Twisted Structure Research Articles

Thermal stability of the magnetic moment in amorphous carbon thin film - An experimental and ab-initio study

The effect of vacuum annealing on the microstructure and its consequence on the thermal stability of magnetic moment in amorphous carbon (a-C) thin film is studied. The magnetic a-C thin film of thickness 8 nm is vacuum annealed for 2 h at 523 K and 923 K. Microstructural and chemical characterization using Raman spectroscopy and x-ray photoelectron spectroscopy, respectively, reveals that with increasing annealing temperature, the sp2 fraction in the film increases. The magnetic measurement carried out at room temperature (RT) using SQUID-VSM reveals a weak ferromagnetic signal in the film due to the interaction between the unpaired sp2 sites, which prevails till 923 K. In the as-deposited sample, an isolated sp2 atom surrounded by sp3 atom results in the paramagnetic contribution, and an sp2-sp2 atom with twisted π-orbitals results in weak ferromagnetic coupling. Compared with the as-deposited case, initially, the saturation magnetization increases when the sample is annealed at 523 K and later decreases when annealed at 923 K. Subsequently, the ab-initio molecular dynamics calculation predicts that due to the increase in sp2 fraction, the net magnetization of the system increases from 300 K to 523 K. π-Orbital Axis Vector (POAV) analysis shows that further annealing to 923 K enhances π-orbital overlapping, which leads to the annihilation of moments sites. The present study differentiates between the two structures that contribute to the magnetism in a-C in terms of their thermal stability. Our simulation indicates that the twisted π-orbitals structure is thermodynamically more stable than the structure where sp3 surrounds sp2 hybridized atom.

Templated Twist Structure Liquid Crystals and Photonic Applications.

Twist structure liquid crystals (TSLCs) have attracted increasing attention in photonic applications due to their distinct properties: Bragg reflection, scattering, and optical rotation. However, there exist some issues due to the defects of TSLCs: weak thermal stability, narrow bandwidth, and complicated fabrication. In this review, we introduce the templating technique which includes device structure, templating process, and photonic properties of templated TSLCs to improve the issues. Furthermore, a variety of photonic applications including lasing, optical filters and gratings based on TSLCs with polymer templates are presented. Additionally, other applications of TSLCs are briefly introduced. Finally, the remaining challenges and future perspectives of templated TSLCs are proposed.

Effect of elastic constants on electrically induced transition in twisted radial cholesteric droplets

In this work, we investigated the behavior of cholesteric droplets with homeotropic boundary conditions experimentally and by computer simulations. Small droplets forming twisted radial structures were studied. We obtained two different paths of structural transformations under electric field in such droplets. The choice between these paths has probabilistic nature. The ratio between the two transition types was found to be sensitive to the elastic constants of LC forming the droplet. We suggest the principal approach for in situ estimation of ratios between elastic constants in cholesteric LCs deposited in polymer-dispersed LC material and discuss its strong and weak sides.

Synthesis and characterisation of triphenylmethine dyes for colour conversion layer of the virtual and augmented reality display

Five triphenylmethine dyes were designed and synthesised for the blue colour conversion layer of virtual and augmented reality displays. To form subpixel patterns suitable for high-brightness microdisplay panels, the prepared dyes must exhibit high solubility, colour strength, durability, and colour purity. For this purpose, three major strategies were introduced: dimerisation of triphenylmethine, chlorination, and counterion exchange. The electrostatic and spectroscopic characteristics of the synthesised dyes were investigated and predicted using computational calculations. The counter anion-modified dyes exhibited superior optical properties and thermal- and photo-stabilities compared to their parent dyes. The modified dyes also showed enhanced solubility toward industrial solvents because of their highly twisted chemical structures and weakly coordinating counter anion substituents. The synthesised dyes were chlorinated to optimise blue colour tuning and prevent the agglomeration of dyes. DTPM-Cl-HFPSI was selected as the main colourant, and EV-HFPSI was selected as the colour-matching colourant to manufacture optimal deep blue colour resists. The optimised spin-coated films exhibited high transmittance in the blue region and excellent properties in terms of brightness and colour purity by absorption over a wide and appropriate visible region.

π-Expansion of 2,3,6,7-Tetraazanaphthalene with Two Embedded Heptagons: Highly Twisted Structure and Lone-Pair/π* Interaction in the Crystal.

