Gilles S.,Jülich Research Center |
Gilles S.,RWTH Aachen |
Kaulen C.,JARA Fundamentals of Future Information Technology |
Kaulen C.,RWTH Aachen |
And 5 more authors.
Nanotechnology | Year: 2011
Chemical templates for the patterned immobilization of gold nanoparticles were fabricated by soft UV nanoimprint lithography. The template structures were fabricated by means of the consecutively performed process steps of nanoimprint lithography, reactive ion etching, chemical functionalization with amino groups, and lift-off of imprint resist. These chemical templates were used for the defined assembly of 20nm diameter citrate stabilized gold nanoparticles from aqueous solution. By reducing the ionic strength of the solution, one-and zero-dimensional particle assemblies were generated on sub-100-nm template structures. By this means, the pattern resolution predefined by the lithography process could be easily enhanced by dilution of the nanoparticle solution. © 2011 IOP Publishing Ltd.
Schulenborg J.,Chalmers University of Technology |
Saptsov R.B.,RWTH Aachen |
Haupt F.,JARA Fundamentals of Future Information Technology |
Haupt F.,RWTH Aachen |
And 3 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2016
We study the transient heat current out of a confined electron system into a weakly coupled electrode in response to a voltage switch. We show that the decay of the Coulomb interaction energy for this repulsive system exhibits signatures of electron-electron attraction, and is governed by an interaction-independent rate. This can only be understood from a general duality that relates the nonunitary evolution of a quantum system to that of a dual model with inverted energies. Deriving from the fermion-parity superselection postulate, this duality applies to a large class of open systems. © 2016 American Physical Society.
Bruggemann D.,Jülich Research Center |
Bruggemann D.,Trinity College Dublin |
Michael K.E.,JARA Fundamentals of Future Information Technology |
Wolfrum B.,Jülich Research Center |
Offenhausser A.,Jülich Research Center
International Journal of Nano and Biomaterials | Year: 2012
Cell-electrode interfaces play a critical role in extracellular recording. Enlarging the electrode surface area with nanostructures yields higher signal-to-noise-ratios due to lower interface impedance. Adhesion and viability of various cell types on large-scale gold nanopillar electrodes to improve cell-electrode coupling were investigated. Cardiac muscle and human embryonic kidney cells survived and adhered well on gold nanopillars. The muscle cells even protruded into inter-pillar cavities with diameters below 100 nm. However, an unexpectedly low viability and adhesion of primary rat neurons was observed on nanopillars. A cross-sectional analysis of the cell-nanopillar interface showed large distances between neuronal cell bodies and nanopillars, whereas the neurites adhered tightly. Furthermore, actin assembly within the neuronal growth cones was modified on nanopillars. In summary, the adhesion response of the investigated cell lines will be beneficial for improved extracellular signalling, whereas a better understanding of neuronal responses to nanotopographies is required to enhance the neuronal viability. Copyright © 2012 Inderscience Enterprises Ltd.
Kugeler C.,Jülich Research Center |
Kugeler C.,Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research |
Rosezin R.,Jülich Research Center |
Linn E.,JARA Fundamentals of Future Information Technology |
And 4 more authors.
Applied Physics A: Materials Science and Processing | Year: 2011
The paper reports on the characterization of bipolar resistive switching materials and their integration into nanocrossbar structures, as well as on different memory operation schemes in terms of memory density and the challenging problem of sneak paths. TiO 2, WO 3 , GeSe, SiO 2 and MSQ thin films were integrated into nanojunctions of 100 × 100 nm 2. The variation between inert Pt and Cu or Ag top electrodes leads to valence change (VCM) switching or electrochemical metallization (ECM) switching and has significant impact on the resistive properties. All materials showed promising characteristics with switching speeds down to 10 ns, multilevel switching, good endurance and retention. Nanoimprint lithography was found to be a suitable tool for processing crossbar arrays down to a feature size of 50 nm and 3D stacking was demonstrated. The inherent occurrence of current sneak paths in passive crossbar arrays can be circumvented by the implementation of complementary resistive switching (CRS) cells. The comparison with other operation schemes shows that the CRS concept dramatically increases the addressable memory size to about 10 10 bit. © Springer-Verlag 2011.
Gilles S.,Jülich Research Center |
Gilles S.,RWTH Aachen |
Winter S.,Jülich Research Center |
Michael K.E.,Jülich Research Center |
And 7 more authors.
Small | Year: 2012
Guiding of neuronal cells on surfaces is required for the investigation of fundamental aspects of neurobiology, for tissue engineering, and for numerous bioelectronic applications. A modular method to establish nanostructured chemical templates for local deposition of gold nanoparticles is presented. A process comprising nanoimprint lithography, silanization, lift-off, and gold nanoparticle immobilization is used to fabricate the particle patterns. The chemical composition of the surface can be modified by in situ adsorption of cell-binding ligands to locally addressed particles. The versatility of this approach is demonstrated by inverting the binding affinity between rat cortical neurons and nanopatterned surfaces via wet-chemical means and thereby reversing the pattern of guided neurons. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Ohm C.,RWTH Aachen |
Stampfer C.,JARA Fundamentals of Future Information Technology |
Stampfer C.,RWTH Aachen |
Stampfer C.,Jülich Research Center |
And 3 more authors.
