Twist Angle Research Articles

Modulating electronic structure by interlayer spacing and twist on bilayer bismuthene.

Modulation of the electronic structure has played a crucial role in advancing the field of two-dimensional materials, but there are still many unexplored directions, such as the twist angle for a novel degree of freedom, for modulating the properties of heterostructures. We observed a distinct pattern in the energy bands of bilayer bismuthene, demonstrating that modulating the twist angle and interlayer spacing significantly influences interlayer interactions. Our study of various interlayer spacings and twist angles revealed a close relationship between bandgap size and interlayer spacing, while the twist angle notably affects the shape of the energy bands. Furthermore, we observed a synergistic effect between these two factors. As the twist angle decreases, the energy bands become flat, and flat bands can be generated without requiring a specific angle on bilayer bismuthene. Our results suggest a promising way to tailor the energy band structure of bilayer 2D materials by varying the interlayer spacing and twist angle.

Flexural–torsional buckling with enforced axis of twist and related problems

The classical lateral–torsional instability of a cantilever beam with continuous elastic lateral restraint and a transverse point-load applied at the free end is discussed here through the lens of asymptotic simplifications. One of our main goals is to provide analytical approximations for the critical buckling load, as well as its dependence on various key non-dimensional groups. The first part of this study is concerned with a scenario in which a doubly symmetric beam is constrained to rotate about a fixed axis situated at an arbitrary height above the shear centroidal axis. The second part examines a beam that features a continuous elastic lateral restraint spanning its entire length. Assuming that the stiffness of the constraint, [Formula: see text] (say), is finite, the buckling equations in the second case are described by a system of two coupled fourth-order differential equations in the lateral displacement and the angle of twist. We show that as [Formula: see text], the problem discussed in the first part provides an outer solution for the aforementioned system; the relevant boundary conditions for the next-to-leading-order outer approximation are also derived using matched asymptotics. Our theoretical findings are confirmed by comparisons with direct numerical simulations of the full buckling problem.

Highly Twisted Ladder Oligosilanes Bearing Phenyl and tert‐Butyldimethylsilyl Groups

Two stereoisomers of bicyclic ladder oligosilanes bearing phenyl and tert‐butyldimethylsilyl groups were synthesized, and their structures and electronic properties are compared with previously reported perisopropyl‐substituted analog. These novel ladder oligosilanes have highly twisted structures with the twist angles between the two terminal Si–Si bonds of av. 37.7 and 39.8°. The UV spectra of these compounds show bathochromically shifted absorption maxima with the longest wavelength compared with that of the perisopropyl‐substituted bicyclic ladder oligosilane. The electronic properties of the ladder oligosilanes were analyzed by theoretical calculations.

Hexabenzoheptacene: A Longitudinally Multihelicene Nanocarbon with Local Aromaticity and Enhanced Stability

We report the synthesis of a longitudinally helical molecular nanocarbon, hexabenzoheptacene (HBH), along with its dimethylated derivative (HBH‐Me), which are composed of six benzene rings periodically benzannulated to both zigzag edges of a heptacene core. This benzannulation pattern endows the resulting nanocarbons with a helical heptacene core and local aromaticity, imparting enhanced solubility and stability to the system. The chiral HBH‐Me adopts a more highly twisted conformation with an end‐to‐end twist angle of 95°, enabling the separation of the enantiomers. Both HBH and HBH‐Me can be facilely oxidized into their corresponding dications, which exhibit enhanced planarity and aromaticity upon loss of electrons. Notably, both longitudinally helical nanocarbons readily promote solid state packing into two‐dimensional (2D) arrangement. Single‐crystal microbelts of HBH‐Me show hole mobility up to 0.62 cm2 V‐1 s‐1, illustrating the promising potential of these longitudinally helical molecules for organic electronic devices.

Hexabenzoheptacene: A Longitudinally Multihelicene Nanocarbon with Local Aromaticity and Enhanced Stability.

