Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
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Doctoral Thesis Investigation of Organic Field Effect Transistors With Interdigitated Ito Source and Drain Electrodes Patterned by Laser Cut Pvc Tapes(01. Izmir Institute of Technology, 2024) Bozkurt, Hakan; Varlıklı, Canan; Özçelik, SerdarBu tezde başlangıçta ışık yayan dikey bir transistör üretmeyi amaçlamıştık. Ancak, başarısız denemeler sonucunda, test amaçlı yatay bir transistör üretme kararı alınmış ve bu transistörün optimizasyonu üzerinde çalışılmıştır. Daha sonra dikey transistör üretimi, yatay optimizasyonlar ve lazer kesim teknikleri bir araya getirilerek araştırmanın ana odağı değiştirilmiştir. Islak aşındırma süreci ile elektrot desenlemek için düşük maliyetli bir üretim yöntemi olarak lazer kesim denenmiştir. İç içe geçmiş (taraklı) ITO kaynak ve drenaj elektrotları hazırlanmış, ardından organik yarıiletken olarak P3HT ve dielektrik malzeme olarak PMMA sırasıyla dönü kaplama yöntemiyle kaplanmıştır. Üst elektrot olarak da alüminyum (Al), fiziksel buhar biriktirme tekniği kullanılarak kaplanmıştır. Nihai cihaz yapısı olarak ITO(KveA)/P3HT(Organik Yarıiletken)/PMMA(Dielektrik Malzeme) /Al(Kapı) şeklinde geleneksel bir OFET mimarisi oluşturulmuştur. Üretim süreci, katman kaplama parametreleri ve lazer kesim konfigürasyonları göz önünde bulundurularak en iyileştirilmiştir. Elektriksel ölçümler, soy atmosfer koşullarında bir eldivenli kutu sistemi içinde gerçekleştirilmiştir. Üretilen OFET'ler hem tükenme hem de geliştirme modlarında çalışabilmiştir. Yapılan en iyileştirmeler sonucunda yük taşıyıcı hareketliliği artırılmış, eşik gerilimi düşürülmüş ve sıfır kapı geriliminde akım seviyeleri azaltılmıştır. P-tipi tükenme modu OFET'ler, hem ticari uygulamalarda hem de akademik literatürde nadir görülür. Bu tür transistörlerin ekran uygulamaları için umut vadeden bir aday olabileceği düşünülmektedir.Doctoral Thesis Development of Colloidal Alloyed Nanocrystals for Quantum Dot Based Device Applications(Izmir Institute of Technology, 2018) Sevim Ünlütürk, Seçil; Özçelik, Serdar; Varlıklı, CananQuantum dots (QDs) are very attractive luminescent semiconducting nanoparticles. In this study, our aim was to synthesize Cd and/or Zn based QDs with tunable optical properties by the particle size and the alloy composition. Colloidal water dispersible Mn-doped and nondoped ZnSxSe1-x QDs were synthesized by the one-pot aqueous method. Optical measurements indicate that photoluminescent properties are strongly depended on the capping agent. While MPA capped QDs showed an emission peak in the blue region, others did not show any photoluminescence at all. Mn doping up to 10% resulted in no significant effect on the optical spectra. However structural characterizations, EPR and XRD, supported that Mn ions were bounded to the 220 and 311 facets of QD. ZnxCd1-xSySe1-y quaternary nanoalloys were synthesized by using a modified two-phase approach for the first time in the literature. Optical properties of highly luminescent ZnxCd1-xSySe1-y nanoalloys were tuned from blue to yellow by the particle size, the alloy composition, and thickness of shell layer. The reactivity of the reactants, initial mole ratios, and other reaction parameters was adjusted to control alloy composition and alloy type: homogeneous and gradient. The reaction time controls the size of particles. The PL QE (up to 52%) and lifetimes (about 25 ns) were found similar regardless of core and core-shell nanoalloys. MicroPL measurements were carried out on ZnxCd1-xSySe1-y nanoalloys by fiber spectrometer integrated to confocal microscope. Photobleaching and blue-shifting, about 6 nm, were observed in the microPL spectra. Photobleaching times and rate constants obtained from single exponential decay curves showed that purification and exposure time are strongly effective. Additionally, the power the excitation light is essential that below 11 μW, photobleaching slows down, and at 2 μW there is no photobleaching. Scale-up methods with high-volume batch and flow reactor were used to synthesize CdTe and ZnxCd1-xSySe1-y QDs. LEFETs were fabricated with TUBITAK support in collaboration with Heidelberg