Multistage Growth Research Articles

Quantitative characterization on multistage formation of sedimentary pyrite driven by H2S derived from biogenic process in the northeastern Ordos Basin, China

Negative δ34S values of sedimentary pyrite associated with organic matter are routinely assumed to be the result of biogenic process. However, the distribution and evolution of isotopic values mediated by bacteria across sedimentary strata remains poorly understood. Abundant pyrite-rich nodules (PyRNs) are distributed in the bottom of the sandstone unconformably overlying the coal in middle Jurassic strata in the northeastern Ordos Basin, providing a good opportunity to quantitatively characterize the distribution, morphology and compositions of sulfur isotope and trace element of pyrite in the sandstone influenced by organic matter in the coal. A total of 1007 PyRNs occurs within a range of 4 m from the coal. From bottom to top in the sandstone, the shape of the nodule changes from oval to round on the vertical section, and the length and number gradually decrease at the rate of ~45 mm and ~ 228 for every 1 m increase in distance, respectively. Microscopically, pyrite occurs as euhedral crystals, and trace element mapping reveals multistage growth (up to a dozen times) and a marked compositional zoning with respect to Co, Ni, As, Se and Mo. The positive correlation between Co and Ni, with ratios of Co/Ni ranging from 0.06 to 0.45, indicates that Fe and those trace elements are sourced from diagenetic fluid. The organic sulfur in coal, serving as a sulfur source, is reduced by bacteria to generate H232S at a slow reduction rate. The H232S migrates upwards and reacts with Fe to form pyrite in the sandstone, resulting in extremely low δ34S values (from −53.9 to −43.1 ‰), which gradual decrease both from core to margin in individual grain and at the rate of 2.2 to 8.8 ‰ for every 1 m increase in distance away from the coal. This study highlights the significant variability of mineralogical (e.g., number, size, morphology) and geochemical (trace elements, sulfur isotope) characteristics of sedimentary pyrite. Results allow the relation of multistage growth of pyrite to biogenic fractionation, and provide fresh insights into biogenically derived sulfur from coals to be fixed in sandstones, which can be applied to quantitative characterization of formation processes of sedimentary minerals controlled by organic matter in sedimentary environments worldwide.

Investigating the mechanism of time dependent evolution of vertical graphene nanowalls

This work presents a time dependent multistage growth model for vertical graphene nanowalls (VGN). Factors mediating growth of VGN in both vertical and spatial direction at different stages were discussed. VGN films were deposited on Si (100) substrate using Radio Frequency Plasma-Enhanced Chemical Vapor Deposition technique by increasing the deposition time systematically for 15 min, 30 min, 60 min, 120 min, and 240 min, respectively. Scanning electron microscopy was carried out in both planar and cross section view to confirm the growth of VGN and quantification of its height. Atomic force microscopy was used to characterize the spatial growth of VGN. Raman scattering and in-plane GIXRD measurements were carried out to characterize the microstructure of VGN, which unveils that the strain relaxation and defects annihilation followed by increase in average crystallite size plays crucial role. Eventually, a schematic diagram was presented for time dependent evolution of VGN at different stages.

Evolution of reservoir quality related to clay coating overgrowths in tight sandstone in the fluvial facies of the southeastern Sichuan Basin

