Spiral Growth Research Articles

Spiral Growth of Adlayer Graphene.

The morphology of as-grown graphene in chemical vapor deposition (CVD) experiments is sensitive to the reaction environment. Understanding the mechanism of formation of different graphene morphologies is essential to achieve controlled graphene CVD growth. Here the growth and formation mechanism of adlayer graphene spirals are reported. An adlayer graphene spiral is formed by fast propagation of the tips of spiral arms along the edge of the first graphene layer. The driving force to form spirals is the limited availability of carbon diffusing from the Cu surface through the edge of the first graphene layer. In addition, it is found that graphene onions are formed by overlapping graphene spirals with clockwise and anticlockwise arms. Based on these features, a kinetic Monte Carlo (kMC) method is demonstrated using which all the observed graphene spiral structures are successfully reproduced at the atomic level. This study thus unravels the hither-to unresolved mechanism of graphene onion growth and paves the way to the controllable growth of few-layer graphene by increasing the carbon supply at the edge of the first layer graphene.

The Composition and Growth Mechanism of Coexisting 4M2 and 4A8 Biotite Polytypes from Rhyolite of Long Valley Caldera, California

AbstractPolytypism is common in micas, and the frequency of polytype occurrence is believed to be related closely to the crystallization conditions and chemical compositions of the corresponding fluids and melts. Coexisting multiple standard and complex/disordered polytypes in igneous rocks generally reflect a complicated magma evolution history. The purpose of the current study was to clarify the origin of coexisting biotite polytypes and their growth mechanism. Micro-X-ray diffraction (μXRD) and transmission electron microscopy (TEM) were used to investigate Fe-rich biotite phenocrysts in rhyolite from the Long Valley Caldera, California, USA. The μXRD analyses characterized various polytypes, and TEM observations revealed that common polytypes (e.g. 1M, 2M1, and 3T) and rare polytypes (e.g. 4M2 and 4A8) coexist within biotite monocrystals. The two 4-layer polytypes of Fe-rich biotite, 4M2 and 4A8, were identified via selected-area electron diffraction (SAED) and high-resolution scanning transmission electron microscopy (HRSTEM) at the atomic resolution, with unique stacking sequences ([0222] for 4M2 and [0022¯] for 4A8). Energy-dispersive X-ray spectroscopy (EDS) results showed differences in their chemical compositions, especially Fe and K. The 4A8 polytype is reported for the first time. The present study suggested that environmental changes, such as rapid cooling and inhomogeneous compositional distribution, led to chemical and structural oscillations and complex nucleation of the two 4-layer polytypes. Screw dislocations producing spiral growth enhance polytype stability and form ordered long-period/complex polytypes. These results are useful to understand the origin of long-period/complex polytypes and the intergrowths of diverse polytypes formed in non-equilibrium crystallization environments.

Growth Behaviors of GaN on Stripes of Patterned c-Plane GaN Substrate

Growth behaviors of GaN on patterned GaN substrate were studied herein. Spiral and nucleation growth were observed after miscut-induced atomic steps disappeared. The morphology of nucleation growth at different temperature is explained by a multi-nucleation regime introducing critical supersaturation. Simulated results based on a step motion model successfully explain the growth behaviors on stripes. These findings can be applied to control the surface kinetics of devices such as laser diodes grown on patterned substrate.

The Origin and Formation Mechanism of an Inclined Line‐like Defect in 4H‐SiC Epilayers

The origin and the formation mechanism of a surface morphological defect in 4H‐SiC epilayers are reported. The defect appears on the surface of an epilayer as an inclined line‐like feature at an angle of ±80° to the step‐flow direction . The defect is confirmed to originate from a threading screw dislocation intersecting the surface and its orientation is controlled by the sign of the Burgers vector of the dislocation. The defect forms through the interaction of local spiral growth associated with threading screw dislocations and step‐flow growth related to the substrate offcut. The defect mainly appears in the epilayers grown through chloride‐based chemistry, where in situ surface preparation of the substrate is performed in H2 + HCl at a relatively high temperature.

