Iron(II) spin crossover complexes display a reversible transition from low-spin (LS) state to high-spin (HS) state by e.g. variation of temperature, pressure or by irradiation with light. Therefore, these systems are promising candidates for information storage materials. In view of practical device applications thin films of these materials are needed. The SCO-compound [Fe(Htrz)2(trz)] (BF4) (1) switches between the LS and the HS state with a 50 K wide thermal hysteresis loop above room temperature. We have prepared thin films of 1 on a SiO2 substrate by spin coating. The spin states of the films have been characterized by Mössbauer spectroscopy in reflection mode using a MIMOS II spectrometer. A low quadrupole splitting (LS state) at 300 K and a high quadrupole splitting (HS state) at 400 K were found for the film, as well as for bulk powder of 1. This confirms that a spin crossover occurs above room temperature. Furthermore, synchrotron based nuclear resonance scattering measurements from 80 K to 400 K indicate that the hyperfine parameters are similar to those of the bulk powder of 1. DFT calculations reproduce the experimentally determined Fe-vibrational density of states of the bulk and of the thin film sample of 1. These results indicate that a higher fraction of HS Fe atoms is present in the film of 1. Therefore, we conclude different SCO properties of the thin film and the bulk material of 1.

We present thermal tuning of air-suspended SU-8 polymer waveguide grating couplers for TEpolarized light. Numerical simulations have been performed to estimate the wavelength shift caused by the change of temperature. Due to the small positive thermal expansion and large negative thermo-optic coefficient of SU-8, a shift toward shorter wavelengths is expected. In the experimental evaluation, a negative wavelength shift from 1542 nm at 20 degrees C toward 1527 nm at 56 degrees C is obtained with approximately -0.42 nmK(-1) matching the theoretical considerations. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)

This work presents the design, numerical simulation, fabrication and characterization of a label-free optofluidic refractive index sensor that is based on air-suspended SU-8 grating couplers. By exploiting a polymer-onto-polymer lamination method for thin structured SU-8 films, waveguide grating couplers can be fabricated in a film on top of a microfluidic channel system. A capillary force valve, integrated into the microchannels, precisely positions the employed test analytes, which are different DI water based sugar solutions, below the sensing grating coupler. By performing numerical simulations, the sensing grating coupler is optimized to a center wavelength of 1550 nm in the case that pure DI water (n = 1.33) is applied to the microfluidic channel. When a supported mode, guided in the waveguide, reaches the sensing grating region, it is exposed to the test solution resulting in a change of the effective refractive index of the mode. Similar to the simulation results, the experimental characterization of the sensor structure demonstrates a refractive index sensitivity of approximately 400 nm per refractive index unit (RIU) with respect to the wavelength shift of the grating coupler response, and 17 dB RIU-1 with respect to the intensity decrease at the individual center wavelengths for refractive index variations between n = 1.33 and n = 1.36. Due to the combination of microfluidic channels and air-suspended grating couplers, analytes can directly be probed in-line in an integrated microfluidic channel making the presented principle suitable for low-cost, in-line polymer optofluidic and photonic sensing applications. (C) 2017 Elsevier B.V. All rights reserved.

Ga(Sb)As quantum dots (QDs) are usually grown on plane GaAs substrates by self-organization in the Stranski-Krastanov mode. Here we report on Ga(As) Sb QD growth on a pre-structured GaAs substrate to achieve highly ordered QDs. The structure consists of a two-dimensional array of holes/troughs milled into the substrate (wafer with initial epitaxial buffer layer) with a gallium focused ion beam (Ga-FIB). Thus, the area density of the QDs can be controled. For exact positioning of the QDs in the milled holes it is important that the diameter of the dots equals the diameter of the milled holes. In a previous publication we have shown that we are able to change the diameter as well as the height of the QDs by controlled variation of growth temperature, Ga/Sb ratio, and nominal coverage. The diameter and depth of the milled holes as well as their separation are varied. Also, different milling techniques are examined to optimize milling time and procedure. The pre-structured GaAs substrate is overgrown in a second molecular-beam-epitaxial (MBE) step, first with another thin GaAs buffer layer, then with a QD layer. With the optimum of the milling and growth parameter sets the diameter of the QDs equals the size of the milled holes and the QDs can be grown highly ordered in the given pre-structured array. To the best of our knowledge this is the first report about exact positioning of Ga(As) Sb QDs on GaAs.

