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Özdemir, Mehtap
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Ozdemir, Mehtap.
Özdemir, M.
Ozdemir, M.
Özdemir, M.
Ozdemir, M.
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04.05. Department of Pyhsics
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Sustainable Development Goals
1NO POVERTY
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2ZERO HUNGER
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3GOOD HEALTH AND WELL-BEING
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4QUALITY EDUCATION
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5GENDER EQUALITY
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6CLEAN WATER AND SANITATION
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7AFFORDABLE AND CLEAN ENERGY
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8DECENT WORK AND ECONOMIC GROWTH
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9INDUSTRY, INNOVATION AND INFRASTRUCTURE
3
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10REDUCED INEQUALITIES
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11SUSTAINABLE CITIES AND COMMUNITIES
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12RESPONSIBLE CONSUMPTION AND PRODUCTION
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13CLIMATE ACTION
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14LIFE BELOW WATER
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15LIFE ON LAND
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16PEACE, JUSTICE AND STRONG INSTITUTIONS
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Scholarly Output
19
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17
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132550/7868
Supervised MSc Theses
2
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WoS Citation Count
362
Scopus Citation Count
401
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0
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1
WoS Citations per Publication
19.05
Scopus Citations per Publication
21.11
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12
Supervised Theses
2
| Journal | Count |
|---|---|
| Physica Scripta | 2 |
| Journal of Materials Science: Materials in Electronics | 2 |
| Applied Surface Science | 2 |
| Vacuum | 2 |
| Applied Optics | 1 |
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19 results
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Now showing 1 - 10 of 19
Article Citation - WoS: 6Citation - Scopus: 6Nanolitography Based on Electrospun and Etched Nanofibers(Elsevier, 2021) Noori, Aileen; Özyüzer, Lütfi; Döğer, Hilal; Demirhan, Yasemin; Demirhan, Yasemin; Özdemir, Mehtap; Özdemir, Mehtap; Aygün, Gülnur; Özyüzer, Lütfi; Aygün, Gülnur; Sağlam, Özge; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyIn this study, we propose a new type of nanolithography procedure to fabricate orderly patterned metallic nanostructures using the electrohydrodynamic method and the reactive ion etching process. The electrohydrodynamic process parameters were tuned so as to create patterning with precision, and fibers in nanoscale on silver-coated substrates. We also studied reactive ion etching with different durations on the well-patterned samples. The experiments show that applying a voltage of 400 V resulted in straight patterned fibers with a diameter of 208.7 ? 30.3 nm. The statistical analysis on scanning electron microscope (SEM) images showed a significant difference in the diameter of the fibers fabricated at 400 V compared to those at 500 V and 600 V. We also confirm that the etching process has no affect on the fiber diameter. Moreover, electron dispersive X-Ray spectrometer (EDX) results suggest that an etching duration of 7 min is sufficient to remove the silver coating that is not covered with the fibers, and protect the silver nanostructures underneath the fibers. Utilizing a lowcost nanolithography procedure, we obtain the orderly patterned silver nanostructures for possible integration into miniaturized devices.Article Citation - WoS: 15Citation - Scopus: 17Effect of Substrate Rotation Speed and Off-Center Deposition on the Structural, Optical, and Electrical Properties of Azo Thin Films Fabricated by Dc Magnetron Sputtering(American Institute of Physics, 2018) Aygün, Gülnur; Aygün, Gülnur; Köseoğlu, Hasan; Özdemir, Mehtap; Özdemir, Mehtap; Özyüzer, Lütfi; Özyüzer, Lütfi; Özyüzer, Gülnur Aygün; Özyüzer, Lütfi; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyIn this study, aluminum-doped zinc oxide (AZO) thin films were deposited by DC magnetron sputtering at room temperature. The distance between the substrate and target axis, and substrate rotation speed were varied to get high quality AZO thin films. The