Synthesis and characterization of doubly diphenylene-fused 2,3,6,7-tetraazanaphthalene 1 are described. Single-crystal X-ray diffraction analysis showed the highly twisted structure of 1 with a degree of twisting of 13.0°/Å, which is one of the largest values for a π-system. In the crystal, molecules of 1 formed an orthogonal one-dimensional column with π-stacking of diphenylene moieties and a short intermolecular C···N distance due to lone-pair/π* interaction, which is a rare example of lone-pair/π* interaction in a supramolecular assembly.

Analysis and Calculation of Crosstalk for Twisted Communication Cables in Umbilical Cable

An umbilical cable is a compactly integrated cable consisting of electrical power cables, communication (electric signal) cables, and chemical transposition tubes. An umbilical cable is widely used in developing oil and gas resources of deep and ultra-deep water. With the increment of the length and the functional integration of umbilical cables, the crosstalk becomes a crucial issue in the cable design, and needs to be evaluated carefully before the fabrication and installation. Moreover, the twisted structure of communication cable cores has incurred extra difficulties to the crosstalk calculation. Nevertheless, it is not an easy task to model the complex twisted structure in existing models and methods of the crosstalk computation. In this regard, this paper proposes a numerical methodology for the crosstalk calculation considering the multi-conductor twisted structure of the cable cores. In the methodology, the four-wire twisted structure is modelled as a cascade of uniform multiconductor transmission line (MTL) sections, each wire section covering a length of 1/4 pitch, with abrupt interchanges of wire positions at the ends. The chain-parameter equation is introduced to describe the voltage and current transfer relationship in each MTL section. To obtain the numerical solutions of the twisted cable system, the port constraint equations and the permutation matrices are also required and developed. The per-unit-length parameters of the umbilical cable system are computed by numerical methods. The feasibility to engineering applications and accuracy of the proposed methodology is validated by experimental results, and the crosstalk characteristics of communication cables in a typical umbilical cable under different operating conditions are investigated.

Air Stable Chalcogen-Doped Rubicenes with Diradical Character

Air Stable Chalcogen-Doped Rubicenes with Diradical Character

AIEE-TICT quadrupolar push-pull quinoxaline derivatives displaying solvatochromism, acidofluorochromism and logic gate operation

A series of novel quadrupolar push-pull molecules based on quinoxaline moiety as an electron acceptor, biphenyl as a spacer and methoxy groups as electron donors was designed, synthesized and characterized. Their structural, photophysical, thermal, aggregation and acidofluorochromic properties were investigated. Photophysical studies showed that the introduction of an electron withdrawing group onto the quinoxaline moiety caused red shifts in absorption and emission maxima due to enhanced ICT. A positive solvatochromic behavior with large bathochromic shifts, up to 106 nm, was observed in the emission wavelength upon increasing solvent polarity from toluene to DMSO. All compounds displayed TICT-AIEE characteristics in DMSO-Water. Single crystal X-ray diffraction studies of QM2, QM4-QM6 revealed highly twisted structures and the absence of π-π stacking interactions. A visual color change from colorless to yellow accompanied by fluorescence quenching was observed in the molecules upon treatment of DCM solution with TFA and the changes were reversed upon addition of TEA. Reversible acidofluorochromism was also observed in the solid state. Filter paper strips coated with QM1 and QM4 were fabricated for detecting TFA. An IMPLICATION molecular logic gate operation can be performed on these molecules using acid and base as chemical inputs.

An Automated Image Segmentation and Useful Feature Extraction Algorithm for Retinal Blood Vessels in Fundus Images