Applied Physics Letters | Year: 2012
We propose a scheme for spin-based detection of the bending motion in suspended carbon-nanotubes, using the curvature-induced spin-orbit interaction. We show that the resulting effective spin-phonon coupling can be used to down-convert the high-frequency vibration-modulated spin-orbit field to spin-flip processes at a much lower frequency. This vibration-induced spin-resonance can be controlled with an axial magnetic field. We propose a Pauli spin blockade readout scheme and predict that the leakage current shows pronounced peaks as a function of the external magnetic field. Whereas the resonant peaks allow for frequency readout, the slightly off-resonant current is sensitive to the vibration amplitude. © 2012 American Institute of Physics.
Mikulics M.,Jülich Research Center |
Kordos P.,JARA Fundamentals of Future Information Technology |
Kordos P.,Slovak University of Technology in Bratislava |
Kordos P.,Slovak Academy of Sciences |
And 8 more authors.
IEEE Photonics Technology Letters | Year: 2011
We have fabricated and characterized ultrafast metal-semiconductor-metal (MSM) photodetectors integrated with metal-semiconductor-field-effect- transistors (MESFETs) integrated in coplanar strip lines in the GaN/AlN/SiC material system. We recorded electrical transients of the single photodetector as short as 0.9 ps wide by optoelectric pump-probe measurements using 360-nm-wavelength and 100-fs-duration laser pulses. Electric photoresponse transients of the photodetector with 6-mV peak amplitude were amplified by the MESFET, resulting in 4-ps-wide and 35-mV peak amplitude signals. This monolithically integrated optoelectronic circuit is presented as a potential candidate for high-speed ultraviolet optoelectronics. © 2011 IEEE.
Kuhlen S.,RWTH Aachen |
Schmalbuch K.,RWTH Aachen |
Hagedorn M.,RWTH Aachen |
Schlammes P.,RWTH Aachen |
And 5 more authors.
Physical Review Letters | Year: 2012
Full electric-field control of spin orientations is one of the key tasks in semiconductor spintronics. We demonstrate that electric-field pulses can be utilized for phase-coherent ±π spin rotation of optically generated electron spin packets in InGaAs epilayers detected by time-resolved Faraday rotation. Through spin-orbit interaction, the electric-field pulses act as local magnetic field pulses. By the temporal control of the local magnetic field pulses, we can turn on and off electron spin precession and thereby rotate the spin direction into arbitrary orientations in a two-dimensional plane. Furthermore, we demonstrate a spin-echo-type spin drift experiment and find an unexpected partial spin rephasing, which is evident by a doubling of the spin dephasing time. © 2012 American Physical Society.
Spilla S.,RWTH Aachen |
Spilla S.,University of Palermo |
Hassler F.,JARA Fundamentals of Future Information Technology |
Hassler F.,RWTH Aachen |
Splettstoesser J.,RWTH Aachen
New Journal of Physics | Year: 2014
We study a flux qubit made of a superconducting loop interrupted by three Josephson junctions, which is subject to a temperature gradient. We show that the heat current induced by the temperature gradient, being sensitive to the superconducting phase differences at the junctions, depends significantly on the state of the qubit. We furthermore investigate the impact of the heat current on the coherence properties of the qubit state. We have found that even small temperature gradients can lead to dephasing times of the order of microseconds for the Delft-qubit design. © 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Gottel S.,RWTH Aachen |
Andergassen S.,RWTH Aachen |
Andergassen S.,University of Vienna |
Honerkamp C.,JARA Fundamentals of Future Information Technology |
And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2012
We apply a recently developed functional renormalization group (FRG) scheme for quantum spin systems to the spin-1/2 antiferromagnetic XXZ model on a two-dimensional square lattice. Based on an auxiliary fermion representation we derive flow equations which allow a resummation of the perturbation series in the spin-spin interactions. Spin susceptibilities are calculated for different values of the anisotropy parameter. The phase transition between planar and axial ordering at the isotropic point is reproduced correctly. The results for the critical scales from the FRG as quantitative measures for the ordering temperatures are in good agreement with the exact solution only in the Ising limit. In particular on the easy-plane side, the deviations from critical temperatures obtained with quantum Monte Carlo are rather large. Furthermore, at the isotropic point the Mermin-Wagner theorem is violated such that a description of the critical behavior and an extraction of scaling exponents is not possible. We discuss possible reasons for these discrepancies. © 2012 American Physical Society.