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Two-dimensional hafnium-based semiconductors and their heterostructures with native oxides have been shown unique physical properties and potential electronic and optoelectronic applications. However, the scalable synthesis methods for ultrathin layered hafnium-based semiconductor laterally epitaxy growth and its heterostructure are still restricted, also for the understanding of its formation mechanism. Herein, we report the stable sublimation of alkali halide vapor assisted synthesis strategy for high-quality 2D HfSe 2 nanosheets via chemical vapor deposition. Single-crystalline ultrathin 2D HfSe 2 nanosheets were systematically grown by tuning the growth parameters, reaching the lateral size of 6‒40 μm and the thickness down to 4.5 nm. The scalable amorphous HfO 2 and HfSe 2 heterostructures were achieved by the controllable oxidation, which benefited from the approximate zero Gibbs free energy of unstable 2D HfSe 2 templates. The crystal structure, elemental, and time dependent Raman characterization were carried out to understand surface precipitated Se atoms and the formation of amorphous Hf−O bonds, confirming the slow surface oxidation and lattice incorporation of oxygen atoms. The relatively smooth surface roughness and electrical potential change of HfO 2−HfSe 2 heterostructures indicate the excellent interface quality, which helps obtain the high performance memristor with high on/off ratio of 10 5 and long retention period over 9000 s. Our work introduces a new vapor catalysts strategy for the synthesis of lateral 2D HfSe 2 nanosheets, also providing the scalable oxidation of the Hf-based heterostructures for 2D electronic devices.

Enrichment of the heavy rare earth elements (HREE) in carbonatites is rare as carbonatite petrogenesis favours the light (L)REE. We describe HREE enrichment in fenitized phonolite breccia, focusing on small satellite occurrences 1–2 km from the Songwe Hill carbonatite, Malawi. Within the breccia groundmass, a HREE-bearing mineral assemblage comprises xenotime, zircon, anatase/rutile and minor huttonite/thorite, as well as fluorite and apatite. A genetic link between HREE mineralization and carbonatite emplacement is indicated by the presence of Sr-bearing carbonate veins, carbonatite xenoliths and extensive fenitization. We propose that the HREE are retained in hydrothermal fluids which are residually derived from a carbonatite after precipitation of LREE minerals. Brecciation provides a focusing conduit for such fluids, enabling HREE transport and xenotime precipitation in the fenite. Continued fluid–rock interaction leads to dissolution of HREE-bearing minerals and further precipitation of xenotime and huttonite/thorite. At a maximum Y content of 3100 µg g−1, HREE concentrations in the presented example are not sufficient to constitute ore, but the similar composition and texture of these rocks to other cases of carbonatite-related HREE enrichment suggests that all form via a common mechanism linked to fenitization. Precipitation of HREE minerals only occurs where a pre-existing structure provides a focusing conduit for fenitizing fluids, reducing fluid – country-rock interaction. Enrichment of HREE and Th in fenite breccia serves as an indicator of fluid expulsion from a carbonatite, and may indicate the presence of LREE mineralization within the source carbonatite body at depth.

Memristive logic device is a promising unit for beyond von Neumann computing systems and 2D materials are widely used because of their controllable interfacial properties. Most of these 2D memristive devices, however, are made from semiconducting chalcogenides which fail to gate the off‐state current. To this end, a crossbar device using 2D HfSe2 is fabricated, and then the top layers are oxidized into “high‐k” dielectric HfSexOy via oxygen plasma treatment, so that the cell resistance can be remarkably increased. This two‐terminal Ti/HfSexOy/HfSe2/Au device exhibits excellent forming‐free resistive switching performance with high switching speed (<50 ns), low operation voltage (<3 V), large switching window (103), and good data retention. Most importantly, the operation current and the power consumption reach 100 pA and 0.1 fJ to 0.1 pJ, much lower than other HfO based memristors. A functionally complete low‐power Boolean logic is experimentally demonstrated using the memristive device, allowing it in the application of energy‐efficient in‐memory computing. An energy‐efficient memristive device based on 2D HfSe2 oxides is fabricated, which is able to implement functionally complete Boolean logic with operation current down to 100 pA. The low‐power switching is realized by the formation and rupture of cone‐shaped O‐vacancy filaments in the ultrathin Hf−Se−O layer.

