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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Item Metadata only 3D-printed microrobots: translational challenges(MDPI, 2023) 0000-0003-4604-217X; 0000-0002-5295-5701; 0000-0003-0519-4513; Yetisen, Ali K.; Department of Mechanical Engineering; N/A; N/A; Taşoğlu, Savaş; Sarabi, Misagh Rezapour; Karagöz, Ahmet Agah; Faculty Member; PhD Student; PhD Student; KU Arçelik Research Center for Creative Industries (KUAR) / KU Arçelik Yaratıcı Endüstriler Uygulama ve Araştırma Merkezi (KUAR); Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); Koç Üniversitesi İş Bankası Yapay Zeka Uygulama ve Araştırma Merkezi (KUIS AI)/ Koç University İş Bank Artificial Intelligence Center (KUIS AI); College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 291971; N/A; N/AThe science of microrobots is accelerating towards the creation of new functionalities for biomedical applications such as targeted delivery of agents, surgical procedures, tracking and imaging, and sensing. Using magnetic properties to control the motion of microrobots for these applications is emerging. Here, 3D printing methods are introduced for the fabrication of microrobots and their future perspectives are discussed to elucidate the path for enabling their clinical translation.Item Metadata only Ti3C2MXene/polyaniline/montmorillonite nanostructures toward solvent-free powder coatings with enhanced corrosion resistance and mechanical properties(Amer Chemical Soc, 2023) 0000-0003-1164-1973; 0000-0003-3243-6442; Hosseini, Seyyedeh Fatemeh; Dorraji, Mir Saeed Seyed; Rasoulifard, Mohammad Hossein; Department of Chemistry; N/A; Aydemir, Umut; Nazarlou, Ziba; Faculty Member; PhD Student; Koç University Boron and Advanced Materials Application and Research Center (KUBAM) / Koç Üniversitesi Bor ve İleri Malzemeler Uygulama ve Araştırma Merkezi (KUBAM); College of Sciences; Graduate School of Sciences and Engineering; 58403; N/ASolvent-free powdercoatings have become very popular in the coatingindustry in replacing conventional liquid coatings for the last decades.However, poor adhesion of powder coatings to the substrate and microporesinevitably created during the curing process of coatings lead to localizedcorrosion and reduced mechanical resistance. For this purpose, Ti3C2 MXene/polyaniline (PANI)/montmorillonite (MMT)nanocomposites with superior conductivity and adhesion capabilitieswere incorporated into the eco-friendly powder coating. The as-synthesizednanocomposites were analyzed using various techniques such as Fouriertransform infrared spectroscopy, X-ray diffraction, X-ray photoelectronspectroscopy, high-resolution transmission electron microscopy, field-emissionscanning electron microscopy, and Raman spectroscopy. To evaluatethe effectiveness of the powder coating in preventing corrosion ona mild steel substrate, two methods were employed: potentiodynamicpolarization and electrochemical impedance spectroscopy. The electrochemicaltests revealed that an excellent dispersion of 1.5 wt % Ti3C2 MXene/PANI/MMT nanosheets in a polyester/epoxy powdercoating resulted in superior anti-corrosion performance (4.8 x10(6) omega) after 42 days of immersion in 3.5 wt % NaClas compared to blank samples (7.2 x 10(2) omega).According to Tafel analysis, the corrosion potential of the optimalsample is -0.062 V, which is more positive than that of thepristine powder coating (-0.83 V). The polarization resistance(R (p)) and corrosion current (i (corr)) of the optimal sample are determined to be 3.39x 10(6) omega center dot cm(2) and 7.69 x10(-9) A center dot cm(-2), respectively.Moreover, the optimal sample marginally increased the hardness (229.42MPa) compared to the pure sample (152.68 MPa) due to the synergisticeffect of Ti3C2 MXene and flake-like MMT nanoparticles,which results in an improvement in the mechanical strength of powdercoatings. Additionally, the presence of PANI caused further crosslinkingand modulation of the electrical conductivity of the produced nanocomposites.The present study proposes a practical method to enhance the mechanicaland shielding properties of solvent-free powder coatings, making themsuitable for use in various real-world applications, including commercial,medical, and household sectors.Publication Metadata only Microfluidic pulse shaping methods for molecular communications(Elsevier, 2023) Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; Kahvazi Zadeh, Maryam; Bolhassan, Iman Mokari; Kuşcu, Murat; Graduate School of Sciences and Engineering; College of EngineeringMolecular Communication (MC) is a bio-inspired communication modality that utilizes chemical signals in the form of molecules to exchange information between spatially separated entities. Pulse shaping is an important process in all communication systems, as it modifies the waveform of transmitted signals to match the characteristics of the communication channel for reliable and high-speed information transfer. In MC systems, the unconventional architectures of components, such as transmitters and receivers, and the complex, nonlinear, and time-varying nature of MC channels make pulse shaping even more important. While several pulse shaping methods have been theoretically proposed for MC, their practicality and performance are still uncertain. Moreover, the majority of recently proposed experimental MC testbeds that rely on microfluidics technology lack the incorporation of programmable pulse shaping methods, which hinders the accurate evaluation