Surface Growth Research Articles

Engineering Crystal Growth and Surface Modification of Na3 V2 (PO4 )2 F3 Cathode for High-Energy-Density Sodium-Ion Batteries.

Na3 V2 (PO4 )2 F3 (NVPF) is a suitable cathode for sodium-ion batteries owing to its stable structure. However, the large radius of Na+ restricts diffusion kinetics during charging and discharging. Thus, in this study, a phosphomolybdic acid (PMA)-assisted hydrothermal method is proposed. In the hydrothermal process, the NVPF morphologies vary from bulk to cuboid with varying PMA contents. The optimal channel for accelerated Na+ transmission is obtained by cuboid NVPF. With nitrogen-doping of carbon, the conductivity of NVPF is further enhanced. Combined with crystal growth engineering and surface modification, the optimal nitrogen-doped carbon-covered NVPF cuboid (c-NVPF@NC) exhibits a high initial discharge capacity of 121mAhg-1 at 0.2C. Coupled with a commercial hard carbon(CHC) anode, the c-NVPF@NC||CHC full battery delivers 118mAhg-1 at 0.2C, thereby achieving a high energy density of 450Whkg-1 . Therefore, this work provides a novel strategy for boosting electrochemical performance by crystal growth engineering and surface modification.

Growth modification via indium surfactant for InGaN/GaN green LED

In this work, indium (In) was introduced as a surfactant during growth of high temperature GaN quantum barriers (QBs) and GaN interlayer of InGaN/GaN green LEDs. A reference LED grown without In-surfactant was also included for comparison. Results suggested that the LED growth was improved by introducing the In-surfactant, especially during the growth of the GaN interlayer. The In-surfactant improved the morphology of the interlayer, hence allowed it to serve as a good surface growth for the LED. Moreover, the LED showed the lowest full width at half maximum of each x-ray diffraction satellite peak when the In-surfactant was introduced in the GaN interlayer, suggesting an effective way to improve the multi-quantum wells. The introduction of the In-surfactant in the GaN interlayer and GaN QBs growths shifted the emission wavelength of the corresponding LEDs towards red (λ emission = 534 nm) with respect to the reference LED where λ emission = 526 nm. Furthermore, the In-surfactant introduction reduced the forward voltage, V f of the corresponding LEDs down to 4.56 V, compared to the reference LED with V f of 5.33 V. It also allowed the LEDs to show faster carrier decay lifetime, and hence higher radiative recombination, particularly when it was introduced in the GaN interlayer growth.

From Antibacterial to Antibiofilm Targeting: An Emerging Paradigm Shift in the Development of Quaternary Ammonium Compounds (QACs).

In a previous development stage, mostly individual antibacterial activity was a target in the optimization of biologically active compounds and antiseptic agents. Although this targeting is still valuable, a new trend has appeared since the discovery of superhigh resistance of bacterial cells upon their aggregation into groups. Indeed, it is now well established that the great majority of pathogenic germs are found in the environment as surface-associated microbial communities called biofilms. The protective properties of biofilms and microbial resistance, even to high concentrations of biocides, cause many chronic infections in medical settings and lead to serious economic losses in various areas. A paradigm shift from individual bacterial targeting to also affecting more complex cellular frameworks is taking place and involves multiple strategies for combating biofilms with compounds that are effective at different stages of microbiome formation. Quaternary ammonium compounds (QACs) play a key role in many of these treatments and prophylactic techniques on the basis of both the use of individual antibacterial agents and combination technologies. In this review, we summarize the literature data on the effectiveness of using commercially available and newly synthesized QACs, as well as synergistic treatment techniques based on them. As an important focus, techniques for developing and applying antimicrobial coatings that prevent the formation of biofilms on various surfaces over time are discussed. The information analyzed in this review will be useful to researchers and engineers working in many fields, including the development of a new generation of applied materials; understanding biofilm surface growth; and conducting research in medical, pharmaceutical, and materials sciences. Although regular studies of antibacterial activity are still widely conducted, a promising new trend is also to evaluate antibiofilm activity in a comprehensive study in order to meet the current requirements for the development of highly needed practical applications.

