Chiral Angle Research Articles

Mechanical properties of diamane: Orientation dependence of strength and fracture strain

Diamane, the two-dimensional counterpart of diamond, is very promising for novel electronic and nanomechanical devices, which requires additional studies on their physical and mechanical properties. In the present work, the orientation dependence of diamane strength with the detailed analysis of the deformation behavior was carried out by molecular dynamics. Two stacks of diamane layers covered with hydrogen with different chirality θ from 0 to 30° were considered. The atomic stacking of diamane has no effect on its strength. It was found that diamane strength depends non-monotonously on the diamane chirality: the highest strength was found for θ = 10°. The fracture strain decreases with the increase of chiral angle from 0 to 20° and does not change for chirality from 20 to 30°. However, the Young’s modulus does not depend on the diamane chirality. The main deformation mechanisms were revealed: elongation of covalent bonds and rotation of valence angles. For chiral angles from 0 to 20°, the diamane chirality can be controllably changed during tension which results in the increase in fracture strength and strain. The obtained results allow a better understanding of the effect of the diamane morphology on their mechanical properties for future applications.

High‐Efficiency Separation of Near‐Zigzag Single‐Chirality Carbon Nanotubes by Gel Chromatography

High‐efficiency production of near‐zigzag single‐chirality single‐wall carbon nanotubes (SWCNTs) is of great importance for their property study and applications. The key to separate near‐zigzag single‐chirality SWCNTs by gel chromatography is to selectively adsorb them in the gel medium. In this study, by using a high surfactant ratio of sodium dodecyl sulfate and sodium cholate (≥4:1) to modulate the selective adsorption of distinct (n, m) SWCNTs in a gel column, a high enrichment of near‐zigzag SWCNTs adsorbed in the gel column is achieved, which usually have a low abundance in raw materials due to their low growth efficiency. Afterward, (7, 3), (8, 3), (8, 4), (9, 1), and (9, 2) single‐chirality SWCNTs are separated with small chiral angles less than 17° by following a stepwise elution for their selective desorption. This simple and efficient separation technique will promote the research and application of near‐zigzag SWCNTs.

Diameter-dependent thermal conductivity of carbon nanotubes

Carbon nanotubes are uniquely featured by the nanoscale tubular structure with a highly-curved surface and defined chirality. The diameter and chirality fundamentally determine their stability and electrical and thermal properties. Up to now, the relationship between the intrinsic thermal conductivity and the atomic features of CNTs has not been established, due to the challenges in precise measurements and characterizations. In this work, we develop a micro electro-thermal device enabling simultaneous thermal measurements by Raman spectroscopy and atomic structural characterization by transmission electron microscopy for individual CNTs. The influence of diameter and chirality is systematically investigated. In addition, the temperature dependence of the thermal conductivity was extracted from parameter optimization of finite-element modeling. It is found that the thermal transport of CNTs depends mainly on the diameter, while the chiral angle has no significant influence. Along with increasing diameter, the room temperature thermal conductivity increases and eventually approaches the limit of flat graphene.

Force-field modeling of single-chirality-angle multi-walled WS2 nanotubes

The experimentally observed dependencies of the average interwall distances on the number of walls and diameters of multi-walled WS2 nanotubes were reproduced in molecular mechanics simulations based on a recently developed force field. A common chiral angle was used for all walls inside each nanotube to ensure its one-dimensional periodicity. The data obtained make it possible to determine the nature of changes in the diameters of single-wall components inside the nanotube and variations in the distances between the walls in its inner, middle and outer parts. The stability of multi-walled nanotubes with respect to WS2 nanolayers and free single-wall components was evaluated.

