SOI-based optical board technology

A SOI-based optical board technology is presented. Hybrid integration combines the strength of silicon and InP. The SOI board provides passive optical components and acts as the mounting platform. Adapted active III/V devices are integrated using Au/Sn solder technology and passive alignment. Precise mounting of lasers on the board is necessary to ensure low coupling losses.     

Organic field effect transistors with ferroelectric hysteresis

The ferroelectric copolymer Poly(vinylidene fluoride trifluoroethylene) is used as insulating material for capacitor structures and organic field effect transistors. For capacitors, we find the typical hysteresis in the capacitance-voltage characteristic upon increasing the voltage scan window. A writing process with adequate electric fields causes shifts in the flatband voltage. Based on these results, we fabricate organic transistors with regioregular poly(3-hexylthiophene) as organic semiconductor. The transistors are constructed in bottom gate architecture with thin layers (100 nm) of spincoated copolymer as gate insulation. The drain source current of the transistor is reversible affected by the polarized gate, which gives opportunities for fabrication of organic nonvolatile memory elements.     

Punching behavior of biaxial hollow slabs

The invention of a new kind of hollow slab with plastic balls as hollow bodies entailed the necessity to investigate its structural behavior. Because of its main field of application as a flat slab, the punching shear capacity is one of the most interesting properties of this slab. To investigate the influence of the cavities on the punching behavior, tests were carried out at the Institute for Concrete Structures in Darmstadt. In addition to these tests nonlinear computations using the Finite Element Method were performed. The computations allowed parametric studies to get a better understanding of the structural behavior without doing further expensive tests. Finally, necessary modifications of existing design recommendations according to the German design code DIN 1045 [1] were developed.     

Hydrodechlorination of chloroorganic compounds in ground water by palladium catalysts: Part 1. Development of polymer-based catalysts and membrane reactor tests

A polymer-based catalytic membrane reactor was developed and applied for hydrodechlorination of chlorobenzene as a model compound of ground and waste water contaminants. The catalytically active membrane consists of a non-porous, thin film (about 3–7 μm) of poly(dimethylsiloxane) (PDMS) loaded with nano-sized Pd clusters. They were built-in either directly or as nano-sized, supported catalysts. A composite membrane, consisting of porous poly(acrylonitrile) (PAN) support and a Pd-loaded thin PDMS film, was fabricated on a coating machine. Defect-free membrane envelopes of 0.1 m² were produced and fitted into a membrane test cell. Gaseous hydrogen as reductant for hydrodechlorination is fed from the membrane’s back side directly to the catalyst, embedded in the PDMS layer. The chemical reactions at the Pd surface are accompanied by absorption of chlorobenzene from the water phase into the PDMS layer and desorption of benzene and HCl back to the water phase. The specific activity of supported catalysts decreased only slightly by PDMS incorporation, e.g., from 31 l/g(Pd) min for Pd/Fe on titania to 16 l/g(Pd) min for the same catalyst built-in a 7 μm thick supported PDMS membrane and measured in the membrane test cell. Directly built-in Pd clusters are less active and more difficult to prepare on a larger scale. Some catalyst deactivation was observed and may be balanced by development of more suited nano-sized supported catalysts.     

Plasmagestützte Oberflächenfunktionalisierung komplex strukturierter,miniaturisierter Kunststoff‐Formteile. Plasma assisted surface functionalization of miniaturized plastic devices

Different methods can be used for chemical surface functionalization of devices made from plastics in order to prepare them for coating, joining and similar purposes. The methods exhibit different usage properties concerning achievable surface effects as well as processing conditions. Methods based on low pressure plasmas can be demonstrated to be favorable in both aspects for functionalization of geometrically complex devices. Especially, the gap penetration capability of plasma proves to be unique. Even extremely small sized and complex miniaturized devices can be treated this way. Investigations using gas phase grafting reactions revealed access to and homogenous treatment of very small gap structures which can not be treated otherwise.     