Varying growth behavior of redox-sensitive nanoparticles on 1:1 and 2:1 clay surfaces: Mechanistic insights on preferential toxic ions removal in mono, co, and multi-metal contaminated waters

In the current study, contrasting growth behaviour of redox sensitive Fe0 nanoparticles (nZVI) was observed on different clay surfaces i.e., 1:1 non-swelling kaolinite (K-nZVI) and 2:1 swelling bentonite (B-nZVI). Osmotic swelling of bentonite led to Fe0 nucleation and growth of 5–7 nm size particles in the broadened interlayer spaces. B-nZVI had negative zeta potential due to the domination of the surface charge of bentonite clay. In contrast, kaolinite has shown dominant surface growth of nZVI particles (>24.8 ± 7.4 nm) and positive zeta potential, suggesting domination of Fe0 nanoparticles (nZVI) characteristics. This surface-dependent variation led to higher and faster removal of oxy-anions with K-nZVI, i.e., chromium and arsenic (87.5 and 157.35 mg/g) than B-nZVI (18.4 and 86.9 mg/g). In comparison, B-nZVI has shown higher sorption of cations i.e., nickel and cadmium (36 mg/g and 46 mg/g) than K-nZVI (25 and 27 mg/g). XPS and pXRD analysis of reaction precipitates confirmed reductive sorption of chromium, co-precipitation/ complexation of arsenic, electrostatic attraction and complexation of nickel and cadmium as major removal mechanisms. Drastically higher total contaminant sorption capacities of B-nZVI (327 mg/g) and K-nZVI (372 mg/g) in multi-contaminant (Cr + As + Ni + Cd) solutions than individual capacities in mono-ionic solutions was due to co-operative effects and newer sites induced via sorption and redox-transformation of other ionic species. K-nZVI removed chromium and arsenic to below drinking water permissible limits whereas B-nZVI succeeded in separating nickel and cadmium to drinkable levels in groundwater, freshwater, river water, and wastewater samples, emphasizing their applicability in high cationic—low anionic and low cationic-higher anionic species contaminated waters, respectively.

Formation and Thermal Stability of Ordered Self-Assembled Monolayers by the Adsorption of Amide-Containing Alkanethiols on Au(111).

We examined the surface structure, binding conditions, electrochemical behavior, and thermal stability of self-assembled monolayers (SAMs) on Au(111) formed by N-(2-mercaptoethyl)heptanamide (MEHA) containing an amide group in an inner alkyl chain using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) to understand the effects of an internal amide group as a function of deposition time. The STM study clearly showed that the structural transitions of MEHA SAMs on Au(111) occurred from the liquid phase to the formation of a closely packed and well-ordered β-phase via a loosely packed α-phase as an intermediate phase, depending on the deposition time. XPS measurements showed that the relative peak intensities of chemisorbed sulfur against Au 4f for MEHA SAMs formed after deposition for 1 min, 10 min, and 1 h were calculated to be 0.0022, 0.0068, and 0.0070, respectively. Based on the STM and XPS results, it is expected that the formation of a well-ordered β-phase is due to an increased adsorption of chemisorbed sulfur and the structural rearrangement of molecular backbones to maximize lateral interactions resulting from a longer deposition period of 1 h. CV measurements showed a significant difference in the electrochemical behavior of MEHA and decanethiol (DT) SAMs as a result of the presence of an internal amide group in the MEHA SAMs. Herein, we report the first high-resolution STM image of well-ordered MEHA SAMs on Au(111) with a (3 × 2√3) superlattice (β-phase). We also found that amide-containing MEHA SAMs were thermally much more stable than DT SAMs due to the formation of internal hydrogen networks in MEHA SAMs. Our molecular-scale STM results provide new insight into the growth process, surface structure, and thermal stability of amide-containing alkanethiols on Au(111).

