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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3

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Department: search.filters.department.Department of PhysicsSubject: search.filters.subject.Materials science

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    Objective-free ultrasensitive biosensing on large-area metamaterial surfaces in the near-IR
    (AMER CHEMICAL SOC, 2024) Department of Physics; Ramazanoğlu, Serap Aksu; Öktem, Evren; Department of Physics; College of Sciences; Graduate School of Sciences and Engineering
    Plasmonic metamaterials have opened new avenues in medical diagnostics. However, the transfer of the technology to the markets has been delayed due to multiple challenges. The need of bulky optics for signal reading from nanostructures patterned on submillimeter area limits the miniaturization of the devices. The use of objective-free optics can solve this problem, which necessitates large area patterning of the nanostructures. In this work, we utilize laser interference lithography (LIL) to pattern nanodisc-shaped metamaterial absorber nanoantennas over a large area (4 cm(2)) within minutes. The introduction of a sacrificial layer during the fabrication process enables an inverted hole profile and a well-controlled liftoff, which ensures perfectly defined uniform nanopatterning almost with no defects. Furthermore, we use a macroscopic reflection probe for optical characterization in the near-IR, including the detection of the binding kinematics of immunologically relevant proteins. We show that the photonic quality of the plasmonic nanoantennas commensurates with electron-beam-lithography-fabricated ones over the whole area. The refractive index sensitivity of the LIL-fabricated metasurface is determined as 685 nm per refractive index unit, which demonstrates ultrasensitive detection. Moreover, the fabricated surfaces can be used multiple times for biosensing without losing their optical quality. The combination of rapid and large area nanofabrication with a simple optical reading not only simplifies the detection process but also makes the biosensors more environmentally friendly and cost-effective. Therefore, the improvements provided in this work will empower researchers and industries for accurate and real-time analysis of biological systems.
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    Cooper pairing, flat-band superconductivity, and quantum geometry in the pyrochlore-Hubbard model
    (American Physical Society, 2024)  ; Department of Physics; Işkın, Menderes; Department of Physics;  ; College of Sciences;  
    We investigate the impacts of the quantum geometry of Bloch states, specifically through the band -resolved quantum -metric tensor, on Cooper pairing and flat -band superconductivity in a three-dimensional pyrochloreHubbard model. First we analyze the low-lying two -body spectrum exactly, and show that the pairing order parameter is uniform in this four -band lattice. This allows us to establish direct relations between the superfluid weight of a multiband superconductor and (i) the effective mass of the lowest -lying two -body branch at zero temperature, (ii) the kinetic coefficient of the Ginzburg-Landau theory in proximity to the critical temperature, and (iii) the velocity of the low -energy Goldstone modes at zero temperature. Furthermore, we perform a comprehensive numerical analysis of the superfluid weight and Goldstone modes, exploring both their conventional and geometric components at zero temperature.
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    Versatile liquid-core optofluidic waveguides fabricated in hydrophobic silica aerogels by femtosecond-laser ablation
    (Elsevier, 2015) Yalizay, Berna; Morova, Yagiz; Dincer, Koray; Jonas, Alexandr; Akturk, Selcuk; N/A; Department of Chemical and Biological Engineering; Department of Physics; Özbakır, Yaprak; Erkey, Can; Kiraz, Alper; PhD Student; Faculty Member; Faculty Member; Department of Chemical and Biological Engineering; Department of Physics; Graduate School of Sciences and Engineering; College of Engineering; College of Science; N/A; 29633; 22542
    We report on the fabrication and characterization of versatile light waveguides exploiting filaments of a polar liquid confined within hydrophobic silica aerogels. Aerogels are highly porous materials with extremely low refractive index which makes them suitable as rigid cladding of liquid-core optofluidic waveguides based on total internal reflection of light. In this article, we introduce a new microfabrication technique that allows direct and precise processing of monolithic silica aerogels by ablation with femtosecond laser pulses. Using fast scanning of the focused laser ablation beam synchronized with the motion of the processed aerogel sample, we created high-quality straight microchannels of similar to 5 mm length with controlled cross-sections inside monolithic aerogels. After the ablation, we filled the channels with high-refractive index ethylene glycol, forming multimode liquid core - solid cladding optofluidic waveguides. Subsequently, we carried out light-guiding experiments to measure overall optical attenuation of these waveguides. The characterization of waveguide transmission yielded values of propagation losses lower than 10 dB cm(-1), demonstrating that the liquid-core waveguides with laser-ablated aerogel cladding represent an attractive alternative in optofluidic applications targeting controlled routing of light along arbitrary three-dimensional paths.