As a result of silicate overgrowth, clay coatings influence the evolution of reservoir quality during diagenesis. Most studies indicate coatings can resist compaction and inhibit cementation, thus preserving primary porosity and serving as one of the primary controlling factors for improving reservoir quality. However, some research suggests clay coatings have insufficient hardness to resist compaction and could potentially block pore throats and prevent fluid flow within the sandstone, negatively affects reservoir quality. Therefore, to address whether coatings are positive to reservoir evolution, this study employs polarized light microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and porosity-permeability testing to investigate the characteristics of clay coatings within the fluvial facies sandstone of the Xiashaximiao Formation. The microscopy reveals abundant clay coatings were found, mainly in lithic-arenite with 30%–45% feldspar and rock fragments. The underlying Lianggaoshan Formation locally exhibits interbedded siltstones with volcanic rock fragments, providing material sources for the clay coatings formation. SEM and EDX analyses indicate two predominant forms of clay coatings: single-layer (primarily chlorite) and double-layer (inner smectite/illite, outer ferroan chlorite). Single-layer overgrowths primarily consist of thin layers of chlorite (5–15 μm), whereas double-layer overgrowths consist of a thin inner zone (1–5 μm) covering the grain surface and a thicker outer zone (10–20 μm) covering the inner zone, demonstrating characteristics indicative of multi-stage growth. Porosity-permeability testing results the sandstone samples have <10% porosity, which are typically tight sandstones, but those with clay coatings have higher porosity. Nevertheless, sandstones with double-layer overgrowths exhibit lower permeability relative to those with single-layer overgrowths or without overgrowths. Therefore, based on the integration of morphological and physical properties of silicate overgrowths, it is proposed the efficiency of clay coatings in resisting compaction, inhibiting cementation, and preserving primary porosity increases with the number of growth stages, layers, and thickness, which in turn depends on the abundance of source materials. Single-layer coatings facilitate fluid migration, whereas thicker double-layer overgrowths are prone to occluding narrow pore throats, thereby restricting fluid mobility. Consequently, this study establishes a model for the multi-stage evolution of clay coatings overgrowths, elucidating the varying fluid migration behaviors across different stages and providing a more detailed investigation of the implication of clay coatings on reservoir quality, thus offering new theoretical insights into diagenesis and the evolution of tight sandstone reservoirs.

Multiscale kinetic modeling for biohydrogen production: A study on membrane bioreactors

Hydrogen can be a capable alternative to fossil fuels due to its carbon-free characteristics, in this content, biological hydrogen production is considered a practical approach because technology is green. Due to parameters affecting biohydrogen production, such as operating conditions, it is crucial to predict the process to see the proper yield. There are several conventional and unconventional models used in biohydrogen production prediction. This paper derived a triple first-order prediction model from a previously presented multi-scale kinetic model polynomial built upon the multi-stage growth hypothesis for bio-hydrogen production prediction. The original model was applied to batch and continuous stirred tank reactor studies for their model evaluation, this study evaluated the newly derived model for studies of membrane bioreactors. Due to their increased production yield, membrane bioreactors are an emerging field in biohydrogen production. Although the previous study was mainly applied for batch dark fermentations consisting of various microorganisms, the results presented in this study indicate that it is also applicable for continuous and photo fermentation systems. The original model results reported significant fitness accuracy among different datasheets compared to conventional models like the modified Gompertz model, considering essential factors impacting biohydrogen production suggested in the original model, this paper investigated eleven case studies of dynamic membrane bioreactors with modeling fitness of 99% for most cases. This study reports even higher fitness accuracy compared to the original model, even with different operating conditions.

Polychronous and Multi-stage Growth History of Ladakh Batholith, Trans-Himalaya, through Mafic-Felsic Magma Mixing and Fractionation

Polychronous and Multi-stage Growth History of Ladakh Batholith, Trans-Himalaya, through Mafic-Felsic Magma Mixing and Fractionation

Aqueous growth of titania subnanoparticles: an understanding of the ultrasmall visible-light-absorbing unit of (TiO2)8(H2O)16.

An atomistic understanding of the initial hydrothermal growth of titania remains crucial for the development of nanosized materials, where the presence of water strongly affects the particle growth in comparison to the vapor-phase growth. Herein, we explore the structural evolution of aqueous titania from its salt precursors and determine the nanoparticle configurations in the practical environment by invoking ab initio molecular dynamic simulations and a machine-learning accelerated structural search. Thermodynamically, Ti(OH)4·2H2O serving as the hydrated monomer undergoes planar-to-tubular-to-spherical multistage growth in the Ti(OH)4/H2O hydrothermal system, in which large-sized (TiO2)n(H2O)m particles (n = 1-20) are generated via the olation/oxolation reaction. Importantly, in a mixture of particles of different sizes, we identify that (TiO2)8(H2O)16 is one of the most abundant species in solution with peculiar metastability and exhibits extraordinary visible-light absorption ability, which may be the smallest aqueous titania subnanoparticle in the form of suspension and worth exploring for photocatalytic applications.