In the last two decades, focused ion beam (FIB) systems have been used for sample preparation. For example, the edges of a sample can be polished for analytical measurements or continuous cross-sections can be milled for three-dimensional (3D) tomography and reconstruction. One major challenge in both procedures is the so-called curtaining effect, i.e., increasing surface roughness in the direction of the milling depth. The roughness of the cut can influence the result of the measurement and the segmentation process. In the present study, the authors report on two different methods to reduce the curtaining effect, namely, a hardware- and a software-based solution. For instance, Tescan implemented the so-called “rocking stage” in its plasma FIB. However, this is not available for other FIB systems. Therefore, for our FEI gallium FIB, an inhouse-developed goniometer stage is installed, which can be adapted as necessary. With this relatively inexpensive solution, the sample can be rotated around an additional axis and tilted by ±8°. Different sample heights are adjustable, and the sample's edge can be polished and imaged without stage movement. However, for automated milling and imaging procedures such as 3D tomography, such a tilting stage is not feasible. Therefore, as a second option, an image processing method is proposed that can be applied after the milling procedure on a whole image stack. A novel variation of this method for mathematical image processing is developed to reduce milling artifacts. Besides the curtaining effect, additional artifacts such as discontinuities caused by redeposition of previously removed materials or charging effects can be removed. The method is applied to the entire 3D dataset, and distortions are reduced by using information of their particular structure and directional dependence. The resulting new image stack can then be used to compose a 3D volume reconstruction. As an example, the geometries of silicon carbide particles reinforcing an aluminum matrix can be measured with nearly no milling artifacts.

We present SU-8 polymer waveguide grating couplers for TE mode with enhanced refractive index contrast by employing air as upper and lower cladding layer. Numerical simulations predict a coupling loss of 4.9 dB, indicating a coupling efficiency of 32% at a maximum spectral response of 1550 nm. Based on a polymer lamination method, air-suspended waveguide grating couplers were successfully fabricated and characterized. Due to current limitations in the fabrication process, the perturbation of the experimental grating couplers is weaker than the original simulation. However, transmission measurements have shown that a single grating coupler exhibits approximately 8 dB coupling loss at a center wavelength of 1557 nm, indicating a coupling efficiency of 16% with respect to a single-mode optical fiber. The demonstrated parallel fabrication method employing the widely used SU-8 photoresist makes the polymer waveguide grating couplers very attractive for a wide range of low-cost polymer photonic applications.

A new transversal pumping scheme of fiber lasers based on the optimized manufacturing of an array of large scale ridge waveguides in fused silica is presented. Moreover their application as directional couplers interacting with a double clad optical active fiber for laser application is discussed. Conventional broad area emitters without slow axis collimation (SAC) can be used to couple light (wavelength lambda(p) = 976 nm) into the waveguide array.

A combined Raman and atomic force microscope (AFM) has been installed at beamline P01, PETRA III, DESY in Hamburg and is now available for all users of this beamline. With this unique setup nuclear resonance scattering and simultaneously performed Raman or Atomic Force Microscopy experiments are possible. Here we report on technical details of this new sample environment and on first tests with respect to the study of microstructures of spin crossover materials using 57Fe nuclear resonance scattering.

A technology for the fabrication of metallic waveguide mirrors is developed. Plane and curved waveguide mirrors, the latter acting in the same way as cylindrical lenses, are realized in benzocyclobutene (BCB) film waveguides. The waveguide mirror structure is dry-etched into the BCB film waveguide. To enhance the reflectivity of the waveguide mirrors, the waveguide edge is metallized. The BCB film waveguide mirrors are characterized with respect to waveguide attenuation and mirror reflectivity. The waveguide attenuation of the processed BCB waveguide is 0.5 dB/cm. Ag-coated BCB waveguide mirrors show a reflectivity of 71%. The efficiency of total internal reflection (TIR, i.e. in the case without metallization) at the dry-etched waveguide edge is 74%. As an application of the BCB waveguide mirrors a hybrid integrated optical module for Fourier-optical transverse mode selection in broad area lasers (BAL) is proposed.

