Sputtered NbN Films for Ultrahigh Performance Superconducting Nanowire Single-Photon Detectors

Nowadays ultrahigh performance superconducting nanowire single-photon detectors are the key elements in a variety of devices from biological research to quantum communications and computing. Accurate tuning of superconducting material properties is a powerful resource for fabricating single-photon detectors with a desired properties. Here, we report on the major theoretical relations between ultrathin niobium nitride (NbN) films properties and superconducting nanowire single-photon detectors characteristics, as well as ultrathin NbN films properties dependence on reactive magnetron sputtering recipes. Based on this study we formulate the exact requirements to ultrathin NbN films for ultrahigh performance superconducting nanowire single-photon detectors. Then, we experimentally study ultrathin NbN films properties (morphology, crystalline structure, critical temperature, sheet resistance) on silicon, sapphire, silicon dioxide and silicon nitride substrates sputtered with various recipes. We demonstrate ultrathin NbN films (obtained with more than 100 films deposition) with a wide range of critical temperature from 2.5 to 12.1 K and sheet resistance from 285 to 2000 ~$\Omega$/sq, as well as investigate a sheet resistance evolution over for more than 40\% within two years. Finally, we found out that one should use ultrathin NbN films with specific critical temperature near 9 K and sheet resistance of 400 ~$\Omega$/sq for ultrahigh performance SNSPD.Comment: The following article has been submitted to APL Materials. After it is published, it will be found at https://pubs.aip.org/aip/apm. Copyright 2023 Author(s). This article is distributed under a Creative Commons Attribution (CC BY) Licens

Phenological shifts of abiotic events, producers and consumers across a continent

Ongoing climate change can shift organism phenology in ways that vary depending on species, habitats and climate factors studied. To probe for large-scale patterns in associated phenological change, we use 70,709 observations from six decades of systematic monitoring across the former Union of Soviet Socialist Republics. Among 110 phenological events related to plants, birds, insects, amphibians and fungi, we find a mosaic of change, defying simple predictions of earlier springs, later autumns and stronger changes at higher latitudes and elevations. Site mean temperature emerged as a strong predictor of local phenology, but the magnitude and direction of change varied with trophic level and the relative timing of an event. Beyond temperature-associated variation, we uncover high variation among both sites and years, with some sites being characterized by disproportionately long seasons and others by short ones. Our findings emphasize concerns regarding ecosystem integrity and highlight the difficulty of predicting climate change outcomes. The authors use systematic monitoring across the former USSR to investigate phenological changes across taxa. The long-term mean temperature of a site emerged as a strong predictor of phenological change, with further imprints of trophic level, event timing, site, year and biotic interactions.Peer reviewe

Monazite control on Th, U and REE redistribution during partial melting: experiment and application to the deeply subducted crust

Rare earth elements (REE), Th and U are elements with similar geochemical properties. In crustal rocks these elements are hosted by the light REE (LREE) phosphate mineral monazite. Piston-cylinder experiments were conducted to constrain monazite solubility and monazite/melt partitioning in hydrous granitic melts at conditions relevant to crustal anatexis and subduction zone melting. Monazite has strong preference for LREE and Th; REE heavier than Nd have decreasing compatibility in monazite, and U is less compatible than LREE and Th. New experimental data and reconciliation with previous studies led to a new formulation of LREE solubility in granitic melts as a function of temperature, pressure, monazite composition and water content in melt. The behaviour of monazite during high-pressure and ultra-high pressure (UHP) metamorphism was studied using a suite of rocks from the Kokchetav massif, Kazakhstan. Detailed petrographic and geochronologic study of the samples from the Kokchetav UHP complex was combined with investigation of trace element geochemistry and mineral inclusions of garnet, monazite and zircon. These data demonstrated that (a) on prograde evolution rocks did not experience a linear increase of pressure and temperature (P and T), but had stages of almost isothermal increase of pressure and heating stage with a small increase of pressure, (b) exhumation produced a close association of UHP gneisses with rocks that experienced metamorphism at lower PT conditions and/or along different paths from typical UHP rocks. The geochemistry of the UHP gneisses of the Kokchetav complex is a perfect target for the application of the new experimental data, because these rocks experienced metamorphism and melting at the highest PT conditions recorded in crustal rocks. Bulk rock geochemistry of the UHP gneisses shows pronounced depletion in LREE, Th and U, and a smaller degree of depletion or enrichment in other elements that are often considered as incompatible. The variation in composition of UHP gneisses is explained by a new petrological model, which takes into account the fact that restites are composed of residual assemblage together with a residual melt. It is demonstrated that together with the residual mineral association, the degree of melting and melt extraction efficiency play an important role in controlling of trace element behaviour. Polyphase inclusions trapped in garnet were found in samples of some UHP gneisses. The original composition of inclusions was obtained by high pressure rehomogenisation experiments. The experiments demonstrated that polyphase inclusions represent former melts of variable compositions, varying from high temperature high-LREE melts formed at peak conditions to low-LREE melts formed during exhumation. These inclusions are the first natural examples of melts formed by melting of sediments at subarc depth. This partial melting led to the complete dissolution of monazite and a strong depletion of LREE, Th and U in the UHP gneisses. Melt inclusions and bulk rock geochemistry provide evidence for the release of high LREE melts from melting of crustal metasediments. Partial melting is thus an important process changing the physical and chemical properties of deeply subducted crustal rocks

