Uniform Composition Research Articles

Investigation of Sub-Bandgap Emission and Unexpected n-Type Behavior in Undoped Polycrystalline CdSexTe1-x.

Se alloying has enabled significantly higher carrier lifetimes and photocurrents in CdTe solar cells, but these benefits can be highly dependent on CdSexTe1-x processing. This work evaluates the optoelectronic, chemical, and electronic properties of thick (3µm) undoped CdSexTe1-x of uniform composition and varied processing conditions (CdSexTe1-x evaporation rate, CdCl2 anneal, Se content) chosen to reflect various standard device processing conditions. Sub-bandgap defect emission is observed, which increased as Se content increased and with "GrV-optimized CdCl2" (i.e., CdCl2 anneal conditions used for group-V-doped devices). Low carrier lifetime is found for GrV-optimized CdCl2, slow CdSexTe1-x deposition, and low-Se films. Interestingly, all films (including CdTe control) exhibited n-type behavior, where electron density increased with Se up to an estimated ≈1017cm-3. This behavior appears to originate during the CdCl2 anneal, possibly from Se diffusion leading to anion vacancy (e.g., VSe, VTe) and ClTe generation.

Exploring Elemental Powder Approach for Making Al and Ti Containing High-Entropy Alloys by Powder Bed Fusion

This research aimed to produce high-entropy alloys (HEA), namely Mn–Fe–Co–Ni + 5Al and Mn–Fe–Co–Ni + 5Al + 5Ti, through the Powder Bed Fusion technique using elemental powders. Alloy composition has been selected to achieve a HEA matrix with strengthening intermetallic precipitates. Thermo-Calc software has been used to predict solidification behavior and phase stability for non-equilibrium conditions. The experiment involved the execution of an additive manufacturing process with a laser working in point-by-point exposure mode to produce samples using varying laser power and exposure time. The samples underwent investigation via macroscopic examination, porosity analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and hardness testing. Results have shown that processing parameters and alloy constituents directly influenced processability and sample traits. What is more, a high-energy laser beam introduction to the material during the process has helped mitigate the formation of large Ti or Al oxides. In addition, EDS analysis indicated that higher Volumetric Energy Density values enhanced the uniformity of chemical composition, indicating that homogeneity can be achieved by selecting appropriate melting parameters. The results clearly show that these alloys can be successfully (by means of porosity and homogeneity) manufactured from elemental powders via the powder bed fusion technique.

Elemental analysis of “kampong” chicken egg shell content using a Nd-YAG laser induced breakdown spectroscopy

Abstract Distinguishing between eggs laid by chickens fed organic versus chemical feed poses a formidable challenge, particularly when relying on eggshell characteristics alone. As such, this investigation was undertaken to conduct a qualitative exploration of the eggshell composition in free-range chickens, employing laser induced breakdown spectroscopy (LIBS) to discern varying feed treatments within the samples. To initiate the formation of micro-plasma, a Nd:YAG LIBS system has been utilized as the excitation source. The eggshells used in the study were sourced from seven distinct chicken groups subjected to diverse feeding protocols, including 100% industrial feed, 100% village feed, and its combination, and also along with eggshells from purebred chickens purchased from traditional markets. Based on the spectroscopic analysis, the seven samples utilized in this study exhibit a uniform chemical composition, encompassing both organic and inorganic elements, specifically C, O, H, Ca, Mg, Fe, Al, K, Si, and S.

Cd0.90Mn0.10Te single crystal for γ – Ray detector application: A comprehensive analysis of structural and compositional homogeneity

