Molecular recognition capabilities are evoked at artificial materials by the NANOCYTES®-technology of the Fraunhofer IGB, Stuttgart, Germany. The biomimetic nanoparticles described here possess such molecularly recognizing properties. For this purpose they carry molecularly defined binding sites at their surface. In this particular case molecularly imprinted nanospheres (nanoMIPs) were developed for the specific adsorption of micropollutants from hospital waste water. Active pharmaceutical substances and their metabolites which were not decomposed by waste water plants were chosen as model compounds. One of this model compounds is Pentoxifylline. The nanoMIPs are prepared by a miniemulsion polymerization technique, where the monomer, the template, the cross-linker, and the initiator do react in the droplet cavities of the miniemulsion. The reaction to obtain nanoMIP particles is complex, but nevertheless it runs in a single reaction chamber and in a single step chemical process. For synthesis of the polymer system p(methacrylicacid-co-ethylenglycoldimethacrylate), p(meth-acrylicacid-co-methylmethacrylate-co-ethylenglycoldimethacrylate) and p(4-vinylpyridin-co-ethylenglycoldimethacrylate) are used. The technique of miniemulsion polymerization results in particles with a typical size distribution of 50 nm to 500 nm. Additionally, an introduced magnetic core will allow the final separation of the nanoMIPs and more important of the recognized pollutants from (waste) water. We demonstrate that magnetite can be incorporated into the polymer system, and that the template Pentoxifylline does not affect the polymerization process.

The mechanical properties of materials designated for vascular tissue replacement are of crucial importance. The elastic modulus, the tensile strength as well as the suture tear resistance have to be adjusted. Our approach is to use photopolymers for artificial vascular grafts. Via the layer-by-layer photopolymerization of suitable resin formulations as performed in additive manufacturing (AM) very complex structures are realizable. Hence AM offer the possibility to create cellular structures within the artificial grafts that might favor the ingrowth of new tissue. Commercially available urethane acrylates (UA) were chosen as base monomers since urethane groups are known to have good cell-adhesion behavior and poly-UAs show adequate mechanical performance. The mechanical properties of the photoelastomers can be tailored by addition of reactive diluents (e.g. 2-hydroxyethyl acrylate, HEA) and thiols (e.g. 3,6 dioxa-1,8-octane-dithiol) as chain transfer agents to comply with the mechanical properties of natural blood vessels. To examine the suture tear resistance a new testing method has been developed. Finally, a formulation containing 30 wt% UA and 70 wt% HEA complies with the mechanical properties of natural blood vessels, shows good biocompatibility in in-vitro tests and was successfully 3D-printed with digital light processing AM.

Thin film hydrogenated amorphous silicon (a-Si:H) is widely used in photovoltaics. In order to get the best possible performance of the a-Si:H solar cells it is important to optimize the amorphous film and solar cells in terms their parameters such as mobility gap, p-, i- and n-layer doping levels, electron and hole lifetime and their mobilities, resistance of p-, i- and n-layers, contact grid geometry and parameters of the transparent conducting and antireflecting layers, and others. To maximize thin a-Si:H film based solar cell performance we have developed a general numerical formalism of photoconversion, which takes into account all the above parameters for the optimization. Application of the formalism is demonstrated for typical a-Si:H based solar cells before Staebler-Wronski (SW) light soaking effect. This general formalism is not limited to a-Si:H based systems only, and it can be applied to other types of solar cells as well.

In this work, aluminum weld beads were deposited on aluminum plates of commercial purity (12.7 mm thick), using an ER-5356 filler wire. The aim of the experiments was to assess the effects that yield the induction of an axial magnetic field (AMF) during the application of the weld beads using the direct current gas metal arc welding process (DC-GMAW). An external power source was use to induce magnetic fields between 0 to 28 mT. The effects of the magnetic fields were assessed in terms of the macrostructural features of the deposits, morphology of the grain structure, grain size and grain size distribution in the weld metal. Macrostructural characteristics of the weld beads revealed that increasing the intensity of the magnetic induction to produce a magnetic field above 14 mT, leads to a significant loss of feeding material and there is a tendency of the deposits to increase their width and reduce penetration. Perturbation of the weld pool induced by the application of the AMF noticeably modified the grain structure in the weld metal. In particular, for the intensities of 5 and 14 mT, columnar growth was essentially non-existent. Grain size distribution plots showed, generally speaking, that the use of magnetic fields is an efficient method to produce homogeneous grain structures within the weld metal. Finite element analysis was used to explain the weld bead geometry with the intensity of the magnetic field.

