Fabrication of double mesa structures from superconducting Bi2Sr2CaCu2O8+d by e-beam lithography for terahertz emission

Thesis (Master)--Izmir Institute of Technology, Physics, Izmir, 2011Includes bibliographical references (leaves: 81-87)Text in English; Abstract: Turkish and Englishxii, 87 leavesTerahertz 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

Besi sığırlarına rasyona anason ilavesinin performans ve bazı kan parametreleri üzerine etkileri etkisi

In the current study, 14 male Holstein calves aged 11-12 months were used from the Usak Cattle Breeders Association Research Farm. In this study lasting for 60 days, 14 cattle were used and divided into 2 groups as control and treatment. The feeding method, which is routinely applied in the enterprise, was applied to the control group. In addition to the same ration, 250 gr/head/day crushed anise seed powder feed additive was poured on the feed of the treatment group consisting of the other 7 animals. The live weight yields of all animals were weighed on the 30th and 60th days of the study, the individual daily live weight gains of the animals were calculated. Animals in the treatment group gained 286 gr more live weight per day. Some blood parameters (glucose, total protein, albumin, AST, GGT, cholesterol, TAS, TOS) were examined in blood samples taken from the tail vein at the beginning and end of the study. In the study, it was determined that the statistical difference between the control and experimental groups in terms of fattening performance and blood parameters was insignificant. The results of the current study have revealed that more comprehensive studies should be carried out on the addition of anise seed powder to cattle feed.Bu çalışma Uşak Damızlık Sığır Yetiştiriciler Birliği Araştırma Çiftliğinde 11-12 aylık yaşta 14 baş erkek Holştayn dana kullanılmıştır. 60 gün süren çalışmada 14 adet sığır kullanılmış olup kontrol ve deneme grubu olacak şekilde 2 gruba ayrılmıştır. Kontrol grubuna işletmede rutin olarak uygulanan besleme yöntemi uygulanmıştır. Diğer 7 hayvandan oluşan deneme grubuna ise aynı rasyona ilave olarak 250gr/baş/gün anason tohumu tozu yem üzerine dökülerek verilmiştir. Tüm hayvanların canlı ağırlık verimleri denemenin 30. ve 60. günlerinde tartılmıştır ve hayvanların bireysel günlük canlı ağırlık artışları hesaplanmıştır. Deneme gurubundaki hayvanlar günlük 286 g daha fazla canlı ağırlık kazanmışlardır. Denemenin başında ve sonunda kuyruk venasından alınan kan örneklerinde bazı kan parametreleri (glikoz, total protein, albümin, AST, GGT, kolesterol, TAS, TOS) incelenmiştir. Yapılan çalışmada elde edilen verilere göre kontrol ve deneme gurubu arasında besi performansı ve kan parametreleri bakımından istatistiksel olarak önemli bir fark bulunmadığı belirlenmiştir. Sonuç olarak bu çalışma ile sığır yemlerine anason tohumu ilavesiyle ilgili daha kapsamlı çalışmaların yapılması gerekliliği ortaya çıkmıştır

Comparative study of annealing and gold dopant effect on DC sputtered vanadium oxide films for bolometer applications

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.TUBITAK (Scientific and Technological Research Council of Turkey); 115F54

Chiral Devices for Terahertz Waves Based on Tunable Metamaterials

There are exceptional advantages in the region where Terahertz (THz) frequency takes place that could be identified as; a non-ionizing bio-innocuous property, transparent characteristics in cardboard or textiles, and extremely discriminating absorption spectral lines which can provide a “genetic code” of various bio-materials. [1,2]. The resonant effects at various terahertz frequencies that were displayed by metamaterials have created to accomplish a very important situation. Metamaterials are virtually desirable platforms for investigating chiral effects. In order to enhance these effects, producing the tunable chiral devices attracted lots of attention. Among the phase change materials for chiral metamaterials, graphene is a promising candidate due to its astonishing properties specifically in the THz and far infrared region. In this study, a chiral metamaterial gammadion structure is designed and fabricated on both sides of the sapphire substrates. A commercial COMSOL and CST Microwave Studio programs are used to design and optimize the chiral metamaterial. Numerical simulations are based on the interaction of the chiral structure with linearly and circularly polarized light. In the experimental side, a resistive evaporation and dc magnetron sputtering method is used for the deposition of gold and Sb2Se3 films respectively. A single layer graphene is used, that is grown on a copper foil by chemical vapor deposition. The thin graphene layer transferred on the Sb2Se3 coated sapphire substrates. The conventional UV lithography and ion beam etching techniques are used for patterning process. The THz characterization measurements were performed in order to assess the THz frequency response and to demonstrate the dynamically tunable chiroptical response using optical pumping [3,4]. The active polarization manipulation capability of the Sb2Se3/graphene chiral metamaterial with frequency tunability are investigated both numerically and experimentally.XVI Photonics Workshop : Book of abstracts; March 12-15, 2023; Kopaonik, Serbi