This study provides a comprehensive examination of the Cd0.90Mn0.10Te (CMT) single crystal in its role as a radiation detector. Covering aspects from the growth process to detector performance, the primary emphasis is placed on ensuring the uniformity of composition along the growth axis. A cost-effective custom-built vertical Bridgman (VB) setup is developed for the growth of highly homogeneous Cd0.90Mn0.10Te (CMT) single crystal. CMT single crystals of 10 mm diameter and 130 mm length with near uniform stoichiometry along the growth axis were grown using VB method. Laue diffraction confirms the single crystallinity of the grown crystal. The measured lattice constant is comparable to the theoretical value calculated using Vegard’s law. The two mode vibrations of the CdTe and MnTe sublattices were confirmed by Raman spectroscopy. The observed high optical transmittance in the mid-infra-red (IR) region and a nearly constant bandgap of ∼1.6 eV for the wafers taken at different locations along the growth axis reveals the IR transparency and compositional uniformity of the grown crystal. The energy dispersive X-ray spectroscopy proved that the elemental distribution is uniform in the grown crystal. The IR microscopic imaging shows Te inclusions with a number density in the range of ∼2.6–4.5 × 104 cm−2. The resistivity of the CMT crystal for all wafers was found to be in the order of 109 Ωcm. The γ–ray spectral resolution of ∼22 % of 59.5 keV irradiation from 241Am source is achieved.

Enhanced thermal stability and power factor in layered Bi2Se0.5Te2.5 Thin films across a broad temperature range

Bi2Te3-based n-type thin films with high thermoelectric performances are typically synthesised through the formation of dense structures, a process conventionally conducted at high temperatures. However, this method compromises thermal stability. In this study, structural design and multiple-step annealing were employed to enhance the thermal stability of high-performance Bi2Se0.5Te2.5 thin films. Post-annealing, the disparity in the values of the Seebeck coefficient over the entire test temperature range, was reduced to 20 μV K−1, which is approximately 32 % compared to pre-annealing measurements. The layered Bi2Se0.5Te2.5 thin film demonstrated an elevated power factor (28 × 10−4 W m−1K−2), which was maintained across a broad temperature spectrum. This multiple-step annealing approach not only refines the structural integrity by extending the atomic diffusion duration but also mitigates defects and augments compositional uniformity at reduced temperatures. Consequently, layered Bi2Se0.5Te2.5 films emerge as promising candidates for thermoelectric materials, offering enhanced long-term stability for diverse applications, including electric and hybrid electric vehicles, and portable electronic devices.

Early Triassic high-K granitoids and enclaves of the Daheba pluton, West Qinling (China): Implications for relative contributions of crust and mantle

Early Triassic granitoids are widespread in the northwestern West Qinling Orogen, China, but their petrogenesis and geodynamic implications remain unclear. In this study, we integrated new field and petrological observations, mineralogical compositions, zircon U-Pb dating, Hf isotopic and whole-rock geochemical analyses for the early Triassic granitic pluton in the Daheba area to determine its magma source and geodynamic scenario. The pluton is composed of granodiorite and syenogranite and carries microgranular enclaves (MEs) which formed at ca. 253–249 Ma. The granitoids show wide SiO2 contents of 63.73–77.49 wt% (av. 69.89), high K2O contents of 3.4–5.4 wt% (av. 4.1) and moderate Mg# of 16–51 (av. 36), belonging to high-K, calc-alkaline I-type granites. These rocks have high radiogenic but uniform Hf isotopic compositions with 176Hf/177Hf and ɛHf(t) of 0.282511–0.282658 and −3.85 – +1.25, respectively. The MEs hosed within the granite are characterized by high Mg# of 35–58 (av. 46) and variable εHf(t) of −4.64 – +9.35, which likely represent a hybridized melt derived from a slab-modified mantle and lower crust. In combination with coeval magmatic rocks in the western Gonghe-East Kunlun area, we propose a genetic model where mafic magmas derived from an enriched mantle and underplated beneath the overlying lower crust are considered to have produced the high-K felsic magma. Further, the hybridized melt ascended to shallower crustal levels to generate a series of rocks ranging from dioritic MEs to granodiorite to syenogranite. Mass balances modeling suggests that the generation of these rocks involved 36 % of the lower crustal-derived melt and 64 % of the SCLM (R2 = 0.9). Our new data, in tandem with published results suggest that the Daheba pluton formed during the subduction stage of the Paleo-Tethyan Ocean and that a local extensional episode occurred at 253–249 Ma in the western Gonghe area.