Advanced nuclear energy systems, both fission- and fusion-based, aim to operate at higher temperatures and greater radiation exposure levels than experienced in current light water reactors. Additionally, they are envisioned to operate in coolants such as helium and sodium that allow for higher operating temperatures. Because of these unique environments, different requirements and challenges are presented for both structural materials and fuel cladding. For core and cladding applications in intermediate-temperature reactors (400–650°C), the primary candidates are 9–12Cr ferritic–martensitic steels (where the numbers represent the weight percentage of Cr in the material, i.e., 9–12 wt%) and advanced austenitic steels, adapted to maximize high-temperature strength without compromising lower temperature toughness. For very high temperature reactors (>650°C), strength and oxidation resistance are more critical. In such conditions, high-temperature metals as well as ceramics and ceramic composites are candidates. For all advanced systems operating at high pressures, performance of the pressure boundary materials (i.e., those components responsible for containing the high-pressure liquids or gases that cool the reactor) is critical to reactor safety. For some reactors, pressure vessels are anticipated to be significantly larger and thicker than those used in light water reactors. The properties through the entire thickness of these components, including the effects of radiation damage as a function of damage rate, are important. For all of these advanced systems, optimizing the microstructures of candidate materials will allow for improved radiation and high-temperature performance in nuclear applications, and advanced modeling tools provide a basis for developing optimized microstructures.

We have investigated efficient energy transfer (ET) between CdS quantum dots (QDs) measuring photoluminescence dynamics in layer-by-layer (LBL) self-assembled films. The assembly of negatively charged colloidal QDs and positively charged polyelectrolytes results in QD/polymer multilayers. Furthermore, to reveal how the ET rate depends on the distance between CdS QDs, we fabricated bilayer structures consisting of differently sized CdS QDs. It is experimentally verified that ET between the donor and acceptor QDs is conclusively dominated by the dipole-dipole interaction.

Point defect scattering via the formation of solid solutions to reduce the lattice thermal conductivity has been an effective method for increasing ZT in state-of-the-art thermoelectric materials such as Si-Ge, Bi2Te3-Sb2Te3 and PbTe-SnTe. However, increases in ZT are limited by a concurrent decrease in charge carrier mobility values. The search for effective methods for decoupling electronic and thermal transport led to the study of low dimensional thin film and wire structures, in particular because scattering rates for phonons and electrons can be better independently controlled. While promising results have been achieved on several material systems, integration of low dimensional structures into practical power generation devices that need to operate across large temperature differential is extremely challenging. We present achieving similar effects on the bulk scale via high pressure sintering of doped and undoped Si and Si-Ge nanoparticles. The nanoparticles are prepared via techniques that include high energy ball milling of the pure elements. The nanostructure of the materials is confirmed by powder X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and dynamic light scattering. Thermal conductivity measurements on the densified pellets show a drastic 90% reduction in the lattice contribution at room temperature when compared to doped single crystal Si. Additionally, Hall effect measurements show a much more limited degradation in the carrier mobility. The combination of low thermal conductivity and high power factor in heavily doped n-type nanostructured bulk Si leads to an unprecedented increase in ZT at 1275 K by a factor of 3.5 over that of single crystalline samples. Experimental results on both n-type and p-type Si are discussed in terms of the impact of the size distribution of the nanoparticles, doping impurities and nanoparticle synthesis processes.

