Center for Functional Nanostructures

Karlsruhe, Germany

Center for Functional Nanostructures

Karlsruhe, Germany
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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.

Engel M.,Karlsruhe Institute of Technology | Engel M.,Center for Functional Nanostructures | Steiner M.,IBM | Lombardo A.,University of Cambridge | And 7 more authors.
Nature Communications | Year: 2012

Graphene has extraordinary electronic and optical properties and holds great promise for applications in photonics and optoelectronics. Demonstrations including high-speed photodetectors, optical modulators, plasmonic devices, and ultrafast lasers have now been reported. More advanced device concepts would involve photonic elements such as cavities to control light-matter interaction in graphene. Here we report the first monolithic integration of a graphene transistor and a planar, optical microcavity. We find that the microcavity-induced optical confinement controls the efficiency and spectral selection of photocurrent generation in the integrated graphene device. A twenty-fold enhancement of photocurrent is demonstrated. The optical cavity also determines the spectral properties of the electrically excited thermal radiation of graphene. Most interestingly, we find that the cavity confinement modifies the electrical transport characteristics of the integrated graphene transistor. Our experimental approach opens up a route towards cavity-quantum electrodynamics on the nanometre scale with graphene as a current-carrying intra-cavity medium of atomic thickness. © 2012 Macmillan Publishers Limited. All rights reserved.

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.

Rauhut N.,Ludwig Maximilians University of Munich | Engel M.,Karlsruhe Institute of Technology | Engel M.,Center for Functional Nanostructures | Steiner M.,IBM | And 5 more authors.
ACS Nano | Year: 2012

We present the first photocurrent measurements along single carbon nanotube (CNT) devices with 30 nm resolution. Our technique is based on tip-enhanced near-field optical microscopy, exploiting the plasmonically enhanced absorption controlled by an optical nanoantenna. This allows for imaging of the zero-bias photocurrent caused by charge separation in local built-in electric fields at the contacts and close to charged particles that cannot be resolved using confocal microscopy. Simultaneously recorded Raman scattering images reveal the structural properties and the defect densities of the CNTs. Antenna-enhanced scanning photocurrent microscopy extends the available set of scanning-probe techniques by combining high-resolution photovoltaic and optical probing and could become a valuable tool for the characterization of nanoelectronic devices. © 2012 American Chemical Society.

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.

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.

Marquardt C.W.,Karlsruhe Institute of Technology | Grunder S.,University of Basel | Blaszczyk A.,Karlsruhe Institute of Technology | Blaszczyk A.,Poznań University of Economics | And 9 more authors.
Nature Nanotechnology | Year: 2010

The positioning of single molecules between nanoscale electrodes 1-8 has allowed their use as functional units in electronic devices. Although the electrical transport in such devices has been widely explored, optical measurements have been restricted to the observation of electroluminescence from nanocrystals and nanoclusters9,10 and from molecules in a scanning tunnelling microscope setup11,12. In this Letter, we report the observation of electroluminescence from the core of a rod-like molecule between two metallic single-walled carbon nanotube electrodes forming a rigid solid-state device. We also develop a simple model to explain the onset voltage for electroluminescence. These results suggest new characterization and functional possibilities, and demonstrate the potential of carbon nanotubes for use in molecular electronics. © 2010 Macmillan Publishers Limited. All rights reserved.

Lemasson F.,Karlsruhe Institute of Technology | Berton N.,Karlsruhe Institute of Technology | Tittmann J.,Karlsruhe Institute of Technology | Hennrich F.,Karlsruhe Institute of Technology | And 5 more authors.
Macromolecules | Year: 2012

To date, (n, m) single-walled carbon nanotubes (SWNTs) cannot be selectively synthesized. Therefore, postprocessing of SWNTs including solubilization and sorting is necessary for further applications. Toward this goal, we have synthesized a polymer library consisting of fluorene- and carbazole-based homo- and copolymers. Variations of the connection of these aromatics together with the incorporation of further conjugated monomers give access to a broad diversity of polymers. Their ability to selectively wrap specific (n, m) species is investigated toward HiPco SWNTs raw material which contains more than 40 (n, m) species. Absorption and fluorescence spectroscopies were used to analyze SWNTs/polymer suspensions. These results provide evidence for selective SWNTs/polymer interactions and allow a more detailed assessment of polymer structure-property relationships, thus paving the way toward custom synthesis of polymers for single (n, m) SWNTs extraction. © 2011 American Chemical Society.

Schwab P.M.,Karlsruhe Institute of Technology | Moosmann C.,Karlsruhe Institute of Technology | Wissert M.D.,Karlsruhe Institute of Technology | Schmidt E.W.-G.,Karlsruhe Institute of Technology | And 6 more authors.
Nano Letters | Year: 2013

We experimentally determine the order of multiphoton induced luminescence of aluminum nanoantennas fabricated on a nonconductive substrate using electron-beam lithography to be 2.11 (±0.10). Furthermore, we optically characterize these nanostructures via linear dark-field microscopy and nonlinear multiphoton laser excitation. We hereby observe different spectral response functions that can be seen as a splitting of peak positions when the antenna arm length is increased to Larm > 150 nm which has not yet been reported for aluminum nanostructures. © 2013 American Chemical Society.

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.

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