The manual segmentation of the blood vessels in retinal images has numerous limitations. It is very time consuming and prone to human error, particularly with a very twisted structure of the blood vessel and a vast number of retinal images that needs to be analysed. Therefore, an automatic algorithm for segmenting and extracting useful clinical features from the retinal blood vessels is critical to help ophthalmologists and eye specialists to diagnose different retinal diseases and to assess early treatment. An accurate, rapid, and fully automatic blood vessel segmentation and clinical features measurement algorithm for retinal fundus images is proposed to improve the diagnosis precision and decrease the workload of the ophthalmologists. The main pipeline of the proposed algorithm is composed of two essential stages: image segmentation and clinical features extraction stage. Several comprehensive experiments were carried out to assess the performance of the developed fully automated segmentation algorithm in detecting the retinal blood vessels using two extremely challenging fundus images datasets, named the DRIVE and HRF. Initially, the accuracy of the proposed algorithm was evaluated in terms of adequately detecting the retinal blood vessels. In these experiments, five quantitative performances were measured and calculated to validate the efficiency of the proposed algorithm, which consist of the Acc., Sen., Spe., PPV, and NPV measures compared with current state-of-the-art vessel segmentation approaches on the DRIVE dataset. The results obtained showed a significantly improvement by achieving an Acc., Sen., Spe., PPV, and NPV of 99.55%, 99.93%, 99.09%, 93.45%, and 98.89, respectively.

Two‐Photon Printing of Shape‐Memory Microstructures and Metasurfaces via Radical‐Mediated Thiol‐Vinyl Hydrothiolation

AbstractShape‐memory resists capable of high‐resolution curing into arbitrarily designed structures are increasingly demanded for soft robotics, optical sensors, microscale manufacturing, and biomedicine. Amorphous, shape‐memory thiol‐vinyl networks are printed using two‐photon polymerization (2PP) curing of a simple resin formulated with commercially available reagents. The ability to print high‐resolution feature sizes down to 200 nm is attributed to the use of radical‐mediated, thiol‐vinyl step‐growth polymerization that quickly cross‐links the resin, limiting diffusive transport. The thermomechanical behavior of the 2PP‐cured material analyzed in compression, tension, and three‐point bending is similar to the behavior of the UV‐polymerized samples. To demonstrate the ability to design, field, and test 4D responsive microstructures, an array of nine springs with coil diameters of 330 µm is printed. Following compressive shape‐fixing, printed arrays can release 11 µJ of stored elastic strain energy when reheated. Further, a new concept of dichroic‐memory of a metamaterial device is demonstrated by printing a twisted woodpile structure with circular dichroism as characterized by Mueller Matrix ellipsometry. The results of this study demonstrate how combining high‐resolution 2PP curing with stimuli‐responsive molecular architectures can further the engineering of responsive microstructures and metamaterials.

Twist Structures and Nelson Conuclei

Motivated by Kalman residuated lattices, Nelson residuated lattices and Nelson paraconsistent residuated lattices, we provide a natural common generalization of them. Nelson conucleus algebras unify these examples and further extend them to the non-commutative setting. We study their structure, establish a representation theorem for them in terms of twist structures and conuclei that results in a categorical adjunction, and explore situations where the representation is actually an isomorphism. In the latter case, the adjunction is elevated to a categorical equivalence. By applying this representation to the original motivating special cases we bring to the surface their underlying similarities.

Damage tolerance mechanism of bioinspired hybridization helical composite in lobster homarus americanus

A typical twisted laminar structure was an essential feature for the exoskeleton of the lobster Homarus americanus to resist impact damage and penetration. In fact, two kinds of helical structures were observed in the exoskeleton with different pitch angles and ply thicknesses in the exocuticle and endocuticle. It is worth investigating the evolutionary mechanism of the hybrid helicoidal structure rather than a single helix. In this paper, two pitch angles and ply thickness were introduced to reproduce the hybridization helicoidal structures of crustacean ectoskeletons. Numerical investigations were carried out, including low-velocity impact and compression after impact (CAI). The results showed that the bionic architectures need to balance the protection function provided by the endocuticle and load-carrying performance provided by the exocuticle. In addition, the qualitative relationship between design parameters and performance was analysed. The decrease in angle and the increase in layer thickness will lead to an increase in energy dissipation during the impact process and a decrease in residual strength. The research results provide a reference for the design of hybrid bionic structures with multimechanism cooperation.