The IOCG deposit at Olympic Dam (South Australia) is hosted within the Roxby Downs Granite, which displays a weakly mineralised contact to the orebody (hereafter ‘outer shell’). In a mineralogical-geochemical characterisation of Fe-oxides from the outer shell, we show silician magnetite (Si-magnetite) and HFSE-bearing hematite define the early stages of alkali-calcic alteration. This association forms in the presence of hydrothermal K-feldspar and calc-silicates via overprinting of magmatic magnetite and ilmenite breakdown. Geochemical modelling, at ≥ 400 °C, shows such reactions occur at pH-fO2 conditions coinciding with shifts from K-feldspar to sericite, and ilmenite to rutile stability. The subsequent Si-magnetite+siderite association forms down-T in the absence of K-feldspar. Transition from granular to bladed morphologies in Si-magnetite is part of a series of Fe-oxide interconversions, followed by formation of zoned, U-W-Sn-Mo-bearing hematite. Enrichment in REE, Y and U in Si-magnetite and the prevalence of U-W-Sn-Mo-bearing hematite support a granite-derived fluid. Combined, petrographic and geochemical evidence show a transition among Fe-oxides from the outer shell to the orebody attributable to the evolution of the same fluid. Unusual massive magnetite intervals and Fe-oxide nodules in granite are considered due to either the presence of inherited lithologies, metasomatic products, or the result of magnetite-rich, crystal mush forming in the melt. We propose a model, corroborated by recently published data including high-precision U-Pb dating of magmatic zircon and hydrothermal hematite, in which an ‘outer shell’ is initiated at the 6–8 km depth of granite emplacement during volatile release from fluids ponding at intrusion margins. Granite cupola collapse at shallower levels (2–3 km?) follows via uplift along faults, facilitating intense brecciation and ore formation.

The Bohemian Massif hosts significant hydrothermal U-deposits associated with shear zones in the high-grade metamorphic basement. But there is a lack of evidence of a genetic link between mineralization and U-fertile igneous rocks. This contribution provides constraints on the major U source of the vein-type U-deposits, the timing of ore formation and the metallogenetic model. The anomalous trace element signatures of the low-temperature hydrothermal deposits (high Zr, Y, Nb, Ti, ∑REE) and their close spatial relation with ultrapotassic rocks of the durbachite series point to a HFSE and REE enriched source rock. The durbachites have high U content (13.4–21.5 ppm) mainly stored in magmatic uraninite and other refractory minerals (e.g., thorite, zircon, allanite) that became metamict over a time interval sufficient to release U from their crystal structure, as suggested by the time gap between emplacement of the durbachites (EMP uraninite U–Pb age ~ 338 Ma) and hydrothermal activity (SIMS uranium ore U–Pb age ~ 270 Ma). Airborne radiometric data show highly variable Th/U ratios (1.5–6.0), likely reflecting a combination between (1) crystallization of magmatic uraninite, (2) hydrothermal alteration, and (3) leaching and mobilization of U along NW–SE-trending fault zones, manifested by elevated Th/U values in the radiometric map. The presence of rare magmatic uraninite in durbachites suggests almost complete uraninite dissolution; EMP imaging coupled with LA-ICP-MS analyses of refractory accessory phases revealed extensive mobilization of U together with HFSE and REE, providing direct evidence for metal leaching via fluid-driven alteration of radiation-damaged U-rich minerals. The large-scale HFSE and REE mobilization, demonstrated by the unusual trace element signatures of the U-deposits, was likely caused by low-temperature (270–300 °C), highly alkaline aqueous solutions containing F-, P-, and K-dominated complexing ligands. The first SIMS U–Pb age of 270.8 ± 7.5 Ma obtained so far for U-mineralization from the Bohemian Massif revealed a main Permian U mineralizing event, related to crustal extension, exhumation of the crystalline basement, and basin formation, as recorded by U–Pb apatite dates (280–290 Ma) and AFT thermal history models of the durbachites. The Permo-Carboniferous sedimentary cover probably represented a source of oxidized basinal brines infiltrating the basement-hosted durbachite plutons and triggering massive metal leaching. The interaction between basin-derived brines and durbachites resulted in significant modification of the chemical composition of the hydrothermal system (K and F release during biotite chloritization, P liberation through monazite alteration), leading to the formation of ore-bearing fluids responsible for the metallogenesis of the basement-hosted unconformity-related U-deposits in shear zones in the Bohemian Massif.

In principle, compositional profiling of the near-rim region of minerals can provide insight into cooling rates, but presumes that loss or gain of material from the crystal rim is not kinetically restricted. Trace element depth profiles collected for Zr, Hf, Ta, Nb, and U in amphibolite-facies rutile grains of the Catalina Schist, southern California, show significant variability within a single rock: Profiles of the same element among different grains can have significantly different slopes, grains with indistinguishable Zr profiles show vastly different Nb profiles, and grains with indistinguishable Nb profiles show different Zr profiles. Textural and kinetic idiosyncrasies within the matrix apparently affect the ability of specific crystals to accept or release trace elements, and impugn the common assumption that mineral surfaces maintain equilibrium at amphibolite-facies conditions. A new model that limits the flux of Zr from rutile grains helps explain commonly observed compositional profiles, and implies that inversion of compositional profiles assuming equilibrium among grain surfaces will invariably overestimate cooling rates. Few grains may record the low closure temperatures that experimentally determined diffusivities imply. Rather, higher temperatures will be retained, depending on the proximity of reactants and products in the matrix. Silicon diffusion does not control Zr reequilibration in rutile, and relative diffusion coefficients ( D ’s) of trace elements in rutile are D Zr  ~  D Hf  ~ 10 D Nb  ~ 20 D Ta  ~ 40 D U .

