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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 Electrical and Electronics EngineeringSubject: search.filters.subject.Chemistry

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    Stabilization and adiabatic control of antiferromagnetically coupled skyrmions without the topological hall effect
    (Royal Soc Chemistry, 2023) Department of Electrical and Electronics Engineering; Yağan, Rawana; Cheghabouri, Arash Mousavi; Onbaşlı, Mehmet Cengiz; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering
    Synthetic antiferromagnetically coupled (SAF) multilayers provide different physics of stabilizing skyrmions while eliminating the topological Hall effect (THE), enabling efficient and stable control. The effects of material parameters, external current drive, and a magnetic field on the skyrmion equilibrium and propagation characteristics are largely unresolved. Here, we present a computational and theoretical demonstration of the large window of material parameters that stabilize SAF skyrmions determined by saturation magnetization, uniaxial anisotropy, and Dzyaloshinskii-Moriya interaction. Current-driven SAF skyrmion velocities reach & SIM;200 m s(-1) without the THE. The SAF velocities are about 3-10 times greater than the typical ferromagnetic skyrmion velocities. The current densities needed for driving SAF skyrmions could be reduced to 10(8) A m(-2), while 10(11) A m(-2) or above is needed for ferromagnetic skyrmions. By reducing the SAF skyrmion drive current by 3 orders, Joule heating is reduced by 6 orders of magnitude. These results pave the way for new SAF interfaces with improved equilibrium, dynamics, and power savings in THE-free skyrmionics.
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    Colloidal aluminum antimonide quantum dots
    (Amer Chemical Soc, 2019) Sahin, Mehmet; Öztürk, Hande; Ow-Yang, Cleva W.; N/A; N/A; Department of Electrical and Electronics Engineering; Jalali, Houman Bahmani; Sadeghi, Sadra; Nizamoğlu, Sedat; PhD Student; PhD Student; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 130295
    AlSb is a less studied member of the III-V semiconductor family, and herein, we report the colloidal synthesis of AlSb quantum dots (QDs) for the first time. Different sizes of colloidal AlSb QDs (5 to 9 nm) were produced by the controlled reaction of AlCl3 and Sb[N(Si(Me)(3))(2)](3) in the presence of superhydride. These colloidal AlSb quantum dots showed excitonic transitions in the UV-A region and a tunable band edge emission (quantum yield of up to 18%) in the blue spectral range. Among all III-V quantum dots, these quantum dots show the brightest core emission in the blue spectral region.
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    3D coffee stains
    (Royal Soc Chemistry, 2017) N/A; N/A; Department of Electrical and Electronics Engineering; N/A; N/A; N/A; Department of Molecular Biology and Genetics; Department of Chemistry; Department of Chemistry; Department of Electrical and Electronics Engineering; Doğru-Yüksel, Itır Bakış; Söz, Çağla Koşak; Press, Daniel Aaron; Melikov, Rustamzhon; Begar, Efe; Çonkar, Deniz; Karalar, Elif Nur Fırat; Yılgör, Emel; Yılgör, İskender; Nizamoğlu, Sedat; PhD Student; PhD Student; Researcher; PhD Student; PhD Student; PhD Student; PhD Student; Faculty Member; Researcher; Faculty Member; Faculty Member; Department of Molecular Biology and Genetics; Department of Chemistry; Department of Electrical and Electronics Engineering; N/A; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/A; N/A; N/A; N/A; N/A; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; College of Sciences; College of Engineering; N/A; N/A; N/A; N/A; N/A; N/A; 206349; N/A; 24181; 130295
    When a liquid droplet (e.g., coffee, wine, etc.) is splattered on a surface, the droplet dries in a ring-shaped stain. This widely observed pattern in everyday life occurs due to the phenomenon known as a coffee stain (or coffee ring) effect. While the droplet dries, the capillary flow moves and deposits the particles toward the pinned edges, which shows a 2D ring-like structure. Here we demonstrate the transition from a 2D to a 3D coffee stain that has a well-defined and hollow sphere-like structure, when the substrate surface is switched from hydrophilic to superhydrophobic. The 3D stain formation starts with the evaporation of the pinned aqueous colloidal droplet placed on a superhydrophobic surface that facilitates the particle flow towards the liquid-air interface. This leads to spherical skin formation and a cavity in the droplet. Afterwards the water loss in the cavity due to pervaporation leads to bubble nucleation and growth, until complete evaporation of the solvent. In addition to the superhydrophobicity of the surface, the concentration of the solution also has a significant effect on 3D coffee stain formation. Advantageously, 3D coffee stain formation in a pendant droplet configuration enables the construction of all-protein lasers by integrating silk fibroin with fluorescent proteins. No tools, components and/or human intervention are needed after the construction process is initiated; therefore, 3D coffee-stains hold promise for building self-assembled and functional 3D constructs and devices from colloidal solutions.