We report the synthesis of a longitudinally helical molecular nanocarbon, hexabenzoheptacene (HBH), along with its dimethylated derivative (HBH-Me), which are composed of six benzene rings periodically benzannulated to both zigzag edges of a heptacene core. This benzannulation pattern endows the resulting nanocarbons with a helical heptacene core and local aromaticity, imparting enhanced solubility and stability to the system. The chiral HBH-Me adopts a more highly twisted conformation with an end-to-end twist angle of 95°, enabling the separation of the enantiomers. Both HBH and HBH-Me can be facilely oxidized into their corresponding dications, which exhibit enhanced planarity and aromaticity upon loss of electrons. Notably, both longitudinally helical nanocarbons readily promote solid state packing into two-dimensional (2D) arrangement. Single-crystal microbelts of HBH-Me show hole mobility up to 0.62 cm2 V-1 s-1, illustrating the promising potential of these longitudinally helical molecules for organic electronic devices.

Delusive chirality and periodic strain pattern in moiré systems

Geometric phase analysis (GPA) is a widely used technique for extracting displacement and strain fields from scanning probe images. Here, we demonstrate that GPA should be implemented with caution when several fundamental lattices contribute to the image, in particular in twisted heterostructures featuring moiré patterns. We find that in this case, GPA is likely to suggest the presence of chiral displacement and periodic strain fields, even if the structure is completely relaxed and without distortions. These delusive fields are subject to change with varying twist angles, which could mislead the interpretation of twist angle-dependent properties.

Interfacial molecular structure and orientation evolution of the polystyrene under confinement during annealing revealed by sum frequency generation vibrational spectroscopy

The geometrical confinement directly affects many crucial properties of polymer thin films by interfacial interactions. A key to understanding the role of these interfacial interactions is to specifically probe the confined interface at the molecular level and in situ. However, the direct and nondestructive detection of interfacial polymer structures under confinement is very difficult. In this study, specific interface-sensitive sum frequency generation (SFG) spectroscopy was applied to study the deuterated PS (d8-PS) film confined between hydrogenated poly (methyl methacrylate) (PMMA) films at the molecular level and in situ. The results showed that the ordering/orientation of the PS chain (backbone and phenyl group) evolved at the buried d8-PS/PMMA interface during annealing. The tilt angle of the PS phenyl group increased while the twist angle decreased with elevated annealing temperature. Both overall SFG ssp and ppp intensities decreased after annealing at 433 K for 24 h, indicating that PS chains entangled with or penetrated the PMMA chains at the confined interface. This study qualitatively and quantitatively revealed the interfacial structure and structural evolution of the PS chain confined between PMMA films in situ during annealing, which is beneficial to the molecular-level understanding of the interfacial chain conformational relaxation of polymers under confinement.

The experimental and numerical investigation of fracture behaviour in PMMA notched specimens under biaxial loading conditions – Tension with torsion

This paper presents the results of experimental fracture test of flat PMMA specimens under biaxial loading condition tension with torsion (proportional). The specimens were made in two thicknesses: 5 and 15 mm and were weakened with V-type edge notches with different root radii: 0.5; 2 and 10 mm. Thanks to the ARAMIS 3D 4 M non-contact vision system, measurement of the elongation and twist angle were recorded. During experimental part all of the deformation processes were observed using PHANTOM cameras. Obtained records made it possible to precisely indicate the moment of crack initiation (tensile force and torsional moment values). Using the microscopic observations the location of crack initiations were determined. Results obtained for biaxial loading were compared with those obtained for uniaxial tension and torsion. Based on experimental data the numerical calculation with FEM were carried out. The principal stress and plastic strain distribution under critical load, were obtained. The points of occurrence of stress maxima and plastic strain were indicated, which were taken as potential crack initiation sites. On the basis of the stress and plastic strain values measured at the critical points, a stress–strain fracture criterion was formulated, which was then positively verified. Additionally, new form of stress–strain fracture criterion was proposed. The bilinear form of the fracture criterion can be successfully used to predict fracture in PMMA flat specimens, regardless of the notch root radius, type of load or element thickness.