Substrate-dependent fractal growth and wettability of N+ ion implanted V2O5 thin films

Wettability of active material surface affects the electrolyte and electrode-material interaction in electrochemical applications. An increase in the V2O5 electrode's wetting behaviour allows for better contact with the electrolyte. The surface properties of the V2O5 sample were examined in order to evaluate its wettability. In this work, the surface growth of V2O5 thin films on three different substrates (glass, silicon, and sapphire) after 16 keV N+ ion implantation is presented as a function of ion dose. Thin films of 500 nm V2O5 deposited on different substrates show the formation of the nanocrystalline structure over the surface after thermal annealing. Silicon substrate shows the formation of V2O5 nanorods over the surface. Surface morphology shows the growth dynamics of the surface in terms of roughness (α) and growth (β) exponents. Lateral growth of surface features has been quantified in terms of co-relation length (ξ) and fractal dimensions (Df). The scaling laws studies of the surfaces in terms of exponents and co-relation length shows the role of N+ implantation in structural modifications. Furthermore, wetting dynamics have been co-related with fractal growth of the films under ion implantation. The contact angle of V2O5 thin films is found to be higher for V2O5 nanorods on silicon substrate as compared to crystallite grains on sapphire. The present study showed that the surface morphology and wettability of V2O5 are mainly substrate-dependent and can be controlled by surface fractal parameters.

Transformation of amorphous calcium carbonate in the presence of magnesium, phosphate, and mineral surfaces

Amorphous calcium carbonate (ACC) is known as a precursor to crystalline calcium carbonate polymorphs (CaCO3) in various natural and synthetic systems. While ACC has been shown to form by heterogeneous nucleation in biological systems, it is less obvious whether it plays any role in inorganic settings where carbonate minerals grow on pre-existing surfaces. Tight assemblies of calcium carbonate (CaCO3) phases and clay minerals occur in rock-forming quantities in marlstones, are abundant in Earth’s critical zone, in the sediments of aqueous environments, and in the atmosphere as aerosol particles. Previous studies suggested that the co-occurrence of clay and carbonate minerals (especially smectite and calcite) results from the heterogeneous nucleation of CaCO3 on the surface of smectite. In order to understand the role of ACC in the heterogeneous nucleation of carbonate minerals and the effects of common silicate mineral surfaces on the stability of ACC, we synthesized ACC both in the presence and absence of smectite, kaolinite, and quartz, monitored the pH of the solution during the experiments, and studied the precipitated phases with various transmission electron microscopy techniques. Since Mg2+ and (PO43−) ions are known to prolong the lifetime of ACC and are important components in natural aqueous environments, we tested their effects on ACC transformation in both homogeneous and heterogeneous systems.In all studied systems ACC was the first condensed carbonate phase. The presence of smectite in the solution reduced the lifetime of ACC and led to the rapid formation of calcite. We suggest that the main factor driving the transition was the enhanced growth of ACC particles on the surfaces of smectite flakes. On the other hand, the presence of kaolinite and quartz slightly increased ACC stability; ACC typically rimmed the silicate particles and transformed slower than separated, individual ACC particles. When Mg2+ was present in the solution, ACC stability significantly increased and led to the formation of aragonite instead of calcite in both homogeneous and heterogeneous systems. The presence of (PO4)3− ions caused only a minor delay in ACC transformation and the crystalline product was calcite, irrespective of the presence of silicate minerals. These observations suggest that smectite minerals play important roles in the formation of carbonate minerals by providing a suitable surface for the rapid growth and coalescence of ACC particles, leading to larger particle sizes which, in turn, result in the conversion of ACC into calcite.