We examined crystalline-texture evolution during ion-beam-assisted deposition (IBAD) of MgO thin films. We have demonstrated for the first time that in-plane crystalline texturing in IBAD of MgO scales with deposition rate. At high ion currents an in-plane texture full width at half-maximum (FWHM) of 10° can be achieved in less than 1 s, and 6° in 2.2 s. MgO texture further improves with thickness of a homoepitaxial layer deposited on top. We have developed an empirical quantification of the texture evolution in both IBAD and homoepitaxial layers. The best texture attained thus far in the MgO layer on polished Hastelloy tape has an in-plane FWHM of 1.6°. The high deposition rates demonstrated here make high-throughput manufacturing of IBAD textured templates a practical and cost-effective concept.

The goal of this research is to develop a process suitable for producing monolithic conformal substrates with a spatial arrangement of material cells according to a particular design creating novel material systems, useful for many multi- functional electronic and Radio Frequency devices. In this study, MCT ceramics (Mg-Ca-Ti-O systems) and organic binders (polymer solution) are mixed and fabricated as films through a process called tape casting to compromise between high dielectric constant and flexibility. Prior to optimizing the process, several characterization studies are carried out: Commercial spray dried MCT powders (Transtech Inc.) with dielectric constant k=70 and k=20 were analyzed as pressed and produced into tape cast films. Dielectric properties are then measured by an Agilent 16451B material analysis kit and their microscopic behavior is examined by scanning electron microscopy. Results show that flexible composite films show a maximum dielectric constant of ε∼22 unlike their powder pressed form with ε ∼16 but their loss behavior deteriorates when compared with their sintered form and a loss tangent factor of 0.001. The difference is attributed to the air content vs. polymer presence of the material in powder pressed form. Also, these substrates naturally are no longer flexible; hence studies are focused on their tape cast form. The potential of these dielectric shades to serve as candidate constituents for producing monolithic textured polymer-ceramic-composites with controllable loss is studied further. Four properties are of prime importance: tunability of dielectric constants to achieve miniaturization, flexibility via low temperature processing of polymers and loss controllability.

A nonvolatile memory device with the multi-layered SiC nanocrystals embedded in the SiO2 dielectrics for long-term data storage was fabricated and its electrical properties were evaluated. The SiC nanocrystals were formed by using post thermal annealing process. The transmission electron microscope analysis showed the multi-layered SiC nanocrystals between the tunnel and the control oxide layers. The average size and density of the SiC nanocrystals were approximately 5 nm and 2×1012 cm-2, respectively. The memory window of nonvolatile memory devices with the multi-layered of SiC nanocrystals was about 2.7 V during the operations at ±10 V for 700 ms, and then it was maintained around at 1.1 V after 105 sec.

We have studied the low-temperature growth of GaNAs layers on sapphire substrates by plasma-assisted molecular beam epitaxy. We have succeeded in achieving GaN1-xAsx alloys over a large composition range by growing the films at temperature much below the normal GaN growth temperatures with increasing the As2 flux as well as Ga:N flux ratio. We found that the alloys with high As content x>0.1 are amorphous. Optical absorption measurements reveal a continuous gradual decrease of band gap from ˜3.4 eV to ˜1.4 eV with increasing As content. The energy gap reaches its minimum of ˜1.4 eV at the x˜0.6-0.7. For amorphous GaAsN alloys with x<0.3 the composition dependence of the band gap follows the prediction of the band anticrossing model developed for dilute alloys. This suggests that the amorphous GaN1-xAsx alloys have short-range ordering that resembles random crystalline GaN1-xAsx alloys. Such amorphous GaN1-xAsx alloys with tunable electronic structure may be useful as photoanodes in photo-electrochemical cells for hydrogen production.

We present the polarization behavior of the exciton-polariton luminescence of a ZnO-based all-oxide resonator. A splitting in the emission energy between the s- and p-polarized pho-toluminescence of the lower polariton branch was observed which increases with increasing emission angle. It is caused by the polarization behavior of the uncoupled cavity-photon mode, and reaches a maximum of about 5 meV at an emission angle near the bottleneck region. For lar-ger angles the energy splitting decreases. Additionally to the energy splitting, we observed dif-ferences in the photoluminescence intensity which we trace back to different occupation of the lower polariton branch for the two polarizations. Whereas for p-polarization a bottleneck effect is clearly observable, this effect is much weaker for s-polarization. These findings indicate that the relaxation of hot carriers into the bottleneck region is enhanced for the p-polarized photolumi-nescence compared to the s-polarized one. The differences between these two polarizations are most pronounced for a very large negative detuning and vanish with increasing detuning.