Development of pyrargyrite Ag3SbS3 absorber films through sulfurization of Ag–Sb stacks for thin-film photovoltaics

Pyrargyrite Ag3SbS3, which consists of naturally abundant and non-toxic elements, has attracted attention as a promising solar cell material. A two-stage fabrication method has been developed to synthesize Ag3SbS3 thin films through a solid-state reaction between Sb and Ag metallic layers by sulfurizing at 250–350 oC. The Ag3SbS3 film prepared at a sulfurization temperature of 250 °C contained Ag2S and Sb2S3 secondary phases with non-stoichiometric composition, distinct grain growth, a bandgap energy of 1.4 eV, and an electrical resistivity of 5.74 × 10−4 Ω cm. Through sulfurization of the stacks at 300 °C, the Ag2S and Sb2S3 secondary phases disappeared, and dominant Ag3SbS3 films were obtained with a minor AgSbS2 secondary phase. A compact and uniform near-stoichiometric Ag3SbS3 composition with large grains was obtained with an increased bandgap energy of 1.64 eV and electrical resistivity of 6.19 × 104 Ω cm. A further increase in the sulfurization temperature to 350 °C resulted in an increase in the crystallite and grain sizes of Ag3SbS3 with a decreased bandgap energy of 1.62 eV and electrical resistivity of 2.90 × 104 Ω cm. AgSbS2 remained as a minor secondary phase in this film. Thin-film solar cells prepared with the Ag3SbS3 absorber synthesized at a sulfurization temperature of 300 °C exhibited an open-circuit voltage of 473.85 mV, short-circuit current density of 1.47 mA/cm2, fill factor of 41.6 %, and an efficiency of 0.3 %. These results demonstrate that Ag3SbS3 is a potential candidate for thin-film solar cells.

Mid‐Infrared Top‐Gated Ge0.82Sn0.18 Nanowire Phototransistors

AbstractAchieving high crystalline quality germanium‐tin (Ge1 − xSnx) semiconductors at Sn content exceeding 10% is quintessential to implement the long sought‐after silicon‐compatible mid‐infrared photonics. Herein, by using sub‐20 nm Ge nanowires as compliant growth substrates, Ge1 − xSnx alloys with a Sn content of 18% exhibiting a high composition uniformity and crystallinity along a few micrometers in the nanowire axial direction are demonstrated. The measured bandgap energy of the Ge/Ge0.82Sn0.18 core/shell nanowires is 0.322 eV enabling the mid‐infrared photodetection with a cutoff wavelength of 3.9 µm. These narrow bandgap nanowires are also integrated into top‐gated field‐effect transistors and phototransistors. Depending on the gate design, these transistors are found to exhibit either ambipolar or unipolar behavior with a subthreshold swing as low as 228 mV/decade at 85 K. Moreover, varying the top gate voltage from ‐1 to 5 V yields nearly one order of magnitude increase in the photocurrent of the nanowire phototransistor under a 2330 nm illumination. This study shows that the core/shell nanowire architecture with a very thin core not only mitigates the challenges associated with strain build‐up observed in thin films but also provides a promising platform for all‐group IV mid‐infrared photonics and nanoelectronics paving the way toward sensing and imaging applications.

Low temperature crystallization of atomic-layer-deposited SrTiO3 films with an extremely low equivalent oxide thickness of sub-0.4 nm

Despite SrTiO3(STO) possessing a high dielectric constant, its application as a capacitor dielectric in dynamic random-access memory(DRAM) capacitors faces challenges due to the high-temperature annealing for crystallization, its compositional inhomogeneity, and the high leakage currents of STO films. To address these issues, we employ atomic layer deposition(ALD) of STO films onto Pt substrates at elevated temperatures(340–380 °C). The use of low-reactivity Pt electrodes effectively mitigates the initial growth of excess Sr, ensuring enhanced compositional uniformity along the film growth direction. Coupled with ALD at high temperatures, this approach facilitates the crystallization of STO films in the as-grown state, further enhancing the crystallinity with increasing film thickness. Subsequent low-temperature post-deposition annealing (PDA) at 400 and 500 °C achieves full crystallization. This process results in a remarkable increase in the dielectric constant, reaching approximately 150. Furthermore, the absence of microcracks after PDA, attributed to the formation of adequately dense films, contributes to substantially improved dielectric properties. Consequently, these STO films exhibit an exceptionally low equivalent oxide thickness of 0.34 nm coupled with an ultralow leakage current of 3.7 × 10−8 A/cm2 at an operation voltage of 0.8 V, promising for advancing DRAM capacitors. This study presents a pathway for the sustainable scaling of DRAMs, addressing challenges in ALD-grown STO films.

