Influence of composition on hyperfine interactions in FeMoCuB nanocrystalline alloy

Influence of varying Fe/B ratio upon hyperfine interactions is investigated in the Fe_91?x Mo₈Cu₁B_x rapidly quenched alloys. They are studied both in the as-quenched (amorphous) state as well as after one-hour annealing at different temperatures ranging from 330 °C up to 650 °C. Such a heat treatment causes significant structural changes featuring a formation of nanocrystalline bcc-Fe grains during the first crystallization step. At higher annealing temperatures, a grain growth of bcc-Fe and occurrence of additional crystalline phases are observed. The relative fraction of the crystalline phase governs the development of magnetic hyperfine fields in the residual amorphous matrix even if this was fully paramagnetic in the as-quenched state. The development of hyperfine interactions is discussed as a function of annealing temperature and composition of the investigated alloys. ⁵⁷Fe Mössbauer spectrometry was used as a principal analytical method. Additional information related to the structural arrangement is obtained from X-ray diffractometry. It is shown that in the as-quenched state, the relative fraction of magnetic hyperfine interactions increases as the amount of B rises. In partially crystalline samples, the contribution of magnetic hyperfine interactions inside the retained amorphous matrix increases with annealing temperature even though the relative fraction of amorphous magnetic regions decreases.     

Polarizing beam splitter of a deep-etched fused-silica grating

We described a highly efficient polarizing beam splitter (PBS) of a deep-etched binary-phase fused-silica grating, where TE- and TM-polarized waves are mainly diffracted in the -1st and 0th orders, respectively. To achieve a high extinction ratio and diffraction efficiency, the grating depth and period are optimized by using rigorous coupled-wave analysis, which can be well explained based on the modal method with effective indices of the modes for TE/TM polarization. Holographic recording technology and inductively coupled plasma etching are employed to fabricate the fused-silica PBS grating. Experimental results of diffraction efficiencies approaching 80% for a TE-polarized wave in the -1st order and more than 85% for a TM-polarized wave in the 0th order were obtained at a wavelength of 1550 nm. Because of its compact structure and simple fabrication process, which is suitable for mass reproduction, a deep-etched fused-silica grating as a PBS should be a useful device for practical applications.     

Semiconductor Emitters in Entropy Sources for Quantum Random Number Generation

Random number generation (RNG) is needed for a myriad of applications ranging from secure communication encryption to numerical simulations to sports and games. However, generating truly random numbers can be elusive. Pseudorandom bit generation using computer algorithms provides a high random bit generation rate. Nevertheless, the reliance on predefined algorithms makes it deterministic and predictable once initial conditions are known. Relying on physical phenomena (such as measuring electrical noise or even rolling dice) can achieve a less predictable sequence of bits. Furthermore, if the physical phenomena originate from quantum effects, they can be truly random and completely unpredictable due to quantum indeterminacy. Traditionally, physical RNG is significantly slower than pseudorandom techniques. To meet the demand for high-speed RNG with perfect unpredictability, semiconductor light sources are adopted as parts of the sources of randomness, i.e., entropy sources, in quantum RNG (QRNG) systems. The high speed of their noise, the high efficiency, and the small scale of these devices make them ideal for chip-scale QRNG. Here, the applications and recent advances of QRNG are reviewed using semiconductor emitters. Finally, the performance of these emitters is compared and discuss their potential in future technologies.     