Molecular Dynamics Simulations of Effects of Geometric Parameters and Temperature on Mechanical Properties of Single-Walled Carbon Nanotubes

Carbon nanotubes (CNTs) are considered an advanced form of carbon. They have superior characteristics in terms of mechanical and thermal properties compared to other available fibers and can be used in various applications, such as supercapacitors, sensors, and artificial muscles. The properties of single-walled carbon nanotubes (SWNTs) are significantly affected by geometric parameters such as chirality and aspect ratio, and testing conditions such as temperature and strain rate. In this study, the effects of geometric parameters and temperature on the mechanical properties of SWNTs were studied by molecular dynamics (MD) simulations using the Large-scaled Atomic/Molecular Massively Parallel Simulator (LAMMPS). Based on the second-generation reactive empirical bond order (REBO) potential, SWNTs of different diameters were tested in tension and compression under different strain rates and temperatures to understand their effects on the mechanical behavior of SWNTs. It was observed that the Young’s modulus and the tensile strength decreases with increasing SWNT tube diameter. As the chiral angle increases, the tensile strength increases, while the Young’s modulus decreases. The simulations were repeated at different temperatures of 300 K, 900 K, 1500 K, 2100 K and different strain rates of 1 × 10−3/ps, 0.75 × 10−3/ps, 0.5 × 10−3/ps, and 0.25 × 10−3/ps to investigate the effects of temperature and strain rate, respectively. The results show that the ultimate tensile strength of SWNTs increases with increasing strain rate. It is also seen that when SWNTs were stretched at higher temperatures, they failed at lower stresses and strains. The compressive behavior results indicate that SWNTs tend to buckle under lower stresses and strains than those under tensile stress. The simulation results were validated by and consistent with previous studies. The presented approach can be applied to investigate the properties of other advanced materials.

Nanotubes from Transition Metal Dichalcogenides: Recent Progress in the Synthesis, Characterization and Electrooptical Properties.

Inorganic layered compounds (2D-materials), particularlytransition metal dichalcogenide (TMDC), are the focus of intensive research in recent years. Shortly after the discovery of carbon nanotubes (CNTs) in 1991, it was hypothesized that nanostructures of 2D-materials can also fold and seam forming, thereby nanotubes (NTs). Indeed, nanotubes (and fullerene-like nanoparticles) of WS2 and subsequently from MoS2 were reported shortly after CNT. However, TMDC nanotubes received much less attention than CNT until recently, likely because they cannot be easily produced as single wall nanotubes with well-defined chiral angles. Nonetheless, NTs from inorganic layered compounds have become a fertile field of research in recent years. Much progress has been achieved in the high-temperature synthesis of TMDC nanotubes of different kinds, as well as their characterization and the study of their properties and potential applications. Their multiwall structure is found to be a blessing rather than a curse, leading to intriguing observations. This concise minireview is dedicated to the recent progress in the research of TMDC nanotubes. After reviewing the progress in their synthesis and structural characterization, their contributions to the research fields of energy conversion and storage, polymer nanocomposites, andunique optoelectronic devices are being reviewed. These studies suggest numerous potential applications for TMDC nanotubes in various technologies, which are briefly discussed.

Dirac Field, van der Waals Gas, Weyssenhoff Fluid, and Newton Particle

This article considers the Dirac field in polar formulation and shows that when torsion is taken in effective approximation the theory has the thermodynamic properties of a van der Waals gas. It is then shown that in the limit of zero chiral angle the van der Waals gas reduces to a Weyssenhoff fluid, and in spinlessness regime the Weyssenhoff fluid further reduces to a Newton particle. This nesting of approximations allows us to interpret the various spinor quantities. We will see that torsion will provide a form of negative pressure, while the chiral angle will be related to a type of temperature.

Anomalous buckling of odd elastic plates

Buckling of thin-walled structures such as plates and shells is a consequence of in-plane stress being released through out-of-plane displacements. Generally, thin-walled structures that are subjected to tension or zero stress conditions remain stable. In this article, the anomalous tension buckling and stress-free active buckling of odd elastic plates are reported, which are a novel instability caused by odd elastic effects. The latter can only occur in the form of left- or right-handed chiral deformation and it does not involve external loads or internal active stress in a critical state. We demonstrate that the chiral rotation angle deformation is responsible for the active buckling of the plates, because the energy required for instability can be obtained based on the odd elastic effect. These findings can serve as an interpretation in a novel way for the occurrence of surface morphologies with biological activities, as well as provide references for buckling designs and applications of active structures.