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    MEMS biosensor for detection of Hepatitis A and C viruses in serum
    (Elsevier Advanced Technology, 2011) N/A; N/A; Department of Mechanical Engineering; Department of Chemical and Biological Engineering; Department of Electrical and Electronics Engineering; Timurdoğan, Erman; Alaca, Burhanettin Erdem; Kavaklı, İbrahim Halil; Ürey, Hakan; PhD Student; Faculty Member; Faculty Member; Faculty Member; Department of Mechanical Engineering; Department of Chemical and Biological Engineering; Department of Electrical and Electronics Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; College of Engineering; N/A; 115108; 40319; 8579
    Resonant microcantilever arrays are developed for the purpose of label-free and real-time analyte monitoring and biomolecule detection. MEMS cantilevers made of electroplated nickel are functionalized with Hepatitis antibodies. Hepatitis A and C antigens at different concentrations are introduced in undiluted bovine serum. All preparation and measurement steps are carried out in the liquid within a specifically designed flowcell without ever drying the cantilevers throughout the experiment. Both actuation and sensing are done remotely and therefore the MEMS cantilevers have no electrical connections, allowing for easily disposable sensor chips. Actuation is achieved using an electromagnet and the interferometric optical sensing is achieved using laser illumination and embedded diffraction gratings at the tip of each cantilever. Resonant frequency of the cantilevers in dynamic motion is monitored using a self-sustaining closed-loop control circuit and a frequency counter. Specificity is demonstrated by detecting both Hepatitis A and Hepatitis C antigens and their negative controls. This is the first report of Hepatitis antigen detection by resonant cantilevers exposed to undiluted serum. A dynamic range in excess of 1000 and with a minimum detectable concentration limit of 0.1 ng/ml (1.66 pM) is achieved for both Hepatitis A and C. This result is comparable to labeled detection methods such as ELISA.
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    RuO2 supercapacitor enables flexible, safe, and efficient optoelectronic neural interface
    (Wiley-V C H Verlag Gmbh, 2022) Ulgut, Burak; N/A; N/A; N/A; N/A; Department of Electrical and Electronics Engineering; Karatüm, Onuralp; Yıldız, Erdost; Kaleli, Humeyra Nur; Şahin, Afsun; Nizamoğlu, Sedat; PhD Student; PhD Student; PhD Student; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM; Graduate School of Sciences and Engineering; Graduate School of Health Sciences; Graduate School of Health Sciences; School of Medicine; College of Engineering; N/A; N/A; N/A; 171267; 130295
    Optoelectronic biointerfaces offer a wireless and nongenetic neurostimulation pathway with high spatiotemporal resolution. Fabrication of low-cost and flexible optoelectronic biointerfaces that have high photogenerated charge injection densities and clinically usable cell stimulation mechanism is critical for rendering this technology useful for ubiquitous biomedical applications. Here, supercapacitor technology is combined with flexible organic optoelectronics by integrating RuO2 into a donor-acceptor photovoltaic device architecture that facilitates efficient and safe photostimulation of neurons. Remarkably, high interfacial capacitance of RuO2 resulting from reversible redox reactions leads to more than an order-of-magnitude increase in the safe stimulation mechanism of capacitive charge transfer. The RuO2-enhanced photoelectrical response activates voltage-gated sodium channels of hippocampal neurons and elicits repetitive, low-light intensity, and high-success rate firing of action potentials. Double-layer capacitance together with RuO2-induced reversible faradaic reactions provide a safe stimulation pathway, which is verified via intracellular oxidative stress measurements. All-solution-processed RuO2-based biointerfaces are flexible, biocompatible, and robust under harsh aging conditions, showing great promise for building safe and highly light-sensitive next-generation neural interfaces.
