Nanoteknoloji ve Nanotıp BölümüNanoteknoloji ve Nanotıp Bölümühttps://hdl.handle.net/11655/5902024-03-29T08:33:44Z2024-03-29T08:33:44ZKatkılanmış Grafen Temelli Nanomalzemelerin Nöral Kayıt ve Uyarım Yeteneğinin AraştırılmasıDoğan, Muhammed Zahidhttps://hdl.handle.net/11655/335252023-07-05T11:13:28Z2022-12-01T00:00:00ZKatkılanmış Grafen Temelli Nanomalzemelerin Nöral Kayıt ve Uyarım Yeteneğinin Araştırılması
Doğan, Muhammed Zahid
Neural electrodes serve as the interface material for interaction of electrical circuits
with neural cells in neural stimulation and recording applications. In this study, it was
aimed to investigate the effect of doping of graphene-based materials (GBM) on the
recording and excitation performance of electrochemically interacted composite neural
electrodes. For this purpose, we have utilized oxidation-reduction and electrochemical
exfoliation methods to synthesize graphene oxide; pristine, nitrogen-doped and
phosphorus-doped reduced graphene oxide and electrochemically exfoliated
graphene materials. Samples of interest have characterized by their doping level,
oxygen ratio, particle size, number of layers, defect density and exfoliation
homogeneity with the help of energy dispersive X-ray analysis (EDX), scanning
electron microscopy (SEM), scanning transmission electron microscopy (STEM), Xray diffraction analysis (XRD), Fourier-transform infrared spectroscopy (FT-IR) and
Raman spectroscopy analysis. Measurements of the electrochemical properties was
carried out with composite electrodes prepared with Polyvinylidene fluoride (PVDF)
insulating polymer and GBM. Electrochemical analyzes of samples were interpreted
with their physical-chemical characteristics and it was observed that the heteroatom
doping in the C/O ratios of the GBM samples synthesized within the scope of the thesis
did not exhibit a significant difference in the electrochemical measurements but the
edge functionalization density formed by the oxygenated groups was effective on the
electrochemical properties.
2022-12-01T00:00:00ZDonepezil Yüklü Nanopartiküler İlaç Taşıyıcı Sistemlerin Hazırlanması ve In Vitro DeğerlendirilmesiŞahan, Sevdahttps://hdl.handle.net/11655/271712022-12-05T13:09:24Z2018-01-01T00:00:00ZDonepezil Yüklü Nanopartiküler İlaç Taşıyıcı Sistemlerin Hazırlanması ve In Vitro Değerlendirilmesi
Şahan, Sevda
There are about 46 million dementia worldwide today. The cause of disease is
unknown and there is currently no treatment to stop or slow the degenerative
process.1
However, there are some symptomatic treatment approaches to
partially improve the cognitive functions of Alzheimer’ s Disease, to control
emotional and psycologycal changes, and to improve the quality of life of patients
with clinical practice. 2 Donepezil is a reversible cholinesterase inhibitor used in the
treatment of Alzheimer’ s Disease. The cholinergic system plays an important role
in learning, memory, and severe memory impairment due to cholinergic
dysfunctions in Alzheimer’ s Disease.
3 New strategies are needed, such as
osmotically opening the blood brain barrier or devoloping drug delivery systems, in
order for drug molecule to bypass the blood brain barrier because of the
inadequacy of traditional transport mechanisms. Interventional techniques that
bypass blood brain barrier include the use of drug carrying nanoparticle systems
and intranasal pathway.1 Polymeric nanoparticles protect nanoparticles in vitro and
in vivo degradation, release drugs in a controlled manner, and offer the possibility
of drug targeting.4
In this study, PLGA nanoparticles loaded with Donepezil agent were prepared by
solvent evaporation technique. Several techniques have been tried for preparation
of nanoparticles and the activity of these techniques in preparing nanoparticles
has been observed. Parameters affecting the particle size were investigated and
reported in the optimal technique for preparing Donepezil active substance loaded
PLGA nanoparticles. For the characterization of the prepared nanoparticles,
HPLC, FTIR, particle size measurements were performed, particle preparation
efficiency, encapsulation efficiency and loading rates were calculated.