Light-cone and quasigeneralized parton distributions in the ’t Hooft model

We present a comprehensive study of the light-cone generalized parton distribution (GPD) and quasi-GPD of a flavor-neutral meson in the ’t Hooft model, i.e., two-dimensional QCD (QCD2) in the Nc→∞ limit. With the aid of the Hamiltonian approach, we construct the light-cone GPD in terms of the meson’s light-cone wave function in the framework of light-front quantization and express the quasi-GPD in terms of the meson’s Bars-Green wave functions and the chiral angle in the framework of equal-time quantization. We show that, both analytically and numerically, the quasi-GPD does approach the light-cone GPD when the meson is boosted to the infinite momentum frame, which justifies the tenet underlying the large momentum effective theory for the off-forward parton distribution. Upon taking the forward limit, the light-cone and quasi-GPDs reduce to the light-cone and quasi parton distribution functions (quasi-PDFs). As a bonus, we take this chance to correct the incomplete expression of the quasi-PDFs in the ’t Hooft model reported in our preceding work [Y. Jia , ]. Published by the American Physical Society 2024

Effects of Topological Parameters on Thermal Properties of Carbon Nanotubes via Molecular Dynamics Simulation

Due to their unique properties, carbon nanotubes (CNTs) are finding a growing number of applications across multiple industrial sectors. These properties of CNTs are subject to influence by numerous factors, including the specific chiral structure, length, type of CNTs used, diameter, and temperature. In this topic, the effects of chirality, diameter, and length of single-walled carbon nanotubes (SWNTs) on the thermal properties were studied using the reverse non-equilibrium molecular dynamics (RNEMD) method and the Tersoff interatomic potential of carbon–carbon based on the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS). For the shorter SWNTs, the effect of chirality on the thermal conductivity is more obvious than for longer SWNTs. Thermal conductivity increases with increasing chiral angle, and armchair SWNTs have higher thermal conductivity than that of zigzag SWNTs. As the tube length becomes longer, the thermal conductivity increases while the effect of chirality on the thermal conductivity decreases. Furthermore, for SWNTs with longer lengths, the thermal conductivity of zigzag SWNTs is higher than that of the armchair SWNTs. Thermal resistance at the nanotube–nanotube interfaces, particularly the effect of CNT overlap length on thermal resistance, was studied. The simulation results were compared with and in agreement with the experimental and simulation results from the literature. The presented approach could be applied to investigate the properties of other advanced materials.

Predicting the mechanical properties of pristine and defective carbon nanotubes using a random forest model.

Data-driven models have lately emerged as a faster and less time-consuming method for computing material properties than computationally expensive conventional molecular dynamics and density functional theory-based simulations. Here, we developed a random forest (RF) model for comprehensively predicting mechanical properties such as stress and Poisson's ratio under varying strain and ultimate tensile strain of pristine and defective carbon nanotubes (CNTs). The variations in stress and Poisson's ratio with the strain of CNTs with a 0.4-2 nm diameter range were calculated by classical molecular dynamics simulations and characterized using parameters extracted from fitting polynomial equations. The fitting parameters and ultimate tensile strength showed distinct dependency on chiral indices, chiral angles, radii, and the presence of defects in CNTs, which constituted the target dataset. The dataset features were selected through principal component analysis, and the correlation with targets was scrutinized. We performed a comparative analysis of different machine learning algorithms for predicting mechanical properties, revealing the RF model as the best-performing algorithm. The RMSE for the stress-strain curve had a maximum value of 0.013 and 0.0143 for pristine and defective CNTs, respectively, while the correlation coefficients were ≫ 0.99 for all CNTs, showcasing the excellent predictive power of the model. The model made excellent predictions of properties for CNTs with diameters >2 nm, which is beyond the training dataset range, demonstrating the robustness of the model as a substitute for MD simulation. The insight gained from this study will benefit the research of nanocomposites, nanoelectronics, and nanomechanical systems incorporating CNTs.