Multistage growth of garnet fingerprints the behavior and property of metamorphic fluids in a Paleotethyan oceanic subduction zone

Metamorphic fluids released from the subducting crust are of great importance to understand the recycling of volatile materials at convergent plate margins. Garnet in metamorphic rocks can retain chemical zonation and crystal inclusions produced during crustal subduction, providing the record of geochemical recycling in subduction zones. This paper presents a combined study of mineralogy and geochemistry for metamorphic garnets in oceanic-type eclogite from the Paleotethyan subduction zone in the Hong'an orogen, east-central China. The results show distinct zonation of major and trace elements, crystal inclusions, water contents, and oxygen fugacity in garnet. Five stages of garnet growth were recognized based on the garnet composition and phase equilibrium modelling. Growth of Stage I to IV garnets occurs during prograde metamorphism of the Paleotethyan oceanic crust from blueschist to eclogite facies along low geothermal gradients of 7.8–9.7 °C/km. Stage V garnet was formed through dissolution and reprecipitation during mineral-fluid reaction in the early exhumation stage. Garnet grains exhibit a decrease of water content from core to rim, indicating a gradual decrease of bulk water content in host eclogite during the garnet growth. Combined with the theoretical calculation based on the mineral modes and mineral water contents, it is suggested that the subducting oceanic crust would release reduced amounts of fluids during prograde metamorphism from greenschist to eclogite facies. The different garnet zones have f O 2 values varying from ΔFMQ+1.77 to ΔFMQ+3.26, suggesting that the fluids released from the subducting oceanic crust were oxidizing during subduction to peak eclogite facies and its early exhumation stage. These garnet f O2 values are correlated with the water contents of water-saturated garnet, implying that the water content of metamorphic garnet is a potential means to recover the redox state of its host eclogite. The increase of f O2 values during prograde metamorphism of the eclogite indicates the breakdown of chlorite and possible fluid influx from serpentinite, whereas the significant drop of f O2 values during the early exhumation stage indicates the breakdown of lawsonite to release the oxidized fluid. This study demonstrates that a combined study of water content, major and trace elements, and mineral inclusions in metamorphic garnet can potentially provide a new perspective into the behavior and property of fluids released from the subducting oceanic crust. • Garnet exhibits zoning in inclusions, major-trace elements, water content and oxygen fugacity. • Multiple stages of garnet growth were recognized along the P-T path of Hong'an eclogite. • Garnet water contents reflect decrease of fluid release from subducting oceanic crust. • Garnet water contents are correlated with redox conditions of its host eclogite. • Oxidized fluid is released during the dehydration of the subducting oceanic crust.

Revealing multi-stage growth mechanism of Kirkendall voids at electrode interfaces of Bi2Te3-based thermoelectric devices with in-situ TEM technique

The thermal stability of the electrode interface is always a critical concern in the long-term service of thermoelectric power generators (TEGs). This work has systematically investigated the thermal stability of the interfaces of Ni/Bi2Te2.7Se0.3 and Ni/Bi0.4Sb1.6Te3 of the Bi2Te3-based Thermoelectric generator (TEG) device by using high-resolution transmission electron microscopy (HRTEM) with in-situ heating technique. Kirkendall voids (KVs) were directly observed in the electrode interfaces of both Ni/Bi2Te2.7Se0.3 and Ni/Bi0.4Sb1.6Te3, providing thus the microscopic reason for the naked-eye cracks causing thermal failure. The growth of KVs of the as-investigated interfaces shows multi-stage behavior. This effect is attributed to the superimposition of vacancy coalesce due to the interdiffusion and interface stress mechanisms owing to the plastic difference and volume shrinkage relative to the interface reaction. Among the various interface reactions, the reaction of 3Ni+2Bi2Te3=3NiTe2+4Bi has the largest volume shrinkage, and hence decisively affects the growth of KVs. An outlook relative to the design of the thermal stability is also provided from the point of view of reducing the local stress to suppress the formation of KVs, which is regarded as a valuable guideline for the electrode interface design of TEGs.

