Demirhan, Yasemin

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https://hdl.handle.net/11147/16325
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04.05. Department of Pyhsics
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External
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Sustainable Development Goals

NO POVERTY1
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ZERO HUNGER2
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GOOD HEALTH AND WELL-BEING3
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QUALITY EDUCATION4
QUALITY EDUCATION
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GENDER EQUALITY5
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CLEAN WATER AND SANITATION6
CLEAN WATER AND SANITATION
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AFFORDABLE AND CLEAN ENERGY7
AFFORDABLE AND CLEAN ENERGY
1
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DECENT WORK AND ECONOMIC GROWTH8
DECENT WORK AND ECONOMIC GROWTH
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INDUSTRY, INNOVATION AND INFRASTRUCTURE9
INDUSTRY, INNOVATION AND INFRASTRUCTURE
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REDUCED INEQUALITIES10
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SUSTAINABLE CITIES AND COMMUNITIES11
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RESPONSIBLE CONSUMPTION AND PRODUCTION12
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PEACE, JUSTICE AND STRONG INSTITUTIONS16
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Scholarly Output

28

Articles

18

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100262/10550

Supervised MSc Theses

1

Supervised PhD Theses

1

WoS Citation Count

190

Scopus Citation Count

203

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WoS Citations per Publication

6.79

Scopus Citations per Publication

7.25

Open Access Source

20

Supervised Theses

2

JournalCount
Optical and Quantum Electronics4
Vacuum2
Modern Physics Letters B2
NATO Advanced Research Workshop Terahertz and Mid Infrared Radiation: Basic Research and Practical Applications, TERA-MIR 20092
NATO Science for Peace and Security Series B: Physics and Biophysics2
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Scholarly Output Search Results