Thin films of 3 different thicknesses each of Ni83.2Fe3.3Mo13.5 and Ni83.1Fe6.0Mo10.9alloys have been grown using Pulsed Laser Deposition (PLD) technique. Our motivation is to investigate the magnetic properties of a few nm thick Ni alloys with mostly Mo (4d element) addition since the corresponding soft ferromagnetic bulk alloys have shown very small coercivity of ˜ 0.1 Oe. Detailed structural characterization has been undertaken before probing the magnetic properties. Arc melted alloy buttons after homogenization are used directly as targets for the deposition. Films were deposited on single crystal Sapphire (0001) substrates using excimer laser. The structural characterization has been done by X-ray diffraction (XRD), X-ray reflectivity (XRR), Energy dispersive x-ray spectroscopy (EDS), and Atomic force microscopy (AFM). The X-ray diffraction pattern shows that the films are highly textured and grown along [111] direction of the alloys. They have high lattice strain which makes the films highly resistive and the resistance decreases with increasing thickness. The EDS measurements, using Scanning electron microscope (SEM), indicate that the compositions of the films are almost the same as those of the targets. Thickness, roughness, and density gradients are estimated using XRR measurements. The thinner films have higher roughness compared to the thicker ones for both the compositions. The films have density gradient across their thickness. The bottommost low density layer has high roughness which is supposed to be the result of initial non uniform coverage of the substrate. The density of the middle layer, having the lowest roughness, is approximately near the bulk value and it increases with increasing film thickness. The change in density is not due to the variation of composition; instead it is due to the variation of void densities in the layers. The topmost layer, having the lowest density and the highest roughness, is interpreted as a porous layer which is also evident from the AFM images.

The AC powered electric arc has been used to synthesize single wall carbon nanohorns aggregates with Ca dispersed inside. To this purpose the electric arc has been ignited between two electrodes, one of which was constituted by a mixture of graphite and CaCO3. The experimental evidence on the microstructure and on the chemical composition has been obtained by observation with a transmission electron microscope equipped with X-ray microanalysis. X-ray diffraction revealed the presence of residual CaCO3 indicating that the process has still to be optimized. The experiment represents a first attempt to decorate carbon nanostructures with alkaline earth metals, in particular Ca, by this relatively simple method. These composites are theorized to adsorb relevant amounts of hydrogen. Further work will be focused to optimize the dispersion of Ca atoms in the carbon nanostructure.

White organic LEDs are seen as one of the next generation light-sources, with their potential to reach internal efficiencies of unity and their unique appearance as large-area and ultrathin devices. However, to replace existing lighting technologies, they have to be at least on par with the state-of-the-art. In terms of efficiency, the fluorescent tube with 60-70 lumen per Watt (lm W-1) in a fixture is the current benchmark. In the scientific literature, so far only values of 44 lm W-1 have been published for white OLEDs.

Here, we present results (Reineke et al., Nature 459, 234 (2009)) of white OLEDs with 90 lm W-1 at an illumination relevant brightness of 1,000 candela per square meter (cd m-2). Extracting all light from the glass substrate using a 3D light extraction system, we even obtain 124 lm W-1. In order to achieve such high efficacy values, we reduced the energetic losses prior to photon emission that include ohmic and thermal relaxation losses, leading to very low operating voltages. This is accomplished by the use of doped transport layers and a novel, very energy efficient emission layer concept. Equally important, we addressed the optics of the OLED architecture, because about 80% of the generated light remains trapped in conventional devices. Therefore, we used high refractive index substrates to couple out more light and placed the emission to the second field antinode to avoid plasmonic losses. Our devices are also characterized by an outstandingly high efficiency at high brightness, reaching 74 lm W-1 at 5,000 cd m-2.

