Excitation energy-dependent nature of Raman scattering spectrum in GaInNAs/GaAs quantum well structures

The excitation energy-dependent nature of Raman scattering spectrum, vibration, electronic or both, has been studied using different excitation sources on as-grown and annealed n- and p-type modulation-doped Ga(1 − x)In(x)N(y)As(1 − y)/GaAs quantum well structures. The samples were grown by molecular beam technique with different N concentrations (y = 0%, 0.9%, 1.2%, 1.7%) at the same In concentration of 32%. Micro-Raman measurements have been carried out using 532 and 758 nm lines of diode lasers, and the 1064 nm line of the Nd-YAG laser has been used for Fourier transform-Raman scattering measurements. Raman scattering measurements with different excitation sources have revealed that the excitation energy is the decisive mechanism on the nature of the Raman scattering spectrum. When the excitation energy is close to the electronic band gap energy of any constituent semiconductor materials in the sample, electronic transition dominates the spectrum, leading to a very broad peak. In the condition that the excitation energy is much higher than the band gap energy, only vibrational modes contribute to the Raman scattering spectrum of the samples. Line shapes of the Raman scattering spectrum with the 785 and 1064 nm lines of lasers have been observed to be very broad peaks, whose absolute peak energy values are in good agreement with the ones obtained from photoluminescence measurements. On the other hand, Raman scattering spectrum with the 532 nm line has exhibited only vibrational modes. As a complementary tool of Raman scattering measurements with the excitation source of 532 nm, which shows weak vibrational transitions, attenuated total reflectance infrared spectroscopy has been also carried out. The results exhibited that the nature of the Raman scattering spectrum is strongly excitation energy-dependent, and with suitable excitation energy, electronic and/or vibrational transitions can be investigated

Dilute nitride resonant-cavity light emitting diode

Resonant cavity LEDs (RCLEDs) are a viable and low-cost alternative light source to lasers for optical communication systems in the 1.3 µm O-band. Most work in this area has been conducted on InP-based material, which is inherently costly, devices often require cooling and the refractive index contrast for constructing mirrors is low. Here, we demonstrate a high-performance GaAs-based RCLED using a dilute nitride GaInNAs active layer emitting in the 1.3 μm wavelength window. While previous 1.3 µm RCLEDs have used metallic mirrors on the back of the device, we exploit the high refractive index contrast of the GaAs/AlAs system to place Distributed Bragg mirrors on both sides of the active layer and achieve superior performance. The external quantum efficiency of the devices is 20% and the full width at half maximum of the emission spectrum is 5.2 nm at room temperature, into a narrow angular cone. The emission power from an 88 μm diameter aperture is 0.5 mW, which, together with the narrow spectral linewidth, makes the device suitable for deployment in a coarse Wavelength Division Multiplexing (WDM) communications system

Understanding the impact of heavy ions and tailoring the optical properties of large-area Monolayer WS2 using Focused Ion Beam

Focused ion beam (FIB) has been used as an effective tool for precise nanoscale fabrication. It has recently been employed to tailor defect engineering in functional nanomaterials such as two-dimensional transition metal dichalcogenides (TMDCs), providing desirable properties in TMDC-based optoelectronic devices. However, the damage caused by the FIB irradiation and milling process to these delicate atomically thin materials, especially in the extended area, has not yet been elaboratively characterised. Understanding the correlation between lateral ion beam effects and optical properties of 2D TMDCs is crucial in designing and fabricating high-performance optoelectronic devices. In this work, we investigate lateral damage in large-area monolayer WS2 caused by the gallium focused ion beam milling process. Three distinct zones away from the milling location are identified and characterised via steady-state photoluminescence (PL) and Raman spectroscopy. An unexpected bright ring-shaped emission around the milled location has been revealed by time-resolved PL spectroscopy with high spatial resolution. Our finding opens new avenues for tailoring the optical properties of TMDCs by charge and defect engineering via focused ion beam lithography. Furthermore, our study provides evidence that while some localised damage is inevitable, distant destruction can be eliminated by reducing the ion beam current. It paves the way for the use of FIB to create nanostructures in 2D TMDCs, as well as the design and realisation of optoelectrical devices on a wafer scale

An analysis of Hall mobility in as-grown and annealed n- and p-type modulation-doped GaInNAs/GaAs quantum wells

