Browsing by Subject "Clusters"

Filter results by typing the first few letters
Now showing 1 - 3 of 3
  • Thumbnail Image
    ItemOpen Access
    Fano resonances in THz metamaterials composed of continuous metallic wires and split ring resonators
    (Optical Society of America, 2014) Li, Z.; Cakmakyapan, S.; Butun, B.; Daskalaki, C.; Tzortzakis, S.; Yang, X.; Özbay, Ekmel
    We demonstrate theoretically and experimentally that Fano resonances can be obtained in terahertz metamaterials that are composed of periodic continuous metallic wires dressed with periodic split ring resonators. An asymmetric Fano lineshape has been found in a narrow frequency range of the transmission curve. By using a transmission line combined with lumped element model, we are able to not only fit the transmission spectra of Fano resonance which is attributed to the coupling and interference between the transmission continuum of continuous metallic wires and the bright resonant mode of split ring resonators, but also reveal the capacitance change of the split ring resonators induced frequency shift of the Fano resonance. Therefore, the proposed theoretical model shows more capabilities than conventional coupled oscillator model in the design of Fano structures. The effective parameters of group refractive index of the Fano structure are retrieved, and a large group index more than 800 is obtained at the Fano resonance, which could be used for slow light devices. (C) 2014 Optical Society of America
  • Thumbnail Image
    ItemEmbargo
    Greasy cations bind to neutral macromolecules in aqueous solution
    (American Chemical Society, 2024-06-05) Ertekin, Umay Eren; Okur, Halil İbrahim
    Ions influence the solution properties of macromolecules. Although much is known about anions, cationic effects are considered mostly in terms of weak interactions or exclusion from neutral interfaces. Herein, we have systematically studied the effect of quaternary tetraalkylammonium cations ($NH_4+, NMe_4+, NEt_4+, NPr_4+, NBu_4+$) on the phase transition of poly(N-isopropylacrylamide) (PNIPAM) in aqueous solution. Solubility measurements were coupled to H-1 NMR and ATR-FTIR spectroscopic measurements. The solubility and NMR measurements revealed a direct binding between the greasiest cations and the isopropyl group of the macromolecule, evidenced from the nonlinear, Langmuir-type chemical shift response only at the isopropyl NMR signals with increasing salt concentrations. The ATR-FTIR measurements focusing on the amide oxygen showed that it is not the main direct-binding site. Additionally, the salting-out effects of the greasier cations correlate with their hydration entropies. These results demonstrate that the most weakly hydrated cations can bind to macromolecules as strongly as the weakly hydrated Hofmeister anions.
  • Thumbnail Image
    ItemOpen Access
    Interaction of CO2 with MnOx/Pd(111) reverse model catalytic interfaces
    (Wiley, 2023-07-03) Anıl, Arca; Sadak, Ömer Faruk; Karakurt, Bartu; Koçak, Yusuf; Lyubinetsky, Igor; Özensoy, Emrah
    Understanding the activation of CO2 on the surface of the heterogeneous catalysts comprised of metal/metal oxide interfaces is of critical importance since it is not only a prerequisite for converting CO2 to value-added chemicals but also often, a rate-limiting step. In this context, our current work focuses on the interaction of CO2 with heterogeneous bi-component model catalysts consisting of small MnOx clusters supported on the Pd(111) single crystal surface. These metal oxide-on-metal ‘reverse’ model catalyst architectures were investigated via temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS) techniques under ultra-high vacuum (UHV) conditions. Enhancement of CO2 activation was observed upon decreasing the size of MnOx nanoclusters by lowering the preparation temperature of the catalyst down to 85 K. Neither pristine Pd(111) single crystal surface nor thick (multilayer) MnOx overlayers on Pd(111) were not capable of activating CO2, while CO2 activation was detected at sub-monolayer (∼0.7 ML) MnOx coverages on Pd(111), in correlation with the interfacial character of the active sites, involving both MnOx and adjacent Pd atoms. © 2023 The Authors. ChemPhysChem published by Wiley-VCH GmbH.