and explored the resolution limit put in place by thermal crosstalk. We compared the measured crosstalk to theory and found a very good agreement. We quantified the crosstalk for our pixels. We then explored substrate etching method to decrease crosstalk via thermal isolation.Master Thesis Reactive Ion Beam Etching and Characterization of High-Tc Superconductor Bi2212(Izmir Institute of Technology, 2009) Köseoğlu, Hasan; Özyüzer, Lütfi; Özyüzer, Lütfi; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThe lack of coherent, continuous and tunable compact solid-state sources of electromagnetic radiations at terahertz (THz) frequency range (0.3-30 THz) can be solved by high temperature superconductors (HTS) which are better candidates for generation of THz radiation. THz sources have potential application areas in materials characterization, biology, communication, medicine and security. The HTSs have large energy gap intervals which are available for radiations at THz frequency range, so recently, they were used as better converters from DC-voltage to high frequency radiation in junction technologies. Bi2Sr2CaCu2O8+. (Bi2212) HTS single crystals include natural superconductor-insulator-superconductor multi-junctions called intrinsic Josephson junctions. For generation of coherent continuous and powerful THz radiations, we have fabricated large and tall mesas on Ca rich Bi2212, although mesas with small planar and lateral dimensions were preferred in recent studies because of the heating effect. We have used underdoped Bi2212 to control the heating problem. By using the vacuum thermal evaporation, optical photolithography, magnetron sputtering and reactive ion beam etching techniques, the mesas with size of 40-100x300 um2 have been fabricated by using single layer mask (PR) and two different multilayer masks, which are Ta/PR and PR./Ta/PR. Their heights and lateral dimensions were analyzed by Atomic Force Microscopy, profilometer and SEM. We have investigated temperature dependence of c-axis resistivity and current-voltage (I-V) tunneling characteristics of under-doped Bi2212 which exhibit exponentially increases in resistivity from 300 K to Tc. The influences of heating effect were analyzed at temperature evolution of I-V measurements. Finally, bolometric detections of emission from long edges of mesas were done.Master Thesis Investigation of Magnetic Dead Layer Formation at the Interfaces of Sputtered Ni80 Fe20 Thin Films(Izmir Institute of Technology, 2009) Alagöz, Hüseyin Serhat; Tarı, Süleyman; Tarı, Süleyman; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyIn this thesis, magnetic dead layer formation at the interfaces of the sputtered Ni80Fe20 thin films has been investigated experimentally. Different insulators such as Ta2O5, Al2O3 and metallic Ta thin films have been deposited as seed and cap layers to determine the MDL formation at the interface of Ni80Fe20. The magnetization of samples has been probed by Vibrating sample magnetometry and X-ray reflectivity measurements have been carried out to investigate the thickness and roughness of the interlayers. Ta films cause the most MDL formation when grown as seed as well as cap layer. It has been observed that the thickness of MDL is strongly temperature dependent. MDL thickness decreases for all trilayers deposited except for Ta2O5/Ni80Fe20/Ta2O5 when they are exposed to 300 .C annealing temperature. Further annealing at 500 .C causes an interdiffusion between the layers and the thickness of the MDL increases. According to XRR measurements, the thickness of the inter alloy layers between the Ni80Fe20 and its adjacent layers is consistent with the thickness of magnetic dead layer calculated from Liebermann equation. MDL calculations reveal that SiO2/Ta/Ni80Fe20/Al2O3 multilayer has the lowest MDL thickness therefore might be a possible candidate to be used in spin valve structures.Master Thesis Temperature Dependence of Tunneling in Intrinsic Josephson Junctions of High Temperature Superconductors(Izmir Institute of Technology, 2008) Şimşek, Yılmaz; Özyüzer, Lütfi; Özyüzer, Lütfi; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThe lack of coherent, continuous and tunable compact solid-state sources of electromagnetic radiations at terahertz (THz) frequency range (0.3-30 THz) can be solved by high temperature superconductors (HTS) which are better candidates for generation of THz radiation. THz sources have potential application areas in materials characterization, biology, communication, medicine and security. The HTSs have large energy gap intervals which are available for radiations at THz frequency range, so recently, they were used as better