of MC techniques in practical settings. To address the challenges associated with pulse shaping in microfluidic MC systems, we provide a comprehensive overview of practical microfluidic chemical waveform generation techniques that have been experimentally validated and whose architectures can inform the design of pulse shaping methods for microfluidic MC systems and testbeds. These techniques include those based on hydrodynamic and acoustofluidic force fields, as well as electrochemical reactions. We also discuss the fundamental working mechanisms and system architectures of these techniques, and compare their performances in terms of spatiotemporal resolution, selectivity, system complexity, and other performance metrics relevant to MC applications, as well as their feasibility for practical MC applications.Publication Metadata only Stabilization and adiabatic control of antiferromagnetically coupled skyrmions without the topological hall effect(Royal Soc Chemistry, 2023) Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; Yağan, Rawana; Cheghabouri, Arash Mousavi; Onbaşlı, Mehmet Cengiz; Graduate School of Sciences and Engineering; College of EngineeringSynthetic 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.Publication Metadata only Metal-support interaction in PT nanodisk-carbon nitride catalyst: insight from theory and experiment(MDPI, 2024) Doustkhah, Esmail; Kotb, Ahmed; Assadi, Mohammad Hussein Naseef; Balkan, Timuçin; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM)Metal-support interaction plays a critical role in determining the eventual catalytic activity of metals loaded on supporting substrates. This interaction can sometimes cause a significant drop in the metallic property of the loaded metal and, hence, a drop in catalytic activity in the reactions, especially in those for which low charge carrier transfer resistance is a necessary parameter. Therefore, there should be a case-by-case experimental or theoretical (or both) in-depth investigation to understand the role of support on each metal. Here, onto a layered porous carbon nitride (g-CN), we grew single crystalline Pt nanodisks (Pt@g-CN) with a lateral average size of 21 nm, followed by various characterisations such as electron microscopy techniques, and the measurement of electrocatalytic activity in the O-2 reduction reaction (ORR). We found that intercalating Pt nanodisks in the g-CN interlayers causes an increase in electrocatalytic activity. We investigated the bonding mechanism between carbon support and platinum using density functional theory and applied the d-band theory to understand the catalytic performance. Analysis of Pt's density of states and electronic population across layers sheds light on the catalytic behaviour of Pt nanoparticles, particularly in relation to their thickness and proximity to the g-CN support interface. Our simulation reveals an optimum thickness of similar to 11 angstrom, under which the catalytic performance deteriorates.Publication Metadata only Silk as a biodegradable resist for field-emission scanning probe lithography(Institute of Physics (IOP) Publishing, 2020) Sadeghi, Sadra; Rangelow, Ivo W.; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; N/A; N/A; Department of Electrical and Electronics Engineering; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; Alaca, Burhanettin Erdem; Kumar, Baskaran Ganesh; Melikov, Rustamzhon; Doğru-Yüksel, Itır Bakış; Nizamoğlu, Sedat; Faculty Member; Other; PhD Student; PhD Student; Faculty Member; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştirmalari Merkezi (KUYTAM); N/A; N/A; N/A; N/A; College of Engineering; College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; 115108; N/A; N/A; N/A; 130295The patterning of silk allows for manufacturing various structures with advanced functionalities for optical and tissue engineering and drug delivery applications. Here, we propose a high-resolution nanoscale patterning method based on field-emission scanning probe lithography (FE-SPL) that crosslinks the biomaterial silk on conductive indium tin oxide (ITO) promoting the use of a biodegradable material as resist and water as a developer. During the lithographic process, Fowler-Nordheim electron emission from a sharp tip was used to manipulate the structure of silk fibroin from random coil to beta sheet and the emission formed nanoscale latent patterns with a critical dimension (CD) of similar to 50 nm. To demonstrate the versatility of the method, we patterned standard and complex shapes. This method is particularly attractive due to its ease of operation without relying on a vacuum or a special gaseous environment and without any need for complex electronics or optics. Therefore, this study paves a practical and cost-effective way toward patterning biopolymers at ultra-high level resolution.Publication Metadata only Structural changes in a Schiff base molecular assembly initiated by scanning tunneling microscopy tip(Institute of Physics (IOP) Publishing, 2016) Tomak, A.; Bacaksiz, C.; Mendirek, G.; Sahin, H.; Hur, D.; Gorgun, K.; Senger, R. T.; Peeters, F. M.; Zareie, H. M.; N/A; Birer, Özgür; Researcher; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/AWe report the controlled self-organization and switching of newly designed Schiff base (E)-4-((4-(phenylethynyl) benzylidene) amino) benzenethiol (EPBB) molecules on a Au (111) surface at room temperature. Scanning tunneling microscopy and spectroscopy (STM/STS) were used to image and analyze the