In this study, we investigate the effect of annealing and nitrogen amount on electronic transport properties in n- and p-type-doped Ga(0.68)In(0.32)N(y)As(1 − y)/GaAs quantum well (QW) structures with y = 0%, 0.9%, 1.2%, 1.7%. The samples are thermal annealed at 700°C for 60 and 600 s, and Hall effect measurements have been performed between 10 and 300 K. Drastic decrease is observed in the electron mobility of n-type N-containing samples due to the possible N-induced scattering mechanisms and increasing effect mass of the alloy. The temperature dependence of electron mobility has an almost temperature insensitive characteristic, whereas for p-type samples hole mobility is decreased drastically at T > 120 K. As N concentration is increased, the hole mobility also increased as a reason of decreasing lattice mismatch. Screening effect of N-related alloy scattering over phonon scattering in n-type samples may be the reason of the temperature-insensitive electron mobility. At low temperature regime, hole mobility is higher than electron mobility by a factor of 3 to 4. However, at high temperatures (T > 120 K), the mobility of p-type samples is restricted by the scattering of the optical phonons. Because the valance band discontinuity is smaller compared to the conduction band, thermionic transport of holes from QW to the barrier material, GaAs, also contributes to the mobility at high temperatures that results in a decrease in mobility. The hole mobility results of as-grown samples do not show a systematic behavior, while annealed samples do, depending on N concentration. Thermal annealing does not show a significant improvement of electron mobility

Dağıtılmış Alt Bragg Dielektrik Yansıtıcılı Işık Yayan Diyot

Bu çalışmada alt Bragg yansıtıcısına sahip yakın kızılötesi bölgede ışıma yapan p-i-n diyotun tasarımı, fabrikasyon detayları ve elektro-optik özellikleri incelenmektedir.İncelenen ışık yayan aygıtın aktif ışıma bölgesi 20 adet GaInNAs/GaNAs (7 nm /13 nm) kuantum kuyusu sisteminden oluşmaktadır. Alt dielektrik aynası ise 15 adet GaAs/AlAs Bragg yansıtıcı çiftlerinin üst üste tabakasal olarak büyütülmesinden oluşmaktır. Aygıtın ışıma merkez dalgaboyu 1310 nm olup, spektral yarı genişliği 14.4 nm’dir. Işıma eşik akımı 20 nA olan aygıtın, 200 mA sürülen akım varlığında maksimum ışıma gücü 38 mW’dır. Bu çalışmada, yakın kızılötesi bölgede ışıma yapan aygıt üretilmesinin ve karakterize edilmesinin yanı sıra sadece alt Bragg yansıtıcı kullanılarak bile geleneksel ışık yayan diyotlara göre ışıma spektral genişliğinin ve ışıma profilinin iyileştirilebileceğini gösterilmiştir

ZnO nanoparticles-based vacuum pressure sensor

ZnO nanoparticles synthesized using the sol-gel technique with an average diameter of 11.5 nm are used to fabricate a vacuum pressure sensor in the range of 1 mbar to 10(+3) mbar (low vacuum limit). A drastic increase in the current of the drop-casted ZnO on glass with 30 mu m separated Au contacts defined by e-beam lithography is observed. The sensor reveals a linear relationship in current versus pressure in a logarithmic plot. In the range of 1 mbar to 10(+3) mbar, the sensor sensitivity is found be 110. Using the resistance-time plot of the vacuum pressure, the rise (response) and fall (recovery) times of the sensor are determined as 6.6 and 15.6 s, respectively. The power consumption of the sensor is 6.5 mu W. The operational parameters of the proposed sensor are found be much better than those of previously reported ZnO nanostructure-based sensors and, indeed, traditional ones. The sensing mechanism of the sensor is explained by the adsorption/desorption of OH(-)ions from the surface of the ZnO nanoparticles, leaving behind oxygen ions combined with oxygen vacancy states

