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Biyolojik uygulamalar için, kırınım ızgaraları kullanılan mikro-gravimetrik bir ölçüm metodu geliştirilmesi
A micromechanical system is developed utilizing a diffraction grating for high-precision displacement measurements. The device is in the form of released cantilevers and bridges made of Ni suspended over a Si surface.. Hence, an operational diffraction grating is obtained. The structures are actuated in their resonant mode through magnetic means. A photodetector setup is built to track changes in the resonance behavior. The quality of the setup is evaluated using a well-calibrated sputtering system and applicability of the device to biosensing is demonstrated with human opioid receptors.
Suda asılı kalan kuantum noktacıkların ve hibrid nano parçacıkların geliştirilmesi
Nanoparticles are one of the major areas of nanotechnology where size confinement provided a dramatic differentiation in material properties enabling numerous applications for many disciplines. Among these superparamagnetic iron oxides and semiconductor quantum dots are possibly the most widely studied nanoparticles due to their great potential in broad application areas, most significantly in health, defense and energy. The target area for the nanoparticles described in this thesis is the biotechnology and medicine.The premise of this thesis is to synthesize aqueous magnetic luminescent hybrid nanoparticles. To achieve such a goal, highly luminescent, water soluble and biocompatible colloidal CdS and CdTe QDs were synthesized first. Then, as prepared colloidal QD solution was used to coat and stabilize magnetic iron oxide nanoparticles in a unique, safe and economical one-pot reaction. The approach involves utilization of biocompatible multifunctional coating molecule, primarily L-cysteine, which can stabilize both nanoparticles and keep them in water simultaneously. The cell uptake and cell viability studies confirmed suitability for bio applications.Development of such a multi-functional single entity will provide dual sensing modes (optical and magnetic detection) as well as combined sensing and separation capabilities.
Silikon-üre kopolimer ve kompozitlerinin sentez ve karakterizasyonu
Novel, segmented thermoplastic silicone-urea (TPSU) copolymers based on fairly high molecular weight aminopropyl terminated polydimethylsiloxane (PDMS) soft segments ( 10,800 and 31,500 g/mole), a cycloaliphatic diisocyanate (HMDI) and various low molecular weight diamine chain extenders were prepared and characterized. One of our goals in this study was to understand the influence of PDMS soft segment length on the tensile properties and hysteresis behavior TPSU copolymers. Copolymers with very low urea hard segment contents of 1.24 to 5.14% by weight were prepared. Although the copolymers had fairly low hard segment contents, they all formed films, showed very good microphase separation and displayed reasonably good mechanical properties. When silicone urea copolymers with identical urea hard segment contents were compared, those based on PDMS-31,500 showed higher tensile strengths than those of PDMS-10,800. In addition, PDMS-31,500 based silicone-urea copolymers also displayed lower hysteresis values when compared with PDMS-10,800 based TPSU or even with chemically crosslinked silicone rubbers. Critical entanglement molecular weight (Me) of PDMS is about 25,000 g/mol. We believe chain entanglement in PDMS-31,500 have a synergistic effect on the tensile properties and hysteresis behavior of the silicone-urea copolymers. Second goal of our research effort was to understand the effect of fumed silica fillers on the properties of silicone-urea copolymers. Hydrophobic silica filled silicone-urea copolymers, containing up to 37.5% by weight of silica were prepared for the first time. Incorporation of hydrophobic silica into silicone-urea copolymers based on PDMS-31,500 dramatically increased the modulus, tensile strength and elongation at break values of these copolymers. Silica incorporation had a slight negative effect on the hysteresis behavior. Presence of interaction between silica and the TPSU copolymers were also investigated by FTIR spectra.