Effects of Al doping on dislocation inclinations and strain of GaN films on Si substrates

We present how the interaction between Al dopants and threading dislocations affects dislocation inclinations and then plays an important role in controlling residual strain in GaN-on-Si epitaxial films. When the Al concentration in the GaN epitaxial film is increased to 0.85%, the dislocations extend almost in the growth direction, contributing to a strain-free epitaxial film. We suggest that the Al atoms could substitute for Ga vacancies at the dislocation cores on the growth surface and then inhibit the dislocation inclinations. The suppressed dislocation inclinations lead to a reduced relaxation of compressive strain. The results pave a new way to control dislocation movements and strain in GaN epitaxial films on Si substrates.

Effect of H2 addition on growth rate and surface morphology of GaN(0001) grown by halide-vapor-phase epitaxy using GaCl3

We investigated the effect of H2 addition in halide-vapor-phase epitaxy of GaN on Ga-polar GaN(0001) using an external GaCl3 supply method. To overcome the problem of the very low growth rate on GaN(0001) using GaCl3, we intentionally added H2 to convert GaCl3 to GaCl in the reactor. Using this approach, we successfully increased the growth rate, and also improved the surface morphology of the grown layer.

Microstructure and Fatigue Performance of Ti6Al4V Produced by Laser Powder Bed Fusion after Post-Heat Treatment

With the development of additive manufacturing (AM), the Ti-6Al-4V alloy manufactured by laser powder bed fusion (LPBF) is becoming more widely studied. Fatigue fracture is the main failure mode of such components. During LPBF processing, porosity defects are unavoidable, which hinders the exploration of the relationship between fatigue performance and microstructure. In this study, a laser remelting method was used to reduce porosity defects inside the Ti-6Al-4V alloy. Three annealing treatments (AT) and three solution-aging treatments (SAT) were used to study the effect of the two-phase zone (α + β) microstructure on fatigue life and fatigue crack growth behavior. Fatigue life and crack growth rate (CGR) curves were obtained, and fatigue fracture surface and crack growth fracture surface were analyzed. The results show that microstructure influences fatigue life but has little effect on CGR. Compared with the as-built specimen, the fatigue life of the AT and SAT specimens increased significantly at 850℃ by 101 and 63.7 times, respectively. The thickness of the α lath and the location of crack nucleation together affect the fatigue life. In the stable growth stage, the layered microstructure of α colonies is the most resistant to crack growth.

Development of a practical soot model for diesel surrogate fuels and oxygenated fuels with specific soot precursor tracking and uniform model structure

Soot formation and oxidation involve several complex processes, which are driven by gas-phase chemistry and soot particle dynamics. An effective soot model for diesel surrogate and practical oxygenated fuels is necessary for predicting the soot emissions to meet the emission regulations in engines. To develop a practical and universal soot model for various fuels without tuning any model parameters under wide operating conditions, it is important to reproduce the soot behaviors for different fuels with distinct molecular structures. In this work, a practical soot model was developed to describe the soot behaviors for diesel surrogate fuels comprising large n-alkane, isoalkane, cycloparaffin, and aromatic hydrocarbon, as well as oxygenated fuels including alcohol and ether. The influence of the fuel molecular structures on the soot behaviors was emphasized by utilizing the specific reaction pathways of polycyclic aromatic hydrocarbon (PAH) production and the specific reaction channels of the soot formation including soot nucleation and PAH condensation for different fuels. An efficient method named the moment projection method (MPM) was employed to describe the soot particle dynamics by directly solving the moment transport equations and track the number of soot particles. By coupling a reduced chemical reaction model for describing the fuel oxidation chemistry and PAH formation, it is found that the soot volume fraction and number density are well predicted for iso-octane, n-heptane, toluene, methanol, n-butanol, dimethyl ether, their mixtures, and diesel surrogate in shock tubes and laminar premixed flames without tuning any model parameters. The effects of equivalence ratio, temperature, and fuel type on soot production are analyzed through the rates of soot nucleation, surface growth, PAH condensation, and oxidation. The computational results indicate that the present model can satisfactorily reproduce the soot characteristics of different fuels with distinct soot formation and oxidation processes.