Logarithmic and hyperbolic spirals associated with Schrodinger's equation

We investigate the equationQ″+N−1ζQ′−Q+ia(ζQ)′=0,0<ζ<∞, where N≥2 is spatial dimension, and a>0 is a parameter. This equation plays an important role in analyzing a nonlinear Schrodinger equation self-focusing model. Setting N=3, Q=ρeiθ, we getρ″+2ζρ′=ρ((θ′)2+aζθ′+1),ρθ″+2ζρθ′+2ρ′θ′=−a(ζρ)′ We analyze three diverse solutions of this system. The first two, Q1=ρ1eiθ1 and Q2=ρ2eiθ2 exist ∀ζ>0, and become singular as ζ→0+. They rotate around (0,0) in the (Re(Q),Im(Q)) plane, with θ1′(ζ)<0 and θ2′(ζ)<0∀ζ>0, and form logarithmic and hyperbolic spirals when ζ≫1. The third solution, Q3=ρ3eiθ3 is different. First, 0<limζ→0+⁡ρ3(ζ)<∞. Second, θ3′(ζ) changes sign infinitely often on 0<ζ<∞, causing the formation of “internal oscillations” in the trajectory of the solution.

Використання властивості періодичності для генерування комбінаторних конфігурацій

Introduction. Sign combinatorial spaces that exist in two states: convolute (tranquility) and deployed (dynamics), are considered. Spaces, in particular biological, physical, informational and some others, for which the axioms of sign combinatorial spaces, are valid, have a combinatorial nature. When they are deployed, combinatorial numbers (Fibonacci numbers) are formed, through which logarithmic spirals appear in living nature. These spirals are formed due to the finite sequences that take place during the deployment of the agreed spaces and which are presented geometrically using polar coordinates. Formulation of the problem. The logarithmic spiral is geometrically represented through a “golden rectangle” in which one side is 1,618 times longer (“golden” number or golden section). The presence of the golden ratio in nature is manifested through Fibonacci numbers, which are formed from an arithmetic triangle from elements of finite sequences formed by the deployment of sign combinatorial spaces. But this spiral is transmitted through the “golden rectangle” indirectly. The problem is to trace its formation in nature through constructed sequences, the elements of which are represented by polar coordinates. The approach proposed. Using the finite sequences that are formed during the unfolding of sign combinatorial spaces and the representation of their elements in polar coordinates, we can trace the dynamics of the formation of logarithmic spirals in nature. Conclusion. Representation of biological space as a sign combinatorial space can explain various phenomena in nature. When unfolding these spaces from the convolute spaces finite sequences are formed, the sums of the members of which determine the number of combinatorial configurations in a subset of isomorphic combinatorial configurations and form an arithmetic triangle (Pascal’s triangle). Fibonacci numbers and, accordingly, a golden number are formed from an arithmetic triangle. The logarithmic spiral fits into a golden rectangle. The dynamics of the formation of the logarithmic spiral is traced due to the finite sequences formed as a result of the deployment of the sign combinatorial spaces, the elements of which are presented in polar coordinates.

Retracted] Knowledge Graph Analysis of Digital Emergency Management Research Based on CiteSpace Visualisation: Comparative Analysis of WOS and CNKI Databases

Facing the dual background of risk society and the fourth scientific and technological revolution, digital emergency management (DEM) research has attracted wide attention worldwide. Based on the comparative analysis of data from Web of Science (WOS) and China National Knowledge Infrastructure (CNKI) databases, the research draws the knowledge map by CiteSpace, in order to analyse the spatiotemporal distribution, hotspots, and trends of DEM research. The following are the results: (1) DEM research shows a spiral growth, with a significant increase in the number of papers. Existing highly cited references are mainly carried out from the perspective of management or technology. (2) The complex countries’ cooperation network has been formed from the USA, China, and other countries; the complexity of the institutions’ cooperation network must be strengthened, and the density of the authors’ cooperation network is low; DEM research has significant interdisciplinary attributes. (3) The hotspots of DEM research can be divided into three categories: means, processes, and objects, but the research emphases between international and China are different. (4) The evolution of DEM research can be divided into three stages between international and China: embryonic, development, and deepening stages, and research contents in each stage show some differences. (5) The trends of DEM research between international and China are different. The former are information technology, artificial intelligence, and machine learning, whereas the latter are emergency decision making, scenario analysis, and public health.