Observationally constrained regional variations of shortwave absorption by iron oxides emphasize the cooling effect of dust

Abstract. The composition of soil dust aerosols derives from the mineral abundances in the parent soils that vary across dust source regions. Nonetheless, Earth system models (ESMs) have traditionally represented mineral dust as a globally homogeneous species. The growing interest in modeling dust mineralogy, facilitated by the recognized sensitivity of the dust climate impacts to composition, has motivated state-of-the-art ESMs to incorporate the mineral speciation of dust along with its effect upon the dust direct radiative effect (DRE). In this work, we enable the NASA Goddard Institute for Space Studies ModelE2.1 to calculate the shortwave (SW) DRE accounting for the regionally varying soil mineralogy. Mineral–radiation interaction at solar wavelengths is calculated according to two alternative coupling schemes: (1) external mixing of three mineral components that are optically distinguished, one of which contains embedded iron oxides; (2) a single internal mixture of all dust minerals with a dynamic fraction of iron oxides that varies regionally and temporally. We link dust absorption to the fractional mass of iron oxides based on recent chamber measurements using natural dust aerosol samples. We show that coupled mineralogy overall enhances the scattering by dust, and thus the global cooling, compared to our control run with globally uniform composition. According to the external mixing scheme, the SW DRE at the top of atmosphere (TOA) changes from −0.25 to -0.30Wm-2, corresponding to a change in the net DRE, including the longwave effect, from −0.08 to -0.12Wm-2. The cooling increase is accentuated when the internal mixing scheme is configured: the SW DRE at the TOA becomes -0.34Wm-2 with a net DRE of -0.15Wm-2. The varying composition modifies the regional distribution of single scattering albedo (SSA), whose variations in specific regions can be remarkable (above 0.03) and significantly modify the regional SW DRE. Evaluation against the AErosol RObotic NETwork (AERONET) shows that explicit representation of soil mineralogy and its regional variations reduces the low bias of model dust SSA while improving the range of variability across stations and calendar months. Despite these improvements, the moderate spatiotemporal correlation with AERONET reveals remaining modeling challenges and the need for more accurate measurements of mineral fractions in soils.

Carrier mobility dependence of indium antimonide-bismide on carrier concentration, temperature, and bismuth composition grown on semi-insulating gallium arsenide substrate

We explore the impact of carrier concentration, temperature, and bismuth (Bi) composition on the carrier mobility of indium antimonide-bismide (InSb1−x Bi x ) material. Utilizing the molecular beam epitaxy method, we achieved high Bi composition uniformity. This method also enables the InSb1−x Bi x to be grown on semi-insulating GaAs substrate, effectively preventing parallel electrical conduction during Hall effect measurement. Our findings reveal that InSb1−x Bi x doped with silicon (Si) and tellurium (Te) consistently exhibit n-type conductivity. In contrast, InSb1−x Bi x doped with beryllium (Be) exhibit a transition from n to p type conductivity, subjected to the Be doping level and the measurement temperature. Based on these observations, we proposed an empirical model describing the dependence of InSb1−x Bi x electron mobility on carrier concentration, temperature, and Bi composition, specifically for Si and Te-doped InSb1−x Bi x samples. These insights gained from this study hold potential application in photodetector device simulations.