Growth Story of One Diamond: A Window to the Lithospheric Mantle

A diamond plate cut out of a transparent, colorless octahedral diamond crystal of gem quality, with a small chromite inclusion in the core, sampled from the XXIII CPSU Congress kimberlite (Yakutia, Mirny kimberlite field, vicinities of Mirny city), has been studied by several combined methods: absorption spectroscopy at different wavelengths (UV-visible, near- and mid-IR); photoluminescence, cathodoluminescence, and Raman spectroscopy (local version) and lattice strain mapping; birefringence in cross-polarized light; and etching. The diamond plate demonstrates a complex growth history consisting of four stages: nucleation and growth to an octahedron → habit change to a cuboid → habit change to octahedron-1 → habit change to octahedron-2. The growth history of the diamond records changes in the crystallization conditions at each stage. The revealed heterogeneity of the crystal structure is associated with the distribution and speciation of nitrogen defects. The results of this study have implications for the information value of different techniques as to the diamond structure defects, as well as for the as yet poorly known evolution of the subcontinental lithospheric mantle in the Siberian craton, recorded in the multistage growth of the diamond crystal. At the time of writing, reconstructing the conditions for each stage is difficult. Meanwhile, finding ways for such reconstruction is indispensable for a better understanding of diamond genesis, and details of the lithosphere history.

A case-driven hypothesis for multi-stage crack growth mechanism in fourth-generation ceramic head fracture

BackgroundCeramic bearings are used in total hip arthroplasty due to their excellent wear behaviour and biocompatibility. The major concern related to their use is material brittleness, which significantly impacts on the risk of fracture of ceramic components. Fracture toughness improvement has contributed to the decrease in fracture rate, at least of the prosthetic head. However, the root cause behind these rare events is not fully understood. This study evaluated head fracture occurrence in a sizeable cohort of patients with fourth-generation ceramic-on-ceramic implants and described the circumstances reported by patients in the rare cases of head fracture.MethodsThe clinical survivorship of 29,495 hip prostheses, with fourth-generation ceramic bearings, was determined using data from a joint replacement registry. The average follow-up period was 5.2 years (range 0.1–15.6). Retrieval analysis was performed in one case for which the ceramic components were available.ResultsClinical outcomes confirmed the extremely low fracture rate of fourth-generation ceramic heads: only two out of 29,495 heads fractured. The two fractures, both involving 36 mm heads, occurred without a concurrent or previous remarkable trauma. Considering the feature of the fractured head, a multi-stage crack growth mechanism has been hypothesized to occur following damage at the head–neck taper interface.ConclusionsSurgeons must continue to pay attention to the assembly of the femoral head: achieving a proper head seating on a clean taper is a prerequisite to decrease the risk of occurrence of any damage process within head–neck junction, which may cause high stress concentration at the contact surface, promoting crack nucleation and propagation even in toughened ceramics.

Modeling of biohydrogen production using generalized multi-scale kinetic model: Impacts of fermentation conditions

This paper presents a new multi-scale kinetic model built upon the multi-stage growth Hypothesis for predicting biohydrogen production. The proposed model represents the significant factors affecting biohydrogen production using a sum of first-order kinetic terms with varying dynamics from slow to fast one. The current work investigates 52 case studies of biohydrogen production that show the double first-order kinetic model provides the best modeling fitness (R2 > 0.99). This result suggests two prevalent pathways or microbial groups with distinct dynamics (i.e., fast and slow modes) in biohydrogen production. An increase in temperature (30 °C–43 °C) or substrate concentration (10 g/L to 40 g/L) and the use of simple substrates or mixed cultures can increase the fast-mode dominance up to 100% contribution. Model analysis suggests that the fast mode corresponds to the butyrate production pathway, the growth-associated hydrogen-producing activity, the easily-biodegradable substrates, or the quick hydrogen-producing groups.

Formation of mixed paragenesis diamonds during multistage growth – Constraints from in situ δ13C–δ15N–[N] analyses of Koidu diamonds