Homoepitaxial lateral growth of single-crystal diamond with eliminating PCD rim and enlarging surface area

Avoiding the appearance of polycrystalline diamond (PCD) rim during the epitaxial lateral outward growth of single-crystal diamond (SCD) by microwave plasma chemical vapor deposition (MPCVD) is still full of difficulties and challenges. Herein, the enlarged SCD without PCD rim was synthesized via different growth modes. The core strategy is the self-formation of off-angles on (001) crystal face by regulating the radicals distribution and reducing the temperature at the seed edge. Therefore, the appearance of the secondary nucleation at the edge regions can be inhibited. In a dual-substrate reactor, the SCD surface displayed a typical terrace flow growth pattern. The growth steps on the SCD surface are directed from the center to the edge which coincides with the distribution of carbon-related radicals and temperature. In addition, a spiral growth mode appeared in the homoepitaxial growth of SCD by a single-substrate reactor. Under a spiral growth mode, the top surface of SCD in an off-axis direction was contributed to form a smooth interface. The SCD surface increased by 88.15% from 3 × 3 mm2 to 4.11 × 4.12 mm2 after 82 h. And the crystalline quality of the CVD epitaxial layer is higher than that of the type Ib seed.

Strength of Curvilinearly Reinforced Plates in a Polar Coordinate System

А computer simulation of flat structures to create a fiber composite with curved reinforcement along spiral trajectories in the polar coordinate system has been performed. Numerical comparisons of the reachability of limit states for various reinforcement structures by two families of continuous curved fibers have been made. The calculations take into account the influence of a constant temperature field. In this paper, analytical solutions of the reinforcement intensity function of the differential equation of the constancy of the fiber cross sections for the families of logarithmic and algebraic spirals are found. The analysis of the results shows that due to the choice of curved laying of reinforcing fibers, it is possible to obtain a structure with predetermined properties

SELF-SIMILARITY TECHNIQUES FOR CHAOTIC ATTRACTORS WITH MANY SCROLLS USING STEP SERIES SWITCHING

Highly applied in machining, image compressing, network traffic prediction, biological dynamics, nerve dendrite pattern and so on, self-similarity dynamic represents a part of fractal processes where an object is reproduced exactly or approximately exact to a part of itself. These reproduction processes are also very important and captivating in chaos theory. They occur naturally in our environment in the form of growth spirals, romanesco broccoli, trees and so on. Seeking alternative ways to reproduce self-similarity dynamics has called the attention of many authors working in chaos theory since the range of applications is quite wide. In this paper, three combined notions, namely the step series switching process, the Julia’s technique and the fractal-fractional dynamic are used to create various forms of self-similarity dynamics in chaotic systems of attractors, initially with two, five and seven scrolls. In each case, the solvability of the model is addressed via numerical techniques and related graphical simulations are provided. It appears that the initial systems are able to trigger a self-similarity process that generates the exact or approximately exact copy of itself or part of itself. Moreover, the dynamics of the copies are impacted by some model’s parameters involved in the process. Using mathematical concepts to re-create features that usually occur in a natural way proves to be a prowess as related applications are many for engineers.

Simulation of Opening Angle of Archimedes Wind Turbine Design Based on the Fibonacci Series