Computational study on Thermal and morphological characteristics of Carbazochrome encapsulation capacity in Carbon nanotube

The medical fraternity, nowadays, are focusing on the targeted and controlled delivery of medications. Accordingly, different researchers are utilizing computational resources to promote the understanding of drug-nanocarrier combinations and bolster the development of targeted and controlled drug delivery systems. Therefore, in this work, we have reported the encapsulation capacity of a hemostatic drug Carbazochrome inside Single-Walled Carbon Nanotubes of different morphological variations such as length, radius and chirality, under the room temperature i.e. 298 K, as well as the human body temperature i.e. 310 K. Molecular Dynamics method has been employed in this study and it is observed that the nanotube radius and length have a dominant effect on the Carbazochrome encapsulation capacity, followed weakly by nanotube chirality. Secondly, temperature also affects the encapsulation capacity of this drug within these nanotubes when the nanotube radius is not very large and the nanotube chiral angle is near to 30°. Hence, it can be concluded that for developing a targeted and controlled drug delivery system for Carbazochrome using the Single-Walled Carbon Nanotubes, the appropriate nanotube radius would be in the range of 8 Å − 9 Å while the nanotube chirality would be near to 0°.

Synthetic complex Weyl superconductors, chiral Josephson effect and synthetic half-vortices

We show that the most generic form of spin-singlet superconducting order parameter for chiral fermions in systems with broken time reversal symmetry and inversion symmetry is of the Delta _s+igamma ^5Delta _5 where Delta _s is the usual order parameter and Delta _5 is the pseudo-scalar order parameter. After factoring out the U(1) phase e^{iphi }, this form of superconductivity admits yet additional complex structure in the plane of (Delta _s,Delta _5). The polar angle chi in this plane, which we call the chiral angle, can be controlled by the external flux bias. We present a synthetic setup based on stacking of topological insulators (TIs) and superconductors (SCs). Alternatively flux biasing the superconductors with a fluxes pm Phi leads to Delta _5=Delta _0 sin (chi ), where Delta _0 is the superconducting order parameter of the SC layers, and the chiral angle chi ={2pi }Phi /Phi _0 is directly given by the flux Phi in units of the flux quantum Phi _0=h/(2e). This can be used as a building block to construct a two-dimensional Josephson array. In this setup chi will be a background field defining a pseudoscalar Delta _5 that can be tuned to desired configuration. While in a uniform background field Delta _5 the dynamics of phi is given by standard XY model and its associated vortices, a staggered background pm Delta _5 (or equivalently chi and chi +pi in alternating lattice sites) creates a new set of minima for the phi field that will support half-vortex excitations. An isolated single engineered “half-vortex” in the chi field in an otherwise uniform background will bind a phi -half-vortex. This is similar to the way a p-wave superconducting vortex core binds a Majorana fermion.

Observing Axial Chirality of Chiral Single-Wall Carbon Nanotubes by Helicity-Dependent Raman Spectra.

Helicity-dependent Raman spectra of an isolated, chiral, single-wall carbon nanotube (SWNT) are reported using circularly polarized light. A polar plot of polarized Raman intensity for the radial breathing mode (RBM), which is excited by left-handed or right-handed circularly polarized light, shows asymmetric angle dependence relative to the nanotube axis direction, which reflects the axial chirality of a SWNT. The asymmetry in the polar plot of the RBM can be analyzed by a complex Raman tensor. The complex phase of each component of the Raman tensor has a maximum at chiral angle θ = 15° of a SWNT which is between two achiral SWNTs, that is, zigzag (θ = 0°) and armchair (θ = 30°) SWNTs. Considering the interaction between the chiral SWNT and the circularly polarized light, we discuss the origin of the complex phases excited by the opposite helicity of the circularly polarized light.

