Publications without Fulltext

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

Browse

Filters

Advanced Search

Filter by

Settings

Department: search.filters.department.Department of PhysicsSubject: search.filters.subject.Nanotechnology

Search Results

Now showing 1 - 10 of 21
  • Placeholder
    PublicationMetadata only
    Solid state sensor for simultaneous measurement of total alkalinity and ph of seawater
    (Amer Chemical Soc, 2017) Briggs, Ellen M.; Sandoval, Sergio; Takeshita, Yuichiro; Kummel, Andrew C.; Martz, Todd R.; Department of Physics; Department of Physics; Erten, Ahmet Can; Teaching Faculty; College of Sciences; 233923
    A novel design is demonstrated for a solid state, reagent-less sensor capable of rapid and simultaneous measurement of pH and Total Alkalinity (A(T)) using ion sensitive field effect transistor (ISFET) technology to provide a simplified means of characterization of the aqueous carbon dioxide system through measurement of two "master variables": pH and A(T). ISFET-based pH sensors that achieve 0.001 precision are widely used in various oceanographic applications. A modified ISFET is demonstrated to perform a nanoliter-scale acid base titration of A(T) in under 40 s. This method of measuring A(T), a Coulometric Diffusion Titration, involves electrolytic generation of titrant, through the electrolysis of water on the surface of the chip via a microfabricated electrode eliminating the requirement of external reagents. Characterization has been performed in seawater as well as titrating individual components (i.e., OH-, HCO3-, B(OH)(4)(-), PO43-) of seawater A(T). The seawater measurements are consistent with the design in reaching the benchmark goal of 0.5% precision in A(T) over the range of seawater A(T) of similar to 2200-2500 mu mol kg(-1) which demonstrates great potential for autonomous sensing.
  • Placeholder
    PublicationMetadata only
    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; Department of Physics; Müstecaplıoğlu, Özgür Esat; Faculty Member; 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.
  • Placeholder
    PublicationMetadata only
    Passive sorting of emulsion droplets with different interfacial properties using laser-patterned surfaces
    (Springer Heidelberg, 2019) Erten, Ahmet; Jonas, Alexandr; N/A; Department of Physics; Department of Mechanical Engineering; Department of Physics; Department of Mechanical Engineering; Department of Physics; Rashid, Muhammed Zeeshan; Morova, Berna; Muradoğlu, Metin; Kiraz, Alper; PhD Student; Researcher; Faculty Member; Faculty Member; Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; College of Sciences; N/A; 152935; 22542
    We demonstrate passive sorting of emulsion microdroplets based on differences in their interfacial tension and contact angle. The sorted droplets are flowing inside a microfluidic channel featuring a shallow guiding track (depth similar to 0.6 mu m) defined by femtosecond laser micromachining in polydimethylsiloxane coating deposited on glass. Under these flow conditions, the droplets experience a confinement force that pulls them into the track; this force depends on the interfacial tension and the difference between the contact angles inside and outside the ablated track. The interplay between the confinement force, fluid drag, and wall friction then determines the trajectory of the droplet along the guiding track. We investigate experimentally the droplet trajectory as a function of droplet velocity and angle between the track and the channel axis and demonstrate precise control of droplet direction by adjusting the track angle. Moreover, we show that droplets of liquids with different interfacial tensions and contact angles travel different distances along the guiding track at a constant flow rate, which can be used for droplet sorting. We develop a theoretical model that incorporates the droplet position with respect to the ablated track, interfacial tension, and contact angles to predict the droplet trajectory under given experimental conditions. Thus, the dynamic behavior of the droplets leading to different guiding scenarios can be studied without the need of computationally expensive fluid dynamics simulations. The presented study paves the way for designing and optimizing new systems for advanced manipulation of droplets of different content using potentially reconfigurable guiding tracks.
  • Placeholder
    PublicationMetadata only
    Visible to infrared diamond photonics enabled by focused femtosecond laser pulses
    (Multidisciplinary Digital Publishing Institute (MDPI), 2017) Sotillo, Belen; Bharadwaj, Vibhav; Hadden, John Patrick; Rampini, Stefano; Chiappini, Andrea; Fernandez, Toney T.; Armellini, Cristina; Ferrari, Maurizio; Barclay, Paul E.; Ramponi, Roberta; Eaton, Shane M.; Department of Physics; Department of Physics; Serpengüzel, Ali; Faculty Member; College of Sciences; 27855