Crystal structure of the β2 adrenergic receptor-Gs protein complex

G protein-coupled receptors (GPCRs) are responsible for the majority of cellular responses to hormones and neurotransmitters as well as the senses of sight, olfaction and taste. The paradigm of GPCR signalling is the activation of a heterotrimeric GTP binding protein (G protein) by an agonist-occupied receptor. The β(2) adrenergic receptor (β(2)AR) activation of Gs, the stimulatory G protein for adenylyl cyclase, has long been a model system for GPCR signalling. Here we present the crystal structure of the active state ternary complex composed of agonist-occupied monomeric β(2)AR and nucleotide-free Gs heterotrimer. The principal interactions between the β(2)AR and Gs involve the amino- and carboxy-terminal α-helices of Gs, with conformational changes propagating to the nucleotide-binding pocket. The largest conformational changes in the β(2)AR include a 14 ? outward movement at the cytoplasmic end of transmembrane segment 6 (TM6) and an α-helical extension of the cytoplasmic end of TM5. The most surprising observation is a major displacement of the α-helical domain of Gαs relative to the Ras-like GTPase domain. This crystal structure represents the first high-resolution view of transmembrane signalling by a GPCR.     

Applied Infrared Photoluminescence in Lead Salt Crystals

Results on applied infrared photoluminescence investigations of lead salt chalcogenides are presented. Interpretations of spectra and wafer maps are given. The results obtained may be applied to the investigation of material properties important for laser and detector fabrication.     

Low ohmic multilayer contacts in lead-Tin-Telluride diode lasers

The preparation and the influence of low ohmic multilayer thin film contacts of lead-salt homo- and heterolasers on the degradation of lasing parameters during recycling processes between low working temperatures and room temperatures storage are described and discussed in detail.     

New chlorine-substituted ferroelectric liquid crystals with four aromatic rings in the mesogenic core

New series of liquid crystals with an alkyl-lactate chiral chain and four aromatic rings in the mesogenic core and chloro-substitution were synthesized. For all the compounds studied, SmA and SmC* phases, existing over very broad temperature ranges, were detected and characterized. Mesomorphic properties were analysed with respect to the lengths of the chiral and/or non-chiral chains.     

Construction of aromatic [5,5] spiroketals via hypoiodite-catalyzed etherification combined in relay cascades

An approach is developed for the synthesis of bisbenzannelated spiro[5,5]ketals via a catalytic relay reaction cascade involving a new cyclo-etherification, which is prompted by fluoride and catalyzed by the hypoiodite species generated in situ from irradiative aerobic oxidation of an iodide ion formed in the former step of the reaction cascade.     

Template‐Free Hydrothermal Synthesis of Mesoporous MgO Nanostructures and Their Applications in Water Treatment

The controlled synthesis of Mg(OH)₂ nanowires and microflowers composed of nanoplates was successfully achieved by a template‐free hydrothermal synthetic method. It was found that the reaction medium played a crucial role in the morphological control of the precursor nanostructures. The high polarity of water molecules favored the polar growth of the precursor, resulting in the formation of nanowires with a diameter of 80 nm, whereas a mixed water/ethanol medium with a lower degree of polarity led to the formation of microflowers. Moreover, mesoporous MgO nanostructures could be obtained by further annealing these as‐prepared precursors in air at 500 °C for 2 h. During thermal treatment, the wire‐ and flower‐like morphologies were retained. Porosity formation was due to thermal decomposition of Mg(OH)₂ and release of H₂O. Both the mesoporous MgO nanowires and microflowers showed superior ability of adsorbing the organic dye methyl orange, and thus they are promising candidates for polluted water treatment.     

Copper as an electron trap in GaAs0.6P0.4

An electron trap having an energy level of 0.14 eV from the conduction band edge was found in the bulk of copper-diffused VPE-grown n-GaAs_0.6P_0.4 by conventional DLTS measurements and by pulse-duration dependent capacitance amplitude measurements. The capture cross section at room temperature is about 1.0×10^–21 cm² and has a weak temperature dependence. These properties are attributed to a non-repulsive center having a capturing mechanism which involves multiphonon emission processes with hardly any lattice relaxation. Evolution of the spatial distributions of the traps with time under junction electric field were studied. The results suggest that the trap is positively charged and has a high diffusivity under electric field. The center can thus be identified as positively charged interstitial copper ion rather than some form of copper complexes.