Planets similar in size are often dissimilar in interior

The number of discovered exoplanets now exceeds 5500 allowing statistical analyses of planetary systems. Multi-planet systems are mini-laboratories of planet formation and evolution, and analysing their system architectures can help us to constrain the physics of these processes. Recent works have found evidence of significant intrasystem uniformity in planet properties such as radius, mass, and orbital spacing, collectively termed ‘peas in a pod’ trends. In particular, correlations in radius and mass have been interpreted as implying uniformity in planet bulk density and composition within a system. However, the samples used to assess trends in mass tend to be small and biased. In this paper, we re-evaluate correlations in planet properties in a large sample of systems with at least two planets for which mass and radius have been directly measured, and therefore bulk density can be calculated. Our sample was assembled using the most up-to-date exoplanet catalogue data, and we compute the relevant statistics while using a procedure to ‘weight’ the data points according to measurement precision. We find a moderate correlation in radius and a weak correlation in the densities of adjacent planets. However, masses of neighbouring planets show no overall correlation in our main sample and a weak correlation among pairs of planets similar in size or pairs restricted to Mp<100 M⊕, Rp<10 R⊕. Similarly, we show that the intrasystem dispersion in radius is typically less than that in mass and density. We identify ranges in stellar host properties that correlate with stronger uniformity in pairs of adjacent planets: low Teff for planet masses, and low metallicity and old age for planet densities. Furthermore, we explore whether peas in a pod trends extend into planet compositions or interior structures. For small neighbouring planets with similar radii, we show that their masses and interior structures are often disparate, indicating that even within the same system, similarity in radii is not necessarily a good proxy for similarity in composition or the physical nature of the planets.

Maskelynite- as seen in shocked Lonar target basalt, India, and martian and lunar meteorites

In this study, we investigate the mineralogical and petrochemical characteristics of maskelynite occurring in a shocked basalt boulder from a terrestrial impact crater on a basaltic target – the Lonar impact crater in India, and the martian and lunar meteorites. The majority of Lonar maskelynite experienced solid-state transformation and maintained almost a uniform chemical composition, consistent with the unshocked feldspar. The locally flow-like texture and marginal vesiculation in feldspathic glass are needed in interaction with the impact-melt. The vesiculated melt occasionally occurring at the margins of maskelynite is characterised by Na-loss due to the shock-induced volatility. A shock pressure of ≤42 GPa and at a temperature of ≤1000 °C appear consistent for the formation of Lonar vesiculated melt/ feldspathic glass. Under the impact-induced shock metamorphism, maskelynite samples from the moon retain both the crystalline and amorphous domains with a distinct chemical heterogeneity attributed to different shock metamorphism effects of the plagioclase. In contrast, the martian maskelynites exhibit a smooth, homogeneous composition. The estimated shock pressure is relatively higher at ∼42–45 GPa based on experiments and models. The difference in Si/Al ratio in lunar (1–1.3) and martian maskelynite (1.5–1.9) suggests its inherent difference in composition of the crust, whereas the Lonar maskelynite shows overlapping composition with the martian maskelynite contending Lonar basalt as a potential terrestrial analogue to the martian crust.

Sphalerite Records Cd Isotopic Signatures of the Parent Rocks in Hydrothermal Systems: A Case Study From the Nayongzhi Zn–Pb Deposit, Southwest China

AbstractMetal stable isotopes (e.g., Zn, Cd, and Cu) have been used to track metal sources in different types of hydrothermal systems. However, metal isotopic variations in sulphides could be triggered by various factors such as mineral precipitation and fluid mixing. Thus, tracking the metal sources of hydrothermal systems is still a big challenge for metal isotopes. In this study, we investigated the Cd isotopic systematics of sphalerite from the Nayongzhi Zn–Pb deposit, which is a Mississippi Valley‐type (MVT) deposit in the Sichuan–Yunnan–Guizhou mineralization province (SYGMP). We reinterpreted the published S isotope data for the SYGMP and found that the large S isotopic variations were controlled by Rayleigh fractionation between sulphide and reduced S. As such, a model that involves mixing of a metal‐rich fluid with a reduced S pool formed by thermochemical sulfate reduction (TSR) can explain the ore formation in the Nayongzhi deposit. Based on this model, no Cd isotopic fractionation was observed due to its low solubility in fluids during mixing, and thus the Cd isotopic variations of sphalerite were inherited from the source rocks. The large range of Zn/Cd ratios and uniform Cd isotopic compositions of the sulphides are similar to those of igneous rocks but different from those of sedimentary rocks, indicating that Zn and Cd were derived mainly from basement rocks (e.g., migmatite, gneiss, and granulite). Our results reaffirm that metal stable isotopes, particularly Cd isotope compositions of sphalerite, are powerful geochemical tracers for investigating the formation mechanisms of ore deposits.