Combining a population balance approach with detailed chemistry to model the condensation of oxide smoke during aluminum combustion in spatially homogeneous reactors

At high temperatures, aluminum particles can be burned exothermally in oxidizing atmospheres in a similar way to carbon-based particulate fuels. The main reaction product, aluminum oxide (Al2O3, alumina), is solid under ambient conditions and may form through two distinct chemical pathways. On the one hand, vapourized aluminum burns in the gas phase, leading to the condensation of aluminum oxide into very fine smoke droplets that are thought to be nano-sized. On the other hand, heterogeneous reactions at the particle surface cause a direct conversion of aluminum into aluminum oxide and result in the transformation into a bi-phasic aluminum/alumina particle. As aluminum powder is being investigated as a potential carbon-free, recyclable energy carrier, we face unanswered questions about the droplet sizes within the oxide smoke and the techniques required for extraction from flue gases. This article constitutes a first step towards a detailed modelling framework for predicting alumina smoke size distributions.Physically, the oxide droplet size distribution is influenced by the ambient gas phase composition and shaped by the mutual competition of nucleation, condensational surface growth, evaporation, dissociation and coagulation. The heat release and dispersion temperature, on the other hand, are affected by chemical reactions, the gas-to-liquid phase change and radiation. In this article, we present a complete set of droplet formation and interaction kinetics for alumina droplets and analyze the interaction, competition and mutual reinforcement of the relevant physical processes in a perfectly stirred reactor and a partially stirred reactor. These simplified model formulations are representative of the dynamics that characterize the changes in gas phase composition and droplet size distribution in a single grid cell during the reaction and droplet formation fractional steps of a spatially inhomogeneous laminar reactive flow solver or a one-point, one-time probability density function (PDF) description. The partially stirred reactor model is extended to account for the presence of a reactive surface with small-scale variability in terms of surface composition. Detailed chemical and heterogeneous surface kinetics, also including NOx formation, are taken into account. Finally, we point out open challenges and incomplete kinetic or constitutive information.

Clumped isotope analysis of zoned calcite cement, Carboniferous, Isle of Man

AbstractSequential analyses of δ13C, δ18O and Δ47 values of calcite and dolomite deposited in millimetre‐sized cavities are reported from the Ronaldsway Member packstones, Isle of Man. The Ronaldsway brachiopods have δ13C values of ca +2.3‰ and δ18O values of ca −7.2‰; carbon is like predicted Carboniferous values, while oxygen values are more negative. The brachiopods show preserved microstructure but have marginal alteration and a streaky cathodoluminescence pattern. Crinoid ossicles have δ13C values of ca +2.3‰ and one with a δ18O value of ca −3.1‰, compatible with Carboniferous marine precipitates; three samples have δ18O values of ca −6.5‰ and are 18O‐depleted. Calcite stages 1 and 2 have δ13C values ca +3.2‰ and δ18O values ca −2.5‰, compatible with Carboniferous sea water. Stage 1 and 2 have non‐luminescent to orange CL zones. Stage 1 and early stage 2 contain red luminescent dolomite micro crystals generated during Mg calcite stabilisation. The Δ47 values for stage 1 and 2 cements indicate temperatures of 86 and 105°C that occurred after the stabilisation of Mg calcite. Stage 3–8 zoned cements preserve their original growth surfaces and their δ13C and δ18O values suggest precipitation during burial and exhumation. The Δ47 values of the brachiopods and crinoids indicate temperatures between 85 and 140°C indicating they were either recrystallised at high temperatures or affected by solid state reordering. To evaluate these alternatives two quantitative models, water–rock reaction and reordering models are performed. The allochems and cements are progressively altered by porewater towards the fluid‐buffered behaviour. The quantitative evaluation of calcite and dolomite solid‐state reordering suggests the elevated clumped isotopic temperatures are produced by interaction with hydrothermal fluids. This study improves understanding by applying previously untried techniques; further Δ47 data and quantifying elemental variations would help further interpretation but the poorly documented post‐depositional history is a drawback.

