Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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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, SalihThis 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 Development of Nanopatterns on Self Assembled Monolayer (sam) Organic Films Using Scanning Probe Microscope (spm) Nanolithography Techique(Izmir Institute of Technology, 2006) Gül, Semra; Okur, SalihPatterning and fabrication of nanostructures on surfaces is a great demand for nanoscale electronic and mechanical devices. Current techniques such as electron beam lithography and photolithography provides limited resolution and they are not capable of reproducible in nanoscale. Among those, Scanning Probe Microscopy (SPM) lithography that uses a nanometer sharpened tip has demonstrated outstanding capabilities for nanometer level patterning on various surfaces. Moreover, SPM techniques offer creating nanopatterns of Self Assembled Monolayers (SAMs) with molecular precision and visualizing surfaces with the highest spatial resolution. In this work, nanoscratches on gold surfaces and oxidation patterns on titanium surface were successfully performed as example of SPM lithography. In the second stage, Octadecylamine-HCl, Octadecanetiol (ODT) and Decylmercaptan (DM) SAM organic films were fabricated on various substrates; i.e., mica, silica, titanium surface deposited on silicon, n and p type silicon, using self assembly film preparation techniques. The film thicknesses were measured with Atomic Force Microscope (AFM). Nanopatterns were fabricated on SAM films using AFM tip by exerting a local high pressure at the contact that causes the displacement of SAM molecules by a high shear force. It was observed that there was no formation of SAMs on n type Si and silica substrates whereas there were organic assemblies on the other substrates. Fabricated nanopatterns were examined and thickness measurement was done. Molecular lengths of the organics were evaluated by using of SPARTAM 02 LINUX-UNIX with the method of PM3 and the measured values were compared with the calculated ones and it was concluded that monolayers were formed on the surfaces.Master Thesis Fabrication and Characterization of Mgb2 Powders and Cu-Clad Mgb2 Wires(Izmir Institute of Technology, 2005) Yavaş, Mert; Okur, SalihIn 2001, a new superconducting material, MgB2 (39K), which raised new hopes for electrical power applications due to its superior superconducting properties was discovered.In the first part of this study, elementary B is obtained by reacting B2O3, and Mg in Argon atmosphere at 800°C. EDX results revealed that the powder obtained was Boron in 93% purity with Mg as a major impurity. MgB2 is produced from acquired B and Mg in Ar atmosphere at 900°C by a conventional solid-state reaction. MgB2 powders were pressed to a pellet at 500°C at 1 GPa. Microstructural properties of MgB2 were determined by XRD, EDX, and SEM techniques. Electrical properties of fabricated MgB2 were analyzed by resistivity measurements with closed-cycle cryopump system between 20 and 300K. It is found that the Tc onset value of the pellet is around 32K. In the second part, different weight ratios of C is added to commercial MgB2 and pressed at 500°C at 1 GPa. R-T measurements revealed that transition temperature increases with an increase in the C addition concentration. In the third part, MgB2/Mg composite wires were prepared by packing blend of MgB2 and Mg powders inside Cu tubes using PIT method. The microstructure studies MgB2 and Mg powders inside Cu tubes using PIT method. The microstructure studies using XRD, EDX and SEM techniques showed that MgCu2 layer forms at the interface between Cu sheath and core because of Mg diffusion from superconducting core, and excess Mg prevents further reaction of Cu with MgB2. R-T measurements were performed to investigate the influence of excess Mg on Tc. The effect of annealing showed that excess Mg gives better results at annealing temperature of 400°C for 2 hours.Master Thesis Characterization of Modified Ito Anode Surfaces With 4 [3-Methylphenyl) Phenyl) Anino] Benzoic Acid for Oled Applications(Izmir Institute of Technology, 2011) Yağmurcukardeş, Nesli; Okur, SalihThis thesis focuses on to improve OLED characteristics of fabricated devices by modifying the ITO (anode) surface using novel carboxylic acid based molecule 4-[(3-methylphenyl)(phenyl)amino]benzoic acid (MPPBA). In this study, commercial ITO substrates were used as anodes. To modify the ITO surface, etched ITO substrates