Two-dimensional hafnium-based semiconductors and their heterostructures with native oxides have been shown unique physical properties and potential electronic and optoelectronic applications. However, the scalable synthesis methods for ultrathin layered hafnium-based semiconductor laterally epitaxy growth and its heterostructure are still restricted, also for the understanding of its formation mechanism. Herein, we report the stable sublimation of alkali halide vapor assisted synthesis strategy for high-quality 2D HfSe 2 nanosheets via chemical vapor deposition. Single-crystalline ultrathin 2D HfSe 2 nanosheets were systematically grown by tuning the growth parameters, reaching the lateral size of 6–40 µm and the thickness down to 4.5 nm. The scalable amorphous HfO 2 and HfSe 2 heterostructures were achieved by the controllable oxidation, which benefited from the approximate zero Gibbs free energy of unstable 2D HfSe 2 templates. The crystal structure, elemental, and time dependent Raman characterization were carried out to understand surface precipitated Se atoms and the formation of amorphous Hf–O bonds, confirming the slow surface oxidation and lattice incorporation of oxygen atoms. The relatively smooth surface roughness and electrical potential change of HfO 2 –HfSe 2 heterostructures indicate the excellent interface quality, which helps obtain the high performance memristor with high on/off ratio of 10 5 and long retention period over 9000 s. Our work introduces a new vapor catalysts strategy for the synthesis of lateral 2D HfSe 2 nanosheets, also providing the scalable oxidation of the Hf-based heterostructures for 2D electronic devices.

Context Two-dimensional semiconductor materials have received much attention in recent years due to their wide variety of applications in the field of nano-optoelectronic devices. In this project, we applied stresses ranging from −6 to +6% to the ZrSe 2 /HfSe 2 heterostructure and systematically investigated its electrical and optical properties. It is discovered that stress can effectively modulate the forbidden bandwidth of the ZrSe 2 /HfSe 2 heterojunction; whereas, under compressive stress, the forbidden bandwidth of the material decreases further until the bandgap is zero, leading to the material’s transformation from semiconductor to metal. The forbidden band gap of the ZrSe 2 /HfSe 2 heterojunction increases with increasing horizontal biaxial tensile strain. We discovered that the light absorption performance of this heterostructure is significantly better than that of its similar monomolecular layer and that its light absorption intensity can reach an order of magnitude of 10 4 . Under compressive and tensile stresses, the ZrSe 2 /HfSe 2 heterojunctions exhibit different degrees of red or blue shift. The results indicate that constructing ZrSe 2 /HfSe 2 heterojunctions and applying horizontal biaxial stresses to them can significantly modulate the optoelectronic properties of the materials. ZrSe 2 /HfSe 2 heterojunction is a new type of high-performance photogenerated carrier transport device with a wide range of applications. Methods The calculations in this study are carried out the first principles approach of density functional theory, as implemented in the CASTEP module of Materials-Studio2019. The researchers used an ultrasoft reaction potential to calculate the interactions between the ion core and the electrons and applied the Perdew-Burke-Ernzerhof (PBE) and the generalized gradient approximation (GGA) to perform the calculations. The Monkhorst-Pack technique was employed to create the k-point samples utilized for integration on the Brillouin zone, and the k-point grid was uniformly 6 × 6 × 1. In addition, in order to avoid interactions between the atomic layers affecting the properties and stability of the material, such interactions were prevented by adding a 30 Å vacuum layer. Using a plane-wave energy cutoff of 500 eV and the convergence accuracy of the iterative process was set to 1 × 10 −5 eV to ensure the accuracy of the computational results, and in addition. The maximum stress in the lattice was limited to less than 0.05 GPa or the interaction force between neighboring atoms was lower than 0.03 eV/Å. For the calculation of the properties of the optical properties, a k-point grid of 18 × 18 × 1 is used for optimization, and the polarization direction of the material is not taken into account, considering that the material is isotropic. This study proposes to apply the Tkatchenko-Scheffler (TS) dispersion correction method in DFT-D to appropriately represent the interlayer van der Waals interaction forces to solve inaccuracies in the computation of van der Waals interactions via density functional theory.