The difference in avifauna between 2006 and 2016 in Duzce Efteni Lake

YÖK Tez No: 579167DÜZCE EFTENİ GÖLÜ AVİFAUNASINDA 2006 VE 2016 YILLARINDAKİ ZAMANSAL FARKLILIKLAR Erdinç SARCAN Düzce Üniversitesi Fen Bilimleri Enstitüsü, Orman Mühendisliği Anabilim Dalı Yüksek Lisans Tezi Danışman: Doç. Dr. Akif KETEN Temmuz 2019, 47 sayfa Kuşlar, ekolojik besin zinciri değişikliklerine cevap veren bir canlı sınıfıdır. Bu nedenle habitatların izlenmesinde gösterge grup olarak değerlendirilmektedir. Bu çalışma Düzce Efteni Gölü'ndeki kuşların 2006-2007 ile 2015-2016 dönemleri arasında kuş türü ve popülasyonlarındaki farklılıkları belirlemek amacı ile yapılmıştır. 2006-2007 yıllarında yapılan çalışmanın benzeri 2015-2016 döneminde gerçekleştirilmiştir. Gözlemler 2015 yılında Mart ayında gerçekleşmiş ve bir yıl boyunca her ay kuş gözlemi yapılmıştır. Kuş türlerinin tespiti ve popülasyonun belirlenmesinde noktada sayım ve hat boyu (transekt) sayım yöntemleri kullanılmıştır. Çalışma sonucunda 16 takıma ait 39 familyadan 113 tür tespit edilmiş ve 14802 birey sayılmıştır. Birey sayısı en fazla olan tür 3536 ile Sakarmeke (Fulica atra L. 1758) dir. %51.3 oranla en fazla familya belirlenen takım Passeriformes takımıdır. En fazla tür içeren familya 12 tür ile Anatidae familyasıdır. 2006-2007 yıları arasında yapılan çalışmada ise 129 türe ait 21250 birey sayılmıştır. İki dönem arasında tür sayısı (t testi = 1.268, p = 0.218) ve türlere ait birey sayıları (t testi = 0.893, p = 0.381) önemli bir farklılık göstermemiştir. İki periyot arasındaki benzerlik %76 olarak belirlenmiştir. Yüksek benzerliğe rağmen tür kompozisyonunda değişimler tespit edilmiştir. Tür kompozisyonlarına göre yapılan kümeleme analizinde iki ana donem (Ekim-Mart ve Nisan-Eylül) tespit edilmiştir. Tür sayısı kış aylarında yaz aylarına göre daha düşüktür. Ancak birey sayısı ise soğuk dönemlerde daha yüksek tespit edilmiştir. Kış göçmeni olan türlerin popülasyon düzeyleri yaz göçmeni türlerine göre daha yüksektir. Efteni Gölü yüzeyinde ve kıyısında yapısal değişikliklerin olmaması yani Efteni Gölü'nün ilk çalışmadaki halini korumuş olması tur çeşitliliğinin önemli değişiklik göstermemesinin temel sebebi olabilir. Sulak alanlar gibi doğal ekosistemler karmaşık ve hassastır, bu nedenle uzun dönemli izleme çalışmalarının yapılmasına ihtiyaç vardır. Kuş popülasyon düzeylerinin eğilimi, biyolojik çeşitliliğin izlenmesi ve korunması yönetim uygulamaları için gereklidir. Anahtar sözcükler: Su kuşu, Sulak alan, Kış göçmeni, Biyoçesitlilik, Sorenson benzerlik indeksi.THE DIFFERENCE IN AVIFAUNA BETWEEN 2006 AND 2016 IN DUZCE EFTENI LAKE Erdinç SARCAN Duzce University Graduate School of Natural and Applied Sciences, Department of Forest Engineering Master's Thesis Supervisor: Assoc. Prof. Dr. Akif KETEN July 2019, 47 pages Birds are a class that significantly respond to ecological changes. Therefore, they are evaluated as a indicator group in the monitoring of habitats. The current study was carried out to determine the differences of bird species and populations between the periods 2006-2007 and 2015-2016 in Duzce - Efteni Lake. Similar to the work done in 2006-2007, it was carried out in the period of 2015-2016. Birds surveys was conducted monthly during from March 2015 to February 2016. Point counts and transect methods were used for determining the bird species and the population. A total of 113 species were identified from 39 families of 16 classes, and 14802 individuals were counted. Eurasian coot (Fulica atra L. 1758) were the most dominant species with 3536 numbers of indivudial. Anatidae is family with the most species. The highest number of families determined by 51.3% is the class of Passeriformes. In the period 2006-2007, A total of 113 species were determined, and 14802 individuals were counted. Bird species richness (t test = 1.268, p = 0.218) and the number of individuals (t test = 0.893, p = 0.381) did not vary among observation periods. Community similarity with Sorenson Index was calculated as 0.76 between the two periods. Despite the high similarity, changes in the species composition were determined. Birds community composition were separated two main groups (October-March and April-September) with cluster analisys. Species richness was lower in the winter than in the summer months. However, the number of individuals was higher in cold periods. The population levels of the winter migratory species are higher than summer migratory species. The lack of structural changes in the Efteni Lake, or its preservation of its original form, may be the main reason for the species not to change. Long-term monitoring is needed in the future. Natural ecosystems such as wetlands are complex and sensitive, so they should be monitored long term. Bird trend is essential for management application in the monitoring and conservation of biological diversity in natural areas