Çevrelenmiş geometrilerde tek moleküllerin izlenmesi
Single molecule experiments were performed utilizing total internal reflection fluorescence microscopy technique at room temperature for understanding diffusion dynamics of single molecules in confined geometries of diblock copolymer thin films. The characteristic behavior of single molecules such as blinking and photobleaching were first shown indicating the observation of real dyes rather than some scattering. Then, ~1.5 nm resolution of our experimental setup in positioning fluorescent dyes was shown which allowed us to study the dynamics of single molecules inside the obtained confined geometries (channel diameters ~12-30 nm) and to analyze the surface morphology of different block copolymer thin films. For this purpose, terrylene and rhodamine B dye molecules were used and embedded in PS, PMMA and three different molecular weight PB-PEO diblock copolymers. Rhodamine B and terrylene dye molecules were incorporated with PMMA and PS polymers for understanding and observation of characteristic behavior of single molecules, respectively. They were also utilized for the determination of resolution of our experimental setup in positioning single dye molecules. The usage of terrylene molecules in PB-PEO diblock copolymer samples was for studying the confined diffusion of single molecules.After spun-casting the thin films which were prepared by using PB-PEO diblock copolymer solutions including terrylene molecules, they were annealed to obtain better intended morphology. By this way, cylindrical channels of PB inside PEO crystalline matrix and 2-dimensional layer of PB at air film interface on top of PEO layer were obtained for providing 1- and 2-dimensional diffusion of terrylene dyes. After that, the trajectories of diffusion single molecules were obtained and analyzed. In this manner, the motion of terrylene probe molecules in confined PB channels having different channel diameter of two asymmetric PB-PEO diblock copolymers and the normal diffusion of terrylene dyes in 2-dimensional PB layer of symmetric PB-PEO diblock copolymer were investigated.The distribution of 1-dimensional diffusion coefficients were found to have narrower distribution compared to 2-dimensional diffusion coefficients in PB. In addition to normal diffusion of terrylene dyes, directed motion of them was also observed through the trajectories of some single molecules and their analysis where mean square displacement had parabolic time dependence. The origin of this behavior was explained by the presence of some defects in channel formations, i.e. change in local density inside the channel due to local variations in the PB channel width. Furthermore, effects of non-uniformities and heterogeneities in channels on motion of single molecule were studied demonstrating the sensitivity of single molecule tracking in characterizing self-assembled block copolymer morphologies where the trajectories of single molecules were well correlated with AFM and SEM results.
Genişletilmiş darbeli yükselticiler için femtosaniye Cr:ZnSe laserinin geliştirilmesi
In this thesis work, we describe the three main components of a chirped pulse amplifier (CPA). It is a technique in which nano-joule pulse energies of femtosecond lasers are amplified to micro-joule or milli-joule levels. In particular, the seed laser was experimentally constructed and the numerical design of the stretcher and compressor was completed. The seed laser is a continuous-wave, Kerr-lens mode-locked femtosecond Cr2+:ZnSe laser pumped by a 1800-nm thulium fiber laser. The astigmatically compensated, asymmetric x-cavity contained a 2.4-mm-long Cr2+:ZnSe sample with a pump absorption coefficient of 11.6 cm-1, and it was terminated with a 1% output coupler. Dispersion compensation was achieved by using a MgF2 prism pair. During Kerr-lens mode-locked operation, the laser generated 95-fs pulses at a pulse repetition rate of 94.3 MHz and with 40 mW of output power. The center wavelength of the pulses was 2.42 ?m. The pulses had a spectral width of 69 nm and a time-bandwidth product of 0.335, which is close to the transform limit for hyperbolic secant shaped pulses. In addition, by using the soliton area theorem, the nonlinear refractive index was estimated as 1.4x10-14 cm2/W for Cr2+:ZnSe. The calculated value agrees well with what has been reported in the literature and it is almost 100 times larger than the nonlinear refractive index of sapphire. In the case of the stretcher and compressor design, based on our numerical calculations, the stretcher allows us to stretch 100fs pulses to 100ps by using a diffraction grating pair with a groove density of 300 grooves/mm and separation of 76 cm.
Alev hidrolizi yöntemiyle sentezlenmiş, nano boyuttaki TiO2/SiO2 kompozitlerinin termal ve hidrotermal kararlılıkları
The phase stability of the flame hydrolytic synthesized TiO2/SiO2 nano-sized composites has been investigated under thermal and hydrothermal conditions. The pure titania (P25 Evonik Degussa) annealed under hydrothermal conditions (100 g/m3 absolute humidity, 600 oC) was found to have 85 % rutile fraction which was only 46 % when annealed at 600 oC without the introduction of humidity. The difference was attributed to the formation of oxygen vacancies under hydrothermal conditions possibly increasing the rate of transformation from anatase to rutile TiO2. Even the smallest amount of SiO2 doping was observed to retard the phase transformation and maintain the specific surface area after both thermal and hydrothermal treatments. The highest complete phase transformation temperature (1200 oC) and the maximum BET surface area at 1000 oC (57 m2/g) under H2O atmosphere, were both detected for 24.84 % silica content among TiO2/SiO2 composite series. The results obtained from different characterization methods; X-ray powder diffraction, Raman spectroscopy and BET surface area analysis are in good agreement with each other and support the discussed effects of H2O atmosphere and SiO2 doping.