Inclusion-bearing diamonds from the Koidu kimberlite complex, Sierra Leone (West African Craton) were analyzed in situ for carbon and nitrogen isotope compositions, nitrogen concentrations and nitrogen aggregation states. In a suite of 105 diamonds, 78% contain eclogitic mineral inclusions, 17% contain peridotitic mineral inclusions, and 5% − an unusually high proportion − contain co-occurring eclogitic and peridotitic mineral inclusions indicating a mixed paragenesis. Major and trace element compositions of mineral inclusions from two mixed paragenesis diamonds (one with omphacite + Mg-chromite, the other with eclogitic garnet + forsteritic olivine) were determined. The presence of positive Eu anomalies in centrally located omphacite and eclogitic garnet inclusions indicates derivation from subducted protoliths, formed as igneous cumulates in lower oceanic crust. Mg-chromite (Cr# 85.5; Mg# 65.2) and olivine (Mg# 94.5) inclusions, located in outer portions of the mixed paragenesis diamonds, have compositions indicative of derivation from strongly depleted cratonic peridotites. Given that the olivine Mg# of 94.5 is the highest reported to date for the West African Craton, the eclogitic and peridotitic inclusions in these mixed paragenesis diamonds cannot have precipitated during infiltration of peridotitic substrates by eclogite-derived fluids, as the consequent fluid-rock interaction should lead to Mg# lower than that for the original peridotitic diamond substrate. The different origins of eclogitic and peridotitic inclusions could be explained by physical transport of their host diamonds from eclogitic into peridotitic substrates, possibly along high-strain shear zones, before renewed diamond growth.Based on the δ13C–δ15N systematics of the entire inclusion-bearing diamond suite from Koidu, three major compositional clusters are identified. Cluster 1 (eclogitic diamond cores; δ13C = –33.2 to −14.4‰ and δ15N = −5.3 to +10.1‰) bears the isotopic signature of recycled crustal material (± a mantle component). Cluster 2 (peridotitic diamonds and including the core of a diamond containing omphacite + Mg-chromite; δ13C = −6.0 to −1.1‰ and δ15N = −4.2 to +9.7‰) likely involves mixing of carbon and nitrogen from subducted and mantle sources. Cluster 3 (rims of eclogitic diamonds and including the eclogitic garnet + olivine included diamond and the rim of the omphacite + Mg-chromite included diamond; δ13C = −7.8 to −3.6‰ and δ15N = −7.9 to −2.1‰) matches convecting mantle-derived fluids/melts. The distinct isotopic signatures of the three diamond clusters, together with differences in nitrogen aggregation and cathodoluminescence response between diamond cores and rims, suggest episodic diamond growth during multiple fluid/melt pulses.

Desiccation cracking of soil subjected to different environmental relative humidity conditions

Relative humidity (RH) is among key environmental and climatic factors that affect the evolution of soil desiccation cracking. This study aims to investigate how RH variations influence soil desiccation cracking, addressing an overlooked aspect in prior studies. A set of laboratory tests were performed to examine a fat clay undergoing desiccation cracking at various controlled RH levels of 15.0%, 44.0%, 66.0%, 76.0%, 83.5% and 93.7%. During testing, all samples were weighed and photographed simultaneously to monitor evaporation and surface cracking. The evolution of the surface crack network was quantitatively analyzed by an image processing technique. Results highlight the strong dependence of soil desiccation cracking on RH conditions. Increasing RH is found to decrease the overall evaporation rate and increase the water content at which cracking starts. Under high RH levels, the formation of surface cracks exhibits an evident hierarchical process with wide primary cracks developing first followed by fine sub-cracks propagating from the primary ones. Different cracking developing rates between a primary crack and sub-crack give rise to the remarkable multi-stage growth of crack length. Besides, owing to an increase in RH, desiccation cracks at a given water content tend to be wider and the width distribution of the final crack network changes from a unimodal to a bimodal feature. Lowering RH causes a faster cracking rate and makes the hierarchical process invisible, resulting in the formation of a longer total crack length at the end of evaporation. This study is expected to help analyze the underlying formation mechanisms of desiccation cracking-inducing geohazards and assess the long-term performance of earth structures under future climate changes.

Revealing Multi-Stage Growth Mechanism of Kirkendall Voids at Electrode Interfaces of Bi2te3-Based Thermoelectric Devices by Using In-Situ Heating Tem Technique

Revealing Multi-Stage Growth Mechanism of Kirkendall Voids at Electrode Interfaces of Bi2te3-Based Thermoelectric Devices by Using In-Situ Heating Tem Technique

Historical and morphological evidence for multi-stage growth of El Volcancito, Volcán de Colima