Fabrication of double mesa structures from superconducting Bi2Sr2CaCu2O8+d by e-beam lithography for terahertz emission

Thesis (Master)--Izmir Institute of Technology, Physics, Izmir, 2011Includes bibliographical references (leaves: 81-87)Text in English; Abstract: Turkish and Englishxii, 87 leavesTerahertz 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

Terahertz dalgası uygulamaları için e-demeti şekillendirmesiyle metamalzeme filtre fabrikasyonu

Thesis (Doctoral)--Izmir Institute of Technology, Material Science and Engineering, Izmir, 2017Full text release delayed at author's request until 2020.09.18Includes bibliographical references (leaves: 86-92)Text in English; Abstract: Turkish and EnglishIn the electromagnetic spectrum, terahertz (THz) radiation falls into the region among microwaves and the far-IR. The unique properties of superconducting materials allow them to be utilized in a number of ways for THz device applications. In the first part of this thesis, the spectral performance of THz bandpass filters were produced from titanium, copper and indium tin oxide thin films with a metal-mesh shape on fused silica substrates by uv lithography were investigated. For metamaterial filter fabrication, Bi2Sr2CaCu2O8+x thin films were deposited by DC and RF magnetron sputtering system on saphirre and MgO substrates. After thin film characterizations, it is obtained that the films were not in single phase and could not be used for filter fabrication. A new, unique fourcross shaped metamaterial THz filter was designed and fabricated from both gold thin films and YBa2Cu3O7-d high Tc superconducting thin films. The designed fourcross shaped rectangular filter structure consists of periodic metallic rings where strip lines are located at the sides of the ring. CST Microwave Studio, is used to design and optimize the metamaterial filter structures. To investigate the temperaturedependent resonance behavior and confirm the measurements, simulations are carried out at temperatures above and well below Tc. Fourcross metamaterial filters are fabricated by using e-beam lithography and ion beam etching techniques. The resonance switching of the transmission spectra was investigated by lowering the temperature below the critical transition temperature. This novel fourcross filter holds great potential for active, tunable and lowloss THz devices for imaging, sensing, and detection applications.Elektromanyetik spektrumda, terahertz (THz) radyasyonu mikrodalgalar ve uzak IR arasındaki bölgede yeralır. Süperiletken malzemelerin benzersiz özellikleri, THz aygıt uygulamaları için çeşitli şekillerde kullanılmasına olanak sağlar. Bu tezin ilk bölümünde, titanyum, bakır ve indiyum kalay oksit ince filmlerinden uv litografisi ile fused silika alttaş üzerine metal-örgü şekilli üretilen THz bant geçiren filtrelerin spektral performansı araştırılmıştır. Metamalzeme filtre üretimi için, Bi2Sr2CaCu2O8+x ince filmleri, safir ve MgO altaşlarına DC ve RF magnetron saçtırma sistemi ile kaplanmıştır. İnce film karakterizasyonları sonrasında, filmlerin tek fazda olmadıkları ve filtre üretimi için kullanılamayacağı anlaşılmıştır. Yeni, özgün, dört köşeli THz metamalzeme filtre yapısı tasarlanmış ve hem altın ince filmlerden hem de YBa2Cu3O7-d yüksek Tc süperiletken ince filmlerden üretilmiştir. Tasarlanan dörtlü çapraz şekilli dikdörtgen filtre yapısı, şerit hatların kenarlarına yerleştirildiği periyodik metalik halka yapıdan oluşur. CST Mikrodalga Stüdyosu, metamalzeme filtre yapılarını tasarlamak ve optimize etmek için kullanılmıştır. Sıcaklığa bağlı rezonans davranışını araştırmak ve ölçümleri doğrulamak için, simülasyonlar Tc'nin üstünde ve altında sıcaklıklarda gerçekleştirilmiştir. Dörtlü çapraz metamalzeme filtreler, e-demeti litografisi ve iyon demeti aşındırma teknikleri kullanılarak üretilmiştir. Geçirgenlik spektrumlarında rezonans anahtarlaması, sıcaklığı kritik geçiş sıcaklığının altına düşürerek incelenmiştir. Bu özgün dörtlü çapraz dikdörtgen filtre, görüntüleme, algılama ve spektroskopi uygulamalarında aktif, ayarlanabilir ve düşük kayıplı THz cihazları için büyük potansiyel taşımaktadır.TUBITAK (MFAG/114F091); AQUREC (Applied Quantum Research Center) at IZTEC