This work investigates the critical stress and morphological evolutions which occur during the high-temperature oxidation of metallic alloys for SOFC interconnects. Two mechanisms of stress generation are considered related to (1) the local volume change associated with the direct oxidation of the metal and to (2) a secondary oxidation process within grain boundaries. A specific formulation is developed to include the influence of the stress state at the metal-oxide interface on the local oxidation kinetics. The oxidation of a chromia-forming SOFC interconnect metallic alloy is simulated and stress and morphological evolutions are investigated.

Here we propose to detail an innovative FIB instrumental approach and processing methodologies we have developed for sub-10 nm nanopore fabrication. The main advantage of our method is first to allow direct fabrication of nanopores in relatively large quantities with an excellent reproducibility. Second our approach offers the possibility to further process or functionalize the vicinity of each pore on the same scale keeping the required deep sub-10 nm scale positioning and patterning accuracy.We will summarise the optimisation efforts we have conducted aiming at fabricating thin (10-100 nm thick) and high quality dielectric films to be used as a template for the nanopore fabrication, and at performing efficient and controlled FIB nanoengraving of such a delicate media.Finally, we will describe the method we have developed for integrating these “single nanopore devices” in electrophoresis experiments and our preliminary measurements.

A polycrystalline silicon (pc-Si) thin film with large grains on a low-cost non-Si substrate is a promising material for thin-film solar cells. One possibility to grow such a pc-Si layer is by aluminum-induced crystallization (AIC) followed by epitaxial thickening. The best cell efficiency we have achieved so far with such an AIC approach is 8%. The main factor that limits the efficiency of our pc-Si solar cells at present is the presence of many intra-grain defects. These intra-grain defects originate within the AIC seed layer. The defect density of the layers can be determined by chemical defect etching. This technique is well suited for our epitaxial layers but relatively hard to execute directly on the seed layers. This paper presents a way to reveal the defects present in thin and highly-aluminum-doped AIC seed layers by using defect etching. We used diluted Schimmel and diluted Wright etching solutions. SEM pictures show the presence of intra-grain defects and grain boundaries in seed layers after defect etching, as verified by EBSD analyses. The SEM images of diluted Wright etched pc-Si seed layer shows that grain boundaries become much better visible than with diluted Schimmel etch.

In this work, a commercial zircon flour of 99% purity and mean particle size of 10μm is used. Suspension stabilization process is carried out using the electrostatic stabilization mechanism at pH 11 employing Tetramethylammonium hydroxide (TMAH). Tape casting suspensions are formulated with binding systems obtained by the combination of polyvinyl alcohol with polyethylene glycol, additionally the binding system is added at different binder:plasticizer ratio ranging from 1:1 to 3:1. Suspensions are characterized rheologically determining its type and flow properties by obtaining flow and viscosity curves. Suspensions are tape cast on vinyl-acetate substrates and are dried at room conditions to determine some physical properties of the obtained tapes and to correlate the rheological with the physical properties. The experimental results show that tape casting suspensions have a shear thinning flow type, yield points and flow indexes varying as a function of binder system combination and binder:plasticizer ratio. Also, the binder system has a strong influence on the green tapes characteristics.

Transient photocurrent (TPI) and photocapacitance (TPC) spectroscopy have been applied to a set of compositional graded CuIn1-xGaxSe2 (CIGS) solar cell devices deposited by the vacuum co-evaporation method at the National Renewable Energy Laboratory. These measurements provide a spectral map of the optically induced release of carriers for photon energies from below 1 eV to 2 eV. By comparing the two types of spectra one can distinguish majority from minority carrier processes and they clearly reveal a higher degree of minority carrier collection for devices in which the Ga fraction increased monotonically with distance from the junction. This agrees with notions of how compositional grading improves overall cell performance. Minority carrier collection was even more strongly enhanced in sample devices incorporating v-shaped Ga-grading. Spatial profiles of the free hole carrier densities and deep acceptor concentrations were examined using drive-level capacitance profiling (DLCP). In the compositionally graded sample devices we found that the free carrier density decreased and that defect density increased with increasing Ga fraction toward back contact.