    Diamond's nitrogen-vacancy (NV) centers show great promise in sensing applications and quantum computing due to their long electron spin coherence time and because they can be found, manipulated, and read out optically. An important step forward for diamond photonics would be connecting multiple diamond NVs together using optical waveguides. However, the inertness of diamond is a significant hurdle for the fabrication of integrated optics similar to those that revolutionized silicon photonics. In this work, we show the fabrication of optical waveguides in diamond, enabled by focused femtosecond high repetition rate laser pulses. By optimizing the geometry of the waveguide, we obtain single mode waveguides from the visible to the infrared. Additionally, we show the laser writing of individual NV centers within the bulk of diamond. We use mu-Raman spectroscopy to gain better insight on the stress and the refractive index profile of the optical waveguides. Using optically detected magnetic resonance and confocal photoluminescence characterization, high quality NV properties are observed in waveguides formed in various grades of diamond, making them promising for applications such as magnetometry, quantum information systems, and evanescent field sensors.
  • Placeholder
    PublicationMetadata only
    Silicon microsphere based filtering application for near-infrared optical fiber based telecommunication
    (IEEE, 2011) Tamer, Mehmet Selman; Gurlu, Oguzhan; N/A; N/A; Department of Physics; Department of Physics; Yılmaz, Huzeyfe; Gökay, Ulaş Sabahattin; Serpengüzel, Ali; Master Student; PhD Student; Faculty Member; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 27855
    We demonstrate an optical filter based on the resonances of a silicon microsphere in the near-IR O-Band. The 1300 nm laser light is coupled to the silicon microsphere and optical resonances are observed as dips in the transmission spectrum.
  • Placeholder
    PublicationMetadata only
    Fabrication of ZnO nanowires and nanorods
    (Elsevier, 2012) Öztürk, Sadullah; Kılınç, Necmettin; Öztürk, Zafer Ziya; Department of Physics; Department of Physics; Taşaltın, Nevin; Researcher; College of Sciences; 220956
    In this study, we focused on the fabrication of two types of ZnO nanostructures, nanorods and nanowires, using different techniques. ZnO nanowires were fabricated by cathodically induced sol-gel electrodeposition using an anodic aluminum oxide (AAO) template. ZnO nanowires were approximately 65 nm in diameter and 10 mu m in length. Also, ZnO nanorods were fabricated by a hydrothermal technique using ZnO seed layer coated glass substrate. ZnO nanorods were approximately 30 nm in diameter and 1 mu m in length. Obtained vertical aligned ZnO nanowires and nanorods were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and UV-vis spectrophotometry.
  • Placeholder
    PublicationMetadata only
    The fast-track water oxidation channel on BiVO4 opened by nitrogen treatment
    (Amer Chemical Soc, 2020) N/A; N/A; N/A; N/A; Department of Physics; Department of Chemistry; Department of Physics; Department of Chemistry; Kahraman, Abdullah; Barzgarvishlaghi, Mahsa; Toker, Işınsu Baylam; Sennaroğlu, Alphan; Kaya, Sarp; PhD Student; PhD Student; PhD Student; Faculty Member; Faculty Member; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); 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; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; N/A; 23851; 116541
    BiVO4 is one of the most promising photoanode materials for water-splitting systems. Nitrogen incorporation into a BiVO4 surface overcomes the known bottleneck in its charge-transfer kinetics into the electrolyte. We explored the role of nitrogen in the surface charge recombination and charge-transfer kinetics by employing transient photocurrent spectroscopy at the time scale of surface recombination and water oxidation kinetics, transient absorption spectroscopy, and X-ray photoelectron spectroscopy. We attributed the activity enhancement mechanism to the accelerated V5+/V4+ redox process, in which incorporated nitrogen suppresses a limiting surface recombination channel by increasing the oxygen vacancies.
  • Placeholder
    PublicationMetadata only
    Aerogels for optofluidic waveguides
    (MDPI, 2017) Jonas, Alexandr; N/A; Department of Physics; Department of Chemical and Biological Engineering; Department of Physics; Department of Chemical and Biological Engineering; Özbakır, Yaprak; Erkey, Can; Kiraz, Alper; PhD Student; Faculty Member; Faculty Member; Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; N/A; 29633; 22542
