Search results for "general [planetary nebulae]"
showing 10 items of 29443 documents
Morphological and magnetic analysis of Fe nanostructures on W(110) by using scanning tunneling microscopy and Lorentz microscopy
2016
Abstract We investigated morphological features and magnetic properties of epitaxial Fe nanostructures (films, stripes and nanoparticles) on a W(110) surface with monoatomic steps preferentially along the direction. The nanostructures were prepared in ultra-high vacuum by using electron-beam evaporation and subsequent annealing at different temperatures. Scanning tunneling microscopy measurements in-situ revealed elongated Fe nanostructures with aspect ratios of up to . The observable shape and orientation (along or perpendicular to the monoatomic steps of the substrate) of the nanostructures depended substantially on the preparation parameters. By capping the system with 7 monolayers of Pt…
Mechanical characterisation of pentagonal gold nanowires in three different test configurations: A comparative study.
2019
Abstract Mechanical characterisation of individual nanostructures is a challenging task and can greatly benefit from the utilisation of several alternative approaches to increase the reliability of results. In the present work, we have measured and compared the elastic modulus of five-fold twinned gold nanowires (NWs) with atomic force microscopy (AFM) indentation in three different test configurations: three-point bending with fixed ends, three-point bending with free ends and cantilevered-beam bending. The free-ends condition was realized by introducing a novel approach where the NW is placed diagonally inside an inverted pyramid chemically etched in a silicon wafer. In addition, all thre…
Interaction of carbon with microstructural defects in a W-Re matrix: An ab initio assessment
2019
The interaction of carbon atoms with point defects and the core of edge and screw dislocations with Burgers vector a 0 / 2 ⟨ 111 ⟩ in W and a W-Re matrix is studied by means of ab initio calculations. The structure and energetics of the ground-state atomic configurations are presented and rationalized. It is found that di-vacancies, which are thermally unstable in pure W according to the state-of-the-art ab initio calculations, can nucleate at C and Re-C complexes, which fill the gap in the explanation of the emergence of nanovoids observed experimentally under irradiation. Also, on the basis of the recent experimental evidence and our calculations, the temperature ranges for the manifestat…
Luminescence properties of chlorine molecules in glassy SiO 2 and optical fibre waveguides
2017
The support from Latvian Research Program IMIS 2, project “Photonics and materials for photonics” is acknowledged. K.K. was partially supported by the Collaborative Research Project of Materials and Structures Laboratory, Tokyo Institute of Technology. The publication costs of this article were covered by the Estonian Academy of Sciences and the University of Tartu.
Outstanding nonlinear optical properties of methylammonium- and Cs-PbX3 (X = Br, I, and Br–I) perovskites: Polycrystalline thin films and nanoparticl…
2019
Metal Halide Perovskites (MHPs) have arisen as promising materials to construct cost-effective photovoltaic and light emission devices. The study of nonlinear optical properties of MHPs is necessary to get similar success in nonlinear photonic devices, which is practically absent in the literature. The determination of the third order nonlinear coefficients is typically done by the Z-scan technique, which is limited by the scattering of polycrystalline thin films. In this work, we have studied nonlinear optical properties of polycrystalline CH3NH3PbX3 (MAPbX3) thin films and colloidal CsPbX3 nanoparticles with three different bandgaps (X3 = I3, Br3, and Br1.5I1.5). Their bright generation o…
Temperature dependence of luminescence of LiF crystals doped with different metal oxides
2020
Photoluminescence and cathodoluminescence of LiF crystals doped with different binary metal oxides were measured in the wide temperature range of 50-300 K and time interval of 10−8−10−1 s after the nanosecond electron excitation pulse. Both as-grown those and crystals irradiated by an electron beam in range of absorbed dose up to 103 Gy were studied. It is shown that spectral-kinetic characteristics of the luminescence depend on the absorbed dose (type of created/accumulated color centers), the irradiation temperature, the concentration of hydroxyl, which promotes incorporation of the MeO complex (Me: W, Ti, Fe, Li) into the crystal lattice, and the cation-dopants.
Low-temperature luminescence of ScF3 single crystals under excitation by VUV synchrotron radiation
2020
The work was supported by the Latvian Science Council grant LZP-2018/2-0358. The research leading to this result has also been supported by the project CALIPSO plus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. The author is grateful to K. Chernenko (MAX IV Laboratory, Lund University) for his assistance during beamtime experiments and to A. I. Popov for the fruitful discussions. V.P. also acknowledges Valsts pētījumu programma “Augstas enerģijas fizika un paātrinātāju tehnoloģijas” (Projekta Nr. VPP-IZM-CERN-2020/1-0002). REFERENCES
Low-temperature luminescence of catangasite single crystals under excitation by vacuum ultraviolet synchrotron radiation
2020
The luminescent properties of Ca3TaGa3Si2O14 (CTGS, catangasite) single crystals have been studied by means of the vacuum ultraviolet excitation spectroscopy utilizing synchrotron radiation from 1.5 GeV storage ring of MAX IV synchrotron facility. Two emission bands at 320 nm (3.87 eV) and 445 nm (2.78 eV) have been detected. Examining excitation spectra in vacuum ultraviolet spectral range, the 320 nm emission band was explained as the emission band of self-trapped exciton in CTGS single crystal. Its atomic structure is discussed. It is also proposed that the 445 nm (2.78 eV) emission in the CTGS is due to the F centers, which have shown a well-resolved excitation (absorption) band at 5.1 …
Low-temperature luminescence of CdI2 under synchrotron radiation
2020
Synchrotron radiation is applied to study visible and UV luminescence spectra and their excitation spectra of undoped as well as In and Sb doped cadmium iodide crystals at 10 K. The origin of principal luminescence bands and the role of impurities in the formation of emission centers are discussed. The luminescence properties have been explained based on the electronic structure of CdI2 crystals.
Ab initio calculations of the electronic structure for Mn2+-doped YAlO3 crystals
2020
The electronic structure of Mn2+ ion substituted for the host Y atom in orthorhombic bulk YAlO3 crystals has been calculated by means of hybrid exchange-correlation functional HSE within density functional theory. The supercell approach has been used to simulate in Pbnm YAlO3 crystal the point defects, Mn-dopant and compensated the F+ center (oxygen vacancy with one trapped electron), to make unit cell neutral. Large 2 × 2 × 2 supercells of 160 atoms allow us to simulate substitutional point defect with concentration of about 3%. Mn2+ ions substituting for host Y form covalent Mn–O bonds, in opposite to the mostly ionic Y–O bond. The F center inserted to compensate the Mn2+ dopant in YAlO3 …