Now showing 1 - 10 of 28
  • Article
    Citation - WoS: 7
    Citation - Scopus: 7
    Comparative Study of Annealing and Gold Dopant Effect on Dc Sputtered Vanadium Oxide Films for Bolometer Applications
    (Springer Verlag, 2017) Özyüzer, Lütfi; Demirhan, Yasemin; Yüce, Hürriyet; Yüce, Hürriyet; Özyüzer, Lütfi; Aygün, Gülnur; Demirhan, Yasemin; 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 Technology
    Vanadium oxide (VOx) thin film has been widely used for IR detectors and it is one of the promising materials for THz detectors due to its high temperature coefficient of resistance (TCR) values. VOx films with proper TCR values have also high resistance and it restricts bolometer performance especially for uncooled bolometers. To overcome this problem, deposition at elevated temperatures or annealing approach has been accepted and used but gold co-deposition approach has been proposed recently. In this study, vanadium oxide films were fabricated on high resistivity silicon substrates by reactive direct current magnetron sputtering in different O2/Ar atmosphere at room temperature. We investigated influence of oxygen partial pressure during deposition process and fabricated VOx thin films with sufficient TCR values for bolometer applications. In order to decrease resistivity of the deposited films, post annealing and gold doping approaches were performed separately. Effect of both post annealing process and gold doping process on structural and electrical properties of VOx thin films deposited at room temperature were investigated and detailed comparison between these methods were presented. We obtained the best possible approach to obtain optimum conditions for the highly reproducible VOx thin films which have the best resistivity and suitable TCR value for bolometer applications.
  • Article
    Citation - WoS: 13
    Citation - Scopus: 13
    Fourcross Shaped Metamaterial Filters Fabricated From High Temperature Superconducting Ybco and Au Thin Films for Terahertz Waves
    (IOP Publishing Ltd., 2017) Demirhan, Yasemin; Özyüzer, Lütfi; Nebioğlu, Mehmet Ali; Mulla, B.; Demirhan, Yasemin; Altan, Hakan; Sabah, Cumali; Özyüzer, Lütfi; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
    In this study, we present a new, unique fourcross shaped metamaterial terahertz (THz) filter fabricated from both gold thin films and YBa2Cu3O7-δ high Tc superconducting thin films. A commercial electromagnetic simulation software, CST Microwave Studio, is used to design and optimize the metamaterial filter structures. The proposed fourcross shaped rectangular filter structure consists of periodic metallic rings where strip lines are located at the sides of the ring. Fourcross metamaterial filters are fabricated by using e-beam lithography and ion beam exhing techniques. Terahertz time-domain spectroscopy measurements validated the design predictions for both the center frequencies and bandwidths of the resonances due to the fourcross structures. The resonance switching of the transmission spectra was investigated by lowering the temperature below the critical transition temperature. This resonance switching effect is not observed in filters made up of metals. This novel fourcross rectangular resonator with a temperature-dependent resonance behavior holds great potential for active, tunable and low loss THz devices for imaging, sensing, and detection applications.
  • Article
    Citation - WoS: 6
    Citation - Scopus: 6
    Nanolitography 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 Technology
    In 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.
  • Conference Object
    Spin Polarized Tunneling in Large Area Mesas of Superconducting Bi 2sr2cacu2o8+δ for the Generation of the Thz Waves
    (Institute of Electrical and Electronics Engineers Inc., 2009) Türkoğlu, Fulya; Özyüzer, Lütfi; Şimşek, Yılmaz; Demirhan, Yasemin; Köseoğlu, Hasan; Demirhan, Yasemin; Meriç Polster, Zeynep; Özyüzer, Lütfi; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
    Rectangular intrinsic Josephson junction mesa structures of superconducting Bi2Sr2CaCu2O8+delta (Bi2212) can be used as a source of continuous, coherent and polarized terahertz (THz) radiation. THz emitting mesas are below a certain underdoped level of Bi2212. They have small Josephson critical current in contrast to optimally doped and overdoped Bi2212. We deposited Au/Co/Au multilayer top of mesa and obtained small critical current from mesas fabricated by as-grown Bi2212 single crystals due to injection of spin polarized current. The spin injection eliminates adjustment of doping level for successful THz emission.
  • Article
    Citation - WoS: 39
    Citation - Scopus: 40
    Interferometer Measurements of Terahertz Waves From Bi 2sr 2cacu 2o 8+d Mesas
    (IOP Publishing Ltd., 2012) Türkoğlu, Fulya; Köseoğlu, Hasan; Demirhan, Yasemin; Özyüzer, Lütfi; Preu, Sascha; Özyüzer, Lütfi; Şimşek, Yusuf; Müller, P.; Yamamoto, T.; Kadowaki, K.; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
    We fabricated rectangular mesa structures of superconducting Bi 2Sr 2CaCu 2O 8+d (Bi2212) using e-beam lithography and Ar ion beam etching techniques for terahertz (THz) emission. c-axis resistance versus temperature (R-T), current-voltage (I-V) characteristics and bolometric THz power measurements were performed to characterize Bi2212 mesas. The emission frequency of mesas was determined using a Michelson interferometer setup which also demonstrates polarized emission. Interference patterns of THz radiation from Bi2212 mesas were detected by various detectors such as a liquid helium cooled silicon composite bolometer, a Golay cell and a pyroelectric detector. An emitted power as high as 0.06mW was detected from Bi2212 mesas. For the first time, most of the pumped power was extracted as THz emission from a Bi2212 mesa. The radiation at 0.54THz was detected using the Michelson interferometric setup.
  • Article
    Citation - WoS: 3
    Citation - Scopus: 4
    Terahertz Wavefront Engineering Using a Hard-Coded Metasurface
    (Springer, 2023) Noori, Aileen; Demirhan, Yasemin; Akyürek, Bora; Özyüzer, Lütfi; Demirhan, Yasemin; Aygün, Gülnur; Özyüzer, Lütfi; Güven, Kaan; Altan, Hakan; Aygün, Gülnur; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