conformational changes of the EPBB molecules. The conformational change of the molecules was induced by using the STM tip while increasing the tunneling current. The switching of a domain or island of molecules was shown to be induced by the STM tip during scanning. Unambiguous fingerprints of the switching mechanism were observed via STM/STS measurements. Surface-enhanced Raman scattering was employed, to control and identify quantitatively the switching mechanism of molecules in a monolayer. Density functional theory calculations were also performed in order to understand the microscopic details of the switching mechanism. These calculations revealed that the molecular switching behavior stemmed from the strong interaction of the EPBB molecules with the STM tip. Our approach to controlling intermolecular mechanics provides a path towards the bottom-up assembly of more sophisticated molecular machines.Publication Metadata only Layer-by-layer grown electrodes composed of cationic Fe 3 O 4 nanoparticles and graphene oxide nanosheets for electrochemical energy storage devices(Amer Chemical Soc, 2019) Erdem, Emre; Department of Chemistry; N/A; Department of Chemistry; Department of Chemistry; Department of Chemistry; Öztuna, Feriha Eylül Saraç; Ünal, Özlem; Acar, Havva Funda Yağcı; Ünal, Uğur; Researcher; PhD Student; Faculty Member; Faculty Member; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; 178902; 42079Ultrathin electrodes composed of layer-by-layer assembled (3-aminopropyl)trimethoxysilane functionalized iron oxide nanoparticles and graphene oxide nanosheets were prepared by a simple and low-cost dip coating method without using any binders or conductive additives. The thickness of the Fe3O4/GO films was simply altered with the number of dip coating cycles. Multilayered films were chemically reduced with hydrazine vapor in order to increase the electrical conductivity. Characterization of multilayer films was performed with scanning transmission electron microscopy, UV-vis spectroscopy, atomic force microscopy, quartz crystal microbalance, X-ray photoelectron spectroscopy, and electron paramagnetic resonance spectroscopy. We have performed cyclic voltammetry and electrochemical impedance spectroscopy for the evaluation of Fe3O4/GO multilayers as possible electrochemical capacitor electrodes. Reduced Fe3O4/GO films exhibit high specific capacitances (varying between 200 and 350 F g(-1) at 5 mV s(-1)), Outperforming the layer-by-layer assembled iron oxides/carbon derivatives (carbon nanotube, graphene).Publication Metadata only A universal method for the preparation of magnetic and luminescent hybrid nanoparticles(American Chemical Society (ACS), 2010) Topal, Uğur; N/A; N/A; Department of Chemistry; Department of Chemistry; Kaş, Recep; Sevinç, Esra; Acar, Havva Funda Yağcı; Master Student; Master Student; Faculty Member; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 178902Hybrid nanoparticles (MDOTs) composed of luminescent quantum dots (QDs) and superparamagnetic iron oxides (SPIOs) were prepared by the ligand-exchange mechanism in a simple and versatile extraction method. In this method, aqueous QDs (CdS or CdTe) coated with carboxylated ligands exchange the fatty acid (lauric acid) coating of SPIOs in a water chloroform extraction process. QDs form a coating around SPIOs and transfer them into the aqueous phase in high efficiency. The method worked successfully with both small and polymeric coating molecules selected as cysteine, 2-mercaptopropionic acid, and a poly(acrylic acid)/mercaptoacetic acid mixture. The original properties of the nanoparticles were well-preserved in the hybrid structures: All MDOTS showed ferrofluidic behavior and had a luminescence in the original color of the QD. Magnetic properties and the luminesence intensity of MDOTs can be easily tuned with the SPIO/QD ratio. All particles are small and show very good stability (optical and colloidal) over months. For stable MDOTs with good luminescence properties, highly luminescent aqueous QDs (CdS or CdTe) with the mentioned coatings were prepared. The first examples of CdTe coated with 2MPA emitting from green to red and CdTe-PAA/MAA were provided as well.Publication Metadata only Separation of CO2 mixtures using zn(bdc)(ted)0.5 membranes and composites: a molecular simulation study(amer Chemical Soc, 2011) N/A; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Eruçar, İlknur; Keskin, Seda; PhD Student; Faculty Member; Graduate School of Sciences and Engineering; College of Engineering; 260094; 40548We used grand canonical Monte Carlo and equilibrium molecular dynamics simulations to compute adsorption isotherms and self-diffusivities of CH4/H-2 mixtures in a nanoporous metal organic framework Zn(bdc)(ted)(0.5) in our recent study (J. Phys. Chem. C 2010, 114, 13047). in this work, we extended our calculations to CO2/CH4 and CO2/H-2 mixtures by computing adsorption selectivity, diffusion selectivity, and permeation selectivity of Zn(bdc)(ted)(0.5) for these gas mixtures. Performance of several composite membranes including Zn(bdc)(ted)(0.5) as filler particles in polymer matrices was also examined for separation of CO2 from CH4 and H-2 using a combination of atomistic and continuum modeling. Results showed that adding even a small volume fraction of Zn(bdc)(ted)(0.5) into polymers can significantly enhance the gas permeability and carry the polymer/Zn(bdc)(ted)(0.5) composite membranes above the current upper bound established for pure polymer membranes.