Hexagonal Domains Research Articles

Toward the reproducible fabrication of conductive ferroelectric domain walls into lithium niobate bulk single crystals

Ferroelectric domain walls (DWs) are promising structures for assembling future nano-electronic circuit elements on a larger scale since reporting domain wall currents of up to 1 mA per single DW. One key requirement hereto is their reproducible manufacturing by gaining preparative control over domain size and domain wall conductivity (DWC). To date, most works on DWC have focused on exploring the fundamental electrical properties of individual DWs within single-shot experiments, with an emphasis on quantifying the origins of DWC. Very few reports exist when it comes to comparing the DWC properties between two separate DWs, and literally nothing exists where issues of reproducibility in DWC devices have been addressed. To fill this gap while facing the challenge of finding guidelines for achieving predictable DWC performance, we report on a procedure that allows us to reproducibly prepare single hexagonal domains of a predefined diameter into uniaxial ferroelectric lithium niobate single crystals of 200 and 300 μm thickness, respectively. We show that the domain diameter can be controlled with an uncertainty of a few percent. As-grown DWs are then subjected to a standard procedure of current-limited high-voltage DWC enhancement, and they repetitively reach a DWC increase of six orders of magnitude. While all resulting DWs show significantly enhanced DWC values, their individual current–voltage (I–V) characteristics exhibit different shapes, which can be explained by variations in their 3D real structure reflecting local heterogeneities by defects, DW pinning, and surface-near DW inclination.

Silver-enriched microdomain patterns as advanced bactericidal coatings for polymer-based medical devices

Today, it would be difficult for us to live a full life without polymers, especially in medicine, where its applicability is constantly expanding, giving satisfactory results without any harm effects on health. This study focused on the formation of hexagonal domains doped with AgNPs using a KrF excimer laser (λ=248 nm) on the polyetheretherketone (PEEK) surface that acts as an unfailing source of the antibacterial agent - silver. The hexagonal structure was formed with a grid placed in front of the incident laser beam. Surfaces with immobilized silver nanoparticles (AgNPs) were observed by AFM and SEM. Changes in surface chemistry were studied by XPS. To determine the concentration of released Ag+ ions, ICP-MS analysis was used. The antibacterial tests proved the antibacterial efficacy of Ag-doped PEEK composites against Escherichia coli and Staphylococcus aureus as the most common pathogens. Because AgNPs are also known for their strong toxicity, we also included cytotoxicity tests in this study. The findings presented here contribute to the advancement of materials design in the biomedical field, offering a novel starting point for combating bacterial infections through the innovative integration of AgNPs into inert synthetic polymers.

Accommodating a hexagonal [formula omitted]- phase Mn2N film on a cubic MgO (001) substrate

The thin films of c-plane dominated hexagonal ζ- phase Mn2N were successfully grown on a cubic MgO (001) substrate directly using plasma-assisted molecular beam epitaxy. The surface was comprehensively studied through experimental and theoretical approaches. Reflection high energy electron diffraction revealed two pseudo-cubic domains along [100]MgO and [110]MgO, and one hexagonal domain, which is 30° apart from the [100]MgO direction. Scanning tunneling microscopy was used to image and resolve the high quality surface, revealing a distorted hexagonal surface structure. Furthermore, atomic resolution of the hexagonal domain with a 2 × 2 reconstructed surface is presented. For the c-plane surface, theoretical investigations were carried out using first-principle studies to determine the surface formation energy for various reconstructed surfaces. The theoretical study shows that the nitrogen terminated 2 × 2 structure with a manganese adatom on the surface is the most stable reconstruction that reproduces the experimental results. A corresponding simulated scanning tunneling microscopy model is also presented, providing strong support for the experimentally observed in-plane lattice structures. The manganese:nitrogen stoichiometry within the bulk and surface is in good agreement with the expected ratio of 2:1.

Theory of Moiré Magnetism in Twisted Bilayer α-RuCl3.

Motivated by the recent developments in moiré superlattices of van der Waals magnets and the desire to control the magnetic interactions of α-RuCl3, here we present a comprehensive theory of the long-range ordered magnetic phases of twisted bilayer α-RuCl3. Using a combination of first-principles calculations and atomistic simulations, we show that the stacking-dependent interlayer exchange gives rise to an array of magnetic phases that can be realized by controlling the twist angle. In particular, we discover a complex hexagonal domain structure in which multiple zigzag orders coexist. This multidomain order minimizes the interlayer energy while enduring the energy cost due to domain wall formation. Further, we show that quantum fluctuations can be enhanced across the phase transitions. Our results indicate that magnetic frustration due to stacking-dependent interlayer exchange in moiré superlattices can be exploited to tune quantum fluctuations and the magnetic ground state of α-RuCl3.