Influence of Water Flow Speed on the Torque Behaviour of the Hybrid HKT Having Straight and Helical Bladed Savonius Rotor

Flow streams in rivers, canals, and the tail race of a hydropower plant can be transformed into usable kinetic energy with the help of a hydrokinetic turbine. In this work, the torque characteristics of the hybrid turbine having Savonius helical blade angles of 0˚ and 180˚ have been evaluated using a numerical technique. The characteristics of the turbine are driven for the range of water speed of 0.5 to 2.0 m/s and TSR of 0.3 to 1.5. It is observed from numerical analysis that the flow speed of water significantly affects the mean torque and static torque established by the hybrid turbine. The torque developed by the hybrid turbine enhances as water speed increases. However, the structure of the Savonius blade can alter the torque characteristics of the turbine. The mean torque and static torque growth by the hybrid turbine with a Savonius helical blade angle of 0˚ is more optimum than the hybrid turbine with a Savonius helical blade angle of 180˚. Although, the positive magnitude of torque is achieved at every rotor angle over one revolution by introducing a twist angle to the traditional Savonius blade in the hybrid configuration.

Magnetic Anisotropy and Relaxation in Four-Coordinate Cobalt(II) Single-Ion Magnets with a [CoIIO4] Core.

A mononuclear four-coordinate Co(II) complex with a [CoIIO4] core, namely, PPN[Li(MeOH)4][Co(L)2] (1) (PPN = bis(phosphoranediyl)iminium; H2L = perfluoropinacol), has been studied by X-ray crystallography, magnetic characterization, and theoretical calculations. This complex presents a severely distorted coordination geometry. The O-Co-O bite angle is 83.42°/83.65°, and the dihedral twist angle between the O-Co-O chelate planes is 55.6°. The structural distortion results in a large easy-axis magnetic anisotropy with D = -104(1) cm-1 and a transverse component with |E| = +4(2) cm-1. Alternating current (ac) susceptibility measurements demonstrate that 1 exhibits slow relaxation of magnetization at zero static field. However, the frequency-dependent out-of-phase (χ"M) susceptibilities of 1 at 0 Oe do not show a characteristic maximum. Upon the application of a dc field or the dilution with a diamagnetic Zn matrix, the quantum tunneling of magnetization (QTM) process can be successfully suppressed. Notably, after dilution with the Zn matrix, the obtained sample exhibits a structure different from that of the pristine complex. In this altered sample, the asymmetric unit does not contain the Li(MeOH)4+ cation, resulting in an O-Co-O bite angle of 86.05° and a dihedral twist angle of 75.84°, thereby leading to an approximate D2d symmetry. Although such differences are not desirable for magnetic studies, this study still gives some insights. Theoretical calculations reveal that the D parameter is governed by the O-Co-O bite angle, in line with our previous report for other tetrahedral Co(II) complex with a [CoIIN4] core. On the other hand, the rhombic component is found to increase as the dihedral angle deviates from 90°. These findings provide valuable guidelines for fine-tuning the magnetic properties of Co(II) complexes.

A Small Step for Epitaxy, a Large Step Toward Twist Angle Control in 2D Heterostructures

Abstract2D materials have received a lot of interest over the past decade. Especially van der Waals (vdW) 2D materials, such as transition metal dichalcogenides (TMDCs), and their heterostructures exhibit semiconducting properties that make them highly suitable for novel device applications. Controllable mixing and matching of the 2D materials with different properties and precise control of the in‐plane twist angle in these heterostructures are essential to achieve superior properties and need to be established through large‐scale device fabrication. To gain fundamental insight into the potential control of these twist angles, 2D heterostructures of tungsten disulfide (WS2) and graphene (Gr) grown by bottom‐up synthesis via metal‐organic chemical vapor deposition (MOCVD) are investigated using a scanning transmission electron microscope (STEM). Specifically, the combination of conventional high‐resolution imaging with scanning nanobeam diffraction (SNBD) using advanced 4D STEM techniques is used to analyze moiré structures. The latter technique is used to reveal the epitaxial alignment within the WS2/Gr heterostructure, showing a direct influence of the underlying Gr layers on the moiré structure in the subsequent WS2 layers. In particular, the importance of grain boundaries (GBs) within the underlying WS2 and Gr layers on the structure of moiré patterns with rotation angles below 2° is discussed.