Effect of Cu, Zn and Ag Ion Implantation on the Surface Modification of Bacterial Cellulose Films

The paper presents the preliminary results of cellulose modification by ion implantation. Three types of ions were implanted, i.e., copper, zinc and silver with fluences of 5 × 1014 and 5 × 1015 cm−2, respectively. The acceleration voltage of the implanted ions was 30 kV. The ion penetration depth profiles showed differences, especially in the Cu and Ag cases, due to the different ion beams of these elements. The implantation of cellulose with ions clearly changed the wettability of the material surface in the direction of hydrophobicity. The impact of implantation on the growth of the cellulose surface by mold fungi was also noticeable. Only the silver ion implantation had a negative effect on the growth of the Trichoderma viride fungus but did not cause a complete inhibition of growth. Cellulose implantation with Cu and Zn ions clearly stimulated the growth of fungi on the surface of the polymer.

Development of In Vitro and Ex Vivo Biofilm Models for the Assessment of Antibacterial Fibrous Electrospun Wound Dressings

Increasing evidence suggests that the chronicity of wounds is associated with the presence of bacterial biofilms. Therefore, novel wound care products are being developed, which can inhibit biofilm formation and/or treat already formed biofilms. A lack of standardized assays for the analysis of such novel antibacterial drug delivery systems enhances the need for appropriate tools and models for their characterization. Herein, we demonstrate that optimized and biorelevant in vitro and ex vivo wound infection and biofilm models offer a convenient approach for the testing of novel antibacterial wound dressings for their antibacterial and antibiofilm properties, allowing one to obtain qualitative and quantitative results. The in vitro model was developed using an electrospun (ES) thermally crosslinked gelatin-glucose (GEL-Glu) matrix and an ex vivo wound infection model using pig ear skin. Wound pathogens were used for colonization and biofilm development on the GEL-Glu matrix or pig skin with superficial burn wounds. The in vitro model allowed us to obtain more reproducible results compared with the ex vivo model, whereas the ex vivo model had the advantage that several pathogens preferred to form a biofilm on pig skin compared with the GEL-Glu matrix. The in vitro model functioned poorly for Staphylococcus epidermidis biofilm formation, but it worked well for Escherichia coli and Staphylococcus aureus, which were able to use the GEL-Glu matrix as a nutrient source and not only as a surface for biofilm growth. On the other hand, all tested pathogens were equally able to produce a biofilm on the surface of pig skin. The developed biofilm models enabled us to compare different ES dressings [pristine and chloramphenicol-loaded polycaprolactone (PCL) and PCL-poly(ethylene oxide) (PEO) (PCL/PEO) dressings] and understand their biofilm inhibition and treatment properties on various pathogens. Furthermore, we show that biofilms were formed on the wound surface as well as on a wound dressing, indicating that the demonstrated methods mimic well the in vivo situation. Colony forming unit (CFU) counting and live biofilm matrix as well as bacterial DNA staining together with microscopic imaging were performed for biofilm quantification and visualization, respectively. The results showed that both wound biofilm models (in vitro and ex vivo) enabled the evaluation of the desired antibiofilm properties, thus facilitating the design and development of more effective wound care products and screening of various formulations and active substances.

HROP68: A rare case of medullary pancreatic cancer-characterization and chemosensitivity of the first patient-derived cell line.