converters from DC-voltage to high frequency radiation in junction technologies. Bi2Sr2CaCu2O8+8 (Bi2212) HTS single crystals include natural superconductor-insulator-superconductor multi-junctions called intrinsic Josephson junctions. For generation of coherent continuous and powerful THz radiations, we have fabricated large and tall mesas on Ca rich Bi2212, although mesas with small planar and lateral dimensions were preferred in recent studies because of the heating effect. We have used under-doped Bi2212 to control the heating problem. The mesas with size of 100x300 .m2 have been fabricated by vacuum evaporation, photolithography analyzed by Atomic Force Microscopy. We have investigated temperature dependence of c-axis resistivity and current-voltage (I-V) tunneling characteristics of under-doped Bi2212 which exhibit exponentially increases in resistivity from 300 K to Tc. The influences of heating effect were analyzed at temperature evolution of I-V measurements. Finally, bolometric detections of emission from long edges of mesas were done.Master Thesis Growth and Characterization of Carbon Nanotubes by Thernal Chemical Vapor Deposition Method(Izmir Institute of Technology, 2008) Aksak, Meral; Selamet, Yusuf; Selamet, Yusuf; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThis thesis work is focused on producing carbon nanotubes (CNTs) by methane gas thermal chemical vapor deposition method on very thin Cobalt, Iron, and Nickel catalyst thin films deposited onto SiO2/Si substrates by DC magnetron sputtering. This thesis is also devoted to understanding some parameters affecting the growth of CNTs; such as catalyst material, temperature, and catalyst layer thickness effects In this study, CNT growth was performed on directly Si substrates, which was observed that the growth was too difficult and requiring very high temperatures. Hence, very thin catalyst films were deposited on SiO2/Si substrates, and the CNT growth was observed. The temperature effect was also examined. When the growth temperature was increased, the average diameters of the CNTs were decreased up to a critical temperature, but after this point the average diameter of CNTs were increased. This effect was studied systematically by utilizing Fe and Co catalyst thin films and with the help of Raman spectroscopy and Scanning Electron Microscopy results.Catalyst thickness effect was also examined. For this aim, Ni catalyst thin films with three different thicknesses; 0.7 nm, 1.4 nm, and 6 nm, were utilized. It was observed that CNTs were grown well on 0.7 and 1.4 nm thick Ni films, while there was a little growth on 6 nm thick Ni film. The roughness analysis of 0.7 nm and 1.4 nm thick Ni films were also done. Some of as-grown CNTs were also examined by X-ray diffraction method, and the results were compared one another.Master Thesis The Growth and Characterization of Fe/Tao Multilayers for Spintronics Applications(Izmir Institute of Technology, 2008) Tokuç, Hüseyin; Tarı, Süleyman; Tarı, Süleyman; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyIn this thesis, the effect of Ta buffer layer and the thickness of the Ta2O5 barrier layer on the structural and magnetic properties of Fe/Ta2O5/Co multilayers have been studied. XRD and AFM techniques were used for structural investigations and VSM was used for investigation of magnetic properties. Refractive index of the barrier layer was determined by ellipsometry technique. In this study, magnetic tunnel junctions have also been fabricated by using photolithography technique and then electrical and magnetoresistance measurements were done.The structural investigations showed that Ta under layer increases the crystalline quality of Fe layer and causes a change on magnetic parameters of Fe films. The AFM results showed that the range of the roughness for all layers is between 1.7 A and 6.3 A. When the thickness of the oxide layer was 4 nm, magnetic decoupling appears. Clear differences between the coercive fields of the ferromagnetic layers were observed in further increase of the barrier layer thickness. The effect of annealing on the Fe/TaOx/Co multilayer was studied and it was found that only the coercivity of Fe film increases with increasing temperature up to the 250C. Then, annealing at 400C showed a sharp decrease in the coercivity of Fe film indicating an intermixing at the interface of Fe/TaOx. Co minor loops showed that the magnetostatic coupling is large for thin barriers and decreases with increasing the barrier thickness. Electrical measurements showed that conduction occurs via tunneling electrons. However, no TMR ratio has been observed after magnetoresistance measurements.