Browsing by Subject "Electrolyte"

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Open Access
Electrostatics of Polymer Translocation Events in Electrolyte Solutions
(American Institute of Physics Inc., 2016) Buyukdagli, S.; Ala-Nissila, T.
We develop an analytical theory that accounts for the image and surface charge interactions between a charged dielectric membrane and a DNA molecule translocating through the membrane. Translocation events through neutral carbon-based membranes are driven by a competition between the repulsive DNA-image-charge interactions and the attractive coupling between the DNA segments on the trans and the cis sides of the membrane. The latter effect is induced by the reduction of the coupling by the dielectric membrane. In strong salt solutions where the repulsive image-charge effects dominate the attractive trans-cis coupling, the DNA molecule encounters a translocation barrier of ∼10 kBT. In dilute electrolytes, the trans-cis coupling takes over image-charge forces and the membrane becomes a metastable attraction point that can trap translocating polymers over long time intervals. This mechanism can be used in translocation experiments in order to control DNA motion by tuning the salt concentration of the solution.
Open Access
Graphene based optoelectronics in the visible spectrum
(2015) Polat, Emre Ozan
Graphene, a two dimensional crystal of carbon atoms, emerges as a viable material for optoelectronics because of its electrically-tunable broadband optical properties. Optical response of graphene at visible and near infrared frequencies is defined by inter-band electronic transitions. By electrical tuning of the Fermi energy, the inter-band transitions can be blocked due to Pauli blocking. However, controlling inter-band transitions of graphene in the visible and near infrared wavelengths, has been an outstanding challenge. We developed a new device to control optical properties of graphene in the visible spectra. Our device relies on a graphene supercapacitor which includes two parallel graphene electrodes and electrolyte between them. Mutual gating between graphene electrodes enables us to fabricate optical modulators which can operate in the visible and near-infrared. Single layer graphene, however, has performance limits due to its small optical absorption defined by fundamental constants. We extend our method and we developed a new class of electrochromic devices using multilayer graphene. Fabricated devices undergo a reversible color change with the electrically controlled intercalation process. The electrical and optical characterizations of the electrochromic devices reveal the broadband optical modulation up to 55 per cent in the visible and near-infrared. Integration of semiconducting materials on unconventional substrates enables optoelectronic devices with new mechanical functionalities that cannot be achieved with wafer-based technologies. As a novel application, we demonstrate ultra thin electronic paper displays using the multilayer graphene as a reconfigurable optical medium. We anticipate that the developed devices would find wide range of applications in optoelectronics.