The different generations of calc-silicate assemblages formed during sequential metasomatic events make the Campiglia Marittima magmatic–hydrothermal system a prominent case study to investigate the mobility of rare earth element (REE) and other trace elements. These mineralogical assemblages also provide information about the nature and source of metasomatizing fluids. Petrographic and geochemical investigations of granite, endoskarn, and exoskarn bodies provide evidence for the contribution of metasomatizing fluids from an external source. The granitic pluton underwent intense metasomatism during post-magmatic fluid–rock interaction processes. The system was initially affected by a metasomatic event characterized by circulation of K-rich and Ca(-Mg)-rich fluids. A potassic metasomatic event led to the complete replacement of magmatic biotite, plagioclase, and ilmenite, promoting major element mobilization and crystallization of K-feldspar, phlogopite, chlorite, titanite, and rutile. The process resulted in significant gain of K, Rb, Ba, and Sr, accompanied by loss of Fe and Na, with metals such as Cu, Zn, Sn, W, and Tl showing significant mobility. Concurrently, the increasing fluid acidity, due to interaction with Ca-rich fluids, resulted in a diffuse Ca-metasomatism. During this stage, a wide variety of calc-silicates formed (diopside, titanite, vesuvianite, garnet, and allanite), throughout the granite body, along granite joints, and at the carbonate–granite contact. In the following stage, Ca-F-rich fluids triggered the acidic metasomatism of accessory minerals and the mobilization of high-field-strength elements (HFSE) and REE. This stage is characterized by the exchange of major elements (Ti, Ca, Fe, Al) with HFSE and REE in the forming metasomatic minerals (i.e., titanite, vesuvianite) and the crystallization of HFSE-REE minerals. Moreover, the observed textural disequilibrium of newly formed minerals (pseudomorphs, patchy zoning, dissolution/reprecipitation textures) suggests the evolution of metasomatizing fluids towards more acidic conditions at lower temperatures. In summary, the selective mobilization of chemical components was related to a shift in fluid composition, pH, and temperature. This study emphasizes the importance of relating field studies and petrographic observations to detailed mineral compositions, leading to the construction of litho-geochemical models for element mobilization in crustal magmatic-hydrothermal settings.

Small volumes of felsic melt, commonly known as oceanic plagiogranites, appear as melt pockets or dikes within the gabbroic section and the sheeted dikes root zone of the oceanic crust. Plagiogranites from the Troodos Ophiolite Complex on Cyprus are among the best exposures of felsic rocks that are embedded in a complete section of obducted oceanic lithosphere. Nevertheless, their exact petrogenesis is still a matter of debate, largely due to limited high-quality trace element and radiogenic isotope data. Previously proposed models for Troodos plagiogranites have included both low-pressure dehydration melting and fractional crystallisation at deeper levels of the oceanic crust. To evaluate both models, oceanic plagiogranites from the Troodos Ophiolite Complex were analysed in this study for their major and trace elements, and for the first time also for Hf–Nd–Sr isotope compositions. The trace element measurements also include for the first time high-precision measurements of high-field-strength element (HFSE) abundances that now permit to better unravel the petrogenesis of the Troodos plagiogranites and their possible mantle sources. In general, the Troodos plagiogranites exhibit a narrow range of Nb/Ta and Zr/Hf that overlap the compositions of mid-ocean ridge basalts (MORB). In line with earlier studies, three compositional groups can be identified: two groups formed by either fractional crystallisation or combined fractional crystallisation and wall rock assimilation, and one group derived from partial melting of slightly altered oceanic crust. The majority of the Troodos plagiogranites (Main Group) are the product of extensive fractional crystallisation of ambient arc-tholeiitic mafic melts. A second group of plagiogranites (Spilia Group) is generated by fractional crystallisation of boninitic precursor melts and the assimilation of arc-tholeiitic crustal material. Variable HFSE concentrations and diagnostic Hf–Nd isotope signatures that are unique to both suites allow discriminating between the two parental melts and fractionation processes. A small group of plagiogranites (Zoopigi Group) is interpreted to derive from partial melting in the conductive layer of active magma chamber lenses (AML). Elevated Nb/Ta, Zr/Hf, and light rare-earth element (LREE) enrichments in these rocks are in support of this model. Collectively, our data suggest that low-pressure fractional crystallisation (also in combination with assimilation of wall rocks) might be the predominant process controlling the formation of felsic rocks on Cyprus, whereas dehydration melting appears to be less important. If compared to Archean tonalitic–trondhjemitic–granodioritic suites (TTGs), compositions of plagiogranites from Cyprus mirror shallow-level processes in thin oceanic crust, which is illustrated by their narrow, MORB-like range of HFSE ratios and their distinct enrichment in heavy rare-earth elements (HREE) that distinguishes them from the Archean TTGs.