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    Electrical conduction and NO 2 gas sensing properties of ZnO nanorods
    (Elsevier, 2014) Sahin, Yasin; Öztürk, Sadullah; Kosemen, Arif; Erkovan, Mustafa; Öztürk, Zafer Ziya; Department of Electrical and Electronics Engineering; Kılınç, Necmettin; Researcher; Department of Electrical and Electronics Engineering; College of Engineering; 59959
    Thermally stimulated current (TSC), photoresponse and gas sensing properties of zinc oxide (ZnO) nanorods were investigated depending on heating rates, illumination and dark aging times with using sandwich type electrode system. Vertically aligned ZnO nanorods were grown on indium tin oxide (ITO) coated glass substrate by hydrothermal process. TSC measurements were performed at different heating rates under constant potential. Photoresponse and gas sensing properties were investigated in dry air ambient at 200 degrees C. For gas sensing measurements, ZnO nanorods were exposed to NO2 (100 ppb to 1 ppm) in dark and illuminated conditions and the resulting resistance transient was recorded. It was found from dark electrical measurements that the dependence of the dc conductivity on temperature followed Mott's variable range hopping (VRH) model. In addition, response time and recovery times of ZnO nanorods to NO2 gas decreased by exposing to white light.
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    Excitonic energy transfer within inp/zns quantum dot langmuir-blodgett assemblies
    (Amer Chemical Soc, 2018) N/A; N/A; N/A; N/A; Department of Electrical and Electronics Engineering; Jalali, Houman Bahmani; Melikov, Rustamzhon; Sadeghi, Sadra; Nizamoğlu, Sedat; PhD Student; PhD Student; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; 130295
    Interparticle energy transfer offers great promise to a diverse range of applications ranging from artificial solar energy harvesting to nanoscale rulers in biology. Here, we assembled InP/ZnS core/shell quantum dot monolayers via the Langmuir-Blodgett technique and studied the effect of ZnS shell thickness on the excitonic energy transfer within these core/shell quantum dots. Three types of InP-based core/shell quantum dot Langmuir-Blodgett assemblies with different ZnS shell thicknesses were assembled. The structural and optical properties of colloidal quantum dots reveal the successful multiple ZnS shell growth, and atomic force microscopy studies show the smoothness of the assembled monolayers. Time-resolved photoluminescence (PL) and fluorescence lifetime imaging microscopy (FLIM) studies of the thick-shell QD monolayer reveal narrower lifetime distribution in comparison with the thin-shell QD monolayer. The interparticle excitonic energy transfer was studied by spectrally resolved traces, and higher energy transfer was observed for the thin-shell InP/1ZnS QD monolayer. Finally, we calculated the average exciton energy and indicated that the energy transfer induced exciton energy shift decreased significantly from 95 to 27 meV after multiple ZnS shell growth.
