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Methylammonium-tin-iodide (MASnxI3, 0.9 ≤ x ≤ 1.4) systems were prepared by self assembly process in aqueous solutions. The “as-prepared” MASnxI3 systems exhibit a crystalline tetragonal structure (space group I4cm) with polyhedral-shaped crystallites. The as-prepared samples were annealed at T = 150 °C, t = 8 h under nitrogen and synthetic air. Under nitrogen, the CH3NH3SnxI3 systems adopted a cubic crystalline structure (space group P4mm) with crystallites of 2–4 μm length, whereas under air, the formation of noncrystalline phases was observed. The optical absorption spectra displayed absorption edges at 1107.0 nm (x = 0.9), 1098.6 nm (x = 1.0), and 1073.2 nm (x = 1.1), respectively, whereas at higher Sn-content (x ≥ 1.2), a broad tail of the absorbance profile was observed. The photoluminescence (PL) emission spectra (RT, λexc = 500 nm) showed major PL-events over 1 µm range and the appearance of additional bands at increasing the Sn-content. The fabrication of layers with a semiconducting behavior was demonstrated.
The distribution of alloying elements in the constituent phases of a C-containing γ-TiAl based alloy has been characterized locally by atom probe tomography. The major elements of the alloy under consideration – Ti, Al, Nb, and Mo – are distributed uniformly within each of the constituent phases. Furthermore, Mo is preferentially dissolved in the βo-phase, whereas Nb content is similar in all phases. The selected C concentration of the alloy is below the overall solubility limit as no precipitates have been observed. Therefore, C is enriched in the α2-phase, whereas the βo-phase is depleted of C. In addition, βo/γ-interfaces have been prepared by site specific sample preparation and characterized by atom probe tomography. Segregation of Mo and C into the interfaces and their close vicinity was observed.
An antenna concept for direction of arrival estimation in azimuth and elevation is proposed for 77 GHz automotive radar sensors. This concept uses the amplitude information of the radar signal for the azimuth angle and the phase information for the elevation angle. The antenna consists of a combination of a series-fed-array structure with a cylindrical dielectric lens. This concept is implemented into a radar sensor based on SiGe MMICs for validation. A two- and a four-beam configuration are presented and discussed with respect to angular accuracy and ambiguities.
A general purpose two-channel Frequency modulated continuous wave (FMCW)-sensor in E-band is extended to a digital-beam-forming (DBF) system. The hardware extension contains a transmit multiplexer, which allows switching of the (DBF) transmit signal of the sensor to any of 32 linearly arranged waveguide antennae. To maintain the spatial sampling condition by λ/2 element distance, the antenna ports are arranged in the E-plane. The ports can directly radiate or serve as primary radiators of a cylindrical dielectric lens focusing in the H-plane. By realizing the hardware extension based on a metal-backed substrate, some novel radio frequency (RF) structures became necessary. One of these structures is a special twisting microstrip-to-waveguide-transition to connect the switching matrix to waveguide ports arranged in the E-plane. Key elements of the multiplexer are commercially available pin-diode-based MMIC-switches in microstrip technology. To lower the inductance of the interconnects, they are embedded in cavities in the metal-backed RF-substrate. RF interconnects between the sensor and the extension are all done with waveguide ports. Further interconnects between the module and the extension are low-frequency or digital and are led via cables and removable plugs. Both module and extension can be powered separately. This gives an easily mountable extension for making a two-dimensional (2D) DBF sensor out of a 1D FMCW-sensor.