influences of these deposition parameters on the structural, optical, and electrical properties of the fabricated films were investigated by X-ray diffraction (XRD), Raman spectroscopy, spectrophotometry, and four-point probe techniques. The overall analysis revealed that both sample position and substrate rotation speed are effective in changing the optical, structural, and electrical properties of the AZO thin films. We further observed that stress in the films can be significantly reduced by off-center deposition and rotating the sample holder during the deposition. An average transmittance above 85% in the visible range and a resistivity of 2.02 × 10-3Ω cm were obtained for the AZO films.Article Citation - WoS: 33Citation - Scopus: 33Characterization of Thin Film Li0.5la0.5ti1-Xalxo3 Electrolyte for All-Solid Li-Ion Batteries(Elsevier, 2018) Ulusoy, Seda; Gülen, Sena; Aygün, Gülnur; Özyüzer, Lütfi; Özdemir, Mehtap; Özyüzer, Lütfi; Özdemir, Mehtap; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologySince addition of Al in Li0.5La0.5TiO3 has enhanced ionic conductivity in bulk materials, it is important to apply this material on all solid state thin film batteries. Because some of the good ionic conductors such as Lithium Phosphorus Oxynitride (LiPON) are sensitive to oxygen and moisture and their application is limited, so amorphous Li0.5La0.5Ti1−xAlxO3 (LLTAlO) is a most promising candidate because of its stability. In this study, the crystalline LLTAlO targets were prepared changing the amount of x content by conventional solid state reactions. Using these targets, lithium lanthanum titanium oxide (LLTO) thin film electrolytes were deposited on ITO/SLG substrates by radio frequency magnetron sputtering system in Ar atmosphere. The structural and compositional properties of targets and thin films were characterized by SEM, XRD, Raman spectroscopy and XPS. It was found that all targets are crystalline while the thin films are amorphous. To understand the effect of Al doping on ionic conductivity, electrical measurements were done at room temperature by AC impedance spectroscopy forming ITO/LLTAlO/Al structure like capacitor. Highest ionic conductivity result, 0.96 × 10−6 S·cm−1, is obtained from the nominal thin film composition of Li0.5La0.5Ti1−xAlxO3 (x = 0.05) at room temperature measurements. Heat treatment is also conducted to investigate to understand its effect on ionic conductivity and the structure of the thin films. It is found that ionic conductivity enhances with annealing. Also, temperature dependent ionic conductivity measurements from 298 K to 385 K are taken in order to evaluate activation energy for Li-ion conduction.Article Citation - WoS: 3Citation - Scopus: 3Compact Multilayer Thin-Film Color Filters and Direct Integration on White-Light Diodes for Color Conversion(Optical Society of America, 2021) Yiğen, Serap; Aygün, Gülnur; Ekmekçioğlu, Merve; Yiğen, Serap; Özdemir, Mehtap; Özdemir, Mehtap; Aygün, Gülnur; Özyüzer, Lütfi; Özyüzer, Lütfi; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyWe present highly efficient green, yellow, and red filters based on a metal-dielectric structure. The filters encompass only five layers of alternating zinc tin oxide and silver thin films that are grown on soda lime glass and white light-emitting diodes (LEDs) using direct current magnetron sputtering at room temperature. The designed filters provide efficient color filtering in the visible spectrum. High purity colored light is obtained by direct application of filters on LEDs as color converters. The presented method offers an easy way for realizing different colors by tuning the thicknesses of layers in the structure. (C) 2021 Optical Society of AmericaArticle Citation - WoS: 20Citation - Scopus: 23Surface Free Energy and Wettability Properties of Transparent Conducting Oxide-Based Films With Ag Interlayer(Elsevier, 2021) Özbay, Salih; Erdoğan, Nursev; Aygün, Gülnur; Ekmekçioğlu, Merve; Özyüzer, Lütfi; Özdemir, Mehtap; Aygün, Gülnur; Özyüzer, Lütfi; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyITO, ZTO, AZO and Ag are commonly used in transparent conducting oxide (TCO)/metal/TCO electrodes to form multilayered thin films on a suitable substrate. A detailed surface free energy (SFE) knowledge of these films is critical to design desirable TCO-based sandwich structures. In this study, TCO/Ag/TCO multilayer thin films were coated onto glass substrates using ITO, ZTO, AZO and Ag targets by magnetron sputtering. The wettability properties of TCO, Ag interlayer and TCO/Ag/TCO were evaluated by contact angle measurements of seven different liquids having various surface tension values. The dispersive and polar components of SFE were calculated using