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Karlsruhe, Germany

Liu X.,Light Technology | Liu X.,Institute of Microstructure Technology IMT | Lebedkin S.,Institute of Nanotechnology INT | Besser H.,Karlsruhe Institute of Technology | And 13 more authors.
ACS Nano | Year: 2015

Organic semiconductor distributed feedback (DFB) lasers are of interest as external or chip-integrated excitation sources in the visible spectral range for miniaturized Raman-on-chip biomolecular detection systems. However, the inherently limited excitation power of such lasers as well as oftentimes low analyte concentrations requires efficient Raman detection schemes. We present an approach using surface-enhanced Raman scattering (SERS) substrates, which has the potential to significantly improve the sensitivity of on-chip Raman detection systems. Instead of lithographically fabricated Au/Ag-coated periodic nanostructures on Si/SiO2 wafers, which can provide large SERS enhancements but are expensive and time-consuming to fabricate, we use low-cost and large-area SERS substrates made via laser-assisted nanoreplication. These substrates comprise gold-coated cyclic olefin copolymer (COC) nanopillar arrays, which show an estimated SERS enhancement factor of up to ∼107. The effect of the nanopillar diameter (60-260 nm) and interpillar spacing (10-190 nm) on the local electromagnetic field enhancement is studied by finite-difference-time-domain (FDTD) modeling. The favorable SERS detection capability of this setup is verified by using rhodamine 6G and adenosine as analytes and an organic semiconductor DFB laser with an emission wavelength of 631.4 nm as the external fiber-coupled excitation source. © 2014 American Chemical Society. Source

Comba P.,University of Heidelberg | Grosshauser M.,University of Heidelberg | Klingeler R.,University of Heidelberg | Koo C.,University of Heidelberg | And 8 more authors.
Inorganic Chemistry | Year: 2015

A series of seven isostructural homodinuclear lanthanide complexes are reported. The magnetic properties (ac and dc SQUID measurements) are discussed on the basis of the X-ray structural properties which show that the two lanthanide sites are structurally different. MCD spectroscopy of the dysprosium(III) and neodymium(III) complexes ([DyIII 2(L)(OAc)4]+ and [NdIII 2(L)(OAc)4]+) allowed us to thoroughly analyze the ligand field, and high-frequency EPR spectroscopy of the gadolinium(III) species ([GdIII 2(L)(OAc)4]+) showed the importance of dipolar coupling in these systems. An extensive quantum-chemical analysis of the dysprosium(III) complex ([DyIII 2(L)(OAc)4]+), involving an ab initio (CASSCF) wave function, explicit spin-orbit coupling (RASSI-SO), and a ligand field analysis (Lines model and Stevens operators), is in full agreement with all experimental data (SQUID, HF-EPR, MCD) and specifically allowed us to accurately simulate the experimental χT versus T data, which therefore allowed us to establish a qualitative model for all relaxation pathways. © 2015 American Chemical Society. Source

Schumann M.,Karlsruhe Institute of Technology | Schumann M.,Institute of Nanotechnology INT | Buckmann T.,Karlsruhe Institute of Technology | Gruhler N.,Institute of Nanotechnology INT | And 3 more authors.
Light: Science and Applications | Year: 2014

Integrated optical chips have already been established for application in optical communication. They also offer interesting future perspectives for integrated quantum optics on a chip. At present, however, they are mostly fabricated using essentially planar fabrication approaches like electron-beam lithography or UV optical lithography. Many further design options would arise if one had complete fabrication freedom in regard to the third dimension normal to the chip without having to give up the virtues and the know-how of existing planar fabrication technologies. As a step in this direction, we here use three-dimensional dip-in direct-laser-writing optical lithography to fabricate three-dimensional polymeric functional devices on pre-fabricated planar optical chips containing Si 3 N 4 waveguides as well as grating couplers made by standard electron-beam lithography. The first example is a polymeric dielectric rectangular-shaped waveguide which is connected to Si 3 N 4 waveguides and that is adiabatically twisted along its axis to achieve geometrical rotation of linear polarization on the chip. The rotator's broadband performance at around 1550nm wavelength is verified by polarization-dependent grating couplers. Such polarization rotation on the optical chip cannot easily be achieved by other means. The second example is a whispering-gallery-mode optical resonator connected to Si 3 N 4 waveguides on the chip via polymeric waveguides. By mechanically connecting the latter to the disk, we can control the coupling to the resonator and, at the same time, guarantee mechanical stability of the three-dimensional architecture on the chip. Source

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