We present a multidisciplinary study of an important 1869 eruption of Volcán de Colima, Mexico. This eruption created a parasitic cone, known as El Volcancito, which has traditionally been attributed to a small flank eruption. However, new analysis of historical records suggests that the size, explosivity, and duration of this eruption have been seriously underestimated. While previous reports suggest that activity ceased after ~3 years, our evidence shows that the eruption was highly energetic and constituted multiple eruptive phases over an 8-year period. There was a substantial emission of volcanic material into the atmosphere and the event directly affected communities up to 150 km from the volcano. A new estimate of the volume of material emitted (0.8 km3) is almost four times higher than the previous estimate (0.21 km3), and represents the largest historical andesite lava deposit at Volcán de Colima. At least 10 large explosions with eruptive columns of >6 km occurred. The eruption differed significantly to activity from the central summit cone in terms of eruption dynamics, evolution of activity over time, and petrology; as such, it cannot be explained using the widely accepted eruptive scheme for this volcano. Based on seismic and petrological evidence, we suggest that the highly energetic behavior can be explained by changes in the local stress field following two large regional earthquakes (M > 8.0) and subsequent magma-groundwater interaction. This study challenges the common assumption that most monogenetic cone-building flank eruptions at andesitic volcanoes are low energy compared with edifice-building summit activity, which has important implications for risk analysis at similar volcanoes worldwide.

Constraints on assembly of Tongariro and Ruapehu andesite magmas based on Sr-isotope compositions of plagioclase and groundmass

Sub-crystal scale 87Sr/86Sr analysis of plagioclase phenocrysts and groundmass in andesites reveal cryptic disequilibrium that is not observable in bulk rock-based studies, shedding light on magma assembly. Isotopic, chemical and textural features demonstrate that plagioclase phenocrysts in continental arc andesites from Tongariro and Ruapehu volcanoes are a heterogenous population of various cognate and non-cognate origins. The studied rocks span a wide age range (~270 ka) and have different vent locations but their plagioclase share many characteristics. Most phenocrysts comprise of a relic core surrounded by one or more mantling overgrowths of various textures demonstrating a multi-stage growth during crustal transit. The total compositional range found in a single thin section is wide (~An45–90). Some zoned phenocrysts have a comparable wide range. Inter-crystal 87Sr/86Sr diversity is considerable with differences up to 0.7044–0.7058 within a hand-sized sample. Individual phenocrysts can be isotopically zoned with rim-core differences up to 0.0005, and contrasting isotopic zonation can occur in phenocrysts of the same sample. Overall, more than half the phenocrysts are non-cognate as indicated by their isotopic differences. Phenocrysts with relic calcic (>An85) interiors and low 87Sr/86Sr ratio (<0.7050) are probably antecrysts and xenocrysts from deep mafic cumulates and/or forerunner intrusions. Other phenocrysts have relic sodic interiors (<An55) with high 87Sr/86Sr ratios (~0.7055) compared to the accompanying groundmass, and were probably entrained from country rock and/or differentiated crystal mush in the crust. Phenocrysts most likely cognate because of their concordant composition and isotopic ratio with the groundmass, exhibit oscillatory zoning and lack relic cores, and others display decompression-induced replacement of calcic plagioclase with more sodic compositions. These textures reflect the dynamic processes of magmatic ascent and temporary storage. In some andesites the groundmass (host magma) has a greater mantle-like isotopic affinity than that of the phenocrysts, while in other andesites the reverse is true. This reflects the degree of mingling between the host magma and crustal melts during ascent. The cryptic isotopic disequilibrium revealed highlights the problem of petrogenetic modelling and mineral thermobarometry that assess equilibrium among the phases on elemental abundance. Such concordance could be coincidental rather than co-magmatic.

Violacein-Induced Chaperone System Collapse Underlies Multistage Antiplasmodial Activity.

Antimalarial drugs with novel modes of action and wide therapeutic potential are needed to pave the way for malaria eradication. Violacein is a natural compound known for its biological activity against cancer cells and several pathogens, including the malaria parasite, Plasmodium falciparum (Pf). Herein, using chemical genomic profiling (CGP), we found that violacein affects protein homeostasis. Mechanistically, violacein binds Pf chaperones, PfHsp90 and PfHsp70-1, compromising the latter’s ATPase and chaperone activities. Additionally, violacein-treated parasites exhibited increased protein unfolding and proteasomal degradation. The uncoupling of the parasite stress response reflects the multistage growth inhibitory effect promoted by violacein. Despite evidence of proteotoxic stress, violacein did not inhibit global protein synthesis via UPR activation—a process that is highly dependent on chaperones, in agreement with the notion of a violacein-induced proteostasis collapse. Our data highlight the importance of a functioning chaperone–proteasome system for parasite development and differentiation. Thus, a violacein-like small molecule might provide a good scaffold for development of a novel probe for examining the molecular chaperone network and/or antiplasmodial drug design.