The configuration of new type of turbine is the Archimedes wind turbine with a spiral structure whose design is inspired by logarithmic spirals. This type of wind turbine uses lift and drag to harness the kinetic energy of the wind. The eccentric design has aerodynamic characteristics that have been the focus of previous research. The design is made from the arrangement of the Fibonacci sequence (1x1, 2x2, 3x3, 5x5, 8x8) or commonly known as the golden ratio. This study aims to analyze the coefficient of lift (CL) and coefficient of drag (CD) with variations opening angle of 35°, 45°, 65°, air fluid, turbulent flow, Re 1200, pressure distribution 1 atm, wind speed 5, 5 and 15 m/s. The results is at wind speed of 5.5 m/s, an angle of 35°, the CL value is 1.07E+02, the CD value is 4.02E+04. At wind speed of 5.5 m/s, an angle of 45°, the CL value is 1.08E+04, the CD value is 1.77E+01. At wind speed of 5.5 m/s, an angle of 65°, the CL value is 1.84E+06, the CD value is 3.68E+04. At wind speed of 15 m/s, an angle of 35°, the CL value is 2.20E+03, the CD value is 9.76E+02. At wind speed of 15 m/s, an angle of 45°, the CL value is 5.51E+04, the CD value is 4.12E+02. At wind speed of 15 m/s, an angle of 65°, the CL value is 5.96E+01, the CD value is 1.33E+03. Based on this, it can be concluded that at wind speed of 5.5 m/s the higher the opening angle, the higher CL produced. At wind speed of 15 m/s the larger the opening angle the CD increases. This is because the higher the angle, the more it receives sweeps or catches the wind. While the unstable value generated in this simulation is generally a weakness in the wind turbine design.

Vortices degradation and periodical variation in spiral micromixers with various spiral structures

With significant centrifugal effects and Dean vortices, the spiral microchannels are being widely used in microfluidic systems, especially for high-efficiency mixing. However, the spirals are with various shapes and their radii continuously vary along the spiral, which causes the flow fields and mixing process complicated. This research focused on the flow behaviors and mixing performance of spiral micromixers with various spiral structures. Five classical spirals of Archimedean, Logarithmic, Hyperbolic, Golden and Fibonacci spirals, and two structures of centrosymmetric spiral structure and single spiral structure were investigated. Numerical simulation and experimental validation were conducted with Re from 0.1 to 100. The results showed that the Archimedean spiral presented the best mixing performance among the five spirals, since its radius of curvature kept a small value in the whole flow path which brought about stronger Dean vortices. Moreover, it was found that Dean vortices was inapplicable to characterize chaotic advection in the centrosymmetric spiral structure due to vortices degradation. Vortices degradation resulted from the counter-rotating Dean vortices, which suppressed the chaotic advection and the mixing process. The results also revealed that vortices varied periodically along the flow path in single spiral structure. Increasing the Reynolds number accelerated the periodical variation of vortices, and therefore mixing developed more rapidly. Moreover, a novel parameter named vortices advection intensity (Vai) was proposed to characterize chaotic advection. The calculated results of Vai agreed well with the results of mixing performance under the condition of chaotic advection dominated mixing. The parameter Vai could reliably characterize chaotic advection.

Review and Recalculation of Growth and Nucleation Kinetics for Calcite, Vaterite and Amorphous Calcium Carbonate

The precipitation of calcium carbonate is well studied in many fields of research and industry. Despite the fact that, or perhaps because of the fact that, it is well studied in many fields, different approaches have been used to describe the kinetics of the precipitation process. The aim of this study was to collect and compare the data available in the literature and find a consistent method to describe the kinetics of growth and nucleation of the various polymorphs of calcium carbonate. Inventory of the available data showed that a significant number of the literature sources were incomplete in providing the required information to recalculate the kinetic constants. Using a unified method, we obtained a unique set of parameters to describe the kinetics for growth for calcite, vaterite and amorphous calcium carbonate (ACC) and nucleation for vaterite and ACC. Recalculation of the kinetic constants demonstrated that calcite confirmed there are two growth mechanisms within one polymorph, namely pure spiral growth and spiral growth mixed with surface nucleation. The spiral growth does not show second-order growth, which is typically attributed to it. Re-evaluation of the available nucleation data confirmed the suggested existence of a second pure ACC polymorph with a solubility product between 10−5.87 and 10−5.51 mol2 kgw−2.

Monolayer-Scale GaN/AlN Multiple Quantum Wells for High Power e-Beam Pumped UV-Emitters in the 240-270 nm Spectral Range.

