Master Degree / Yüksek Lisans Tezleri

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  • Master Thesis
    Colloidal Plexcitonic Nanocrystals
    (Izmir Institute of Technology, 2022) Sarısözen, Sema; Yalçın, Şerife Hanım
    Noble metal nanocrystals, especially gold and silver, which have attracted a great deal of attention due to the supporting of surface plasmon polaritons (SPPs), have been extensively investigated and studied. With recent developments in colloid chemistry, synthesis of noble metal nanocrystals with tunable optical properties in the visible region of the electromagnetic spectrum has become easier. Until now, noble metal nanocrystals (NPs) synthesized by using various synthetic methods, have a variety of shapes, such as bipyramid, rod, disk, prism, and ring, etc. In the strong coupling regime, SPPs supported by metal nanocrystals interact strongly with excitons of organic dyes, semiconducting quantum dots (carbon or perovskite quantum dots) to generate a new hybrid optical mode called plexciton (plasmon-exciton). Plexcitonic nanocrystals have received interest owing to their ease of synthesis, scalability, and ability to provide sub-wavelength confinement of incident light and offer promising applications. Plasmon–exciton interaction at nanoscale dimension can be improved by generating new plexcitonic nanoparticles with tunable optical properties, which may be utilized in critical applications such as nanolasers, sensors, nano-optics, solar cells, and light emitting diodes. Therefore, there has been a tremendous amount of interest in the synthesis of new plexcitonic nanocrystals having excellent optical and chemical properties. The main goal of this thesis is to synthesize new plexcitonic nanoparticles with tunable optical properties in the visible spectrum: (i) synthesis of different shaped colloidal monometallic and bimetallic nanocrystals, (ii) synthesis of new colloidal plexcitonic nanocrystals, (iii) synthesis of carbon quantum dots (CDs), (iv) coupling of excitons of CDs and SPPs on the silver thin film.
  • Master Thesis
    Experimental and Theoretical Investigation of Functionalized Perovskites
    (Izmir Institute of Technology, 2020) Özen, Sercan; Şahin, Hasan; Balcı, Sinan
    The last decade witnessed the rapid increase in the interest of the cesium lead halide perovskites (Cs-LHPs) and their successful applications in optoelectronic devices and photovoltaics. Increasing interest in perovskites arises from their extraordinary features such as having a tunable bandgap, variety in the crystal structure and phases, high photoluminescence quantum yield, ease of synthesis, and wide range absorption spectrum. Desiring to go beyond the emerging findings, subsequent studies have focused on the functionalization of perovskite nanocrystals (PNCs) by dimensional modifications and doping. This thesis study focuses on the modification of characteristics of Cs-LHPs by doping scenarios and dimensional reduction. Firstly, we reveal the modifications originated from the intercalation of Cr+3 and Gd+3 dopants into the Cs-LHP crystal structures. Cr+3 doping process is performed by using room temperature anti-solvent crystallization method. It is observed that the doping process leads to the emergence of distinctive signals in the PL spectrum. We clarify the origin of each additional PL peaks by experimental measurements and theoretical calculations. Additionally, white light emission is also achieved by the Cr3+ doping process. On the other hand, by using the hot-injection method, we synthesized neat and Gd+3 doped ?-CsPbI3 NCs. The stability of ?-CsPbI3 NCs is increased by the intercalation of Gd3+ ions into the host lattice. Also, enhancement of PLQY and lifetime is achieved by Gd3+ doping. Besides, to understand the dopant-induced modifications in the electronic and optical characteristics of perovskites, we also performed ab-initio density functional theory (DFT) calculations. In addition, we study how the characteristic properties of Cs-LHPs are modified upon dimensional reduction. By introducing the electrospraying method we reduced the synthesis and coating processes into a single step. Two-dimensional perovskite nanoplatelets were synthesized by electrospraying. We tuned the emission wavelengths of nanoplatelets in the range of 100 nm by thickness modifications. Lastly, by using DFT, we investigated the effect of thickness-dependent modifications on the structural, electronic, and vibrational properties of the orthorhombic CsPbI3 structure. Phonon calculations show that two ultra-thin forms of bulk CsPbI3 are dynamically stable. Also, the increase in the bandgap energy of the CsPbI3 structure by a decrease in thickness is revealed by electronic band dispersion calculations.
