Publications (18) View all
-
Article: Self-assembled ultra-compact energy storage elements based on hybrid nanomembranes.
[show abstract] [hide abstract]
ABSTRACT: Self-assembly methods combined with standard top-down approaches are demonstrated to be suitable for fabricating three-dimensional ultracompact hybrid organic/inorganic electronic devices based on rolled-up nanomembranes. Capacitors that are self-wound and manufactured in parallel are almost 2 orders of magnitude smaller than their planar counterparts and exhibit capacitances per footprint area of around 200 microF/cm(2). This value significantly exceeds that which was previously reported for metal-insulator-metal capacitors based on Al(2)O(3), and the obtained specific energy (approximately 0.55 Wh/kg) would allow their usage as ultracompact supercapacitors. By incorporating organic monolayers into the inorganic nanomembrane structure we can precisely control the electronic characteristics of the devices. The adaptation of the process for creating ultracompact batteries, coils and transformers is an attractive opportunity for reducing the size of energy storage elements, filters, and signal converters. These devices can be employed as implantable electronic circuits or new approaches for energy-harvesting applications. Furthermore, the incorporation of functional organic molecules gives rise to novel devices with almost limitless chemical and biological functionalities.Nano Letters 07/2010; 10(7):2506-10. · 13.20 Impact Factor -
Article: Nonlinearity exponents in lightly doped Conducting Polymers
[show abstract] [hide abstract]
ABSTRACT: The I-V characteristics of four conducting polymer systems such as doped polypyrrole, poly(3,4-ethylenedioxythiophene), polydiacetylene, and polyaniline in as many physical forms have been investigated at different temperatures, quenched disorder, and magnetic fields. Transport data clearly show the existence of a single electric-field scale in each system. Based upon this observation, a phenomenological scaling analysis is performed, leading to the extraction of a numerical value for a nonlinearity exponent called xM which serves to characterize a set of I-V curves. The conductivity starts deviating from an Ohmic value σ0 above an onset electric field Fo which scales according to Fo∼σ0xM. The electric-field-dependent data are shown to be described by the multistep tunneling model of Glazman-Matveev [ JETP 67 1276 (1988)] in a near-perfect manner over nine orders of magnitude in conductivity and five orders of magnitude in electric field. Furthermore, xM is found to possess both positive and negative values lying between −1/2 and 3/4. There is no theory at present for this exponent. Some issues concerning applicability of the Glatzman-Matveev model are discussed.Physical Review B 02/2011; 84:054205. · 3.69 Impact Factor -
Article: Influence of the polymerization potential on the transport properties of polypyrrole films.
[show abstract] [hide abstract]
ABSTRACT: Polypyrrole films have been prepared by potentiostatic electrochemical polymerization at low temperatures. The cyclic voltammograms and the electronic transport properties of the films are investigated as a function of the polymerization potential. As the potential increases from 520 mV to 1.2 V, the oxidation peak moves to larger voltages, while above 1.2 V, the peak voltage drops again. The film conductivity drops monotonously as the polymerization potential is increased. However, the localization length of the current-carrying states, which characterizes the temperature dependence of the conductivity, correlates with the oxidation peak and shows a minimum for films polymerized at 1.2 V. Furthermore, we show that, with an independent doping step after polymerization, the conductivity of the films can be increased by up to 50%. A maximum conductivity of 1360 S/cm has been observed.The Journal of Physical Chemistry B 12/2009; 114(2):714-8. · 3.70 Impact Factor -
Article: Transport properties of chemically synthesized polypyrrole thin films
[show abstract] [hide abstract]
ABSTRACT: The electronic transport in polypyrrole thin films synthesized chemically from the vapor phase is studied as a function of temperature as well as of electric and magnetic fields. We find distinct differences in comparison to the behavior of both polypyrrole films prepared by electrochemical growth as well as of the bulk films obtained from conventional chemical synthesis. For small electric fields F, a transition from Efros-Shklovskii variable range hopping to Arrhenius activated transport is observed at 30 K. High electric fields induce short range hopping. The characteristic hopping distance is found to be proportional to F^(-1/2). The magnetoresistance R(B) is independent of F below a critical magnetic field, above which F counteracts the magnetic field induced localization. Comment: 6 pages, 5 figures07/2007; -
Article: Hybrid organic/inorganic molecular heterojunctions based on strained nanomembranes.
[show abstract] [hide abstract]
ABSTRACT: In this work, we combine self-assembly and top-down methods to create hybrid junctions consisting of single organic molecular monolayers sandwiched between metal and/or single-crystalline semiconductor nanomembrane based electrodes. The fabrication process is fully integrative and produces a yield loss of less than 5% on-chip. The nanomembrane-based electrodes guarantee a soft yet robust contact to the molecules where the presence of pinholes and other defects becomes almost irrelevant. We also pioneer the fabrication and characterization of semiconductor/molecule/semiconductor tunneling heterojunctions which exhibit a double transition from direct tunneling to field emission and back to direct tunneling, a phenomenon which has not been reported previously.Nano Letters 08/2011; 11(9):3727-33. · 13.20 Impact Factor