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    Femtosecond laser written continuous-wave Nd3+:BaY2F8 waveguide laser at 1.3 mu m
    (Elsevier, 2022) Di Lieto, Alberto; Cittadino, Giovanni; Damiano, Eugenio; Tonelli, Mauro; Department of Physics; N/A; N/A; N/A; Department of Physics; Morova, Yağız; Morova, Berna; Jahangiri, Hadi; Toker, Işınsu Baylam; Sennaroğlu, Alphan; Researcher; Researcher; Researcher; PhD Student; Faculty Member; Department of Physics; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; N/A; N/A; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; N/A; 23851
    We experimentally demonstrate, for the first time to our knowledge, robust operation of a Nd3(+:)BaY(2)F(8) waveguide laser at 1.3 mu m without any parasitic lasing at any other wavelength. The best power performance was obtained with a depressed cladding waveguide, having a diameter of 70 mu m, which was fabricated by employing femtosecond laser writing. The propagation loss of the waveguide was measured as 0.33 dB/cm at the wavelength of 761 nm. The power performance of the waveguide laser was investigated for E//z and E//y pumping polarizations by using butt-coupled flat resonator mirrors. Higher power performance was obtained for E//z pumping, where the resonator with the 6.2% transmitting output coupler produced 157 mW of continuous-wave output power at 1318 nm with 882 mW of pump power at 800 nm. The measured power slope efficiency was 19% with respect to the incident pump power. By using a different set of cavity optics, 1050-nm lasing performance was also studied, where E//z pumping at 800 nm with the 12% transmitting output coupler yielded 307 mW of output power with 31% slope efficiency. Use of a host medium with relatively low refractive index around 1.5 was instrumental in reducing the facet reflectivity and eliminating the possibility of parasitic lasing at 1.05 mu m during 1.3-mu m lasing.
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    Analysis of thermal fields in orthogonal machining with infrared imaging
    (Elsevier Science Sa, 2008) Department of Mechanical Engineering; Department of Mechanical Engineering; Department of Physics; Lazoğlu, İsmail; Serpengüzel, Ali; N/A; Faculty Member; Faculty Member; Department of Mechanical Engineering; Department of Physics; Manufacturing and Automation Research Center (MARC); Manufacturing and Automation Research Center (MARC); N/A; College of Engineering; College of Engineering; College of Sciences; N/A; 179391; 27855
    The validation of a previously developed finite difference temperature prediction model is carried out for orthogonal machining process with a high precision infrared camera set-up, considering the temperature distribution in the tool. the thermal experiments are conducted with two different materials; al 7075, AISI 1050, with two different tool geometries; inserts having a rake angle of 6 degrees and 18 degrees, for different cutting velocities and feedrates. an infrared camera set-up is utilized for the thermal experiments. the results of the high precision infrared thermal measurements are compared with the outputs of the finite difference temperature model, considering the maximum and the mean temperatures in the tool-chip interface zone and the temperature distributions on the tool take face. the maximum tool-chip interface temperature increases with increasing cutting velocity and feedrate. the relationship between the maximum tool-chip interface temperature and the rake angle of the tool is not distinctive. the experimental results show good agreement with the simulations. (c) 2007 Elsevier B.V. all rights reserved.
