Integration of quasi-two-dimensional (2D) films of metal–chalcogenides in optical microcavities permits new photonic applications of these materials. Here we present tunable microcavities with ...monolayer MoS2 or few monolayer GaSe films. We observe significant modification of spectral and temporal properties of photoluminescence (PL): PL is emitted in spectrally narrow and wavelength-tunable cavity modes with quality factors up to 7400; a 10-fold PL lifetime shortening is achieved, a consequence of Purcell enhancement of the spontaneous emission rate.
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IJS, KILJ, NUK, PNG, UL, UM
Southeast Asia is recognized as a region of very high biodiversity, much of which is currently at risk due to habitat loss and other threats. However, many aspects of this diversity, even for ...relatively well-known groups such as mammals, are poorly known, limiting ability to develop conservation plans. This study examines the value of DNA barcodes, sequences of the mitochondrial COI gene, to enhance understanding of mammalian diversity in the region and hence to aid conservation planning.
DNA barcodes were obtained from nearly 1900 specimens representing 165 recognized species of bats. All morphologically or acoustically distinct species, based on classical taxonomy, could be discriminated with DNA barcodes except four closely allied species pairs. Many currently recognized species contained multiple barcode lineages, often with deep divergence suggesting unrecognized species. In addition, most widespread species showed substantial genetic differentiation across their distributions. Our results suggest that mammal species richness within the region may be underestimated by at least 50%, and there are higher levels of endemism and greater intra-specific population structure than previously recognized.
DNA barcodes can aid conservation and research by assisting field workers in identifying species, by helping taxonomists determine species groups needing more detailed analysis, and by facilitating the recognition of the appropriate units and scales for conservation planning.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Spin-orbit coupling is a fundamental interaction in solids that can induce a broad range of unusual physical properties, from topologically non-trivial insulating states to unconventional pairing in ...superconductors1, 2, 3, 4, 5, 6, 7. In iron-based superconductors its role has, so far, not been considered of primary importance, with models based on spin- or orbital fluctuations pairing being used most widely8, 9, 10. Using angle-resolved photoemission spectroscopy, we directly observe a sizeable spin-orbit splitting in all the main members of the iron-based superconductors. We demonstrate that its impact on the low-energy electronic structure and details of the Fermi surface topology is stronger than that of possible nematic ordering11, 12, 13. The largest pairing gap is supported exactly by spin-orbit-coupling-induced Fermi surfaces, implying a direct relation between this interaction and the mechanism of high-temperature superconductivity.
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•Crystal growth from melt and quenching prove to increase Er solubility in GaSe.•Growth of Er2Se3 cubic phase in hexagonal ε-GaSe matrix is epitaxial.•Defects are featured as stacking faults ...proceeding from δ-GaSe sheared bands.•Intense lines in photoluminescence spectra are bound to defect states in band gap.•Microhardness of 1 at%Er-doped GaSe crystal is 1.7 times higher than in pure GaSe.
Powder and polycrystals synthesized from Ga, Se, Er components, as well as GaSe and GaSe:Er single crystals grown from melt in argon atmosphere and in vacuum, respectively, are studied. The growth and quenching conditions used in this work provide 2.5 times increase in solubility of erbium in GaSe matrix and a decrease in number of phases to GaSe and Er2Se3, oppositely to multiphase GaSe:Er alloys known from literature. For the first time Er2Se3 phase was detected by XRD in GaSe crystal doped with 1 at%Er. Possible orientation relations are derived for Er2Se3/GaSe epitaxial pair. It has been shown that stretched reflections in electron micro diffraction patterns and scattering of maximums in x-ray diffraction patterns are bound to stacking faults, which appear owing to thin interlayers of δ-GaSe polytype in ε-GaSe matrix of the melt-grown crystals. Morphology of growing crystal surface is studied. Photoluminescence spectra of pure and erbium-doped GaSe display intense photoluminescence bands, which are, presumably, associated with defect states in band gap of GaSe. It is shown that doping with Er has a strong effect on photoluminescence intensity and on its spectral composition. The measured 1.7 times increase in Vickers microhardness (up to 400 MPa) with respect to pure GaSe is due to solid solution hardening and to precipitation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
New ZnSe ceramic material doped with Te is fabricated by nanopowder technology using cold compaction. It is found that phase composition, Te concentration and grain size of the nanopowders produced ...by direct deposition from vapor depend on temperature in a deposition zone. The higher the temperature, the greater is the fraction of stable cubic phase, the higher Te content, the greater grain size. It is shown that annealing of the ceramics brings to phase transition from wurtzite to sphalerite and dissolution of Te in ZnSe(Te) solid solution. Experimental data on the nanopowders and ceramic materials show that intensity of photoluminescence increases with increase in Te concentration in ZnSe(Te) cubic phase.