Preparation and characterization of graphene film using biogas derived from oil palm empty fruit bunch (OPEFB) by chemical vapor deposition (CVD) method

This study aims to fabricate graphene films using biogas derived from oil palm empty fruit bunch (OPEFB) as carbon precursors using chemical vapor deposition (CVD) method under various conditions. The fabricated graphene films were deposited on copper substrates at different temperatures and gas compositions. Scanning Electron Microscopy (SEM), Raman Spectroscopy, and the I-V test were used to analyze and characterize the properties of the fabricated film. From the characterization results, SEM images of films grown at 800°C (without additional H2 gas), and 900°C (without additional H2 gas) show a not so well-defined hexagonal domain shape with non-uniform morphology with variations in domain shape and orientation, while Raman spectra show it has only the D band and G band which are attributed to graphene oxide. On the other hand, at 900°C (with additional H2 gas), the SEM image shows more defined hexagonal domain shape and variations in domain shape and orientation, as well as the D, G and 2D band on the Raman spectra, which are like graphene with defects structure. Hence, it is concluded that graphene film was successfully produced at 900°C with additional H2 gas.

Creation of a Periodic Domain Structure in MgOLN by Femtosecond Laser Irradiation

The systematic imaging of the damaged tracks and domain patterns created in the MgOLN plates by one-step fs-laser irradiation at different depths was carried out. It is shown that the domains in the bulk have a spindle-like shape and start to grow in the Z− direction from the track ends. The domain shape changes from a spindle-like one with charged walls to a hexagonal prism with neutral walls after the domain reaches the polar surface. The length of the domains located in the bulk increases linearly with the pulse energy. The hexagonal domain shape at the surface is typical for the crystals of the lithium niobate family. The obtained effects have been considered in terms of the kinetic approach. After irradiation, the domains appear in the vicinity of the track ends with maximum electric field strength and grow under the action of a spatially nonuniform pyroelectric field. The key role of the pyroelectric field is confirmed by the creation of new domains at the surface without correlation with the position of the focusing point located at the vicinity of the surface. The 3D domain pattern was produced, which represented four layers of the regular matrices consisting of elongated domains about 100 μm in length.

Skew Howe duality and limit shapes of Young diagrams

AbstractWe consider the skew Howe duality for the action of certain dual pairs of Lie groups on the exterior algebra as a probability measure on Young diagrams by the decomposition into the sum of irreducible representations. We prove a combinatorial version of this skew Howe duality for the pairs , , , and using crystal bases, which allows us to interpret the skew Howe duality as a natural consequence of lattice paths on lozenge tilings of certain partial hexagonal domains. The ‐representation multiplicity is given as a determinant formula using the Lindström–Gessel–Viennot lemma and as a product formula. These admit natural ‐analogs that we show equals the ‐dimension of a ‐representation (up to an overall factor of ), giving a refined version of the combinatorial skew Howe duality. Using these product formulas (at ), we take the infinite rank limit and prove that the diagrams converge uniformly to the limit shape.

Approximation on hexagonal domains by Taylor-Abel-Poisson means

Approximative properties of the Taylor-Abel-Poisson linear summation method of Fourier series are considered for functions of several variables, periodic with respect to the hexagonal domain, in the integral metric. In particular, direct and inverse theorems are proved in terms of approximations of functions by the Taylor-Abel-Poisson means and K-functionals generated by radial derivatives. Bernstein type inequalities for L1-norm of radial derivatives of arbitrary order of the Poisson kernel are also obtained.

Relationship between graphene nucleation density and epitaxial growth orientation on Cu(111) surfaces

Crystal domain alignment is required to produce large, single-crystal, two-dimensional materials which are synthesized by epitaxial growth, but it has been unclear what is needed to achieve the alignment. It is presumed to be possible when the symmetries of the two-dimensional material and substrate are consistent. However, experiments show that although graphene and the Cu(111) surface have the same symmetry, graphene domains grown on Cu(111) are not always well aligned. We developed a physical model and used first principles calculations to explain these observations. It is found that small hexagonal graphene domains are always misorientated on the Cu(111) substrate because the vertexes of the graphene domains have preferred binding sites. These misorientation angles vary with the domain size, with near-perfect alignment of the domains on the substrate only being achieved when they become hundreds of nanometers in size. Our results indicate that low nucleation density of graphene on Cu(111) surfaces is necessary to achieve epitaxial alignment of graphene domains.