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    Survival probability in a quantum walk on a one-dimensional lattice with partially absorbing traps
    (American Scientific Publishers, 2013) Gonulol, Meltem; Aydiner, Ekrem; Shikano, Yutaka; Department of Physics; Müstecaplıoğlu, Özgür Esat; Faculty Member; Department of Physics; College of Sciences; 1674
    Time dependence of the survival probability in a one dimensional lattice with randomly distributed and partial absorbing traps is analyzed as a function of concentration and absorption probability of the traps. The short and long time behaviors of the non-interacting quantum walks are identified with stretched exponentials. Dynamical scaling laws of the short and long time regimes as well as the crossover time between them are characterized. It is found that the short time behavior is more sensitive to the absorption probability and the crossover takes longer time for more transparent traps. Moreover, the stretching exponents increase with the transparency of the traps.
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    Total internal reflection-based optofluidic waveguides fabricated in aerogels
    (Springer, 2017) Jona, Alexandr; Department of Physics; Department of Chemical and Biological Engineering; N/A; Kiraz, Alper; Erkey, Can; Özbakır, Yaprak; Faculty Member; Faculty Member; PhD Student; Department of Physics; Department of Chemical and Biological Engineering; College of Sciences; College of Engineering; Graduate School of Sciences and Engineering; 22542; 29633; N/A
    Liquid-core optofluidic waveguides based on total internal reflection of light were built in water-filled cylindrical microchannels fabricated in hydrophobic silica aerogels. Silica aerogels with densities ranging from 0.15 to 0.39 g/cm(3) were produced by aging of alcogels in tetraethylorthosilicate solution for various time periods, followed by supercritical extraction of the solvent from the alcogel network. Subsequently, the resulting hydrophilic aerogel samples were made hydrophobic by hexamethyldisilazane vapor treatment. The synthesized samples retained their low refractive index (below similar to 1.09) and, hence, they could serve as suitable optical cladding materials for aqueous waveguide cores (refractive index n(core) = 1.33). Hydrophobic silica aerogel samples produced by the above technique also had low absorption coefficients in the visible part of the spectrum. Fabrication of microchannels in aerogel blocks by manual drilling preserving nanoporous and monolithic structure of aerogels was demonstrated for the first time. Long channels (up to similar to 7.5 cm) with varying geometries such as straight and inclined L-shaped channels could be fabricated. Multimode optofluidic waveguides prepared by filling the channels in the drilled aerogel monoliths with water yielded high numerical aperture values (similar to 0.8). Efficient guiding of light by total internal reflection in the water-filled channels in aerogels was visually revealed and characterized by monitoring the channel output. The presented technique is expected to open up further possibilities for creating three-dimensional networks of liquid channels in aerogels for optofluidic applications.
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    Bypassing pro-survival and resistance mechanisms of autophagy in EGFR-positive lung cancer cells by targeted delivery of 5FU using theranostic Ag2S quantum dots
    (Royal Soc Chemistry, 2019) Akkoç, Yunus; Gözüaçık, Devrim; N/A; N/A; N/A; N/A; Department of Physics; Department of Chemistry; Demirci, Gözde; Duman, Fatma Demir; Bavili, Nima; Kiraz, Alper; Acar, Havva Funda Yağcı; PhD Student; Master Student; PhD Student; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; School of Medicine; College of Sciences; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); N/A; N/A; N/A; 22542; 178902
    Targeted drug delivery systems that combine imaging and therapeutic functions in a single structure have become very popular in nanomedicine. Near-infrared (NIR) emitting Ag2S quantum dots (QDs) are excellent candidates for this task. Here, we have developed PEGylated Ag2S QDs functionalized with Cetuximab (Cet) antibody and loaded with an anticancer drug, 5-fluorouracil (5FU). These theranostic QDs were used for targeted NIR imaging and treatment of lung cancer using low (H1299) and high (A549) Epidermal Growth Factor Receptor (EGFR) overexpressing cell lines. The Cet conjugated QDs effectively and selectively delivered 5FU to A549 cells and provided significantly enhanced cell death associated with apoptosis. Interestingly, while treatment of cells with free 5FU activated autophagy, a cellular mechanism conferring resistance to cell death, these EGFR targeting multimodal QDs significantly overcame drug resistance compared to 5FU treatment alone. The improved therapeutic outcome of 5FU delivered to A549 cells by Cet conjugated Ag2S QDs is suggested as the synergistic outcome of enhanced receptor mediated uptake of nanoparticles, and hence the drug, coupled with suppressed autophagy even in the absence of addition of an autophagy suppressor.