Geochemistry and zircon U-Pb geochronology constrains late cretaceous plagiogranite intrusions in Mersin ophiolite complex (southern Turkey).

WOS: 000451962500007In this study, LA-ICP-MS U-Pb zircon dating were used to determine the age of the newly discovered plagiogranite suite intruding gabbro and volcanic units of Mersin ophiolites from the Inner Tauride Belt. Obtained U-Pb zircon ages from the plagiogranite yielded crystallization ages of 93.0 +/- 1.5 to 94.2 +/- 2.4Ma (Turonian-Cenomanian) supporting the idea of Late Cretaceous active subduction factory in the Tauride Suture Zone. The plagiogranites are mainly granodioritic, and tonalitic in composition, and contain mafic microgranular enclaves (MME) ranging from 10 to 45cm in size. The plagiogranites are geochemically defined by low K2O (0.02-1.03wt%) and TiO2 (0.17-1.88wt%) and comparatively high Na2O (2.3-10.2wt%) and SiO2 (70-78wt%) compositions together with depletion in Ti, Ta, and Nb. The tectonomagmatic discrimination diagrams, trace, and REE-normalized multi-element patterns indicate that the plagiogranites are distinctive calc-alkaline, I-type volcanic arc granites. Plagiogranites are furthermore characterized by the diffuse presence of isotropic pseudomorphic growth of secondary calcic-amphibole (edenite and actinolite) over a pristine not preserved Ca-inosilicate. Inverse geothermobarometry models indicate a secondary amphibole genesis at ca. 600 degrees C and 1.5-1.7kbar, suggesting HT-metasomatism affecting the already intruded plagiogranites. While it is already accepted that Mersin ophiolite complex is generated in a supra-subduction zone, this study represents a new contribution on the evolution of the Mersin ophiolite during the Late Cretaceous Neotethys subduction and could shed light on the genesis of plagiogranites in arc-environments.Cukurova University Research FoundationCukurova University [FBA-2016-7376]Financial supports from the Cukurova University Research Foundation (Project No: FBA-2016-7376)

ContrastingP-Tpaths within the Barchi-Kol UHP terrain (Kokchetav Complex): Implications for subduction and exhumation of continental crust

The Barchi-Kol terrain is a classic locality of ultrahigh-pressure (UHP) metamorphism within the Kokchetav metamorphic belt. We provide a detailed and systematic characterization of four metasedimentary samples using dominant mineral assemblages, mineral inclusions in zircon and monazite, garnet zonation with respect to major and trace elements, and Zr-in-rutile and Ti-in-zircon temperatures. A typical diamond-bearing gneiss records peak conditions of 49 ± 4 kbar and 950-1000°C. Near isothermal decompression of this rock resulted in the breakdown of phengite associated with a pervasive recrystallization of the rock. The same terrain also contains mica schists that experienced peak conditions close to those of the diamond-bearing rocks, but they were exhumed along a cooler path where phengite remained stable. In these rocks, major and trace element zoning in garnet has been completely equilibrated. A layered gneiss was metamorphosed at UHP conditions in the coesite field, but did not reach diamond-facies conditions (peak conditions: 30 kbar and 800-900°C). In this sample, garnet records retrograde zonation in major elements and also retains prograde zoning in trace elements. A garnet-kyanite-micaschist that reached significantly lower pressures (24 ± 2 kbar, 710 ± 20°C) contains garnet with major and trace element zoning. The diverse garnet zoning in samples that experienced different metamorphic conditions allows to establish that diffusional equilibration of rare earth element in garnet likely occurs at ∼900-950°C. Different metamorphic conditions in the four investigated samples are also documented in zircon trace element zonation and mineral inclusions in zircon and monazite. U-Pb geochronology of metamorphic zircon and monazite domains demonstrates that prograde (528-521 Ma), peak (528-522 Ma), and peak to retrograde metamorphism (503-532 Ma) occurred over a relatively short time interval that is indistinguishable from metamorphism of other UHP rocks within the Kokchetav metamorphic belt. Therefore, the assembly of rocks with contrasting P-T trajectories must have occurred in a single subduction-exhumation cycle, providing a snapshot of the thermal structure of a subducted continental margin prior to collision. The rocks were initially buried along a low geothermal gradient. At 20-25 kbar they underwent near isobaric heating of 200°C, which was followed by continued burial along a low geothermal gradient. Such a step-wise geotherm is in good agreement with predictions from subduction zone thermal models