Silicene Growth through Island Migration and Coalescence

Silicene, the Si based counterpart to graphene is predicted to demonstrate similar desirable features to graphene, possessing a Dirac cone in the band-structure and Fermi velocities comparable to graphene. It has also been predicted to demonstrate several exotic properties such as the quantum spin Hall effect, chiral superconductivity and giant magnetoresistance. It has the added benefit of being easy to integrate into current industrial device engineering processes. Silicene monolayers have been grown on Ag (111) and Ir (111) substrates and recently a working field-effect transistor has been demonstrated at room temperature. While it is possible to characterize the final monolayer structure, it is impossible to probe experimentally the evolving atomic structure during growth.We perform massively-parallel molecular dynamics (MD) simulations to study long time monolayer silicene growth on an Ir (111) surface. We observe an intricate multi-stage growth process driven by atomic and cluster migration on the surface. Initial growth involves formation of sub-nanometer clusters via adatom surface diffusion. Subsequently, these clusters rearrange spontaneously with each additional Si atom, forming clusters containing 4–7 member rings. Growth of each cluster through adatom adhesion is accompanied by the formation of larger islands through cluster migration and coalescence. Coalescence of smaller, more mobile islands into larger clusters is aided by the internal rearrangement of rings within each cluster. This flexibility, both of clusters and their constituent atoms, allows the impinging clusters to reorient after first contact and form a more perfect union. We also report on the effect of temperature and flux on the growth process and the final nanostructure. Our study provides atomistic insights into the early stage growth mechanisms of silicene which can be significant for controlled synthesis of its 2D monolayers. Reference: Cherukara, M. J., Narayanan, B., Chan, H., & Sankaranarayanan, S. K. (2017). Silicene growth through island migration and coalescence. Nanoscale, 9(29), 10186-10192. Figure 1

Characterization and Manipulation of Carbon Precursor Species during Plasma Enhanced Chemical Vapor Deposition of Graphene.

To develop a synthesis technique providing enhanced control of graphene film quality and uniformity, a systematic characterization and manipulation of hydrocarbon precursors generated during plasma enhanced chemical vapor deposition of graphene is presented. Remote ionization of acetylene is observed to generate a variety of neutral and ionized hydrocarbon precursors, while in situ manipulation of the size and reactivity of carbon species permitted to interact with the growth catalyst enables control of the resultant graphene morphology. Selective screening of high energy hydrocarbon ions coupled with a multistage bias growth regime results in the production of 90% few-to-monolayer graphene on 50 nm Ni/Cu alloy catalysts at 500 °C. Additionally, synthesis with low power secondary ionization processes is performed and reveals further control during the growth, enabling a 50% reduction in average defect densities throughout the film. Mass spectrometry and UV-Vis spectroscopy monitoring of the reaction environment in conjunction with Raman characterization of the synthesized graphene films facilitates correlation of the carbon species permitted to reach the catalyst surface to the ultimate quality, layer number, and uniformity of the graphene film. These findings reveal a robust technique to control graphene synthesis pathways during plasma enhanced chemical vapor deposition.

Modelling nanocrystal growth via the precipitation method

A mathematical model for the growth of a single nanocrystal is generalised to deal with an arbitrarily large number of crystals. The basic model is a form of Stefan problem, describing diffusion of monomer over a moving domain. Various levels of approximation (an analytical solution, an ordinary differential equation model and an N particle model) are compared and shown to agree well. The N particle model and analytical solution are then shown to have excellent agreement with experimental data for the growth of CdSe nanocrystals. The theoretical solution clearly shows the effect of problem parameters on the growth process and, significantly, that there is a single controlling group. By increasing the value of N it is shown that in the absence of Ostwald ripening the single particle model may be considered as representing the average radius of a system with a large number of particles. Consequently a system with N=2 may represent either a two particle system or a bimodel initial distribution. The solution of the N=2 model provides an understanding of Ostwald ripening. In general if Ostwald ripening is expected some form of the N particle model should be employed. Finally it is shown how the analytical solution may be employed to represent a multi-stage growth process which can then guide and optimise crystal growth.