Binary surface reliefs with sub-wavelength features making up a pseudorandom pattern based on mathematical Galois fields GF(p^m) [1, 2] can scatter incoming waves into a large number of diffraction maxima within a huge solid angle. A one-dimensional (1D) Galois number sequence can be folded into a two-dimensional (2D) array by the sino-representation [2]. This concept was been verified for acoustic waves a long time ago [3, 4] and is investigated here for visible light and THz waves. Our Galois diffusers are designed as reflection reliefs and realised by electron beam lithography for the optical regime and UV photolithography for the THz regime. Our results show that optical and THz Galois surfaces are excellent diffusers for electromagnetic waves; they distribute the reflected intensity evenly over a large number of maxima nearly within the entire half solid angle in the backward direction.

The aryl hydrocarbon receptor (AHR) is a ligand-dependent transcription factor that mediates the toxicity of dioxins, polycyclic aromatic hydrocarbons and related environmental pollutants. Besides drug metabolism, several studies have provided evidence that the AHR and its downstream targets trigger important developmental, physiological and pathophysiological processes. However, in contrast to the molecular mechanisms of AHR-dependent signaling pathways, the transcriptional regulation of the AHR gene itself is as yet only marginally understood. We found that the pleiotropic interleukin (IL)-6-type cytokine oncostatinM (OSM) is an inducer of AHR mRNA and protein expression in human HepG2 hepatocarcinoma cells. Analyses of the human AHR promoter revealed the existence of a putative signal transducer and activator of transcription (STAT)-binding element 5-upstream of the transcription start site. By means of site-directed mutagenesis, inhibitor experiments and electrophoretic mobility shift assays, we demonstrated that this STAT motif is recognized by STAT3 to regulate basal and cytokine-inducible AHR expression in HepG2 cells. The identification of the AHR as a downstream target of IL-6-type cytokine-stimulated STAT3 signaling may contribute to a better understanding of the multiple facets of AHR during development, physiology and disease.

We report on a technology to reach different etch depths in fused silica simultaneously by using different diameters of the openings in the etch mask. Usually, the etch rate is determined by the etch solution, the temperature, and the concentration of the etch solution as well as the material to be etched. We show that the etch rate will also depend on the diameter of the opening in the etch mask, if the diameter is <150 mu m. This is due to an impeded refreshing of the etch solution in the groove. This effect allows for reaching different etch depths in only one etch step. For certain etch parameters, due to the isotropic nature of the process, etch profiles representing perfect half spheres (grooves) can be achieved by using round openings in the etch mask. Our application is the fabrication of masters for silicone micro-molding of a microscopic iris array. Half spheres with two different radii are etched into fused silica simultaneously. As etch mask a combination of a soft and a hard lithographic mask is used. (C) 2013 Elsevier B.V. All rights reserved.

We have fabricated ridge waveguides in lithium niobate with sidewall roughness of 14 nm (rms) and sidewall angles of more than 71°. The use of thick electroplated metal masks for reactive ion etching (RIE) makes it possible to manufacture ridge structures with several microns in height. For light confinement towards the substrate we investigate direct heterobonding techniques. Due to the expected low transmission losses we envision future applications in the field of quantum optics.