An ultrahigh vacuum fast-scanning and variable temperature scanning tunneling microscope for large scale imaging

We describe the design and performance of a fast-scanning, variable temperature scanning tunneling microscope (STM) operating from 80 to 700 K in ultrahigh vacuum (UHV), which routinely achieves large scale atomically resolved imaging of compact metallic surfaces. An efficient in-vacuum vibration isolation and cryogenic system allows for no external vibration isolation of the UHV chamber. The design of the sample holder and STM head permits imaging of the same nanometer-size area of the sample before and after sample preparation outside the STM base. Refractory metal samples are frequently annealed up to 2000 K and their cooldown time from room temperature to 80 K is 15 min. The vertical resolution of the instrument was found to be about 2 pm at room temperature. The coarse motor design allows both translation and rotation of the scanner tube. The total scanning area is about 8 x 8 microm(2). The sample temperature can be adjusted by a few tens of degrees while scanning over the same sample area.     

Multiphoton fluorescence lifetime imaging of 3D-stem cell spheroids during differentiation

Long-term high-resolution multiphoton imaging of nonlabeled human salivary gland stem cell spheroids has been performed with submicron spatial resolution, 10.5-nm spectral resolution, and picosecond temporal resolution. In particular, the two-photon-excited coenzyme NAD(P)H and flavins have been detected by time-correlated single photon counting (TCSPC). Stem cells increased their autofluorescence lifetimes and decreased their total fluorescence intensity during the adipogenic-differentiation process. In addition, the onset of the biosynthesis of lipid vacuoles was monitored over a period of several weeks in stem-cell spheroids. Time-resolved multiphoton autofluorescence imaging microscopes may become a promising tool for marker-free stem-cell characterization and cell sorting.     

3D Dislocation structure evolution in strontium titanate: Spherical indentation experiments and MD simulations

In the present work, the dislocation structure evolution around and underneath the spherical indentations in (001) oriented single crystalline strontium titanate (STO) was revealed by using an etch‐pit technique and molecular dynamics (MD) simulations. The 3D defect structure at various length scales and subsurface depths was resolved with the help of a sequential polishing, etching, and imaging technique. This analysis, combined with load‐displacement data, shows that the incipient plasticity (manifested as sudden indenter displacement bursts) is strongly influenced by preexisting dislocations. In the early stage of plastic deformation, the dislocation pile‐ups are all aligned in 〈100〉 directions, lying on {110}₄₅ planes, inclined at 45° to the (001) surface. At higher mean contact pressure and larger indentation depth, however, dislocation pile‐ups along 〈110〉 directions appear, lying on {110}₉₀ planes, perpendicular to the (100) surface. MD simulations confirm the glide plane nature and provide further insights into the dislocation formation mechanisms by tracing the evolution of the complete dislocation line network as function of indentation depth.     

Demand Response Potenziale in der chemischen Industrie

A supply system geared to renewable energy sources requires a high degree of flexibility to ensure system stability. Load management can make a big contribution. The chemical industry as one of the largest consumers of electrical energy can play an important role there. The analysis of the so far conducted studies shows great potential for the chlor‐alkali process and air liquefaction. The variable costs are comparable to other flexibility options. To determine the realizable potential further investigations are needed.     

Separation efficiency of particle-packed HPLC microchips

We report an experimental study of separation efficiency in microchip high-performance liquid chromatography (HPLC). For this study, prototype HPLC microchips were developed that are characterized by minimal dead volume, a separation channel with trapezoidal cross section, and on-chip UV detection. A custom-built stainless steel holder enabled microchip packing under pressures of up to 400 bar and ultrasonication. Bed densities were investigated with respect to the packing conditions and consistently related to pressure drop over the packed microchannels and separation efficiency under isocratic elution conditions. The derived plate height curves show a decrease of mobile phase mass transfer resistance with increasing bed density. High bed densities are critical to separation performance in noncylindrical packed beds, because only at low bed porosities does hydrodynamic dispersion in noncylindrical packings come close to that of cylindrical packings. At higher bed porosities, the presence of fluid channels of advanced flow velocity in the corners of noncylindrical packings affects hydrodynamic dispersion strongly. We demonstrate that the separation channels of HPLC microchips can be packed as densely as the cylindrical fused-silica capillaries used in nano-HPLC and that consequently microchip-HPLC separation efficiencies comparable to those of nano-HPLC can be achieved.