Monolayer (ML)-scale GaN/AlN multiple quantum well (MQW) structures for electron-beam-pumped ultraviolet (UV) emitters are grown on c-sapphire substrates by using plasma-assisted molecular beam epitaxy under controllable metal-rich conditions, which provides the spiral growth of densely packed atomically smooth hillocks without metal droplets. These structures have ML-stepped terrace-like surface topology in the entire QW thickness range from 0.75–7 ML and absence of stress at the well thickness below 2 ML. Satisfactory quantum confinement and mitigating the quantum-confined Stark effect in the stress-free MQW structures enable one to achieve the relatively bright UV cathodoluminescence with a narrow-line (~15 nm) in the sub-250-nm spectral range. The structures with many QWs (up to 400) exhibit the output optical power of ~1 W at 240 nm, when pumped by a standard thermionic-cathode (LaB6) electron gun at an electron energy of 20 keV and a current of 65 mA. This power is increased up to 11.8 W at an average excitation energy of 5 µJ per pulse, generated by the electron gun with a ferroelectric plasma cathode at an electron-beam energy of 12.5 keV and a current of 450 mA.

Investigation of Phase Transition from Critical Nucleus to Bi2Te3 Nanoplate Based on Screw Dislocation‐Driven Spiral Growth by Solvothermal Synthesis

AbstractTwo‐dimensional bismuth telluride (Bi2Te3) nanoplates have great potential for thermoelectrics and topological insulators. The material performance increases as the nanoplate size decreases. However, the initial stage of the crystal growth of the nanoplates has not been significantly investigated. The Bi2Te3 nanoplates are prepared by solvothermal synthesis and the phase transition based on the screw dislocation‐driven spiral growth of the nanoplates is investigated. The optimal synthesis conditions are first determined by controlling the Te concentration in the precursor solution. The spiral‐grown nanoplates are collected from the synthesized products. The diameter of the critical nucleus is calculated to be in the range of 5.0–7.2 nm from the step width in the spiral. Subsequently, the solvothermal synthesis is implemented by changing the synthesis time from 15 to 1200 min under the optimal conditions of the precursor solution. Crystals are not grown in the solution at 15 min. At 25 min, an intermediate phase of Bi2TeO5 with an approximate grain size of 5.0 nm is formed, which corresponds to the calculated diameter of the critical nucleus. Another intermediate phase of Te is formed, and the Bi2Te3 nanoplates with a lateral size of 300 nm grow slowly at the expense of Bi2TeO5 and Te.

Topographically Conductive Butterfly Wing Substrates for Directed Spiral Ganglion Neuron Growth.

Spiral ganglion neuron (SGN) degeneration can lead to severe hearing loss, and the directional regeneration of SGNs has shown great potential for improving the efficacy of auditory therapy. Here, a novel 3D conductive microstructure with surface topologies is presented by integrating superaligned carbon-nanotube sheets (SA-CNTs) onto Morpho Menelaus butterfly wings for SGN culture. The parallel groove-like topological structures of M. Menelaus wings induce the cultured cells to grow along the direction of its ridges. The excellent conductivity of SA-CNTs significantly improves the efficiency of cellular information conduction. When integrating the SA-CNTs with M. Menelaus wings, the SA-CNTs are aligned in parallel with the M. Menelaus ridges, which further strengthens the consistency of the surface topography in the composite substrate. The SA-CNTs integrated onto butterfly wings provide powerful physical signals and regulate the behavior of SGNs, including cell survival, adhesion, neurite outgrowth, and synapse formation. These features indicate the possibility of directed regeneration after auditory nerve injury.