Dynamics of Self-Dual Kagome Metamaterials and the Emergence of Fragile Topology.

Recent years have seen the discovery of systems featuring fragile topological states. These states of matter lack certain protection attributes typically associated with topology and are therefore characterized by weaker signatures that make them elusive to observe. Moreover, they are typically confined to special symmetry classes and, in general, rarely studied in the context of phononic media. In this Letter, we theoretically predict the emergence of fragile topological bands in the spectrum of a twisted kagome elastic lattice with threefold rotational symmetry, in the so-called self-dual configuration. A necessary requirement is that the lattice is a structural metamaterial, in which the role of the hinges is played by elastic finite-thickness ligaments. The interplay between the edge modes appearing in the band gaps bounding the fragile topological states is also responsible for the emergence of corner modes at selected corners of a finite hexagonal domain, which qualifies the lattice as a second-order topological insulator. We demonstrate our findings through a series of experiments via 3D scanning laser doppler vibrometry conducted on a physical prototype. The selected configuration stands out for its remarkable geometric simplicity and ease of physical implementation in the panorama of dynamical systems exhibiting fragile topology.

Soft nanostructures out of star-shaped triazines with flexible amide spacers: liquid crystals with a cubic to columnar transition with memory effect, gels and supramolecular chirality

This work reports the synthesis and characterization of a new family of star-shaped tricarboxamides with C3-symmetry that have flexible amide spacers linking a tris(triazolyl)triazine core with three trialkoxyphenyl groups. The presence of amide groups allows the formation of intermolecular hydrogen bonds that reinforce π-stacking and van der Waals interactions, promoting liquid crystalline behavior, and self-assembly in solvents leading to organogels. As determined by polarized optical microscopy, differential scanning calorimetry and X-ray diffraction on powder samples, all the three reported molecules present a hexagonal columnar (Colh) phase stable at room temperature. Interestingly, they show a transition to a cubic micellar mesophase (BCC) at high temperatures. A mechanism for this transition, which is consistent with the fragmentation of columns to form supramolecular spheres, was elucidated from X-ray studies on aligned samples. Moreover, on cooling from the BCC to the columnar phase a preferential orientation of columns occurs, according to which each cubic domain gives rise to four hexagonal domains. The ability of the synthesized structures to aggregate in solvent media was studied in a variety of organic solvents, and all of them were able to gel 1-octanol at low concentrations. X-ray studies of gels and xerogels were carried out and showed a molecular organization consistent with Colh order. FTIR studies were carried out to analyze the formation of hydrogen bonds and the influence of the length of the flexible spacer in the liquid crystalline state and in the organogels. Furthermore, the presence of a stereogenic center in the flexible amide spacer leads to macroscopic chirality in the liquid crystal state and the organogels in 1-octanol as demonstrated by circular dichroism spectroscopy.

Approximation by matrix means on hexagonal domains in the generalized Hölder metric

In this paper the degree of approximation of the function f, which is periodic with respect to the hexagon lattice by matrix means T(A)n(f) of its hexagonal Fourier series in the generalized H?lder metric, where A is a lower triangular infinite matrix of nonnegative real numbers with nonincreasing row is estimated.

Facial Recognition in Hexagonal Domain—A Frontier Approach

Facial Recognition in Hexagonal Domain—A Frontier Approach

Abnormal Domain Growth during Polarization Reversal in Lithium Niobate Crystal Modified by Proton Exchange

The results of an experimental study of the abnormal domain structure kinetics in lithium niobate single crystals with a surface layer modified by soft proton exchange are presented. Domain switching in a wide field range allowed two qualitatively different types of domain structure evolution to be revealed: (1) the traditional growth of hexagonal domains in fields higher than 21.5 kV/mm and (2) the abnormal growth of stripe domains oriented along the Y crystallographic directions in the field range from 3.8 to 21.5 kV/mm. The stripe domains had a width up to 4 µm and depth up to 30 µm. It was shown that the time dependence of the total length of stripe domains could be analyzed in terms of the modified Kolmogorov–Avrami approach, taking into account the transition from the one-dimensional β-model to the one-dimensional α-model. The possibility of the controllable creation of a quasi-periodic structure of stripe domains with an average period of 5 µm by a two-stage polarization switching process was demonstrated. The formation and growth of stripe domains were considered in terms of the kinetic approach to the evolution of the domain structure as a result of the domain walls’ motion under inefficient screening conditions caused by the presence of a modified surface layer. The abnormally low threshold fields were attributed to a presence of a “built-in” field facilitating switching, created by a composition gradient induced by soft proton exchange.