O(N ) ab initio calculation scheme for large-scale moiré structures

We present a two-step method specifically tailored for band structure calculation of the small-angle moir\'{e}-pattern materials which contain tens of thousands of atoms in a unit cell. In the first step, the self-consistent field calculation for ground state is performed with $O(N)$ Krylov subspace method implemented in OpenMX. Secondly, the crystal momentum dependent Bloch Hamiltonian and overlap matrix are constructed from the results obtained in the first step and only a small number of eigenvalues near the Fermi energy are solved with shift-invert and Lanczos techniques. By systematically tuning two key parameters, the cutoff radius for electron hopping interaction and the dimension of Krylov subspace, we obtained the band structures for both rigid and corrugated twisted bilayer graphene structures at the first magic angle ($\theta=1.08^\circ$) and other three larger ones with satisfied accuracy on affordable costs. The band structures are in good agreement with those from tight binding models, continuum models, plane-wave pseudo-potential based $ab~initio$ calculations, and the experimental observations. This efficient two-step method is to play a crucial role in other twisted two-dimensional materials, where the band structures are much more complex than graphene and the effective model is hard to be constructed.

Highly Efficient Aggregation-Induced Enhanced Electrochemiluminescence of Cyanophenyl-Functionalized Tetraphenylethene and Its Application in Biothiols Analysis.

Exploring new electrochemiluminescence (ECL) luminophores with high ECL efficiency and good stability in aqueous solution is in great demand for biological sensing. In this work, highly efficient aggregation-induced enhanced ECL of cyanophenyl-functionalized tetraphenylethene (tetra[4-(4-cyanophenyl)phenyl]ethene, TCPPE) and its application in biothiols analysis were reported. TCPPE contains four 4-cyanophenyl groups covalently attached to the tetraphenylethene (TPE) core, generating a nonplanar three-dimensional twisted conformation structure. TCPPE nanoparticles (NPs) with an average size of 15.84 nm were prepared by a precipitation method. High ECL efficiency (593%, CdS as standard) and stable ECL emission (over one month) were obtained for TCPPE NPs in aqueous solution. The unique properties of TCPPE NPs could be ascribed to the efficient suppression of nonradiative transition, the decrease of the energy gap, and the increase of anionic radical stability, which were proved by theoretical calculation and electrochemical and fluorescence methods. Contrasting aggregation-induced ECL chromic emission was first observed for TCPPE NPs. As a proof-of-methodology, an ECL method was developed for three biothiol assays with detection limits of 6, 7, and 300 nM for cysteine, homocysteine, and glutathione, respectively. This work demonstrates that TCPPE NPs are promising ECL luminophores, and the incorporation of appropriate substituents into luminophores can improve ECL efficiency and radical stability.

Dynamic Response Analysis of Twisted High-Rise Structures according to the Core Location Change

Dynamic Response Analysis of Twisted High-Rise Structures according to the Core Location Change

Analysis of twisted structure absorber tube and effects of specific design factor in solar collectors

Boosting heat transfer rates inside an absorber tube is of significant attention to optimize solar collectors' performance. Generally, the absorber tube comes in the forms of straight and smooth geometries, which besides the poor thermal performance, in some cases, it is subjected to tube deformation due to thermal stress. To overcome such problems, different twisted structures for the absorber tube are considered in this study, and the obtained results are discussed through a synergy analysis. First, a straight tube equipped with a twisted insert is examined compared to the twisted tube. Then, to further fulfill the desired goals, two combinations of the twisted tube with the twisted insert are considered, in which the twisted inserts are placed on the minor and major axes of the twisted tube cross-section. Results show that replacing the smooth tube with twisted structures brings about better thermal performance (between 1.08 and 3.72 times). Flow resistance augmentation reported for the enhanced models is between 1.21 and 2.93 times higher than that of the smooth tube. Likewise, the combined techniques result in great enhancements in performance index and energy efficiency, thus, at N = 12, these parameters increase up to 2.63 and 90%, respectively.

Columnar Structure of Claw Denticles in the Coconut Crab, Birgus latro

Some decapod crustaceans have tooth-like white denticles that exist only on the pinching side of claws. We revealed the denticle microstructure in the coconut crab, Birgus latro, using optical and scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and a focused ion beam (FIB)-SEM. Three-dimensional analysis and fracture surface observation were performed in order to clarify the microstructural differences in two mineralized layers—the exocuticle and the endocuticle. The denticles consist of a columnar structure normal to the surface and are covered with a very thin epicuticle and an exocuticle with a twisted plywood pattern structure. Due to abrasion, the exocuticle layer was lost in the wide area above the large denticles; conversely, these layers remained on the surface of the relatively small denticles and on the base of the denticle. The results showed that the mineralized exoskeleton of the crab’s claw is classified into three structures: a twisted plywood pattern structure stacked parallel to the surface for the exocuticle, a porous structure with many regularly arranged pores vertical to the surface for the endocuticle, and a columnar structure vertical to the surface for the denticle.