Prediction and optimization of 3D-printed sandwich beams with chiral cores

This study pursues two primary objectives concerning sandwich structures with chiral cores. Firstly, it delves into the realm of machine learning-assisted predictions regarding the behavior of these structures under compressive loads. In this way, three key geometric parameters of the repetitive chiral unit cells-thickness, angle, and diameter-are considered as highly influential design factors. Accordingly, a custom method for designing experiments was employed, resulting in achieving 27 totally different sandwich beams. These beam structures were made up of Poly Lactic Acid (PLA) for both their face sheets and cores, employing Fused Deposition Modeling (FDM) printing technology. Subsequently, they underwent compressive loading, where the resulting mechanical responses forming the foundational dataset for training Deep Neural Networks (DNNs). Remarkably, the DNNs were trained utilizing both Bayesian and conjugate gradient algorithms. The outcomes notably demonstrated that DNNs trained with the Bayesian algorithm exhibited superior accuracy in predicting stress-strain responses of the beams. Transitioning to the study's second objective, Response Surface Methodology (RSM) was harnessed to optimize Young's modulus and Specific Energy Absorption (SEA). The application of RSM impressively showcased its robustness in attaining optimal design values for these mechanical properties over the defined range of design parameters. This comprehensive exploration effectively reveals the potential of machine learning predictions and optimization techniques, providing valuable insights into the intricate mechanical behaviors of sandwich structures featuring innovative cores.

Kinetics of Single-Wall Carbon Nanotube Coating Displacement by Single-Stranded DNA Depends on Nanotube Structure.

Time-resolved fluorescence spectroscopy has been used to study the displacement of adsorbed sodium dodecyl sulfate (SDS) from the surface of single-wall carbon nanotubes (SWCNTs) by short strands of single-stranded DNA. Intensity changes in near-infrared emission peaks of various SWCNT structures were analyzed following the addition of six different (GT)n oligomers (n from 3 to 20) to SDS-coated nanotube samples. There is a strong kinetic dependence on the oligomer length, with (GT)3 giving an initial rate more than 300 times greater than that of (GT)20. For shorter oligos in the (GT)n series, we observe an inverse dependence of the displacement rate on the SWCNT diameter, with SDS displaced from (6,5) more than twice as fast as from (8,7). However, this diameter dependence is reversed for oligos with more than six (GT) units. There is also a systematic dependence of the displacement rate on the nanotube chiral angle that is strongest for (GT)5, leading to a factor of ∼3 initial rate difference between (9,1) and (6,5) despite their identical diameters. To account for these findings, we propose a simple two-step kinetic model in which disruption of the original SDS coating is followed by conformational relaxation of ssDNA on the nanotube surface. The relaxation is relatively fast for ssDNA oligos shorter than 12 bp, making the first step rate-determining. Conversely, relaxation of the longer oligomers is slow enough that the second step becomes rate-determining.

(Invited) Kinetics of SWCNT Coating Displacement By ssDNA Depends on SWCNT Structure

Non-covalent hybrids formed by suspending single-wall carbon nanotubes (SWCNTs) in single-stranded DNA (ssDNA) present novel phenomena and suggest potential applications in biomedicine and nanotube sorting. Although the structures of these hybrids have been simulated using molecular dynamics calculations, much more experimental research is needed to understand their properties. In this study, selective interactions between SWCNTs and ssDNA are probed by measuring the kinetics by which ssDNA displaces SDS (sodium dodecyl sulfate) coatings on the nanotube surfaces. We used samples initially suspended in a low concentration of SDS to allow the coating displacement to occur and to suppress formation of free SDS micelles. The displacement process was monitored by time-dependent measurements of SWCNT fluorescence intensities and wavelengths. Our experiments showed very smooth decreases in fluorescence intensity and red-shifts in fluorescence wavelengths during the displacement process. Through a series of measurements, we found that ssDNA sequences with repeated guanine (G) and thymine (T) bases showed systematic patterns in the coating displacement kinetics. One result is that SDS displacement depends strongly on oligo length, with (GT)3 showing an initial rate constant 500 times greater than that of (GT)20. For shorter oligos in the (GT) n series, we observe an inverse dependence of initial rate constant on SWCNT diameter, with SDS displacement from (6,5) more than twice as fast as from (8,7). However, this diameter dependence is not present for (GT) n oligos with n greater than 6. We also find a distinct and systematic dependence of initial rate constant on nanotube chiral angle for (GT)5 and (GT)6. This effect gives a factor of ~3 difference between (9,1) and (6,5) despite their identical diameters. We empirically find these initial rate constants to vary as (SWCNT diameter)-4(cos 3θ)-y with y = -1/2 for (GT)5 and -1 for (GT)6. In addition, the full displacement kinetic traces are well fitted by double exponential kinetics, with rate constants and amplitudes dependent on SWCNT diameter. A two-step kinetic model for the displacement process will be presented to account for these findings.