Unsteady conjugate heat transfer characteristics in hexagonal cavity equipped with a multi-blade dynamic modulator

PurposeThe transient analysis of the thermal response and frictional loss characteristics for flow-modulated conjugate heat transfer phenomena has been investigated in the present study. The flow domain is a partitioned cavity of a hexagonal structure equipped with a multi-blade flow modulator. The clockwise rotating blade is adiabatic and stirrers the internal flow along with the natural convection caused by the bottom heated floor of uniform heat flux. The conjugate behavior is introduced through the solid subdomains consisting of two brick-made partitions and one glass partition of uniform thickness. The material of the partition wall reflects the physical aspects of industrial applications. ApproachThe two-dimensional unsteady continuity, momentum, and energy equations are expressed in a non-dimensional form where the buoyant force is modeled through the Boussinesq approximation. The Arbitrary Lagrangian Euler (ALE) finite element is adopted to solve the moving mesh problem by formulating a free triangular discretization scheme. Parametric computational investigations are carried out for air as the working fluid (Pr = 0.71) and 3 different configurations of the rotating modulator while varying the other parameters, i.e., Reynolds number (Re) and Rayleigh number (Ra) for a fixed Biot number (Bi = 104). This dynamic mesh problem encompasses a wide range of parameters, i.e., (100 ≤Re≤ 103), and (104≤Ra≤ 106) for Bi = 104 to evaluate the thermodynamic response of the present thermo-fluid system. Various thermo-fluid system responses are visualized through the spatially average Nusselt number evaluated on the heated surface, system effectiveness, average thermal storage capacity, and frictional power loss of the flow domain. The thermal response is fragmented into individual responses in terms of component signal frequency by the Fast Fourier Transform (FFT) analysis. FindingsAccording to the current analysis, increasing the number of blades increases the rate of heat transfer by a negligible amount. On the other hand, among three different types of modulators, the three-blade modulator shows the lowest power loss coefficient and the lowest power instability. Thus, a three-blade modulator qualifies as the optimum design to impart external motion to the working fluid to introduce forced convection. LimitationsThis research has some scope for improvement. Future studies can be conducted on the improvement of blade designs, thickness, and size of the blades. Practical ImplicationsThe present study can shed light on the modeling of a better storage system where heat transfer and moisture control are integrated for the proper functioning of the storage, such as food storage, cold storage, garment inventory, etc. OriginalityThis study is original, and no previous research has been conducted considering the hexagonal domain and variation of the number of blades. ConclusionThe present study reveals that a modulator best serves its purpose at low Rayleigh and high Reynolds numbers. Moreover, the three-blade modulator has the lowest power loss coefficient and lowest power instability, making it the most suitable modulator to impart external excitation to the working fluid.

Edge-controlled growth of single-crystal hexagonal boron nitride domains by chemical vapor deposition

Understanding the role of the edge during the growth of hexagonal boron nitride (hBN) by chemical vapor deposition (CVD) is essential for its controllable synthesis and applications. We demonstrated two kinds of hydrogen-induced edge evolution of single-crystal hBN domains over time on liquid Cu via CVD. The morphology and edge evolution of the hBN domains in growth were well explained by the kinetic Wulff construction theory. This work provides a detailed understanding of the role of the edge during the growth progress of hBN, which will be helpful for the production of wafer-scale single-crystalline hBN.

Self-assembly of C60 on a ZnTPP/Fe(001)-p(1 × 1)O substrate: observation of a quasi-freestanding C60 monolayer.