Sedimentation tempo in an Early Jurassic erg system: Refined chronostratigraphy and provenance of the Clarens Formation of southern Africa

AbstractThe Clarens Formation is a widespread aeolianite deposited over southern Gondwana and represents the final phase of erg evolution in the main Karoo Basin during the Early Jurassic. Previous age assessments of the formation hinge on limited detrital zircon data, supplemented by relative ages from the biostratigraphy and geochronology of the adjacent Karoo units. This study refines the depositional history of the Clarens Formation, including its sediment source dynamics as well as basin‐wide geochronological framework, based on U–Pb dating of detrital zircon grains, together with petrographic and sedimentological characterization. The abundant presence of heavy minerals like zircon, tourmaline and rutile suggests large‐scale detritus recycling, while the uniform sandstone composition on a regional scale is an indication of sediment homogenisation across the basin. Based on the prominent detrital zircon age fractions, the sediments are interpreted as having been reworked from pre‐existing rocks of the Karoo Supergroup (Permian), the Damara and Saldania Orogenic belts (650–490 Ma), whereas minor sources can be assigned to the Namaqua‐Natal Mobile Belt (1.35–1.1 Ga) and the western Sierras Pampeanas (1.30–1.33 Ga). Unstable minerals (hornblende, garnet, titanite, feldspar) provide evidence for a nearby granitic source east and southeast of the basin, related to likely Grenvillian rocks (1.0–1.3 Ga). An Early Jurassic zircon age fraction is linked to volcanic activity in the Chon Aike Magmatic Province that, at the time, was situated south and southwest of the study area. Maximum depositional ages derived from these detrital zircon dates suggest that the sedimentation of the Clarens Formation spanned an interval of ~10 Ma during the Pliensbachian and early Toarcian. More specifically, the lower part of the formation is of early Pliensbachian age or younger (~191–192), while the upper part is of early Toarcian age or younger (~181–183 Ma). These age patterns are particularly prominent in the south of the basin that was situated closer to the volcanic source.

Experimental study on the corrosion of AlN refractories used as crucibles for induction melting of TiNi alloys

Vacuum induction melting has proven to be a cost-efficient way to fabricate TiNi alloys with excellent compositional homogeneity and uniformity. However, the high reactivities of TiNi alloys generate aggressive melt attacks with a particular ceramic crucible. Here, the performance of AlN crucible for melting TiNi alloys was investigated, and the underlying mechanisms for the interfacial interactions were revealed. The results demonstrated the feasibility of using AlN crucibles for induction melting of TiNi alloys. Specifically, melt infiltration was suppressed and thus physical erosion was diminished by reducing the apparent porosity of the crucible. Further investigations combined with a theoretical analysis revealed that the TiN barrier layer distributed on the crucible surface was formed in situ due to crucible/melt interactions, which protected the ceramic matrix from further melt attack and limited the contaminant levels. Our work provides a viable pathway for the preparation of high-quality TiNi alloys via induction melting.

The Epitaxial Growth of Ge and GeSn Semiconductor Thin Films on C-Plane Sapphire

Ge1−xSnx growth on a new sapphire platform has been demonstrated. This involved the growth of GeSn on Ge/GaAs layers using the algorithm developed. The resultant growths of Ge on GaAs/AlAs/sapphire and Ge1−xSnx on Ge/GaAs/AlAs/sapphire were investigated by in situ and ex situ characterization techniques to ascertain the surface morphology, crystal structure, and quality. The growth mode of Ge on GaAs was predominantly two-dimensional (2D), which signifies a layer-by-layer deposition, contributing to enhanced crystal quality in the Ge/GaAs system. The growth of Ge1−xSnx with 10% Sn on a graded profile for 30 min shows uniform composition and a strong peak on the reciprocal space map (RSM). On the other hand, the partially relaxed growth of the alloy on RSM was established.