Geochemistry of ultrahigh-pressure anatexis: fractionation of elements in the Kokchetav gneisses during melting at diamond-facies conditions

The Kokchetav complex in Kazakhstan contains garnet-bearing gneisses that formed by partial melting of metasedimentary rocks at ultrahigh-pressure (UHP) conditions. Partial melting and melt extraction from these rocks is documented by a decrease in K2O and an increase in FeO + MgO in the restites. The most characteristic trace element feature of the Kokchetav UHP restites is a strong depletion in light rare earth elements (LREE), Th and U. This is attributed to complete dissolution of monazite/allanite in the melt and variable degree of melt extraction. In contrast, Zr concentrations remain approximately constant in all gneisses. Using experimentally determined solubilities of LREE and Zr in high-pressure melts, these data constrain the temperature of melting to ~1,000 °C. Large ion lithophile elements (LILE) are only moderately depleted in the samples that have the lowest U, Th and LREE contents, indicating that phengite retains some LILE in the residue. Some restites display an increase in Nb/Ta with respect to the protolith. This further suggests the presence of phengite, which, in contrast to rutile, preferentially incorporates Nb over Ta. The trace element fractionation observed during UHP anatexis in the Kokchetav gneisses is significantly different from depletions reported in low-pressure restites, where generally no LREE and Th depletion occurs. Melting at UHP conditions resulted in an increase in the Sm/Nd ratio and a decoupling of the Sm-Nd and Lu-Hf systems in the restite. Further subduction of such restites and mixing with mantle rocks might thus lead to a distinct isotopic reservoir different from the bulk continental crust

Metapyroxenite in the mantle transition zone revealed from majorite inclusions in diamonds

The transition zone of the Earth's mantle (the depth interval between two major seismic discontinuities at 410 km and 660 km) is critical to understanding our planet's evolution. Some diamonds are thought to have originated in the transition zone and th

Platinum-Group Minerals of Pt-Placer Deposits Associated with the Svetloborsky Ural-Alaskan Type Massif, Middle Urals, Russia

The alteration of platinum group minerals (PGM) of eluval, proximal, and distal placers associated with the Ural-Alaskan type clinopyroxenite-dunite massifs were studied. The Isovsko-Turinskaya placer system is unique regarding its size, and was chosen as research object as it is PGM-bearing for more than 70 km from its lode source, the Ural-Alaskan type Svetloborsky massif, Middle Urals. Lode chromite-platinum ore zones located in the Southern part of the dunite “core„ of the Svetloborsky massif are considered as the PGM lode source. For the studies, PGM concentrates were prepared from the heavy concentrates which were sampled at different distances from the lode source. Eluvial placers are situated directly above the ore zones, and the PGM transport distance does not exceed 10 m. Travyanistyi proximal placer is considered as an example of alluvial ravine placer with the PGM transport distance from 0.5 to 2.5 km. The Glubokinskoe distal placer located in the vicinity of the Is settlement are chosen as the object with the longest PGM transport distance (30⁻35 km from the lode source). Pt-Fe alloys, and in particular, isoferroplatinum prevail in the lode ores and placers with different PGM transport distance. In some cases, isoferroplatinum is substituted by tetraferroplatinum and tulameenite in the grain marginal parts. Os-Ir-(Ru) alloys, erlichmanite, laurite, kashinite, bowieite, and Ir-Rh thiospinels are found as inclusions in Pt-Fe minerals. As a result of the study, it was found that the greatest contribution to the formation of the placer objects is made by the erosion of chromite-platinum mineralized zones in dunites. At a distance of more than 10 km, the degree of PGM mechanical attrition becomes significant, and the morphological features, characteristic of lode platinum, are practically not preserved. One of the signs of the significant PGM transport distance in the placers is the absence of rims composed of the tetraferroplatinum group minerals around primary Pt-Fez alloys. The sie of the nuggets decreases with the increasing transport distance. The composition of isoferroplatinum from the placers and lode chromite-platinum ore zones are geochemically similar