After almost three decades of intensive fundamental research and development activities intermetallic titanium aluminides based on the -TiAl phase have found applications in automotive and aircraft engine industries. The advantages of this class of innovative high-temperature materials are their low density as well as their good strength and creep properties up to 750°C. A drawback, however, is their limited ductility at room temperature, which is reflected by a low plastic strain at fracture. This behavior can be attributed to a limited dislocation movement along with microstructural inhomogeneity. Advanced TiAl alloys, such as β-solidifying TNM™ alloys, are complex multi-phase materials which can be processed by ingot or powder metallurgy as well as precision casting methods. Each production process leads to specific microstructures which can be altered and optimized by thermo-mechanical processing and/or subsequent heat-treatments. The background of these heat-treatments is at least twofold, i.e. concurrent increase of ductility at room temperature and creep strength at elevated temperature. In order to achieve this goal the knowledge of the occurring solidification processes and phase transformation sequences is essential. Therefore, thermodynamic calculations were conducted to predict phase fraction diagrams of engineering TiAl alloys. After experimental verification, these phase diagrams provided the base for the development of heat treatments to adjust balanced mechanical properties. To determine the influence of deformation and kinetic aspects, sophisticated ex- and in-situ methods have been employed to investigate the evolution of the microstructure during thermo-mechanical processing and subsequent multi-step heat-treatments. For example, in-situ high-energy X-ray diffraction was conducted to study dynamic recovery and recrystallization processes during hot-deformation tests. Summarizing all results a consistent picture regarding microstructure formation and its impact on mechanical properties in TNM alloys can be given.
Over the last decades, high-throughput screening (HTS) of small molecule libraries has developed into a very powerful tool for drug discovery. Although HTS capabilities initially were developed almost exclusively in the domain of pharmaceutical and biotech commercial ventures, they have more recently become available in academia. The Molecular Library Initiative of the National Institutes of Health (NIH) is one example that HTS has established itself as a routine technology in biomedical research .
The popularity of HTS is due to rapid developments in four different areas:
Robotic systems. Once exotic and expensive, robotic systems and automatic liquid handling have become more affordable and easier to operate. Turnkey systems are available for the most common applications.
Chemical libraries. Chemical libraries are becoming more readily available and affordable to the scientific community in academia and industry. Even large compound libraries, such as the one developed for the above-mentioned Molecular Library Initiative, are accessible to the general scientific community.
Plate reader platforms. Reader platforms have undergone rapid development over the last two decades. As of today, high-speed microplate readers are available to very rapidly scan microplates in the 96-, 384-, and 1536-well formats or even higher densities. Automated confocal and conventional microscopes and other image-based reader platforms have evolved at an astonishing speed. Sophisticated image-based readers and corresponding image recognition and analysis software have led to the development of complex, high-content cell-based assays.
Detection technologies. A whole array of luminescence-based technologies have been developed and commercialized over the last few years. Among those are fluorescent proteins, high-yield fluorochromes, and luminescence substrates.
The development of suitable hot-forming processes, e.g. forging, is an important step towards the serial production of TiAl parts. Several microstructure parameters change during hot-forming. However, the underlying mechanisms can normally only be inferred from post process metallographic studies.
We used a deformation dilatometer modified for working in the HZG synchrotron beamlines at DESY for hot-deformation experiments. This setup enables the in situ monitoring of the interaction and evolution of microstructure parameters during processing. We observed the evolution of phase fractions, grain size and crystallographic texture during deformation while simultaneously recording the process parameters, like temperature, force and length change.
Here we present the hot compressive deformation behaviour of a Ti-43Al-4Nb-1Mo-0.1B (in at.%) alloy. Several specimens were deformed at three temperatures each with two compression rates. During the experiments the Debye-Scherrer diffraction rings were continuously recorded.
In the last decades there was a growing interest in developing new light-weight intermetallic alloys, which are able to substitute the heavy superalloys at a certain temperature range. At present a new Ti-Al-Nb-Mo family, called TNM™ alloys, is being optimized to fulfill the challenging requirements. The aim of the present work was to study the microscopic mechanisms of defect mobility at high temperature in TNM alloys in order to contribute to the understanding of their influence on the mechanical properties and hence to promote the further optimization of these alloys. Mechanical spectroscopy has been used to study the internal friction and the dynamic modulus up to 1460 K of a TNM alloy under different thermal treatments. These measurements allow to follow the microstructural evolution during in-situ thermal treatments. A relaxation process has been observed at about 1050 K and was characterized as a function of temperature and frequency in order to obtain the activation parameters of the responsible mechanism. In particular, the activation enthalpy has been determined to be H= 3 eV. The results are discussed and an atomic mechanism is proposed to explain the observed relaxation process.