Development of carrot genetic map based on SNP molecular markers

Bu araştırmada, havuç bitkisinin Yeni Nesil Sekanslama ile DNA dizilemesi sonrası SNP moleküler işaretleyicilerinin belirlenmesi amaçlanmıştır. Araştırmada, 2 havuç ıslah hattının melezi sonucu oluşan F1 bitkisinin kendilenmesiyle 94 adet F2 bitkisi kullanılmıştır. Wisconsin Üniversitesi Biyoteknoloji Laboratuvarı'nda Illumina HiSeq 2000 sisteminde GBS yöntemi ile ApeKI enzimi kullanılarak üretilen her bir F2 bitkisine ait DNA parçaları STACKS bilgisayar yazılımı ile analiz edilmiştir. Analiz sonucunda oluşan genotipler Joinmap 4.0 programına aktarılarak Genetik Bağlantı Haritası oluşturulmuştur. 13 adet Bağlantı Grubu (LG) oluşturulmuş, sayıları 54 ve 215 arasında değişen toplam 1 464 adet SNP moleküler işaretleyicisi harita üzerine yerleştirilmiştir. Bağlantı gruplarının toplam uzunluğu 793,4 cM olarak belirlenmiştir. Haritanın bütünü ele alındığında moleküler işaretleyiciler arası maksimum mesafe 9,5 cM, her bir moleküler işaretleyici arasındaki ortalama mesafe 0,54 cM olarak belirlenmiştir. Havuç genomunda GBS yöntemi ile SNP keşfi açısından dünyada yapılan ikinci araştırma bu tez çalışması olmuştur. Yapılan bu harita ile önemli ekonomik karakterlerin belirlenmesi amacıyla yapılacak QTL çalışmalarına katkıda bulunulacaktır.In the present research, we aimed SNP discovery via Next Generation DNA Sequencing Technology. In the study, 94 plants belonging to F2 were used because of the hybridization of the F1 plant, which is a cross-breeding line of the 2 carrot breeding lines. In the Illumina HiSeq 2000 system in the University of Wisconsin Biotechnology Laboratory, DNA fragments of each F2 plant produced by the GBS method using ApeKI enzyme were analyzed by STACKS computer software. The genotypes that result from the analysis were transferred to the Joinmap 4.0 program and Genetic Linkage Map was created. 13 Link Groups (LG) were created and a total of 1 464 SNP molecular markers ranging from 54 to 215 were placed on the map. The total length of the linking groups was determined as 793.4 cM. When the whole of the map is considered, the maximum distance between the molecular markers is 9.5 cM, and the average distance between each molecular marker is 0.54 cM. The second research on the carrot genome in the world for the discovery of SNP by the GBS method has been the work of this thesis. This map will contribute to QTL studies to determine important economic characteristics

A socıologıcal assessment of the problems experıenced by famılıes wıth autısm: the case of Bulancak dıstrıct

Her yıl dünyada ve Türkiye’de hızla artan Otizm Spektrum Bozukluğu (OSB), dünyada her 65 çocuktan bir tanesinde görülmektedir. Otizm Spektrum Bozukluğu, özellikle sosyal etkileşim ve iletişim sorunları ve tekrarlayan davranışlarla ortaya çıkan bir rahatsızlıktır ve ömür boyu devam eden bir yaygın gelişim bozukluğudur. Her anlamda sıkıntı yaşayan OSB’li bireylerin aileleri sıkıntılarını dile getirmekte ve sorunlarını gerekli mercilere ulaştırmakta zorlanmaktadırlar. Bu çalışmayla OSB’li bireylere sahip ailelerin yaşadıkları sorunların sosyolojik temelde incelenmesi, böylelikle sorun yaşayan ailelerin temel ihtiyaç ve isteklerinin ortaya konulması amaçlanmıştır. Araştırmada nitel ve nicel veri toplama araçları kullanılarak karma bir yöntem uygulanmıştır. Nitel araştırmada derinlemesine görüşme tekniği, nicel araştırmada ise Aile Gereksinimlerini Belirleme Aracı (AGBA) ölçeği kullanılmıştır. Araştırmanın evreni Giresun İli Bulancak İlçesinde yaşayan OSB’li bireylerin anne ve babaları oluşturmaktadır. Araştırmada ailelerin sosyo- ekonomik temelde, özellikle de eğitim ve aile içi iletişim konularında ciddi sorunlar yaşadıkları, önemli ölçüde kurumsal ve toplumsal desteğe ihtiyaç duydukları yönünde bulgulara ulaşılmıştır.Autism Spectrum Disorder,which is growing in a fast manner every year in the world and Turkey is seen in one of every 65 children in the world. Autism Spectrum Disorder that occurs especially with social interaction and communication problems and repetitive behaviors ans is a lifelong pervasive developmental disorder. The families of individuals with ASD who have difficulties in every sense have difficulty in expressing their problems to reach the necessary authorities. In this study, it was aimed to examine the problems of families with OSB individuals on a sociological basis and to reveal the basic needs and wishes of families with OSB. In the study, a mixed method was applied using qualitative and quantitative data collection tools. In qualitative research in-depth interview technique has been used, and in quantitative research, family needs scale has been used. The population of the study consist of parents of individuals with ASD living in Bulancak district of Giresun province. In this study, it was found that families have serious problems on socio-economic basis, especially education and family communication, and they need significant institutional and social support