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    Real time chemical and mechanical human motion monitoring with aerogel-based wearable sensors
    (Royal Soc Chemistry, 2020) Saraç, Feriha Eylem; Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; N/A; Department of Physics; Department of Chemistry; Ergen, Onur; Çelik, Ecem; Ünal, Ahmet Hamdi; Erdolu, Mert Yusuf; Ünal, Uğur; Researcher; Faculty Member; PhD Student; Undergraduate Student; Undergraduate Student; Faculty Member; Department of Electrical and Electronics Engineering; Department of Physics; Department of Chemistry; College of Engineering; College of Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; 272106; N/A; N/A; 42079
    Wearable bioelectronic systems are one of the most important tools for human health and motion monitoring. However, there is still a great challenge to fabricate high-performance flexible devices with a conformal integration of the human body and there is no single device that can collect and correlate data simultaneously from chemical and mechanical signals of the human body. We recently developed a new method to build aerogel-based strain and sweat sensors (aB-SSS) that can effectively extract real-time information by combining involuntary human motion and chemical signals due to their gradient functionalities. these sensors provide good mechanical integrity and allow high-density power generation during subtle human motion, Allowing sweat monitoring by measuring pH, ion concentration, perspiration rate,etc.
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    Erratum to: exciton recycling via InP quantum dot funnels for luminescent solar concentrators
    (Tsinghua University) Ow-Yang, Cleva W.; N/A; N/A; N/A; N/A; Department of Physics; Department of Electrical and Electronics Engineering; Jalali, Houman Bahmani; Sadeghi, Sadra; Toker, Işınsu Baylam; Han, Mertcan; Sennaroğlu, Alphan; Nizamoğlu, Sedat; PhD Student; PhD Student; PhD Student; Master Student; Faculty Member; Faculty Member; Department of Physics; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; N/A; N/A; 23851; 130295
    The article "Exciton recycling via InP quantum dot funnels for luminescent solar concentrators" written by Houman Bahmani Jalali(1),, Sadra Sadeghi(2),, Isinsu Baylam(3,4), Mertcan Han(5), Cleva W. Ow-Yang(6), Alphan Sennaroğlu(3,4), and Sedat Nizamoğlu(1,2,5) (x2709;), was originally published Online First without Open Access. After publication online first, the author decided to opt for Open Choice and to make the article an Open Access publication. Therefore, the copyright of the article has been changed to (c) The Author(s) 2020 and the article is forthwith distributed under the terms of the Creative Commons Attribution 4.0 International License (), which permits use, duplication, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The original article has been corrected.
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    Effective neural photostimulation using indium-based type-ii quantum dots
    (American Chemical Society (ACS), 2018) Şahin, Mehmet; Ow-Yang, Cleva W.; N/A; N/A; N/A; N/A; Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; Department of Electrical and Electronics Engineering; Jalali, Houman Bahmani; Aria, Mohammad Mohammadi; Dikbaş, Uğur Meriç; Sadeghi, Sadra; Kumar, Baskaran Ganesh; Kavaklı, İbrahim Halil; Nizamoğlu, Sedat; PhD Student; PhD Student; Master Student; PhD Student; Other; Faculty Member; Faculty Member; Department of Chemical and Biological Engineering; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; College of Engineering; N/A; N/A; N/A; N/A; N/A; 40319; 130295
    Light-induced stimulation of neurons via photoactive surfaces offers rich opportunities for the development of therapeutic methods and high-resolution retinal prosthetic devices. Quantum dots serve as an attractive building block for such surfaces, as they can be easily functionalized to match the biocompatibility and charge transport requirements of cell stimulation. Although indium based colloidal quantum dots with type-I band alignment have attracted significant attention as a nontoxic alternative to cadmium-based ones, little attention has been paid to their photovoltaic potential as type-II heterostructures. Herein, we demonstrate type-II indium phosphide/zinc oxide core/shell quantum dots that are incorporated into a photoelectrode structure for neural photostimulation. This induces a hyperpolarizing bioelectrical current that triggers the firing of a single neural cell at 4 mu W mm(-2), 26-fold lower than the ocular safety limit for continuous exposure to visible light. These findings show that nanomaterials can induce a biocompatible and effective biological junction and can introduce a route in the use of quantum dots in photoelectrode architectures for artificial retinal prostheses.