FBE- Nano Bilim ve Nano Mühendislik
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Nano Bilim ve Nano Mühendislik Ana Bilim Dalı altında bir lisansüstü programı olup, yüksek lisans ve doktora düzeyinde eğitim vermektedir.
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Sustainable Development Goal "none" ile FBE- Nano Bilim ve Nano Mühendislik'a göz atma
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ÖgeDevelopment and characterisation of functional nanofibers for face mask applications(Fen Bilimleri Enstitüsü, 2020) Baysal, Tuğba ; Demir, Ali ; 633557 ; Nano Bilim ve Nano MühendislikNowadays, air pollution is a major problem all around the world and human life is seriously and negatively affected by air pollution. It causes serious health problems including cancer. Air pollutants can be classified into three groups as ultra-fine particulates, toxic gases and biological pollutants involving viruses and bacteria. Very recent COVID-19 pandemic has clearly showed all humanity how a minute virus-based air pollution could be a human disaster. In this study, the filtration application of nanofibrous mats to be functionalized with MgO or ZnO nanoparticles have been investigated. Firstly, effect of MgO NP concentration and thickness of nanofiber layer on particulate filtration have been investigated. 25% MgO/PAN filter produced with 60-min electrospinning time have showed high filtration efficiency of 97,6% and low pressure drop of 215 Pa, which meet the face mask standard of EN149+A1. It has been shown that as the nanoparticle concentration in the polymer solution increases; the surface of the nanofiber filter becomes rough, the nanofiber diameters increase, and the particle filtration performance of the filter increases. The increase in filtration efficiency of the filter is related to the adsorption ability of MgO NPs and the decrease in pressure drop value is related to the increased pore size among nanofibers. Secondly, adsorption studies with toluene gas, one of the toxic volatile organic compounds, have been carried out using MgO/PAN NF with various MgO NP concentrations, various nanofiber layer thicknesses and two different adsorption times. Physical adsorption takes places between toluene gase and MgO NP by the means of hydroxyl and oxide groups on the surface of the nanoparticle. We have achieved a high amount of toluene adsorption of 53.31%. Antibacterial efficacy of ZnO/PAN filter have been evaluated by using two types of bacteria, gram positive S. aureus and gramnegative E. coli. The antibacterial activity of ZnO NPs was found to be higher against E. coli than S. aureus due to differences in the cell membrane of two different bacteria type.
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ÖgeInvestigation of electronic properties of twisted graphene layers on HOPG surface by scanning tunneling microscopy(Institute of Science and Technology, 2020-07-21) Tömekçe, Birce Sena ; Gürlü, Oğuzhan ; 513171004 ; Nanoscience and Nanoengineering ; Nanobilim ve NanomühendislikInvention of scanning probe microscopy has enabled real space imaging, detection and investigation of surfaces at the atomic scale for the first time throughout the history, starting the era of nanotechnology. Scanning tunneling microscopy (STM) can be considered as the first scanning probe microscopy technique which brought his inventors a Nobel prize in physics. In addition to characterizing surfaces at the atomic scale, local electronic properties of the surfaces can be explored by STM and scanning tunneling spectroscopy (STS), a technique which is performed by scanning tunneling microscope. Throughout this study, these techniques have been used as main research tools. Graphene is a novel, one-atom thick material composed of carbon atoms. It is the first discovered two-dimensional material, having extraordinary properties. Layer by layer stacked, disordered form of graphene is called graphite, a well-known and simple material that is used in pencils. Graphene layers can easily be removed and displaced on its original substrate graphite, since they are held together by weak van der Waals Interactions. As a result of relative rotation of two graphene layers, moiré superlattices are formed. In fact, moiré pattern is a general name given to the interference pattern with a larger periodicity, generated when two superposed patterns are displaced or rotated relatively. In this thesis study, we refer as moiré patterns or moiré superlattices that are created due to the rotation of the top-most graphene layer on highly oriented pyrolytic graphite (HOPG), used as sample. These twisted graphene areas are encountered on the surface at various sizes and arbitrary moiré superlattice periods which depends on the rotation angle. They were studied by STM tunnel junction bias dependent imaging and differential conductance measurements. Some time ago, a set of magic angles were calculated at which twisted bilayer graphene was predicted to show unusual electronic properties. Two years ago, superconductivity was discovered at the largest of them, the first magic angle. In the first part of the thesis, STM topography images of several moiré superlattices at different bias voltages were acquired. From these data, apparent corrugations of the moiré superlattices and their boundaries with the bare HOPG surface were calculated at each applied bias voltage and their behaviors as a function of bias were investigated. From these information, we aimed to explore whether the measured apparent corrugations completely aroused from an interlayer electronic interaction or structural surface corrugation might also contribute in it. In the second part, we investigated differential conductance (dI/dV) maps of these moiré superlattices and their boundaries by using a lock-in amplifier, in addition to topography images. dI/dV maps give information about the spatial distribution of the local density of states (LDOS) over the surface at various energies which are determined by the value of applied bias voltage. To fully investigate their electronic properties, STS measurements were also performed. Thanks to dI/dV signal provided by lock-in amplifier, dI/dV-V spectra of moiré patterns can be acquired as well as their I-V spectra, without numerical calculation. In the simplest terms, this allows us to detect local variations in the conducting behavior of the surface and variation of local density of states as a function of energy. In the third part of the thesis, a sample biased system combining STM and lock-in amplifier was developed to get rid of disadvantages of the tip biased lock-in amplifier-STM system. An adder circuit was built on a printed circuit board to sum DC bias voltage and AC voltage of lock-in amplifier's reference signal. The output of the circuit was delivered to isolated HOPG sample. Same measurement procedure has been adopted on twisted graphene layers as in the case of tip bias. Finally, the effect of STM bias voltage pulse on moiré superlattices and their boundaries was investigated. Shift and gradual movement of charge densities in dI/dV maps relative to their corresponding topography images were observed.