Furthermore, the analytical method has been developed and its validity proved to
be able to determine the Donepezil drug substance by the HPLC method.
2018-01-01T00:00:00ZHıgh Performance Mıoc (Multıfunctıonal Integrated Optıcal Chıp) Desıgn Fabrıcatıon And Characterızatıon For Fıber Optıc Gyroscope ApplıcatıonsAşık, Fatma Yaseminhttps://hdl.handle.net/11655/269572022-10-26T07:57:23Z2022-01-01T00:00:00ZHıgh Performance Mıoc (Multıfunctıonal Integrated Optıcal Chıp) Desıgn Fabrıcatıon And Characterızatıon For Fıber Optıc Gyroscope Applıcatıons
Aşık, Fatma Yasemin
Laser-based fiber optic gyrometers (FOG) used in navigation systems have been developed for various applications since the 1970s. In this thesis, the working principle of FOG and the sub-components of the system are mentioned. The design, production and optimization studies of the waveguide-based multifunctional integrated optical device (MIOC), which is described as the heart of FOG, are included. The annealed proton exchange (APE) method has been developed for MIOC to show high performance in the system. First of all, straight waveguide fabrication was performed with the APE method, and the width of the waveguide to be integrated to the optical fiber was optimized. With the findings obtained, it was determined that the index change values required for connecting the 7µm wide waveguide to the optical fiber with the least loss (about 60% throughput) were in the range of 0.025-0.030. On the other hand, the importance of temperature and time factors in waveguide formation was investigated. Studies have been carried out that will allow the variations occurring in the first stage of the two-stage APE method to be compensated with the interventions made during the second stage. As a result of the efforts to optimize the design that will allow the MIOC device to split the light into two, it was concluded that a y-coupler design with a bending radius bigger than 4 cm could be selected, but considering the device size, packaging and other factors, the device design for the bending radius larger than 13 cm was decided. In order to carry out the APE process in hot acid safely and in multiples, a custom mechanism was designed and the fabrication was carried to mass production. Preliminary interventions were made during fabrication to eliminate the thermal instabilities that may occur between the MIOC and the optical fiber carrier, which has a different expansion coefficient than MIOC. During the temperature tests carried out in the temperature range of -40 °C – (+85) °C, it was measured that the optical power of the devices changed less than 0.5% and it was observed that the devices were stable against environmental factors. System level tests of fabricated MIOC devices were carried out, and PER values were measured at 49 dB. As a result, MIOC fabrication has been realized with the performance that will allow the external polarizer to be removed from the system. With the removal of the external polarizer from the system, space was saved in the whole FOG system, and with the design and optimization studies carried out during this thesis, the critical technological device supplied from abroad was developed with national resources.
2022-01-01T00:00:00ZGan Tabanlı Güç Aygıtları İçin Pasivasyon Tabakası GeliştirilmesiÇelik, Gülşahhttps://hdl.handle.net/11655/269282022-10-31T12:04:06Z2022-01-01T00:00:00ZGan Tabanlı Güç Aygıtları İçin Pasivasyon Tabakası Geliştirilmesi
Çelik, Gülşah
In this study, various passivation layers are developed and characterized for gallium nitride
(GaN) transistors used in power electronics applications. Dielectric properties of the
passivation material on high breakdown voltage devices directly affect both the breakdown
voltage and efficiency. That’s why, the high voltage strength of the passivation material used
has a crucial importance besides the device structure. Silicon nitride and silicon oxide
passivation layers were grown with different deposition conditions by plasma enhanced
chemical vapor deposition (PECVD) technique. After forming metal-insulator-metal
structure with the deposited dielectric thin films, refractive index, dielectric constant, and
breakdown voltages were determined, by using ellipsometry, capacitance-voltage and
current-voltage measurements, respectively. Thus, the effect of plasma parameters on the
optical and electrical properties of the dielectric materials was investigated. The best
dielectric strength materials achieved were applied on GaN transistors as passivation layers.
And the effect of the passivation layer on the electrical performance of the device was
investigated.
2022-01-01T00:00:00Z