•New ZnSe(Te) ceramic material was produced by cold compaction of nanopowders.•The nanopowder technology was used to obtain ceramics of 95% density.•Annealing of the ceramics brings to phase transition from wurtzite to sphalerite.•The Te-doped ZnSe ceramics show high photoluminescence intensity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
In the family of iron-based superconductors, LaFeAsO-type materials possess the simplest electronic structure due to their pronounced two-dimensionality. And yet they host superconductivity with the ...highest transition temperature Tc ≈ 55K. Early theoretical predictions of their electronic structure revealed multiple large circular portions of the Fermi surface with a very good geometrical overlap (nesting), believed to enhance the pairing interaction and thus superconductivity. The prevalence of such large circular features in the Fermi surface has since been associated with many other iron-based compounds and has grown to be generally accepted in the field. In this work we show that a prototypical compound of the 1111-type, SmFe(0.92)Co(0.08)AsO , is at odds with this description and possesses a distinctly different Fermi surface, which consists of two singular constructs formed by the edges of several bands, pulled to the Fermi level from the depths of the theoretically predicted band structure by strong electronic interactions. Such singularities dramatically affect the low-energy electronic properties of the material, including superconductivity. We further argue that occurrence of these singularities correlates with the maximum superconducting transition temperature attainable in each material class over the entire family of iron-based superconductors.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Gallium chalcogenides are promising building blocks for novel van der Waals heterostructures. We report on the low-temperature micro-photoluminescence (PL) of GaTe and GaSe films with thicknesses ...ranging from 200 nm to a single unit cell. In both materials, PL shows a dramatic decrease by 104-105 when film thickness is reduced from 200 to 10 nm. Based on evidence from continuous-wave (cw) and time-resolved PL, we propose a model explaining the PL decrease as a result of non-radiative carrier escape via surface states. Our results emphasize the need for special passivation of two-dimensional films for optoelectronic applications.
In the family of the iron-based superconductors, the REFeAsO-type compounds (with RE being a rare-earth metal) exhibit the highest bulk superconducting transition temperatures (Tc) up to 55 K and ...thus hold the key to the elusive pairing mechanism. Recently, it has been demonstrated that the intrinsic electronic structure of SmFe0.92Co0.08AsO (Tc = 18 K) is highly nontrivial and consists of multiple band-edge singularities in close proximity to the Fermi level. However, it remains unclear whether these singularities are generic to the REFeAsO-type materials and if so, whether their exact topology is responsible for the aforementioned record Tc. In this work, we use angle-resolved photoemission spectroscopy (ARPES) to investigate the inherent electronic structure of the NdFeAsO0.6F0.4 compound with a twice higher Tc = 38 K. We find a similarly singular Fermi surface and further demonstrate that the dramatic enhancement of superconductivity in this compound correlates closely with the fine-tuning of one of the band-edge singularities to within a fraction of the superconducting energy gap Δ below the Fermi level. Our results provide compelling evidence that the band-structure singularities near the Fermi level in the iron-based superconductors must be explicitly accounted for in any attempt to understand the mechanism of superconducting pairing in these materials.
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The original equipment has been developed and the feasibility has been shown of manufacturing shaped products from refractory metals by 3D printing using a high-pressure electric arc in a ...protective gas atmosphere. The proposed technique is performed using layer-by-layer metal deposition using local electric arc skull melting. In experiments aimed at manufacturing molybdenum crucibles, it has been shown that the speed of 3D printing is higher by 2–3 orders of magnitude than the speed of printing by selective laser sintering.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
GaTe crystals of 20mm in diameter and up to 70mm in length have been grown from melt using the high-pressure vertical zone melting (HPVZM) method. Real defect structure has been evaluated by XRD, ...SEM, EPMA, optical microscopy, microhardness and transparency measurements. The phase transformation of hexagonal GaTe single crystal to monoclinic form by grinding has been detected. Such local defects as dendrites and dendrite clusters have been found at cleaved surface (0001), basal dislocations with density of 2×105cm−2 have been detected by the etch-pit technique.
► High-pressure zone melting was developed for crystal growth of GaTe single crystals. ► Grown crystals have hexagonal structure, which transforms into monoclinic upon grinding. ► Formation and decomposition of dendrites associated with unstable growth have been studied. ► Microhardness of the grown crystals is 350MPa, they are transparent in IR and visible ranges. ► Energy gap measured by absorption edge is Eg=1.5eV.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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