The skin reacts to environmental noxae by inducing cytochrome P450 (CYP)-catalyzed reactions via activation of the aryl hydrocarbon receptor (AhR). A drawback of this response is the generation of oxidative stress, which is especially dangerous for postreplicative cells such as dermal fibroblasts, in which damage may accumulate over time. Accordingly, in dermal fibroblasts, CYP1 expression is repressed and it has been proposed that this is due to the AhR repressor (AhRR), which is supposedly overexpressed in fibroblasts as compared with other skin cells. Here, we revisited this "AhRR hypothesis", which has been mainly based on ectopic overexpression studies and correlation analyses of high AhRR gene expression with CYP1A1 repression in certain cell types. In primary human skin fibroblasts (NHDFs) of 25 individuals, we found that (i) the AhRR was expressed only at moderate RNA copy numbers and that, against the common view, (ii) in some fibroblast strains, CYP1A1 mRNA expression could be induced by AhR activators. However, even the highest induction did not translate into measurable CYP1 enzyme activity, and neither basal expression nor mRNA inducibility correlated with AhRR expression. In addition, enhancement of CYP1A1 mRNA expression by trichostatin A, which inhibits AhRR-recruited histone deacetylases at the CYP1A1 promoter, failed to induce measurable CYP1 activity. Finally, AhRR-deficient ((-/-)) mouse embryonic fibroblasts were not induced to biologically relevant CYP1 enzyme activity despite impressive mRNA induction. These data clearly indicate that repressed CYP1 activity in NHDFs is not causally related to AhRR expression, which may serve a different, yet unknown, biological function. Journal of Investigative Dermatology (2013) 133, 87-96; doi:10.1038/jid.2012.259; published online 6 September 2012

Microelectrode electrophysiology has become a widespread technique for the extracellular recording of bioelectrical signals. To date, electrodes are made of metals or inorganic semiconductors, or hybrids thereof. We demonstrate that these traditional conductors can be completely substituted by highly flexible electroconductive polymers. Pursuing a two-level replica-forming strategy, conductive areas for electrodes, leads and contact pads are defined as microchannels in poly(dimethylsiloxane) (PDMS) as a plastic carrier and track insulation material. These channels are coated by films of organic conductors such as polystyrenesulfonate-doped poly(3,4-ethylenedioxy-thiophene) (PEDOT:PSS) or filled with a graphite-PDMS (gPDMS) composite, either alone or in combination. The bendable, somewhat stretchable, non-cytotoxic and biostable all-polymer microelectrode arrays (polyMEAs) with a thickness below 500 μm and up to 60 electrodes reliably capture action potentials (APs) and local field potentials (LFPs) from acute preparations of heart muscle cells and retinal whole mounts, in vivo epicortical and epidural recordings as well as during long-term in vitro recordings from cortico-hippocampal co-cultures.

Diamond is an attractive material for photonic quantum technologies because its colour centres have a number of outstanding properties, including bright single photon emission and long spin coherence times. To take advantage of these properties it is favourable to directly fabricate optical microcavities in high-quality diamond samples. Such microcavities could be used to control the photons emitted by the colour centres or to couple widely separated spins. Here, we present a method for the fabrication of one- and two-dimensional photonic crystal microcavities with quality factors of up to 700 in single crystal diamond. Using a post-processing etching technique, we tune the cavity modes into resonance with the zero phonon line of an ensemble of silicon-vacancy colour centres, and we measure an intensity enhancement factor of 2.8. The controlled coupling of colour centres to photonic crystal microcavities could pave the way to larger-scale photonic quantum devices based on single crystal diamond.

Spray coating of polymethylmethacrylate (PMMA) as electron beam resist on non planar surfaces is presented as a reliable technique for deposition of uniform resist layers with adjustable thickness at wafer scale. In the experiments a commercial spray coating system with an ultrasonic spray nozzle was used. Parameters which influence the quality of the resist layer with respect to uniformity across a 4in Si wafer, such as ultrasonic power and dispensed volume, were evaluated. The suitability of spray coated PMMA for the pattern transfer on surfaces with high topography was proven by PMMA spray coating of 8@mm deep trenches etched into Si wafers. The PMMA was then electron beam exposed and chromium line patterns were transferred on the Si surface via a lift-off process.

1. Universität des Saarlandes, Fachrichtung 7.2 (Experimentalphysik), 66123 Saarbrücken, Germany 2. Universität des Saarlandes, Fachrichtung 8.4 (Materialwissenschaft und Werkstofftechnik), 66123 Saarbrücken, Germany 3. University of Freiburg, Departement of Microsystems Engineering (IMTEK), Cleanroom Service Center, 79110 Freiburg, Germany 4. TU Kaiserslautern, Nano+Bio Center, 67653 Kaiserslautern, Germany 5. Universität Augsburg, Lehrstuhl für Experimentalphysik IV, 86159 Augsburg, Germany