Inversion domain boundaries in ZnO with additions of Fe2O3 studied by high-resolution ADF imaging

Columns of metal atoms in the polytypoid compound Fe2O3(ZnO)15 could be resolved by high angle annular dark field imaging in a transmission electron microscopy (TEM)/STEM electron microscope--a result which could not be realized by high-resolution bright field imaging due to inherent strain from inversion domains and inversion domain boundaries (IDBs) in the crystals. The basal plane IDB was imaged in [11 00] yielding the spacing of the two adjacent ZnO domains, while imaging in [21 1 0] yields the position of single metal ions. The images allow the construction of the entire domain structure including the stacking sequence and positions of the oxygen ions. The IDB consists of a single layer of octahedrally co-ordinated Fe3+ ions, and the inverted ZnO domains are related by point symmetry at the iron position. The FeO6 octahedrons are compressed along the ZnO c-axis resulting in a FeO bond length of 0.208 nm which is in the range of FeO distances in iron containing oxides. The model of the basal plane boundary resembles that of the IDB in polytypoid ZnO-In2O3 compounds.     

New insight into the role of the β3 subunit of the GABA<Subscript>A</Subscript>-R in development,behavior, body weight regulation,and anesthesia revealed by conditional gene knockout

Background  

The β3 subunit of the γ-aminobutyric acid type A receptor (GABA_A-R) has been reported to be important for palate formation, anesthetic action, and normal nervous system function. This subunit has also been implicated in the pathogenesis of Angelman syndrome and autism spectrum disorder. To further investigate involvement of this subunit, we previously produced mice with a global knockout of β3. However, developmental abnormalities, compensation, reduced viability, and numerous behavioral abnormalities limited the usefulness of that murine model. To overcome many of these limitations, a mouse line with a conditionally inactivated β3 gene was engineered.     

Lidar calibration experiments

A series of atmospheric aerosol diffusion experiments combined with lidar detection was conducted to evaluate and calibrate an existing retrieval algorithm for aerosol backscatter lidar systems. The calibration experiments made use of two (almost) identical mini-lidar systems for aerosol cloud detection to test the reproducibility and uncertainty of lidars. Lidar data were obtained from both single-ended and double-ended lidar configurations. A backstop was introduced in one of the experiments and a new method was developed where information obtained from the backstop can be used in the inversion algorithm. Independent in-situ aerosol plume concentrations were obtained from a simultaneous tracer gas experiment with SF, and comparisons with the two lidars were made. The study shows that the reproducibility of the lidars is within 15%, including measurements from both sides of a plume. The correspondence with in-situ measurements is excellent. Finally, the new backstop method is able to reveal information which can close the lidar equation by obtaining the relation between backscatter and extinction in an aerosol cloud. Received: 21 December 1995 / Revised version: 25 July 1996     

Out of the blue: semiconductor laser pumped visible rare‐earth doped lasers

The rise of semiconductor‐based pump sources such as In_xGa_1‐xN‐laser diodes or frequency‐doubled optically pumped semiconductor lasers with emission wavelengths in the blue encourages a revisitation of the rare‐earth ions Pr³⁺, Sm³⁺, Tb³⁺, Dy³⁺, Ho³⁺ and Er³⁺ with respect to their properties as active ions in crystalline solid‐state laser materials with direct emission in the visible spectral range. Nowadays, some of these blue‐pumped visible lasers compete with Nd³⁺‐lasers in terms of efficiency and direct lasing at various colors from the cyan‐blue to the deep red can be addressed in very simple and compact laser setups. This paper highlights the spectroscopic properties of suitable rare‐earth ions for visible lasing and reviews the latest progress in the field of blue‐pumped visible rare‐earth doped solid‐state lasers.

     

Fabrication of ridge waveguides in zinc-substituted lithium niobate by means of ion-beam enhanced etching

We present results on the fabrication and characterization of ridge waveguides in zinc-substituted lithium niobate. High-quality waveguides were fabricated by a combination of liquid-phase epitaxy and multiple applications of ion-beam enhanced etching. The two major demands on ridge waveguides, a very low side-wall roughness and a rectangle shape with side-wall angles close to 90 degrees , were realized simultaneously by using this technique. Single-mode waveguiding at a wavelength of 1064 nm was demonstrated with attenuation values of 0.9 dB/cm.     

Thermodynamic modeling of Fe–Ni pentlandite

Gibbs energy modeling of iron–nickel pentlandite has been performed using experimental data of ternary phase equilibria. A three-sublattice approach in the framework of the Compound Energy Formalism is developed to refine a two-sublattice model of pentlandite recently applied within a complete assessment of the Fe–Ni–S system. Experimental data about the iron site fraction on the octahedral sublattice at 523.15 K for the composition Fe₅Ni₄S₈ as well as the enthalpy of formation at 298.15 K for the composition Fe_4.5Ni_4.5S₈ are predicted satisfactorily by the novel model. New possibilities to interpret experimental phase equilibrium data on complex phase relations with pentlandite are discussed together on the basis of the recent extension of a second high-temperature heazlewoodite phase to a ternary solution phase.     

Interfaces in ionic devices

The technology of Ionics is based on the availability of materials with fast ion transport. Individual materials are, however, meaningless from a practical point of view; all applications require combinations of materials with appropriate ionic and electronic properties. This situation is similar to Electronics which requires combinations of semi-conducting or metallic conducting materials with differences in the chemical potentials of the electrons. The technology of Ionics requires interfaces between ionic and electronic conductors which generate strong electrical fields or allow to modify the field by the application of external voltages. Ions and electrons equilibrate both at these “ionic junctions”. While semi-conductor junctions have commonly a width in the μm-range, the space charge region is several orders of magnitude smaller in the case of ionic junctions, i.e. in the nm or even sub-nm-range. The interfaces have to be chemically stable for the lifetime of the device which is difficult to achieve in view of the commonly large number of components present in both phases and the existence of mobile species with sometimes large variations in the activity of the electroactive component. Furthermore, the kinetics of transfer of ions across the interface has to be fast to allow high current densities which are required in many cases. In addition, two such interfaces are required to convert the electronic current into an ionic one and again back into an electronic current at the opposite side of the electrolyte. The development of ionic devices depends to the strongest extent on the engineering of appropriate interfaces. Examples of the role and engineering of interfaces will be presented for applicationes such as chemical sensors, electrochromic devices, fuel cells, batteries and photogalvanic solar cells.