University students perceptions with regard to "quality and quality university concepts: Example of Gazi University Faculty of Gazi Education

Bu çalışmada, yükseköğretim kurumlarının en önemli paydaşları olan öğrencilerin kalite, kaliteli üniversite, kaliteli öğretim ve kaliteli öğretim elemanının özelliklerine ilişkin algılarının belirlenmesi amaçlanmıştır. Bu araştırma betimsel türde olup, çalışmada nitel araştırma yöntemi kullanılmıştır. Veri toplama aracı yardımıyla, öğrencilerden elde edilen yazılı yorumların analizi içerik analizi yöntemi kullanılarak gerçekleştirilmiştir. Araştırmada verilerin toplanması amacıyla öğrencilerin kişisel özelliklerinin ve 4 açık uçlu maddenin yer aldığı iki bölümden oluşan bir anket geliştirilmiştir. Çalışmanın hedef evrenini; 20092010 eğitim-öğretim yılında Gazi Üniversitesi'nde öğrenim gören tüm öğrenciler, ulaşılabilir evrenini ise Eğitim Fakültesi'nde öğrenim gören öğrenciler oluşturmaktadır. Örneklem ise; Türkçe, Sosyal Bilgiler, Matematik, Fizik, İngilizce, Müzik, Resim-İş Eğitimi ile Rehberlik ve Psikolojik Danışmanlık Anabilim dallarının birinci ve son sınıflarında okuyan toplam 493 öğrenci olarak seçilmiştir. Örneklem seçiminde seçkisiz olmayan örnekleme yöntemlerinden amaçsal örnekleme yönteminin bir alt boyutu olan maksimum çeşitlilik örnekleme yöntemi kullanılmıştır (Yıldırım ve Şimşek, 2006; Büyüköztürk ve diğerleri, 2008; Böke, 2009). Araştırmanın bulgularında, öğrencilerin Harvey ve Green (1993)'in kalite anlayışlarından en fazla vurgu yaptıkları anlayış amaca uygunluk anlamında kalite olarak belirlenmiştir. Kaliteli bir üniversitede bulunması gereken özellikler sorulduğunda ise, öğrencilerin kaliteli bir üniversitede bulunmasını en çok arzu ettikleri özelliklerin eğitim ve öğretim' alanında gerçekleştirilmesi gereken özellikler olarak vurgulandığı belirlenmiştir. Tüm hizmet alanlarında kalite geliştirme çalışmaları yürütülürken, tüm paydaşların ihtiyaçlarının belirlenmesi, onların görüşlerinin alınması ve bu görüşlerin değerlendirmeye dâhil edilmesi çok önemli bir yaklaşımdır. Yükseköğretim kurumlarında da kalite çalışmaları yapılırken, kurumların bir bütün olarak nitelikli olması için eğitim programlarının, hedeflere ulaşmada kullanılan yöntemlerin, öğrenci başarılarının, mezun sayılarının vb. öğrenci görüşleri dikkate alınarak sürekli olarak gözden geçirilmesi gerekmektedir.In this study, the most important stakeholders of higher education students with quality, quality universities, quality education and quality teaching staff to determine perceptions of the properties. This research is in descriptive form an qualitative research method is used fort his study. With the help of data collection tool, the analysis of written interprotations which were attained from students has been carried out by content analysis method. In research, with the aim of collecting data, a questionary which has including personal features of students and consisting of four open-ended items has been prepared. The target population of the study; all the students who have education in Gazi University during the period 2009-2010, and accessible population is consisted of the pupils are educated in faculty of education. The sample is chosen as 493 students first and serior classes who study in the departments of Turkish, Social Sciences, Physics, Mathematics, English, Music, Art teaching and Psychological Councelling and Guidance. In choosing the sample, maximum variation sampling method is used which is one of the lower dimension of purposeful sampling and that is not from random sampling methods (Yıldırım ve Şimşek, 2006; Büyüköztürk ve diğerleri, 2008; Böke, 2009). In findings of research, it is determined that students focus on the most common point of view from Harvey and Green (1993) is that in the terms of expendiency in quality on the other hand. When pupils are questioned about features of quality of university it is stated that they are features which should be achieved in education. In all service areas, the studies of improving the quality are carried out. So to determine all share holders needs to ask their opinions and to include these opinions in evaluation is so important approach. While quality studies are carried out in institutions of higher education, in order to make institutions qualified in whole, it is a must to review educational curriculum, successes of students the number of graduate students etc. constantly taking students opinions in to consideration