Enhancing the high-temperature oxidation performance of AlCrTiSiN coating by in-situ generation of multi-layer antioxidant composite structures

A novel AlCrTiSiN high-entropy coating with superior thermal stability and high-temperature oxidation resistance, has been produced. The coating is characterized by unique fcc single-phase solid solution structure with uniform composition, severe lattice distortion and low fcc-AlN solubility, which results in the superior thermal stability. The excellent high-temperature oxidation resistance of coating is attributed to the multi-layer composite structures generated by in-situ reaction of element selective diffusion during the oxidation process. The inner dense SiO2-typed amorphous sub-layer and the intermediate (Al,Cr)2O3-typed sub-layer effectively block the O inward diffusion, and thus enhance the high-temperature oxidation resistance of the coating.

Nundorite: a geological oddity of critical minerals significance from the Mount Arrowsmith Volcanics, northwestern NSW

Nundorite is a unique and enigmatic rock type, known only from its type locality within the Koonenberry Belt of western NSW. The rock is highly anomalous in geochemical composition being peralkaline, with low silica and high alumina, but enriched in rare metals such as Zr, Nb and rare earth elements. This study presents a comprehensive mineralogical and geochemical study of nundorite to resolve its origins and its potential to inform on the geological processes that lead to critical metal concentration in the crust. Nundorite is found only at a single outcrop but shows a progression of alteration and deformation over ∼250 m from the northwest to southeast. The least deformed varieties consist of coarse aegirine grains within a matrix composed predominantly of natrolite and microcline with minor albite, nepheline and schizolite. With increasing deformation, the proportion of albite and aegirine decreases, the primary zeolite changes from natrolite to analcime, and the pyroxene and schizolite shift towards the aegirine and serandite (Mn-rich) endmember compositions, respectively. These transitions can be related to progressive hydration and recrystallisation of the rock in response to hydrothermal alteration associated with deformation. Nundorite also contains a diverse suite of accessory rare metal phases such as zircon, monazite, cerite-group minerals, fergusonite, fersmite, natroniobite, galgenbergite, epidote–allanite and a range of Zr alkali silicate minerals. Samarium–Nd isotopic compositions of nundorite (εNd ∼+5.5 at 585 Ma) are comparable with mafic volcanic rocks of the surrounding Mount Arrowsmith Volcanics and are consistent with derivation from a mantle source. These data, together with the uniform peralkaline composition, depletion in Ti and P, and enrichment in incompatible elements, are consistent with an origin as highly fractionated phonolite. Phonolites of similar composition are rare but have been reported from continental rift and intraplate alkaline provinces worldwide. Nundorite, therefore is not just a geological oddity, but also provides reaffirmation of the continental rift setting for the Mount Arrowsmith Volcanics and highlights the critical mineral resource potential of the region, as extensive crystal fractionation is a key mechanism to produce ore grade levels of rare metals in alkaline magmatic systems.

Epitaxial twin coupled microstructure in GeSn films prepared by remote plasma enhanced chemical vapor deposition

Growth of GeSn films directly on Si substrates is desirable for integrated photonics applications since the absence of an intervening buffer layer simplifies device fabrication. Here, we analyze the microstructure of two GeSn films grown directly on (001) Si by remote plasma-enhanced chemical vapor deposition (RPECVD): a 1000 nm thick film containing 3% Sn and a 600 nm thick, 10% Sn film. Both samples consist of an epitaxial layer with nano twins below a composite layer containing nanocrystalline and amorphous. The epilayer has uniform composition, while the nanocrystalline material has higher levels of Sn than the surrounding amorphous matrix. These two layers are separated by an interface with a distinct, hilly morphology. The transition between the two layers is facilitated by formation of densely populated (111)-coupled nano twins. The 10% Sn sample exhibits a significantly thinner epilayer than the one with 3% Sn. The in-plane lattice mismatch between GeSn and Si induces a quasi-periodic misfit dislocation network along the interface. Film growth initiates at the interface through formation of an atomic-scale interlayer with reduced Sn content, followed by the higher Sn content epitaxial layer. A corrugated surface containing a high density of twins with elevated levels of Sn at the peaks begins forming at a critical thickness. Subsequent epitaxial breakdown at the peaks produces a composite containing high levels of Sn nanocrystalline embedded in lower level of Sn amorphous. The observed microstructure and film evolution provide valuable insight into the growth mechanism that can be used to tune the RPECVD process for improved film quality.