Electronic structure investigation of the cubic inverse perovskite Sc3AlN

The electronic structure and chemical bonding of the recently discovered inverse perovskite Sc3AlN, in comparison to ScN and Sc metal have been investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured Sc L, N K, Al L1, and Al L2,3 emission spectra are compared with calculated spectra using first principle density-functional theory including dipole transition matrix elements. The main Sc 3d - N 2p and Sc 3d - Al 3p chemical bond regions are identified at -4 eV and -1.4 eV below the Fermi level, respectively. A strongly modified spectral shape of 3s states in the Al L2,3 emission from Sc3AlN in comparison to pure Al metal is found, which reflects the Sc 3d - Al 3p hybridization observed in the Al L1 emission. The differences between the electronic structure of Sc3AlN, ScN, and Sc metal are discussed in relation to the change of the conductivity and elastic properties.Comment: 11 pages, 5 picture

Origin of the anomalous piezoelectric response in wurtzite Scx_xAl1−x_{1-x}N alloys

The origin of the anomalous, 400% increase of the piezoelectric coefficient in Sc$_x$Al$_{1-x}$N alloys is revealed. Quantum mechanical calculations show that the effect is intrinsic. It comes from a strong change in the response of the internal atomic coordinates to strain and pronounced softening of C$_{33}$ elastic constant. The underlying mechanism is the flattening of the energy landscape due to a competition between the parent wurtzite and the so far experimentally unknown hexagonal phases of the alloy. Our observation provides a route for the design of materials with high piezoelectric response.Comment: 10 pages, 4 figures, accepted for publication in Phys. Rev. Let

Інтеграція знань з астрономії та фізики щодо уявлень про приливи та відливи

(uk) В статті розкриті окремі гравітаційні, енергетичні та екологічні особливості припливів та відливів, які у підручниках для середніх загальноосвітніх навчальних закладів та вищої школи мало висвітлені. Автором якісну картину припливів та відпливів доповнено кількісною.(en) The article revealed specific gravity, energy and environmental features tides and low tides that textbooks for secondary schools and higher education was highlighted. The author of picture quality tides supplemented with quantitative

Some Restrictions Abroad Affecting Corporations

A neutron detector concept based on solid layers of boron carbide enriched in 1 B has been in development for the last few years as an alternative for He-3 by collaboration between the ILL, ESS and Linkoping University. This Multi-Grid detector uses layers of aluminum substrates coated with (B4C)-B-10 on both sides that are traversed by the incoming neutrons. Detection is achieved using a gas counter readout principle. By segmenting the substrate and using multiple anode wires, the detector is made inherently position sensitive. This development is aimed primarily at neutron scattering instruments with large detector areas, such as time-of-flight chopper spectrometers. The most recent prototype has been built to be interchangeable with the He-3 detectors of IN6 at ILL. The 1 B detector has an active area of 32 x 48 cm(2). It was installed at the IN6 instrument and operated for several weeks, collecting data in parallel with the regularly scheduled experiments, thus providing the first side-by-side comparison with the conventional He-3 detectors. Results include an efficiency comparison, assessment of the in-detector scattering contribution, sensitivity to gamma-rays and the signal-to-noise ratio in time-of-flight spectra. The good expected performance has been confirmed with the exception of an unexpected background count rate. This has been identified as natural alpha activity in aluminum. New convertor substrates are under study to eliminate this source of background

Neutron Position Sensitive Detectors for the ESS

The European Spallation Source (ESS) in Lund, Sweden will become the world's leading neutron source for the study of materials. The instruments are being selected from conceptual proposals submitted by groups from around Europe. These instruments present numerous challenges for detector technology in the absence of the availability of Helium-3, which is the default choice for detectors for instruments built until today and due to the extreme rates expected across the ESS instrument suite. Additionally a new generation of source requires a new generation of detector technologies to fully exploit the opportunities that this source provides. The detectors will be sourced from partners across Europe through numerous in-kind arrangements; a process that is somewhat novel for the neutron scattering community. This contribution presents briefly the current status of detectors for the ESS, and outlines the timeline to completion. For a conjectured instrument suite based upon instruments recommended for construction, a recently updated snapshot of the current expected detector requirements is presented. A strategy outline as to how these requirements might be tackled by novel detector developments is shown. In terms of future developments for the neutron community, synergies should be sought with other disciples, as recognized by various recent initiatives in Europe, in the context of the fundamentally multi-disciplinary nature of detectors. This strategy has at its basis the in-kind and collaborative partnerships necessary to be able to produce optimally performant detectors that allow the ESS instruments to be world-leading. This foresees and encourages a high level of collaboration and interdependence at its core, and rather than each group being all-rounders in every technology, the further development of centres of excellence across Europe for particular technologies and niches.Comment: 8 pages, 1 figure. Proceedings from the 23rd International Workshop on Vertex Detectors, 15-19 September 2014, Macha Lake, The Czech Republic. PoS(Vertex2014)02

Characterization of boron-coated silicon sensors for thermal neutron detection

Silicon neutron detectors can operate at low voltage and come with ease of fabrication and the possibility of integration of readout electronics and thus are attractive from an application point of view. In this paper, we have studied thermal neutron capture by silicon diodes coated with boron carbide (B4C). One of the surfaces of the diodes was covered with either natural B4C (B4C) or with enriched B4C (B4C). We have investigated: (a) the effect of increase in the sensitive area of the surface of the diode covered with B4C on the neutron detection efficiency and (b) the effect of enrichment of 10B in B4C. The difference in 10B in B4C (16 at.% in the deposited film) and B4C ( 79 at.% in the deposited film) leads to about three times increase in detection efficiency of the same detector. For the given experimental conditions, we do not observe a direct relationship between increase in the surface area and the detection efficiency. Energy spectra obtained by Geant4 simulations support the experimental observation of finding no direct relation between increase in the surface area and the detection efficiency.publishedVersio