geometric and harmonic mean approaches. The acidic and basic components of SFE were calculated using van Oss-Chaudhury-Good method. Following this, the work of adhesion values between TCO films and Ag interlayer were estimated using SFE values of the films. The results show that the SFE components of the surfaces differ depending on the TCO type, the total SFE values of TCO/Ag/TCO films were lower than that of TCO films, and AZO/Ag adhesion is stronger than the other TCO/Ag structures. The reasons behind these differences were discussed by evaluating the SFE, XRD, AFM and SEM analysis simultaneously.Article Citation - WoS: 5Citation - Scopus: 6A Comprehensive Study of Molybdenum Boats Behavior During Service Life for Continuous Thermal Evaporation Technique, Used in Thin Film Technology(Elsevier, 2020) Rouhi, Sina; Aygün, Gülnur; Martinez-Medina, Jose Enrique; Özdemir, Mehtap; Özdemir, Mehtap; Özyüzer, Lütfi; Ertuğrul, Mehmet; Aygün, Gülnur; Özyüzer, Lütfi; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThe aim of this study is to calculate the optimum lifetime of Molybdenum (Mo) thermal evaporation boats for Copper (Cu) filling in thin film technologies. Three types of Mo boats with thicknesses of 0.2, 0.3 and 0.5 mm were used during the experiments under the high vacuum condition about 6.0 x 10(-6) Torr. The behavior of each boat was investigated by focusing on the total amount of evaporation material, operational time and applied power. Prior to the deposition process, material was loaded on the evaporation boat by two methods. In the first method, Cu wire was cut into 1 cm long, then every boat was filled with this amount of Cu material. The second alternative feeding method is to use a wire-feeder step motor, which refills boat with Cu wire during evaporation process. The latter one is very useful for continuous deposition process since there is no need to break the vacuum state. In both methods, however, the number of failures during operations increases after a series of experiments have been taken place because of boat aging. The results of failures have been analyzed by various methods, and it has been observed that thinner boats showed better stability for long time operation by continuous feeding technique.Article Citation - WoS: 39Citation - Scopus: 46Surface Free Energy Analysis of Ito/Au Multilayer Thin Films on Polycarbonate Substrate by Apparent Contact Angle Measurements(Elsevier, 2020) Özbay, Salih; Aygün, Gülnur; Erdoğan, Nursev; Özyüzer, Lütfi; Erden, Fuat; Özdemir, Mehtap; Ekmekçioğlu, Merve; Özdemir, Mehtap; Aygün, Gülnur; Özyüzer, Lütfi; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyA detailed surface free energy (SFE) knowledge of transparent conducing oxide (TCO)/metal/TCO electrodes is necessary for their applications related to surface wettability. However, SFE analysis of these surfaces has not been performed systematically previously. In this study, ITO and ITO/Au/ITO multilayer thin films were coated onto O-2 plasma treated polycarbonate (PC) substrates by magnetron sputtering. The wettability characteristics of untreated PC, O-2 plasma treated PC, ITO, Au interlayer, and ITO/Au/ITO multilayer thin films were evaluated by apparent contact angle measurements of nine different test liquids having various surface tensions. Following this, Lifshitz-van der Waals, acidic, basic, dispersive, and polar components of SFE were calculated using acidbase, geometric and harmonic mean approaches. In the present study, in which the significance of calculation methods and selected liquid pairs on SFE parameters were investigated, the effect of Au interlayer presence on SFE parameters were also evaluated simultaneously. The results showed that the total SFE values of ITO/Au/ITO multilayer thin films were found to be higher than that of ITO surface. The reasons behind this difference were discussed in terms of SFE components obtained using various liquid pairs by different methods. The results were also supported with XRD, XPS, AFM, and TEM analysis.Article Citation - WoS: 63Citation - Scopus: 72Ito/Au Multilayer Thin Films on Transparent Polycarbonate With Enhanced Emi Shielding Properties(Elsevier, 2020) Erdoğan, Nursev; Özyüzer, Lütfi; Erden, Fuat; Özdemir, Mehtap; Astarlıoğlu, A. Taner; Aygün, Gülnur; Özdemir, Mehtap; Özbay, Salih; Aygün, Gülnur; Özyüzer, Lütfi; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyITO/Au/ITO multilayer thin films were deposited onto polycarbonate substrate via magnetron sputtering technique without intentional heating. The deposition times of both ITO and Au layers were studied to optimize the overall transparency and conductivity. As-prepared thin films were characterized using X-ray diffraction analysis, secondary