University. PbS QDs were used as emitting material at the bottom contact top-gate unipolar LEFETs in which uniform electroluminescence was obtained.Doctoral Thesis Developing Graphene-Organic Hybrid Electrodes for Silicon Based Schottky Devices(Izmir Institute of Technology, 2018) Aydın, Hasan; Çelebi, Cem; Varlıklı, CananThis thesis focused on developing graphene-organic hybrid electrodes for silicon based Schottky devices. Two different sets of carboxylic acid based SAMs were used to improve the rectification character of the Schottky junction formed at graphene/Si interface. While the first set of SAMs consists of MePIFA and DPIFA, the second set of SAMs contains TPA and CAR. In addition to this, P3HT, which is known to be an electron donor and absorb light in the visible spectrum, was utilized to form P3HT-graphene bilayer electrode. Current-voltage characteristics of bare and SAMs modified devices showed rectification behavior confirming a Schottky junction formation at the graphene/Si interface. The DPIFA SAMs device exhibited better diode performance compare to MePIFA SAMs due to the absence of methyl group which hinders π-π interaction between SAMs molecule and graphene. Furthermore, the CAR-based device indicates better diode characteristic with respect to the TPA-based device due to smaller energy differences between graphene and CAR. The effect of P3HT-graphene bilayer electrode on the photoresponsivity characteristics of Silicon based Schottky photodetectors have been also investigated. Current-voltage measurements of graphene/Si and P3HT-graphene/Si revealed rectification behavior confirming Schottky junction formation at the graphene/Si interface. Time-resolved photocurrent measurements exhibited excellent durability and fast response speed. Moreover, the maximum photoresponsivity of P3HT-graphene/Si photodetector increased compared to that of bare graphene/Si photodetector. The observed increment in the photoresponsivity of P3HT-graphene/Si devices was attributed to the charge transfer doping from P3HT to graphene within the spectral range between near-ultraviolet and near-infrared. Finally, P3HT-graphene electrode was found to improve the specific detectivity and noise equivalent power of graphene/Si photodetectors.Doctoral Thesis Structural and Electronic Properties of Organic Layers on Au(111)(Izmir Institute of Technology, 2018) Kap, Özlem; Varlıklı, Canan; Çelebi, CemSelf-assembled monolayers (SAMs) have attracted attention due to their chemical and structural properties providing numerous new applications such as molecular electronics and electrochemistry. SAMs were optimized by experimental techniques including Scanning Tunneling Microscope (STM), Scanning Tunnelling Spectroscopy (STS), X-Ray Photoelectron Spectroscopy (XPS), Polarization-Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRRAS), Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS). The first part of this dissertation deals with the dynamic behaviour of decanethiol SAMs. The dynamic behaviour alkanethiols SAM is unique for its configuration giving indirect evidence for the structural ordering within the formation. Structural stability of decanethiol (decanesulfonates) SAMs were investigated by space- and time- resolved STM. Decanesulfonate phase shows less dynamic behaviour and is structurally more stable compared to the decanethiol phases. The second part of this dissertation describes the binding properties of alkyne molecules adsorbed on gold. Alkyne oxidation occurs at ambient conditions but it is found that unlike thiols, ordered alkyne SAM structure has still chemical bonding between carbon and gold. Alkyne SAMs are good candidates for the ambient molecular electronics application. The last part of this dissertation presents the study of a monolayer of a Ru(II) complex which is prepared on gold substrate. With the help of STM and XPS methods, the ordered structure and binding properties of the CS28 molecules were characterized by providing a deeper insight into the carboxyl and sulfur groups binding affinity to gold substrate. CV and EIS methods were used to compare the adsorption properties and charge transfer process with the bare gold substrate and SAMs.