Fullerene (C60) has been deposited in ultrahigh vacuum on top of a zinc tetraphenylporphyrin (ZnTPP) monolayer self-assembled on a Fe(001)–p(1 × 1)O substrate. The nanoscale morphology and the electronic properties of the C60/ZnTPP/Fe(001)–p(1 × 1)O heterostructure have been investigated by scanning tunneling microscopy/spectroscopy and ultraviolet photoemission spectroscopy. C60 nucleates compact and well-ordered hexagonal domains on top of the ZnTPP buffer layer, suggesting a high surface diffusivity of C60 and a weak coupling between the overlayer and the substrate. Accordingly, work function measurements reveal a negligible charge transfer at the C60/ZnTPP interface. Finally, the difference between the energy of the lowest unoccupied molecular orbital (LUMO) and that of the highest occupied molecular orbital (HOMO) measured on C60 is about 3.75 eV, a value remarkably higher than those found in fullerene films stabilized directly on metal surfaces. Our results unveil a model system that could be useful in applications in which a quasi-freestanding monolayer of C60 interfaced with a metallic electrode is required.

Constructing Interfacial Boron‐Nitrogen Moieties in Turbostratic Carbon for Electrochemical Hydrogen Peroxide Production

AbstractThe electrochemical oxygen reduction reaction (ORR) provides a green route for decentralized H2O2 synthesis, where a structure–selectivity relationship is pivotal for the control of a highly selective and active two‐electron pathway. Here, we report the fabrication of a boron and nitrogen co‐doped turbostratic carbon catalyst with tunable B−N−C configurations (CNB‐ZIL) by the assistance of a zwitterionic liquid (ZIL) for electrochemical hydrogen peroxide production. Combined spectroscopic analysis reveals a fine tailored B−N moiety in CNB‐ZIL, where interfacial B−N species in a homogeneous distribution tend to segregate into hexagonal boron nitride domains at higher pyrolysis temperatures. Based on the experimental observations, a correlation between the interfacial B−N moieties and HO2− selectivity is established. The CNB‐ZIL electrocatalysts with optimal interfacial B−N moieties exhibit a high HO2− selectivity with small overpotentials in alkaline media, giving a HO2− yield of ≈1787 mmol gcatalyst−1 h−1 at −1.4 V in a flow‐cell reactor.

Constructing Interfacial Boron-Nitrogen Moieties in Turbostratic Carbon for Electrochemical Hydrogen Peroxide Production.

The electrochemical oxygen reduction reaction (ORR) provides a green route for decentralized H2O2 synthesis, where a structure–selectivity relationship is pivotal for the control of a highly selective and active two‐electron pathway. Here, we report the fabrication of a boron and nitrogen co‐doped turbostratic carbon catalyst with tunable B−N−C configurations (CNB‐ZIL) by the assistance of a zwitterionic liquid (ZIL) for electrochemical hydrogen peroxide production. Combined spectroscopic analysis reveals a fine tailored B−N moiety in CNB‐ZIL, where interfacial B−N species in a homogeneous distribution tend to segregate into hexagonal boron nitride domains at higher pyrolysis temperatures. Based on the experimental observations, a correlation between the interfacial B−N moieties and HO2 − selectivity is established. The CNB‐ZIL electrocatalysts with optimal interfacial B−N moieties exhibit a high HO2 − selectivity with small overpotentials in alkaline media, giving a HO2 − yield of ≈1787 mmol gcatalyst −1 h−1 at −1.4 V in a flow‐cell reactor.

Numerical simulation of thermal flows and entropy generation of magnetized hybrid nanomaterials filled in a hexagonal cavity

The current study addresses the features of entropy generation and thermal flows regarding magnetized hybrid nanofluid in the presence of a cylinder in a closed hexagonal domain. The hexagonal cavity comprises two heated horizontal walls, and two are insulated while the other walls are cold. The whole system has been modeled as coupled non-linear partial differential equations. Also, normalized the governing coupled equation by utilizing a proper pair of variables and are computed with a finite element approach. For the approximation of velocity profiles, a finite element space involving the quadratic polynomial (P2) is selected whereas the pressure and temperature estimation is accomplished through a space of linear polynomial (P1). An analogy is handed with published findings at confining instance. The degree of freedom and grid convergence test is considered for the kinetic energy (KE) and Bejan number (Be). The study reveals a major role in enhancing the heat transfer rate due to hybrid nano-particles. The results show that the increase of magnetic field effect considers the reduction of the heat transfer because the conduction motion occupies the motion of the fluid flow. When the Hartmann number is increased, the magnetic entropy is raised, too. For intensified the Hartmann numbers, the highest ratio of heat transfer occurs for the case of the hybrid nanoparticles, and then MgO-water, followed by the Ag-water. The nature of thermal flow parameters has been scrutinized.