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Mastronardi M.L.,University of Toronto | Hennrich F.,Karlsruhe Institute of Technology | Henderson E.J.,University of Toronto | Maier-Flaig F.,Karlsruhe Institute of Technology | And 8 more authors.
Journal of the American Chemical Society | Year: 2011

We report the preparation of monodisperse silicon nanocrystals (ncSi) by size-separation of polydisperse alkyl-capped ncSi using organic density gradient ultracentrifugation. The ncSi were synthesized by thermal processing of trichlorosilane-derived sol-gel glasses followed by HF etching and surface passivation with alkyl chains and were subsequently fractionated by size using a self-generating density gradient of 40 wt % 2,4,6-tribromotoluene in chlorobenzene. The isolated monodisperse fractions were characterized by photoluminescence spectroscopy and high-angle annular dark-field scanning transmission electron microscopy and determined to have polydispersity index values between 1.04 and 1.06. The ability to isolate monodisperse ncSi will allow for the quantification of the size-dependent structural, optical, electrical, and biological properties of silicon, which will undoubtedly prove useful for tailoring property-specific optoelectronic and biomedical devices. © 2011 American Chemical Society. Source


Marek P.L.,Karlsruhe Institute of Technology | Hahn H.,Karlsruhe Institute of Technology | Hahn H.,TU Darmstadt | Hahn H.,Center for Functional Nanostructures | Balaban T.S.,CNRS Institute of Molecular Sciences of Marseilles
Energy and Environmental Science | Year: 2011

Efforts for building hybrid solar cells which have an antenna system similar to the chlorosomes of green photosynthetic bacteria are reviewed and discussed in the context of the current state-of-the-art. © 2011 The Royal Society of Chemistry. Source


Tune D.D.,Flinders University | Flavel B.S.,Karlsruhe Institute of Technology | Krupke R.,Karlsruhe Institute of Technology | Krupke R.,Center for Functional Nanostructures | And 2 more authors.
Advanced Energy Materials | Year: 2012

Due to the high cost of silicon photovoltaics there is currently great interest in fi nding alternative semiconductor materials for light harvesting devices. Single-walled carbon nanotubes are an allotrope of carbon with unique electrical and optical properties and are promising as future photovoltaic materials. It is thus important to investigate the methods of exploiting their properties in photovoltaic devices. In addition to already extensive research using carbon nanotubes in organic photovoltaics and photoelectrochemical cells, another way to do this is to combine them with a relatively well understood model semiconductor such as silicon. Nanotube-silicon heterojunction solar cells are a recent photovoltaic architecture with demonstrated power conversion effi ciencies of up to ̃ 14% that may in part exploit the photoactivity of carbon nanotubes. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Kamleitner I.,Karlsruhe Institute of Technology | Shnirman A.,Karlsruhe Institute of Technology | Shnirman A.,Center for Functional Nanostructures
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

For adiabatically and periodically manipulated dissipative quantum systems, we derive, using Floquet theory, a simple Markovian master equation. Contrary to some previous works, we explicitly take into account the time dependence of the Hamiltonian and, therefore, obtain a master equation with a time-dependent dissipative part. We illustrate our theory with two examples and compare our results with the previously proposed master equations. In particular, we consider the problem of Cooper-pair pumping and demonstrate the inadequacy of the secular (rotating-wave) approximation when calculating the pumped charge. The secular approximation producing a master equation of the Lindblad-type approximates well the quantum state (density matrix) of the system, while to determine the pumped charge, a non-Lindblad master equation beyond the rotating-wave approximation is necessary. © 2011 American Physical Society. Source


Sundaram R.S.,Max Planck Institute for Solid State Research | Steiner M.,IBM | Chiu H.-Y.,IBM | Engel M.,Karlsruhe Institute of Technology | And 8 more authors.
Nano Letters | Year: 2011

We combine optical microspectroscopy and electronic measurements to study how gold deposition affects the physical properties of graphene. We find that the electronic structure, the electron-phonon coupling, and the doping level in gold-plated graphene are largely preserved. The transfer lengths for electrons and holes at the graphene-gold contact have values as high as 1.6 μm. However, the interfacial coupling of graphene and gold causes local temperature drops of up to 500 K in operating electronic devices. © 2011 American Chemical Society. Source

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