    Aerogels-solid materials keeping their internal structure of interconnected submicron-sized pores intact upon exchanging the pore liquid with a gas-were first synthesized in 1932 by Samuel Kistler. Overall, an aerogel is a special form of a highly porous material with a very low solid density and it is composed of individual nano-sized particles or fibers that are connected to form a three-dimensional network. The unique properties of these materials, such as open pores and high surface areas, are attributed to their high porosity and irregular solid structure, which can be tuned through proper selection of the preparation conditions. Moreover, their low refractive index makes them a remarkable solid-cladding material for developing liquid-core optofluidic waveguides based on total internal reflection of light. This paper is a comprehensive review of the literature on the use of aerogels for optofluidic waveguide applications. First, an overview of different types of aerogels and their physicochemical properties is presented. Subsequently, possible techniques to fabricate channels in aerogel monoliths are discussed and methods to make the channel surfaces hydrophobic are described in detail. Studies in the literature on the characterization of light propagation in liquid-filled channels within aerogel monoliths as well as their light-guiding characteristics are discussed. Finally, possible applications of aerogel-based optofluidic waveguides are described.
  • Placeholder
    PublicationMetadata only
    Guiding of emulsion droplets in microfluidic chips along shallow tracks defined by laser ablation
    (Springer Heidelberg, 2017) Coskun, Umut Can; Morova, Yagiz; Bozkurt, Asuman Asikoglu; Jonas, Alexandr; Akturk, Selcuk; N/A; Department of Physics; Department of Physics; Department of Physics; Rashid, Muhammed Zeeshan; Erten, Ahmet Can; Kiraz, Alper; PhD Student; Teaching Faculty; Faculty Member; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; 233923; 22542
    We demonstrate controlled guiding of nanoliter emulsion droplets of polar liquids suspended in oil along shallow hydrophilic tracks fabricated at the base of microchannels located within microfluidic chips. The tracks for droplet guiding are generated by exposing the glass surface of polydimethylsiloxane (PDMS)-coated microscope slides via femtosecond laser ablation. The difference in wettability of glass and PDMS surfaces together with the shallow steplike transverse topographical profile of the ablated tracks allows polar droplets wetting preferentially the glass surface to follow the track. In this study, we investigate guiding of droplets of two different polar liquids (water/ethylene glycol) with and without surfactant suspended in an oil medium along surface tracks of different depths of 1, 1.5, and 2 mu m. The results of experiments are also verified with computational fluid dynamics simulations. Guiding of droplets along the tracks as a function of the droplet composition and size and the surface profile depth is evaluated by analyzing the trajectories of moving droplets with respect to the track central axis, and conditions for stable guiding are identified. The experiments and numerical simulations indicate that while the track topography plays a role in droplet guiding using 1.5-and 2-mu m deep tracks, for the case of the smallest track depth of 1 ae m, droplet guiding is mainly caused by surface energy modification along the track rather than the presence of a topographical step on the surface. Our results can be exploited to sort passively different microdroplets mixed in the same microfluidic chip, based on their inherent wetting properties, and they can also pave the way for guiding of droplets along reconfigurable tracks defined by surface energy modifications obtained using other external control mechanisms such as electric field or light.
  • Placeholder
    PublicationMetadata only
    Optofluidic lasers with aqueous quantum dots
    (Amer Chemical Soc, 2015) Chen, Qiushu; Fan, Xudong; Department of Physics; Department of Physics; Kiraz, Alper; Faculty Member; College of Sciences; 22542
    We achieved two types of laser emissions from aqueous quantum dots (Qps) using the same high-Q:factor optofluidic ring resonator (OFRR) platform. In the first type, 2 mu M QDs were in bulk buffer solution that filled the entire OFRR cavity volume. The lasing threshold was 0.1 mu J/mm(2), over 3 orders of magnitude lower than the state-of-the-art. In the second type of laser, the QDs were immobilized as a single layer on the interface between the OFRR inner wall and buffer solution with a surface density as low as 3 X 10(9)-10(10) cm(-2). The lasing threshold of 60 mu J/mm(2) was achieved. In both bulk solution and single-layer lasing cases, the laser emission persisted even under 5-10 min of uninterrupted pulsed optical excitation that was well above the corresponding lasing threshold, indicative of high photostability of the QD laser. This was in sharp contrast to organic-dye-based lasers, which underwent quick photobleaching during the laser operation under similar pumping conditions. Theoretical analysis is also carried out to elucidate the advantages of QD-based optofluidic lasers over those based on dyes. Our work opens the door to a plethora of applications where optofluidic QD lasers can replace dye-based optofluidic lasers in biosensing and on-chip miniaturized laser development.