Medullary pancreatic carcinoma (MPC) is a rare subtype of pancreatic ductal adenocarcinoma. MPCs represent less than 1% of all pancreatic cancers, and, with only 26 cases in the literature, knowledge regarding drug response and treatment outcome is very limited. We present the case of a 64-year-old male patient with MPC who was treated by left pancreatic resection and adjuvant chemotherapy. Due to local recurrence, the patient underwent intended curative reoperation. From both surgical specimens, patient-derived xenografts (PDXs) and, from the recurrence, a patient-derived cell line (PDCL) were established. We subsequently performed an in-depth characterization of this cell line including phenotypic characterization, surface protein expression, growth, and migratory performance as well as mutational analysis using whole-exome sequencing (WES). Additionally, in vitro drug sensitivity toward the standard-of-care chemotherapeutic regimen and selected targeted therapies was evaluated. The pathological and molecular properties of this rare MPC case observed in the patient's tumors are preserved in the corresponding PDX and the PDCL of HROP68Tu2. Despite displaying an "immunogenic phenotype" with marked T-cell infiltration and a high-level expression of HLA II and Programmed death-ligand 1 (PD-L1), molecular analysis revealed microsatellite stability but a multitude of mutations affecting KRAS, TP53, KAT6B, FOXG1, RUNX1, and GRIK2 among others. Furthermore, HROP68Tu2 cells were susceptible toward 5-FU, irinotecan, oxaliplatin, gemcitabine, paclitaxel, and erlotinib as single agents, but only a moderate synergistic response was seen to the drugs of the FOLFIRINOX regimen. Even worse, the drugs of the two combinations gemcitabine plus paclitaxel and gemcitabine plus erlotinib showed antagonistic effects. Moreover, lapatinib, PRIMA-Met1, and olaparib selected as targeted therapeutics according to the mutational profiles and protein expression inhibited HROP68Tu2 cells' growth. This study illustrates the establishment of the first preclinical MPC models as well as the first in-depth characterization of an MPC PDCL. Since the scientific and clinical knowledge of this rare pancreatic cancer type is very limited, the presented models contribute to a better understanding of MPC and might be a valuable tool for the development of future treatment options.

Sb-Mediated Tuning of Growth- and Exciton Dynamics in Entirely Catalyst-Free GaAsSb Nanowires.

Vapor-liquid-solid (VLS) growth is the mainstream method in realizing advanced semiconductor nanowires (NWs), as widely applied to many III-V compounds. It is exclusively explored also for antimony (Sb) compounds, such as the relevant GaAsSb-based NW materials, although morphological inhomogeneities, phase segregation, and limitations in the supersaturation due to Sb strongly inhibit their growth dynamics. Fundamental advances are now reported here via entirely catalyst-free GaAsSb NWs, where particularly the Sb-mediated effects on the NW growth dynamics and physical properties are investigated in this novel growth regime. Remarkably, depending on GaAsSb composition and nature of the growth surface, both surfactant and anti-surfactant action is found, as seen by transitions between growth acceleration and deceleration characteristics. For threshold Sb-contents up to 3-4%, adatom diffusion lengths are increased ≈sevenfold compared to Sb-free GaAs NWs, evidencing the significant surfactant effect. Furthermore, microstructural analysis reveals unique Sb-mediated transitions in compositional structure, as well as substantial reduction in twin defect density, ≈tenfold over only small compositional range (1.5-6% Sb), exhibiting much larger dynamics as found in VLS-type GaAsSb NWs. The effect of such extended twin-free domains is corroborated by ≈threefold increases in exciton lifetime (≈4.5ns) due to enlarged electron-hole pair separation in these phase-pure NWs.

Characterizing urban growth and land surface temperature in the western himalayan cities of India using remote sensing and spatial metrics