were kept in 1mM MPPBA-ethanol solution. As a hole transport layer (HTL), N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD) or N,N'-Di-[(1-naphthyl)-N,N'-diphenyl]-1,1'-biphenyl)-4,4'-diamine (NPB) small molecules were deposited using an organic evaporator system under the vacuum of 10-6 Torr. Finally, as a cathode contact layer, aluminum thin film of 120 nm was deposited on top of the fabricated organic thin film layers. The final structure of the devices was obtained as ITO /SAM (2nm) /HTL (50nm) /Al (120nm). The current-voltage characteristics of devices of unmodified bare ITO and MPPBA modified ITO substrates were analyzed by using the space charge limited current approach and Thermionic Schottky Emission Models. Additionally, surface characterizations of the SAM modified thin films were carried out using Quartz Crystal Microbalance (QCM), Atomic Force Microscopy (AFM), Kelvin Probe Force Microscopy (KPFM), X-ray Photoelectron Spectroscopy (XPS), Cyclic Voltammetry (CV) and Ultraviolet-visible Absorption Spectroscopy (UV-Vis) techniques. The obtained results reveal that the modification of the ITO surface with MPPBA molecules reduces the barrier height difference between the Fermi level of the anode and HOMO level of the HTL. Hence the hole injection increases while the turn-on voltage decreases. As a result of this process OLED characteristics were improved by using the MPPBA SAM molecules.Master Thesis Application of Self Assembled Monolayer Technique To Imporove Hole Transport in Organic Leds(Izmir Institute of Technology, 2011) Şeker, Mavişe; Okur, SalihThis thesis concentrates on the fabrication and characterization of highly efficient Organic Light-Emitting Diode (OLED) with surface modification of indium tin oxide (ITO) anodes by using self-assembled monolayer (SAM) technique. ITO has beencommonly used as an anode for OLEDs, because of the combination of high optical transparency and good electrical conductivity. That is why, ITO substrate is used in this study. On the other hand, the ITO film has often a rough surface, relatively low work function compared with the adjacent organic layer and its surface energy is not well matched to nonpolar organic film. For this purpose, in this work, eleven different SAM molecules were examined to modify ITO surface. Clearly, we aim to reduce the barrier of hole injection, lower the turn-on voltage and improve charge transfer characteristic at the anode-organic film interface using SAM molecules.The ITO work function with the SAM molecules was measured using Kelvin Probe Force Microscopy (KPFM). KPFM measurements were carried out to investigate if there is any increase in ITO work function. Atomic Force Microscopy (AFM) via semi-contact mode was examined the surface morphology of modified ITO. The transmittances of the ITOs with SAM were measured using an UV spectrometer. In addition to these surface analyses, the device performances were characterized by Keithley 236 and High-Resolution Spectrometer. Moreover, Space-Charge-Limited Current (SCLC) and Schottky models were used to analyze the I-V characteristics to calculate hole mobility and barrier heights, respectively.Master Thesis Interface Properties of Modified Indium Tin Oxide Based Organic Light Emitting Diodes Withfunctional Aromatic Molecules(Izmir Institute of Technology, 2011) Aydın, Hasan; Okur, SalihThis thesis focused on modification and characterization of ITO substrates with carboxylic acid based self-assembled monolayers to improve OLED device performance. In this study, ITO was used as anode material in OLEDs. In order to modify ITO electrodes, MePIFA and DPIFA aromatic small molecules with double bound carboxylic acid have been used as self-assembly monolayer (SAM). Characterizations of modified ITO and unmodified ITO surfaces were performed via atomic force microscopy and scanning tunneling microscopy. In addition to surface characterization, I-V measurements of the modified and unmodified ITO were taken via spreading resistance microscopy and scanning tunneling microscopy. Moreover, in order to measure change in the surface potential after the modification of ITO surface with MePIFA and DPIFA SAM molecules, Kelvin Probe Force Microscopy was performed. Finally two different configurations of OLEDs devices were fabricated using thermal evaporator system in order to explore the effect of SAM modified ITO on electrical characterization of OLED devices. It was shown that OLED intensity, and turn on voltage were improved compared to OLED devices with unmodified ITO.