Stacking and Twisting of Layered Materials Enabled by Screw Dislocations and Non-Euclidean Surfaces

ConspectusThe rise of van der Waals layered materials such as graphene, hexagonal boron nitride, and transition-metal dichalcogenides opens up enormous opportunities for exploring novel quantum phenomena at the two-dimensional (2D) atomic limit. The physical properties of van der Waals materials are often affected by the symmetry of the crystal lattices. For example, breaking the inversion symmetry can lead to a variety of phenomena, such as second-harmonic generation, valley polarization, and ferroelectricity. The symmetry and symmetry breaking of layered materials are determined by the atomic arrangements within the layer and the layer stackings. The screw-dislocation-driven growth mechanism is general to 2D materials and can provide effective kinetic pathways to influence the layer stacking and generate diverse and complex layer stackings with different symmetry.Furthermore, different van der Waals layered materials can also be stacked vertically to create artificial new structures. In such stacked structures, the interlayer twist angle between stacked layers results in the formation of large-scale moiré superlattices that manipulate the electronic structures of van der Waals materials and provide an additional degree of freedom for tuning their physical properties. The stacking and twisting of layered materials lead to observations of new quantum phenomena, such as unconventional superconductivity, tunable Mott insulators, moiré excitons, and various magnetic and ferroelectric orderings. Previously, such twisted 2D structures were often fabricated by mechanically stacking exfoliated layers, but it was recently demonstrated that twisted van der Waals structures can form via direct growth. Moreover, continuously twisted structures of 2D materials can be realized through two distinct mechanisms that involve screw dislocations. The Eshelby twist mechanism induced by the strain of screw dislocation gives rise to twisted van der Waals nanowires with small interlayer twists. Beyond the Eshelby twist mechanism, supertwisted spirals have recently been enabled by a non-Euclidean twist mechanism which arises from the mismatched geometry between van der Waals crystals and non-Euclidean (curved) surfaces.In this Account, we start with reviewing the stacking configurations in the diverse polytypic structures of layered materials using transition-metal dichalcogenides as examples. We further discuss the twisted structures of layered materials from a structural point of view. After introducing screw-dislocation-driven growth and showing its generality in the crystal growth of layered materials, we further discuss how the unique structures of screw dislocations influence the stacking and symmetry of layered materials. Moreover, we highlight how screw dislocations enable interlayer twisting through the Eshelby twist mechanism and the non-Euclidean twist mechanism. In the end, the challenges and future perspectives are discussed for the study of screw-dislocated layered materials to control the stacking and twist for exotic physical properties.

Deep Elastic Strain Engineering of 2D Materials and Their Twisted Bilayers.

Conventionally, tuning materials' properties can be done through strategies such as alloying, doping, defect engineering, and phase engineering, while in fact mechanical straining can be another effective approach. In particular, elastic strain engineering (ESE), unlike conventional strain engineering mainly based on epitaxial growth, allows for continuous and reversible modulation of material properties by mechanical loading/unloading. The exceptional intrinsic mechanical properties (including elasticity and strength) of two-dimensional (2D) materials make them naturally attractive candidates for potential ESE applications. Here, we demonstrated that using the strain effect to modulate the physical and chemical properties toward novel functional device applications, which could be a general strategy for various 2D materials and their heterostructures. We then show how ultralarge, uniform elastic strain in free-standing 2D monolayers can permit deep elastic strain engineering (DESE), which can result in fundamentally changed electronic and optoelectronic properties for unconventional device applications. In addition to monolayers and van der Waals (vdW) heterostructures, we propose that DESE can be also applied to twisted bilayer graphene and other emerging twisted vdW structures, allowing for unprecedented functional 2D material applications.

Corrigendum: Transient Heat Transfer Characteristics of Twisted Structure Heated by Exponential Heat Flux

Corrigendum: Transient Heat Transfer Characteristics of Twisted Structure Heated by Exponential Heat Flux