Urban heat islands (UHI) are developing due to increasing urbanization and loss of vegetation in major cities in India. Increased urbanization modifies the urban microclimate that leads to significant land-use changes resulting in surface conversion and heat release, which poses serious risks to human health, environment and the ecosystem of the Himalayan ecosystem. Hence, mitigating UHI becomes important and requires a better understanding of underlying associated biophysical processes. In the study an attempt has been made to demonstrate the impact of urbanization on land surface temperature (LST) in Shimla and Dehradun, capitals of the Western Himalayan states, India using satellite data and spatial metrics. The process was analyzed using urban coverage patterns obtained from Landsat 5, 7, and 8 and corresponding sensors from TM, ETM+, and OLI. The Built-up and Non-Built-up areas were extracted and the biophysical parameters NDVI, NDBI, NDWI and LST were calculated to capture different features of urban growth. The result indicated, that the built-up area increased from 32.19 km2 (2000) to 68.37 km2 (2016) in Dehradun and from 12.38 km2 (2000) to 29.47 km2 (2016) in Shimla during the study period, resulting in an increase in NDBI and LST and Reduction and NDVI and NDWI. Results showed that temperature hotspots were largest in urban areas, followed by vegetation and water bodies. A significant correlation (p < 0.05) was observed between LST and biophysical parameters -NDVI, NDBI, NDWI. Spatial metrics at the class and landscape levels show that increased urban growth from 2000 to 2016 has made the landscape fragmented and more heterogeneous. The Identified trends and changes in landscape patterns and their impact on heterogeneous urban areas suggest that the study is feasible to estimate LST, NDVI, NDBI and NDWI with reasonable accuracy that will likely have influence on policy interventions.

Effects of surface vacancy-adatom pair formation on PFC tungsten surface morphological response

We report a simulation study of the effect of He-irradiation-induced surface vacancy-adatom pair formation on the surface morphological evolution of plasma-facing component (PFC) tungsten and examine a number of factors that impact such evolution. Our analysis is based on self-consistent dynamical simulations according to an atomistically-informed, continuum-scale surface evolution model that has been developed following a hierarchical multiscale modeling strategy and can access the spatiotemporal scales of relevance to fuzz formation. The model accounts for the flux of surface adatoms generated as a result of the surface vacancy-adatom pair formation effect upon He implantation, which contributes to the anisotropic growth of surface nanostructural features due to the different rates of adatom diffusion along and across step edges of islands on the tungsten surface. We have carried out atomic-scale computations of optimal diffusion pathways along and across island step edges on the W(110) surface and calculated Ehrlich–Schwoebel (ES) barriers in adatom diffusion along and across such step edges. This aspect of surface adatom diffusion contributes to anisotropic surface atomic fluxes, terrace and step diffusive currents, and has been incorporated into our PFC surface evolution model, which predicts the formation of preferentially aligned nanoridge stripe patterns on the PFC surface. We establish that these anisotropic diffusive currents accelerate nanotendril growth on the PFC surface and the onset of surface nanostructure pattern formation. We also explore systematically the dependence of the PFC surface morphological response on the surface temperature and He ion incident flux, characterize in detail the resulting surface topographies and growth kinetics, and compare the predicted surface morphologies with experimental observations. Our simulation predictions for the emerging surface nanostructure patterns under certain plasma exposure conditions are consistent with experimental findings in the literature.

Collective polarization dynamics in bacterial colonies signify the occurrence of distinct subpopulations.

Membrane potential in bacterial systems has been shown to be dynamic and tightly related to survivability at the single-cell level. However, little is known about spatiotemporal patterns of membrane potential in bacterial colonies and biofilms. Here, we discovered a transition from uncorrelated to collective dynamics within colonies formed by the human pathogen Neisseria gonorrhoeae. In freshly assembled colonies, polarization is heterogeneous with instances of transient and uncorrelated hyper- or depolarization of individual cells. As colonies reach a critical size, the polarization behavior transitions to collective dynamics: A hyperpolarized shell forms at the center, travels radially outward, and halts several micrometers from the colony periphery. Once the shell has passed, we detect an influx of potassium correlated with depolarization. Transient hyperpolarization also demarks the transition from volume to surface growth. By combining simulations and the use of an alternative electron acceptor for the respiratory chain, we provide strong evidence that local oxygen gradients shape the collective polarization dynamics. Finally, we show that within the hyperpolarized shell, tolerance against aminoglycoside antibiotics increases. These findings highlight that the polarization pattern can signify the differentiation into distinct subpopulations with different growth rates and antibiotic tolerance.