ion mass spectroscopy, scanning and transmission electron microscopy, atomic force microscopy and physical property measurement system. The optical measurement results revealed that the transmittance of the films were enhanced by increasing the gold deposition time up to 15 s. Beyond this point, further increasing the duration caused a decrease in optical transmittance. Upon optimization of the Au deposition time, the deposition duration of ITO layers was also studied to increase electromagnetic interference (EMI) shielding effectiveness (SE). Maximum EMI SE in this work was measured as 26.8 dB, yielding 99.8% power attenuation, which was verified by simulation results.Article Citation - WoS: 21Citation - Scopus: 22Investigation of Electron Beam Lithography Effects on Metal-Insulator Transition Behavior of Vanadium Dioxide(IOP Publishing Ltd., 2017) Yüce, Hürriyet; Alaboz, Hakan; Aygün, Gülnur; Özdemir, M.; Özyüzer, Lütfi; Yüce, Hürriyet; Özdemir, Mehtap; Demirhan, Yasemin; Özyüzer, Lütfi; 04.05. Department of Pyhsics; 03.09. Department of Materials Science and Engineering; 03. Faculty of Engineering; 04. Faculty of Science; 01. Izmir Institute of TechnologyVanadium dioxide (VO2) shows metal-insulator phase transition at nearly 68 °C. This metal-insulator transition (MIT) in VO2 leads to a significant change in near-infrared transmittance and an abrupt change in the resistivity of VO2. Due to these characteristics, VO2 plays an important role on optic and electronic devices, such as thermochromic windows, meta-materials with tunable frequency, uncooled bolometers and switching devices. In this work, VO2 thin films were fabricated by reactive direct current magnetron sputtering in O2/Ar atmosphere on sapphire substrates without any further post annealing processes. The effect of sputtering parameters on optical characteristics and structural properties of grown thin films was investigated by SEM, XRD, Raman and UV/VIS spectrophotometer measurements. Patterning process of VO2 thin films was realized by e-beam lithography technique to monitor the temperature dependent electrical characterization. Electrical properties of VO2 samples were characterized using microprobe station in a vacuum system. MIT with hysteresis behavior was observed for the unpatterned square samples at around 68 °C. By four orders of magnitude of resistivity change was measured for the deposited VO2 thin films at transition temperature. After e-beam lithography process, substantial results in patterned VO2 thin films were observed. In this stage, for patterned VO2 thin films as stripes, the change in resistivity of VO2 was reduced by a factor of 10. As a consequence of electrical resistivity measurements, MIT temperature was shifted from 68 °C to 50 °C. The influence of e-beam process on the properties of VO2 thin films and the mechanism of the effects are discussed. The presented results contribute to the achievement of VO2 based thermochromic windows and bolometer applications.Article Citation - WoS: 2Citation - Scopus: 2Comparison of Photocatalytic Properties of Tio2 Thin Films and Fibers(EDP Sciences, 2016) Özdemir, Mehtap; Kurt, Metin; Özyüzer, Lütfi; Aygün, Gülnur; Özdemir, Mehtap; Aygün, Gülnur; Kurt, Metin; 04.05. Department of Pyhsics; 01. Izmir Institute of Technology; 04. Faculty of ScienceEfficiency of solar panels degrades as a result of organic contamination such as airborne particles, bird droppings and leaves. Any foreign object on photovoltaic panels reduces the sunlight entering the absorbing surface of the solar panels. Since this leads to a major problem decreasing in energy production, solar panels should be cleaned. The self-cleaning method can be preferred. There are some methods to clean the surface of solar panels. Among the self-cleaning materials, TiO2 is the most preferable ones because of its powerful photocatalytic properties. In this study, photocatalytic TiO2 were produced in two different nanostructures: nanofibers and thin films. TiO2 nanofibers were successfully produced by electrospinning. TiO2 thin films were fabricated by reactive magnetron sputtering technique. Both TiO2 nanofiber and thin film structures were heat-treated to form TiO2 in anatase phase at 600 °C for 2 h in air. Then, they were evaluated by SEM analyses for morphology, X-ray diffraction (XRD) analyses for phase structures, X-ray photoelectron spectroscopy (XPS) for the chemical state and atomic concentration, and UV-spectrometer for photocatalytic performance. The results indicate that photocatalytic and transmittance properties of TiO2 thin films are better than those of nanofibers. Consequently, TiO2 based thin films exhibit better performance for solar cell applications due to the surface cleanliness.