Several hundred subglacial lakes have been identified beneath Antarctica so far. Their interaction with the overlying ice sheet and their influence on ice dynamics are still subjects of investigation. While it is known that lakes reduce the ice-sheet friction towards a free-slip basal boundary condition, little is known about how basal melting and freezing at the lake/ice interface modifies the ice dynamics, thermal regime and ice rheology. In this diagnostic study we simulate the Vostok Subglacial Lake area with a coupled full Stokes 3-D ice-flow model and a 3-D lake-circulation model. The exchange of energy (heat) and mass at the lake/ice interface increases (decreases) the temperature in the ice column above the lake by up to 10% in freezing (melting) areas, resulting in a significant modification of the highly nonlinear ice viscosity. We show that basal lubrication at the bottom of the ice sheet has a significant impact not only on the ice flow above the lake itself, but also on the vicinity and far field. While the ice flow crosses Vostok Subglacial Lake, flow divergence is observed and modelled. The heterogeneous basal-mass-balance pattern at the lake/ice interface intensifies this divergence. Instead of interactive coupling between the ice-flow model and the lake-flow model, only a single iteration is required for a realistic representation of the ice/water interaction. In addition, our study indicates that simplified parameterizations of the surface temperature boundary condition might lead to a velocity error of 20% for the area of investigation.
Molybdenum, being a strong β stabilizer, is an important alloying element in TiAl alloys, since a significant volume fraction of the disordered bcc β-phase at elevated temperatures improves the processing characteristics during hot-working. Unfortunately, the effect of Mo on the individual phases and their transition temperatures is not completely known but is necessary for designing engineering applications. In this paper, sections of the Ti-Al-Mo ternary phase diagram derived from thermodynamic calculations as well as experimental data are presented. Further, the phase transition temperatures given by the phase diagrams are compared with results from isothermal heat treatment studies, differential scanning calorimetry measurements and in-situ high-temperature diffraction experiments. Combining all of these results, a revised phase diagram is proposed.
In this paper, the physical metallurgy and properties of a novel family of high-strength γ-TiAl-based alloys is reviewed succinctly. These so-called TNM™ alloys contain Nb and Mo additions in the range of 3 - 7 atomic percent as well as small additions of B and C. For the definition of the alloy composition thermodynamic calculations using the CALPHAD method were conducted. The predicted phase transformation and ordering temperatures were verified by differential scanning calorimetry and in situ high-energy X-ray diffraction. TNM alloys solidify via the β-phase and exhibit an adjustable β-phase volume fraction at temperatures, where hot-working processes are performed. Due to the high volume fraction of β-phase these alloys can be processed isothermally as well as under near conventional conditions. In order to study the occurring deformation and recrystallization processes during hot-working, in situ diffraction experiments were conducted during compression tests at elevated temperatures. With subsequent heat-treatments a significant reduction of the β-phase is achieved. These outstanding features of TNM alloys distinguish them from other TiAl alloys which must exclusively be processed under isothermal conditions and/or which always exhibit a high fraction of β-phase at service temperature. After hot-working and multi-step heat-treatments, these alloys show yield strength levels > 800 MPa at room temperature and also good creep resistance at elevated temperatures.
Templated growth for the fabrication of semiconductor nanostructures such as quantum dots and lattice-mismatched structures has been employed in this study. Self assembly of block copolymers (BCP) has been exploited to create a regular array of nanoscale patterns on a substrate to generate the growth template. These patterned templates were used for the selective area growth of pseudomorphic quantum dots, allowing for precise control over the dot size and spatial distribution. Strain relaxation in lattice-mismatched structures grown past the pseudomorphic limit was also studied. Analysis of the grown structures suggests that this approach using block copolymer templating followed by selective growth can be used for defect reduction in lattice-mismatched materials.