Preparation and growth mechanism of micro spherical ammonium dinitramide crystal based on ultrasound-assisted solvent-antisolvent method

Micro-sized spherical ammonium dinitramide (ADN) crystals are successfully prepared by a facile ultrasound-assisted solvent-antisolvent recrystallization method without introducing any additives. The influences of the volume ratio of solvent to antisolvent, the antisolvent temperature and the ultrasound power on the micro-morphologies and properties of ADN crystals are studied systematically. The changes of morphology, particle size, crystal structure and melting point of the ADN crystals are characterized through scanning electron microscopy (SEM), laser particle size analyzer (LPSA), X-ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively. The results show that the optimal experimental parameters for the ADN crystal of spherical morphology are as follows: the volume ratio of solvent to antisolvent is 1:50, the antisolvent temperature is 20 ℃, and the ultrasound power is 70 W. The predicted hexagonal-flake and spherical morphologies for the ADN are close to the experimental morphologies. The growth mechanism of the spherical ADN crystal changes with supersaturation of the ADN solution. As the degree of supersaturation increases, the growth models of the spherical ADN change from the spiral growth to the rough growth, and the morphologies of ADN change from the large-sized ADN ball to the small-sized ADN ball.

Large cross-section blast chamber: design and experimental characterization

This study shows the basic design and experimental characterization of the advanced blast chamber at Michigan State University. This facility is a large cross-section explosively-driven blast chamber. The cross-section of the facility is 2.03 m × 2.03 m, and the length of its tunnel is 5.5 m. This relatively short length was made possible by introducing a new driver design shaped like a pair of logarithmic spirals with a coincident focus. The experimental characterization of the facility demonstrates that this driver design produces blast fronts with very low curvature, and overpressure durations as short as ∼1.2 ms. Since this was the initial characterization of the facility, the maximum overpressure considered was ∼144 kPa. This facility was conceived to perform studies of blast-induced traumatic brain injury based on full-size models of the human body or large animal models. Its large cross section ensures that area blockage is within permissible values, and its driver design ensures short overpressure durations typical of battle field blast events.

The domain of unknown function 4005 (DUF4005) in an Arabidopsis IQD protein functions in microtubule binding

The dynamic responses of microtubules (MTs) to internal and external signals are modulated by a plethora of microtubule-associated proteins (MAPs). In higher plants, many plant-specific MAPs have emerged during evolution as advantageous to their sessile lifestyle. Some members of the IQ67 domain (IQD) protein family have been shown to be plant-specific MAPs. However, the mechanisms of interaction between IQD proteins and MTs remain elusive. Here we demonstrate that the domain of unknown function 4005 (DUF4005) of the Arabidopsis IQD family protein ABS6/AtIQD16 is a novel MT-binding domain. Cosedimentation assays showed that the DUF4005 domain binds directly to MTs in vitro. GFP-labeled DUF4005 also decorates all types of MT arrays tested in vivo. Furthermore, we showed that a conserved stretch of 15 amino acid residues within the DUF4005 domain, which shares sequence similarity with the C-terminal MT-binding domain of human MAP Kif18A, is required for the binding to MTs. Transgenic lines overexpressing the DUF4005 domain displayed a spectrum of developmental defects, including spiral growth and stunted growth at the organismal level. At the cellular level, DUF4005 overexpression caused defects in epidermal pavement cell and trichome morphogenesis, as well as abnormal anisotropic cell elongation in the hypocotyls of dark-grown seedlings. These data establish that the DUF4005 domain of ABS6/AtIQD16 is a new MT-binding domain, overexpression of which perturbs MT homeostasis in plants. Our findings provide new insights into the MT-binding mechanisms of plant IQD proteins.

Characterization of morphological defects related to micropipes in 4H-SiC thick homoepitaxial layers

A new type of morphological defects related to substrate micropipe is observed in 4H-SiC thick homoepitaxial layers. The structure and formation mechanism are investigated by optical microscopy, laser microscopy, scanning electron microscopy, micro-Raman spectroscopy, micro-photoluminescence spectroscopy and molten KOH etching. The observed new defect has truncated hexagonal prism morphology with a closed-core hexagonal pit, and it is 4H-SiC without polytype transition. It is found that the micropipe in the substrate can not only extend to the epilayer, but also cause a morphological defect to disturb the step-flow growth on the epilayer surface. A model has been proposed to interpret the formation mechanism of the morphological defect. It show that the morphology of the observed defect is mainly determined by the wider terrace in 4° off-angle substrate, the interaction between step-flow growth and spiral growth, and the thickness of the epilayer.