  • Master Thesis
    Production and Characterization of Water Soluble Cdsete Based Core/Shell Nanocrystals and Their Applications in Bioimaging
    (İzmir Institute of Technology, 2009) Özdemir, Seda; Özçelik, Serdar
    In recent years, nanotechnology has become one of the most intensively studied fields. At the nanometer scale, materials have unique electrical, optical, magnetic and chemical properties. They can be used for a wide variety of applications such as electrooptical devices, tagging and medical applications. The goal of this study was to produce water-dispersible alloyed CdSexTe1-x semiconductor nanocrystals, which are suitable to interact with biomolecules. CdSexTe1-x nanocrystals were synthesized by a single step aqueous synthesis method. Monodisperse, CdSexTe1-x nanocrystals with zinc blende structure were obtained in water. Synthesized nanocrystals emit in the range from 528 nm to 620 nm. CdSexTe1-x nanocrystals have 17% photoluminescence quantum yield, after the CdS shell coating the photoluminescence quantum yield increased up to 22%. MTT test and Trypan Blue tests were used to evaluate the toxicity of CdSexTe1-x nanocrystals. MTT measurements reveal that the MCF7 cancer cells are not affected by the nanocrystals at any dosage and exposure condition, but lethal effects are determined at the concentration of 1.0ug/ml for the PC3 cells. The BEAS 2B cells are very sensitive to the nanocrystals and do not proliferate at concentration of 0.5ug/ml. Confocal microscopy studies show that the nanocrystals has ability to penetrate to the cytoplasm of cells.
  • Master Thesis
    The Preparation Characterization and Sintering of Nanocrystalline Ceramics
    (01. Izmir Institute of Technology, 1999) Çağlar, Özlem; Çiftçioğlu, Muhsin
    Nanocrystalline Titania was prepared by a chemical synthesis technique commonly known as sol-gel method. In the sol gel method, Titanium (IV) Isopropoxide was mixed with Isopropanol and Nitric Acid solution in predetermined ratios. A rapid hydrolysis reaction occurs between Titanium (IV) Isopropoxide and water in the Nitric Acid solution resulting in the formation of Titan oxide (Titania). The sols were clear sols and then gelled without any change in its clarity.Nanocrystalline Titania were tried to prepare by two different techniques in this work. The first technique involved the drying of the gel and subsequent sintering of the dried gel. A number of organic additives (oxalic acid, acetic acid, polyacrylic acid and stearic acid) were mixed into the sol before gelation in order to control drying (drying control chemical addives-DCCAs). Powders was prepared from sols and gels by several processes and a solid form was obtained by dry pressing and subsequently sintered in second technique. Oxalic acid was the most efficient DCCA among the others.The dried gels and powder compacts were sintered at 650, 700, 750, 800, and 850C. The sintering behaviors of them were examined. Relative densities of the dried gels were between 79-99% depending on the sintering temperature. The green body density of the pellets were varied between 41-52%. Their relative densities after sintering were varied between 55-83% depending on the sintering temperature. The pellets were pressed at different pressures to observe the pressure effect on the densification. Increase in pressure improve the densification behavior. The best route for the nanocrystalline powder preparation was the Route 4. This powder had smaller size of agglomerate most probably the agglomerates were broken during the ultrasonic radiation.The pore size analyses showed the pore structure of the gel. The pore size of the gels are about 35 nm. FTIR Spectra gave the crystal structure of the sols gels and powders. As a result, the sintering behavior of the dried gels is better than the powder compacts. The pellets can be densified to higher densities by appropriate forming technique. Although, the dried gels have significantly high densities, the shape and the weight of the gels can not be controlled.
  • Master Thesis
    Processing and Characterization of Nanocrystalline Materials
    (Izmir Institute of Technology, 2004) Genç, Gözde; Çiftçioğlu, Muhsin
    Nanocrystalline materials with grain sizes under 100 nm have been counted as a very promising class of ceramic materials. The decrease in grain size imparts superior structural properties to the ceramic materials like increased fracture toughness, wear resistance and superplastic deformation at high temperatures. So, nanocrystalline ceramics can be used as structural materials in a wide range of uses covering advanced engineering applications such as aircraft and automotive technologies as well as electronics, computation and material sciences. Nanocrystalline alumina has been a popular research subject for the last decade because of the superior structural properties of alumina besides lower cost compared to other nanocrystalline materials like zirconia and titania. The raw materials are generally transitional aluminas or aluminum hydroxides such as boehmite and gibbsite all of which are widely used in industry.The main problem in nanocrystalline alumina production is to cope with agglomeration of fine powders or nano-particles in solutions due to interaction forces. Agglomeration cause nonhomogeneous microstructure with respectively larger pores which are very hard to eliminate during sintering. In this study a nanocrystalline commercial boehmite powder is used as the starting material and a homogeneous microstructure with respectively high density is aimed. Ultrasonic treatment is applied in order to reduce particle size and the stable dispersions of boehmite powder with a solid content of 30wt% was dried by spray drying. The effect of ultrasonic treatment, spray drying and compaction conditions were investigated and compared with bodies compacted from untreated powders. To see the effect of seeding on phase transformation behavior of boehmite, alpha alumina particles produced by combustion synthesis and broken into crystallites by ultrasonic treatment were used with a seed content less than 0.5%. Even that low amount of a-alumina reduced the transformation temperature by 100C but did not improve densification of alumina compacts. The homogeneity of microstructure obtained by ultrasonic treatment and granulation by spray drying yielded the highest relative densities of 65.5 % of the theoretical density. The treatment has also led more uniform microstructures compared to untreated and seeded samples during the a-phase transition which is the most important stage for densification.