GCRIS

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Fabrication and Characterization of Soi Based Photodetectors With Graphene Electrode
(01. Izmir Institute of Technology, 2023) Yanılmaz, Alper; Çelebi, Cem; Balcı, Sinan
This thesis presents the pioneering methods for the design, fabrication process, and performance evaluation of graphene (G) and n-type silicon (n-Si) based self-powered one dimensional (1D) and two dimensional (2D) photodetector arrays (PDAs) on a silicon on insulator (SOI) substrate. In the device structure, monolayer G is utilized as hole collecting transparent conductive electrode (TCE) and n-Si is used as light absorbing material, respectively. After analyzing the photo-response characteristics of single pixel G/n-Si diode on SOI, we fabricated G/n-Si based Schottky barrier 1D PDAs with common G electrode, separate G electrode and 2D PDA with individual G electrodes on linearly arrayed n-Si channels, respectively. Each G/n-Si diodes exhibited a clear rectifying Schottky character with low dark current and diode parameters were analyzed using the current-voltage measurement. Besides, all diodes demonstrated a clear photovoltaic activity under the light illumination and maximum responsivity at 660 nm peak wavelength. Each diode in PDA revealed similar device performances under self-powered mode in terms of an Ilight/Idark ratio up to 104, a responsivity of ~0.1 A/W and a response speed of ~1.3 μs at 660 nm wavelength. The optical crosstalk was extremely low between neighboring diodes and also it could be greatly minimized when G is used as separated electrode on arrayed Si up to ~0.10% (-60 dB) per array. Time dependent photocurrent spectroscopy measurements revealed an excellent photocurrent reversibility of both device types. In the diode structure, the homogeneity of the graphene film transferred on n-Si were examined by Raman mapping and correlated with the sensitivity of diode to incoming light. This thesis paves the way for the new generation of optoelectronic devices with various potential by integrating G and SOI technology to PDA devices with ease of fabrication.
Development of Conducting Polymer-Based Fluorescence On/Off Biosensor for Biomolecule Analysis
(01. Izmir Institute of Technology, 2022) Arslantaş, Duygu; Arslan Yıldız, Ahu
Sensitive and selective detection of biomolecules and cells is essential for early diagnosis of diseases, prognosis monitoring, and effective therapy. This thesis aimed to develop a novel fluorescence ‘‘turn-on/off’’ biosensor for biomolecules and cells detection. In this study, cationic polythiophene derivative poly(1,4-dimethyl-1-(3-((4- methylthiophen-3-yl)oxy)propyl)piperazin-1-ium bromide) (PT–Pip) was used as an efficient fluorescence transduction element to discriminate proteins, mammalian cells, and amino acids for the first time. Initially, pH–dependent spectroscopic characterization of the PT–Pip was performed to monitor the conformational and optical changes. The pH sensitivity of the PT–Pip was demonstrated for the first time. Afterwards, the fluorescence ‘‘turn–off’’ phenomena were investigated in detail using citrate–capped gold nanoparticles as an efficient fluorescence quencher. Further, the interaction of target analytes such as proteins, mammalian cells, and amino acids with pre–quenched non–covalent PT–Pip–AuNP complexes was examined. Disruption of the binding equilibrium between PT–Pip and AuNP by analytes resulted in the selective displacement of PT–Pip, which generated signal output as a fluorescence ‘‘turn–on’’ mode. Consequently, for the sensitive detection of biomolecules and cells, chemical tongue sensor arrays were developed utilizing differential sensing approaches. PCA was used for the statistical evaluation of the multi–dimentional fluorescence response patterns. As a result, unique fingerprints were rapidly obtained by the direct sensing of proteins, ratiometric sensing of mammalian cells, and indirect sensing of amino acids. The combination of a differential sensing strategy with an appropriate multivariate statistical technique enabled the selective and sensitive detection and identification of proteins, mammalian cells, and amino acids.

Phd Degree / Doktora

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