Conversion of chirality to twisting via sequential one-dimensional and two-dimensional growth of graphene spirals.

The properties of two-dimensional (2D) van der Waals materials can be tuned through nanostructuring or controlled layer stacking, where interlayer hybridization induces exotic electronic states and transport phenomena. Here we describe a viable approach and underlying mechanism for the assisted self-assembly of twisted layer graphene. The process, which can be implemented in standard chemical vapour deposition growth, is best described by analogy to origami and kirigami with paper. It involves the controlled induction of wrinkle formation in single-layer graphene with subsequent wrinkle folding, tearing and re-growth. Inherent to the process is the formation of intertwined graphene spirals and conversion of the chiral angle of 1D wrinkles into a 2D twist angle of a 3D superlattice. The approach can be extended to other foldable 2D materials and facilitates the production of miniaturized electronic components, including capacitors, resistors, inductors and superconductors.

Selective emergence of photoluminescence at telecommunication wavelengths from cyclic perfluoroalkylated carbon nanotubes

Chemical functionalisation of semiconducting single-walled carbon nanotubes (SWNTs) can tune their local band gaps to induce near-infrared (NIR) photoluminescence (PL). However, tuning the PL to telecommunication wavelengths (>1300 nm) remains challenging. The selective emergence of NIR PL at the longest emission wavelength of 1320 nm was successfully achieved in (6,5) SWNTs via cyclic perfluoroalkylation. Chiral separation of the functionalised SWNTs showed that this functionalisation was also effective in SWNTs with five different chiral angles. The local band gap modulation mechanism was also studied using density functional theory calculations, which suggested the effects of the addenda and addition positions on the emergence of the longest-wavelength PL. These findings increase our understanding of the functionalised SWNT structure and methods for controlling the local band gap, which will contribute to the development and application of NIR light-emitting materials with widely extended emission and excitation wavelengths.

Direct growth of single-chiral-angle tungsten disulfide nanotubes using gold nanoparticle catalysts.

Transition metal dichalcogenide (TMD) nanotubes offer a unique platform to explore the properties of TMD materials at the one-dimensional limit. Despite considerable efforts thus far, the direct growth of TMD nanotubes with controllable chirality remains challenging. Here we demonstrate the direct and facile growth of high-quality WS2 and WSe2 nanotubes on Si substrates using catalytic chemical vapour deposition with Au nanoparticles. The Au nanoparticles provide unique accommodation sites for the nucleation of WS2 or WSe2 shells on their surfaces and seed the subsequent growth of nanotubes. We find that the growth mode of nanotubes is sensitive to the temperature. With careful temperature control, we realize ~79% WS2 nanotubes with single chiral angles, with a preference of 30° (~37%) and 0° (~12%). Moreover, we demonstrate how the geometric, electronic and optical properties of the synthesized WS2 nanotubes can be modulated by the chirality. We anticipate that this approach using Au nanoparticles as catalysts will facilitate the growth of TMD nanotubes with controllable chirality and promote the study of their interesting properties and applications.