    During the past few years, coding metamaterials (MM) drew significant attention, where the far-field scattering/transmission pattern of the electromagnetic wave (particularly in the THz regime) can be encoded into a single or few-bit digitized phase-response of the metasurface, thereby enabling a full digital control. Single-bit MMs contain two types of unit cells where the phase becomes 0 and 1 (in units of ?), respectively. By arranging these unit cells into a 2D surface pattern, the THz wavefront can be shaped. In this work, a novel hard-coded metasurface was designed, fabricated, and experimentally investigated for multi-beam reflection of incident THz beam. The design employs stripe and checkerboard patterns of bilayer MM unit cells consisting of square gold patches with a polymer spacing layer from a gold backplane. Experimental and simulation results show that the incident wave in the 0.500–0.750 THz range can be reflected with > 95% efficiency in uniform amplitude and 1-bit coded phase. For the checkerboard metasurface pattern, the measured and analytically calculated reflection angle shows good agreement. The metasurface design is suitable for large-scale fabrication and can potentially be used as a template in the development of actively coded metasurfaces. © 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
  • Article
    Citation - WoS: 21
    Citation - Scopus: 22
    Investigation 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 Technology
    Vanadium 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: 6
    Citation - Scopus: 7
    Thin Film Like Terahertz Bolometric Detector on Bi2212 Single Crystal
    (Springer Verlag, 2016) Semerci, Tuğçe; Demirhan, Yasemin; Demirhan, Yasemin; Wang, Huabing; Özyüzer, Lütfi; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
    In this study, we developed a microbolometer chip fabricated from high temperature superconducting Bi2Sr2CaCu2O8+δ (Bi2212) single crystals for the terahertz (THz) detection. For the manufacturing of the microbolometer chips, Bi2212 single crystals were transferred on substrate in the thin film like form and electron beam lithography, ion beam etching techniques were used. Resistance versus temperature behavior of the bolometer chips were performed by four probe technique in liquid nitrogen cryostat. Bi2212 microchips were integrated and characterized using in our custom-designed cryogenic bolometer system instead of expensive and massive cooling systems. The fabricated microchips significantly detected signals from the Stefan-Boltzmann lamp which includes a portion of THz radiation. The detected power and response time were studied for Bi2212 thin film like microbolometer chips. Our results demonstrated the feasibility of improved Bi2212 microchips could be used for bolometric detection for THz applications.
  • Book Part
    Citation - Scopus: 1
    Thz Sources and Detectors Fabricated From High Temperature Superconductors
    (Springer, 2021) Demirhan, Yasemin; Demirhan, Yasemin; Türkoğlu, Fulya; Özyüzer, Lütfi; Altan, Hakan; Sabah, Cumali; Özyüzer, Lütfi; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
    High temperature superconductors have unique properties that can be useful in the THz region, single crystal constituted from superconducting CuO2-layers could sustain high voltages across the junctions and they are coupled through the intrinsic Josephson Effect this maintains the potential for very intense, coherent radiation which spreads over the THz gap. We investigated various experimental techniques to fabricate THz sources, bolometers and filters for efficient THz emission and detection. Rectangular mesa structures were fabricated on Bi2Sr2CaCu2O8-x (Bi2212) single crystal superconductors using standard e-beam lithography and Ar ion beam etching systems and an emitted power as high as 60 ?W at frequencies up to 0.85 THz was detected from micron sized continuous wave terahertz sources. We also fabricated bolometric microchips for THz detection purpose from Bi2212 single crystals. Bi2212 microchips detected the signals and response time were calculated, our results have clearly shown that Bi2212 single crystals are potential candidates for THz detection. The detection properties and sensitivity of bolometer chips can be further improved by integrating an antenna and filter structures. In order to investigate this we have fabricated metamaterial THz filters based on metals and YBa2Cu3Ox superconducting thin films with metal-mesh shape and a unique fourcross shape pattern. Both a THz time domain spectrometer and a Fourier transform infrared spectrometer (FTIR) were used to investigate the performance of these filters and the results were compared with simulations done with a commercially available electromagnetic simulation software. © Springer Nature B.V. 2021.
  • Master Thesis
    Fabrication of Double Mesa Structures From Superconducting Bi2sr2cacu2o8+d by E-Beam Lithography for Terahertz Emission
    (Izmir Institute of Technology, 2011) Demirhan, Yasemin; Demirhan, Yasemin; Özyüzer, Lütfi; Özyüzer, Lütfi; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
    Terahertz radiation is part of the electromagnetic spectrum lying between microwaves and the far-IR. This region has frequencies ranging from 0.1 - 10 THz and wavelengths from 3 mm to 0.03 mm. We work on a frequency tunable solid state device to meet the needs of continuous, coherent, powerful terahertz emission sources that fill practically important terahertz gap. Among the cuprates, single crystal of Bi2Sr2CaCu2O8+ (Bi2212) is a potential candidate of compact solid state devices designed for generating electromagnetic waves in terahertz frequency range. Bi2212 crystals are consisting of natural arrays in the form of identical layers called intrinsic Josephson junctions (IJJ). In this study, under optimized doping conditions we aimed to investigate powerful terahertz emission. THz emission in the μW range can be obtained fabricating rectangular-shaped mesa structures on the Bi2212 crystal. In the experimental procedure, in order to obtain various doping levels, we annealed the high temperature superconducting Bi2212 single crystals at various temperatures in vacuum or under argon flow. By using the thermal evaporation, optic and electron beam lithography, ion beam etching techniques single and double mesa structures were fabricated. For the e-beam lithography process, we optimized and improved the required parameters. After the mesa fabrication, the exact dimensions of the mesas were obtained using surface profilometer and atomic force microscope. In order to characterize the Bi2212 mesas,by three probe contact c-axis resistance versus temperature (R-T), and current-voltage behavior (I -V) were measured in a He flow cryostat. Some of the hysteretic quasiparticle branches are seen in the I-V characteristics of Bi2212 crystals.