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    Synthesis and characterization of diffusion-doped Cr2+: ZnSe and Fe2+:ZnSe
    (Elsevier Science Bv, 2006) N/A; Department of Physics; Department of Chemistry; Demirbaş, Ümit; Sennaroğlu, Alphan; Somer, Mehmet Suat; Master Student; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; 20328; 23851; 178882
    This paper provides a detailed description of the preparation and characterization of diffusion-doped Cr2+ :ZnSe and Fe2+ :ZnSe. In the experiments, Cr2+:ZnSe samples with peak absorption coefficients (1775 nm) of as high as 74 cm(-1) and fairly good spatial uniformity were obtained. In the case of Fe2+:ZnSe, samples with a maximum absorption coefficient of 11.6 cm(-1) at 2400 nm were synthesized. A three-dimensional analytical diffusion model was further developed to determine the diffusion coefficient D from absorption data. At 1000 degrees C, D was determined to be 5.4 x 10(-10) cm(2)/s and 7.95 x 10(-10) cm(2)/s for Cr2+:ZnSe and Fe2+:ZnSe, respectively. In the case of Cr2+:ZnSe, we employed an alternative technique to determine the diffusion coefficient from position-dependent absorption data taken with a Cr4+:YAG laser. With this method, the temperature variation of D was further measured in the 800-1100 degrees C temperature ranges. (c) 2005 Elsevier B.V. All rights reserved.
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    Polar solvent-free room temperature synthesis of CsPbX3 (X = Br, Cl) perovskite nanocubes
    (Royal Society of Chemistry, 2023) Güvenç, C. Meriç; Balcı, Sinan; Department of Physics; Kocabaş, Aşkın; Faculty Member; Department of Physics; College of Sciences; 227753
    Conventionally, colloidal lead halide perovskite nanocubes have been synthesized by the hot-injection or ligand-assisted reprecipitation (LARP) methods. We herein demonstrate a polar solvent-free room temperature method for the synthesis of CsPbX3 (X = Br, Cl) nanocubes. In addition to the commonly used ligand pair of oleylamine and oleic acid, guanidinium (GA) has been used to passivate the surface of the nanocrystals. Our study demonstrates that GA inhibits the formation of low dimensional structures such as nanowires and nanoplatelets and further supports the formation of perovskite nanocubes. In fact, GA diminishes the restricted monomer-addition effect of long-chain oleylammonium (OLAM) ions to the nanocrystal. We show that above a critical GA/OLAM molar ratio, the synthesis yields homogeneous CsPbX3 (X = Br, Cl) nanocubes. Importantly, we observe the nucleation and growth kinetics of the GA-assisted CsPbBr3 nanocube formation by using in situ absorption and photoluminescence (PL) measurements. Small nanocrystals with an excitonic absorption peak at around 435 nm and photoluminescence (PL) maxima at 447 nm were nucleated and continuously shifted to longer wavelengths during the growth period. Crucially, our method allows the synthesis of CsPbCl3 nanocubes at room temperature without using polar organic solvents. The synthesized CsPbBr3, CsPb(Cl0.5Br0.5)3, and CsPbCl3 nanocubes have PL peaks at 508 nm, 443 nm, and 405 nm, photoluminescence quantum yields (PLQY) of 85%, 58% and 5%, and lifetimes of 18.98 ns, 18.97 ns, and 14.74 ns, respectively.