Moiré-modulated band gap and van Hove singularities in twisted bilayer germanene

Twisting bilayers of two-dimensional topological insulators has the potential to create unique quantum states of matter. Here, we successfully synthesized a twisted bilayer of germanene on Ge2Pt(101) with a 21.8° twist angle, corresponding to a commensurate (√7×√7) structure. Using scanning tunneling microscopy and spectroscopy, we unraveled the structural and electronic properties of this configuration, revealing a moiré-modulated band gap and a well-defined edge state. This band gap opens at AB/BA stacked sites and closes at AA stacked sites, a phenomenon attributed to the electric field induced by the scanning tunneling microscopy tip. Our study further revealed two van Hove singularities at −0.8 eV and +1.04 eV, resulting in a Fermi velocity of (8 ± 1) × 105 m s−1. Our tight-binding results uncover a unique quantum state, where the topological properties could be regulated through an electric field, potentially triggering two topological phase transitions.

Waveguide-integrated twisted bilayer graphene photodetectors.

Graphene photodetectors have exhibited high bandwidth and capability of being integrated with silicon photonics (SiPh), holding promise for future optical communication devices. However, they usually suffer from a low photoresponsivity due to weak optical absorption. In this work, we have implemented SiPh-integrated twisted bilayer graphene (tBLG) detectors and reported a responsivity of 0.65 A W-1 for telecom wavelength 1,550 nm. The high responsivity enables a 3-dB bandwidth of >65 GHz and a high data stream rate of 50 Gbit s-1. Such high responsivity is attributed to the enhanced optical absorption, which is facilitated by van Hove singularities in the band structure of high-mobility tBLG with 4.1o twist angle. The uniform performance of the fabricated photodetector arrays demonstrates a fascinating prospect of large-area tBLG as a material candidate for heterogeneous integration with SiPh.

Sulfonamide-induced DNA hypomethylation disturbed sugar metabolism in rice (Oryza sativa L.)

DNA methylation is well-accepted as a bridge to unravel the complex interplay between genome and environmental exposures, and its alteration regulated the cellular metabolic responses towards pollutants. However, the mechanism underlying site-specific aberrant DNA methylation and metabolic disorders under pollutant stresses remained elusive. Herein, the multilevel omics interferences of sulfonamides (i.e., sulfadiazine and sulfamerazine), a group of antibiotics pervasive in farmland soils, towards rice in 14 days of 1 mg/L hydroponic exposure were systematically evaluated. Metabolome and transcriptome analyses showed that 57.1–71.4 % of mono- and disaccharides were accumulated, and the differentially expressed genes were involved in the promotion of sugar hydrolysis, as well as the detoxification of sulfonamides. Most differentially methylated regions (DMRs) were hypomethylated ones (accounting for 87–95 %), and 92 % of which were located in the CHH context (H = A, C, or T base). KEGG enrichment analysis revealed that CHH-DMRs in the promoter regions were enriched in sugar metabolism. To reveal the significant hypomethylation of CHH, multi-spectroscopic and thermodynamic approaches, combined with molecular simulation were conducted to investigate the molecular interaction between sulfonamides and DNA in different sequence contexts, and the result demonstrated that sulfonamides would insert into the minor grooves of DNA, and exhibited a stronger affinity with the CHH contexts of DNA compared to CG or CHG contexts. Computational modeling of DNA 3D structures further confirmed that the binding led to a pitch increase of 0.1 Å and a 3.8° decrease in the twist angle of DNA in the CHH context. This specific interaction and the downregulation of methyltransferase CMT2 (log2FC = –4.04) inhibited the DNA methylation. These results indicated that DNA methylation-based assessment was useful for metabolic toxicity prediction and health risk assessment.

Pseudomagnetic fields in fully relaxed twisted bilayer and trilayer graphene

We present simple models to describe the in-plane and the out-of-plane lattice relaxation in twisted bilayer and symmetrically twisted trilayer graphene. Analytical results and series expansions show that for twist angles θ>1.4∘ , the in-plane atomic displacements lead to pseudomagnetic fields weakly dependent on θ. In symmetrically twisted trilayer graphene, the central layer in-plane relaxation is greatly enhanced. The joint effect of the relaxation-induced pseudoscalar potentials and the associated energy difference between interlayer dimer and non-dimer pairs resulted in a significant electron–hole asymmetry both in twisted bilayer and trilayer graphene.

Spinning spoof surface plasmons and their topological responses

Spoof surface plasmons (SSPs) mimic characteristics of optical surface plasmons in microwave and terahertz frequencies. Manipulating SSPs has attracted widespread attention for extending plasmon applications into the low-frequency range. In this Letter, we show that spinning SSPs can be excited on a twisted groove (TG) metallic cylinder by oblique incident waves. The incident angle of waves and the twist angle of the grooves play essential roles in manipulating the propagation orientation and the rotation direction of spinning SSPs (SSSPs). Finally, we discuss an application of the SSSPs in topological photonic systems. By periodically arranging the TG cylinders, we show that this spinning feature will lead to topologically non-trivial bands in such a photonic crystal, where the topologically protected edge modes arise near the boundary.

Maximisation the autonomous flight performance of unmanned helicopter using BSO algorithm

Abstract The usage areas of rotary or fixed wing unmanned aerial vehicles (UAV) have become very widespread with technological developments. For this reason, UAV designs differ in terms of aerodynamic design, flight performance and endurance depending on the intended use. In this study, maximising of the autonomous flight performance of the unmanned helicopter produced at Erciyes University using an optimisation algorithm is discussed. For this purpose, the input parameters of the dynamic model are chosen as blade length, blade mass density, blade chord width and blade twist angle of the unmanned helicopter and the proportional, integral, derivative gain coefficients of the lateral axis of the autopilot. The output parameters of the dynamic model are selected as settling time, rise time and maximum overshoot, which are autonomous performance parameters. The dynamic model consisting of helicopter and autopilot parameters is integrated into the back-tracking search optimisation (BSO) algorithm as an objective function. In the optimization process, where mean squared error (MSE) is used as the performance criterion, optimum input and output values were determined. Thus, helicopter and autopilot parameters, which are among the factors affecting autonomous performance, are taken into account with equal importance and simultaneously. Simulations show that the obtained values are satisfactory. With this approach based on the optimisation method, complex and time-consuming dynamic model calculations are reduced, time and cost are saved, and practicality is achieved in applications. Therefore, this approach can be an innovative and alternative method to improve UAV designs and increase flight performance compared to classical methods.

Pulse pattern manipulation of dichromatic soliton complexes by a twistable tapered-fiber filter

Soliton complexes highlight the particle-like dynamics of dissipative pulses. However, simple and reliable manipulation of bound solitons remains challenging, particularly for all-polarization-maintaining (PM) configurations that are free from random polarization perturbations. Here, we report controllable pulse patterns of robustly coexisting dichromatic soliton complexes in an all-PM fiber laser based on a twistable tapered-fiber filter. According to the twist angle, dichromatic pulses are switched between different patterns, and components at each wavelength can be independently manipulated, extending encodings from the time to the frequency domain. To the best of our knowledge, it is the first experimental demonstration of dual-wavelength soliton complexes that different pulse patterns coexist at separated wavebands.

Design and Analysis of a Polymeric Left Ventricular Simulator via Computational Modelling

Preclinical testing of medical devices is an essential step in the product life cycle, whereas testing of cardiovascular implants requires specialised testbeds or numerical simulations using computer software Ansys 2016. Existing test setups used to evaluate physiological scenarios and test cardiac implants such as mock circulatory systems or isolated beating heart platforms are driven by sophisticated hardware which comes at a high cost or raises ethical concerns. On the other hand, computational methods used to simulate blood flow in the cardiovascular system may be simplified or computationally expensive. Therefore, there is a need for low-cost, relatively simple and efficient test beds that can provide realistic conditions to simulate physiological scenarios and evaluate cardiovascular devices. In this study, the concept design of a novel left ventricular simulator made of latex rubber and actuated by pneumatic artificial muscles is presented. The designed left ventricular simulator is geometrically similar to a native left ventricle, whereas the basal diameter and long axis length are within an anatomical range. Finite element simulations evaluating left ventricular twisting and shortening predicted that the designed left ventricular simulator rotates approximately 17 degrees at the apex and the long axis shortens around 11 mm. Experimental results showed that the twist angle is 18 degrees and the left ventricular simulator shortens 5 mm. Twist angles and long axis shortening as in a native left ventricle show it is capable of functioning like a native left ventricle and simulating a variety of scenarios, and therefore has the potential to be used as a test platform.

Electro-optic characteristics of chiral nematic layers deformed by in-plane electric field

Electro-optic characteristics of chiral nematic layers deformed by in-plane electric field