Vacancy Point Research Articles

Molecular dynamics study of mechanical stability of Ti4C3 MXene subjected to chirality, temperature, strain rate, and point-vacancy for Lithium-ion batteries

Two-dimensional Ti4C3 MXene has recently emerged as a promising electrode for Lithium-ion batteries (LIBs) because of its outstanding ion-transport abilities and high Li-absorbability. This study employed molecular dynamics simulation to explore the mechanical stability of Ti4C3 MXene subjected to various temperatures, strain rates, and vacancy concentrations. A slightly superior tensile strength and elasticity modulus have been observed along zigzag directions, measuring 148.14 GPa and 29.17 GPa, respectively. On the other hand, armchair-oriented Ti4C3 MXene shows a considerably greater fracture strain of 0.259 due to its strain-hardening tendency at lower temperatures. Elevated temperature decreases both fracture strength and fracture strain, which is opposite to the effect of strain rate. Armchair loading has been revealed to be more sensitive to strain rate than its counter direction. Unlike temperature and strain rate, point vacancy significantly deteriorates the elastic modulus of Ti4C3 MXene. Carbon vacancies are more probable than titanium vacancies, which have less formation energy. The atomistic deformation profile supports the predicted values of fracture strain from stress-strain behavior. This in-depth study offers a detailed understanding of the mechanical behavior of Ti4C3 MXene under diverse circumstances, which will aid further experimental study and be beneficial for adopting Ti4C3 as anode materials in LIBs.

Microstructure evolution, dielectric properties, and nonlinear response of Na+-doped CdCu3Ti4O12 ceramics.

In this study, Cd1-x Na x Cu3Ti4O12 (x = 0, 0.02, 0.04, 0.06, and 0.08) ceramics were prepared via a solid-state method. The phase composition, microstructure, and defect characteristics as well as optical, dielectric, and nonlinear properties of the ceramics were systematically studied. A CuO second phase was detected in doped samples. Grain boundary precipitates, Na with a low melting point, and oxygen and cation vacancies together caused the grain size to first increase and then decrease with an increase in the Na+ doping amount. The abundant emerging cation vacancies with an increase in Na+ content led to a decrease in the optical energy band. The sample with x = 0.04 exhibited the highest ε' value (∼35 800) due to its largest grain size. Moreover, it possessed a lower tan δ (∼0.053) at 10 kHz, which was attributed to the multiplication of insulating grain boundaries. The huge dielectric constant originated from Maxwell-Wagner polarization at low frequencies and followed the internal barrier effect model. The lowest tan δ (∼0.037) and optimal nonlinear properties (α = 3.66 and E b = 3.82 kV cm-1) were obtained in the sample with x = 0.08, which were associated with its highest grain boundary resistance and barrier height. Electric modulus data proved that dielectric relaxation at low frequencies was associated with grain boundaries. Dielectric anomalies in the high temperature range were attributed to oxygen vacancies.

Phonon transport in vacancy induced defective stanene/hBN van der Waals heterostructure

In this study, Non-Equilibrium Molecular Dynamics (NEMD) simulation is employed to investigate the phonon thermal conductivity (PTC) of Sn/hBN van der Waals heterostructures with different vacancy-induced defects. We deliberately introduce three types of vacancies in Sn/hBN bilayer point vacancies, bivacancies, and edge vacancies at various concentrations ranging from 0.25% to 2%, to examine their effects on PTC across temperatures from 100 K to 600 K. The key findings of our work are (i) PTC declines monotonically with increasing vacancy concentration for all types of vacancies, with a maximum reduction of ∼62% observed at room temperature compared to its pristine form. (ii) The position of defects has an impact on PTC, with a larger decrease observed when defects are present in the hBN layer and a smaller decrease when defects are in the Sn layer. (iii) The type of vacancy also influences PTC, with point vacancies causing the most substantial reduction, followed by bivacancies, and edge vacancies having the least effect. A 2% defect concentration results in a ∼62% decrease in PTC for point vacancies, ∼51% for bivacancies, and ∼32% for edge vacancies. (iv) Finally, our results indicate that for a given defect concentration, PTC decreases as temperature increases. The impact of temperature on thermal conductivity is less pronounced compared to the effect of vacancies for the defective Sn/hBN bilayer. The presence of vacancies and elevated temperatures enhance phonon-defect and phonon–phonon scattering, leading to changes in the phonon density of states (PDOS) profile and the distribution of phonons across different frequencies of Sn/hBN bilayer, thus affecting its thermal conductivity. This work offers new insights into the thermal behavior of vacancy-filled Sn/hBN heterostructures, suggesting potential pathways for modulating thermal conductivity in bilayer van der Waals heterostructures for applications in thermoelectric, optoelectronics, and nanoelectronics in future.

Effects of vacancy defects on the electronic, mechanical, and optical properties of penta-B2C4

The synthesis of two-dimensional (2D) pentagonal structures has sparked interest in further research on this class of materials. Here, the effects of intrinsic point vacancy defects on the electronic, mechanical, and optical properties of Penta-B2C4 were systematically investigated. The research indicates that three types of point vacancy defects (VB, VC and VBC) cause varying degrees of upward shift in the Fermi level of Penta-B2C4, ultimately leading to its transformation from p-type semiconductor to n-type semiconductor. The VB defect disrupts the mechanical stability of Penta-B2C4 while VC and VBC defects still maintain excellent mechanical properties, exhibiting flexibility even superior to graphene. The three vacancy defects also improve the visible optical absorption properties of Penta-B2C4, but the reflectance and refractive index in the same environment decrease. The research findings provide theoretical support for the application of Penta-B2C4 in flexible devices, mechanical engineering, and optoelectronic devices.

Numerical characterization of thermal transport in hexagonal tungsten disulfide (WS2) nanoribbons

In this study, we have investigated the thermal transport characteristics of single-layer tungsten disulfide, WS2 nanoribbons (SLTDSNRs) using equilibrium molecular dynamics simulations with the help of Green-Kubo formulation. Using Stillinger-Weber (SW) inter-atomic potential, the calculated room temperature thermal conductivities of 15 nm × 4 nm pristine zigzag and armchair SLTDSNRs are 126 ± 10 W m−1K−1 and 110 ± 6 W m−1K−1, respectively. We have explored the dependency of thermal conductivity on temperature, width, and length of the nanoribbon. The study shows that the thermal conductivity of the nanoribbon decreases with the increase in temperature, whereas the thermal conductivity increases with an increase in either the width or length of the ribbon. The thermal conductivity does not increase uniformly as the size of the ribbon changes. We have also observed that the thermal conductivity of SLTDSNRs depends on edge orientations; the zigzag nanoribbon has greater thermal conductivity than the armchair nanoribbon, regardless of temperature or dimension variations. Our study additionally delves into the tunable thermal properties of SLTDSNRs by incorporating defects, namely vacancies such as point vacancy, edge vacancy, and bi-vacancy. The thermal conductivities of nanoribbons with defects have been found to be considerably lower than their pristine counterparts, which aid in enhanced values for the thermoelectric figure of merit (zT). We have varied the vacancy concentration within a range of 0.1% to 0.9% and found that a point vacancy concentration of 0.1% leads to a 64% reduction in the thermal conductivity of SLTDSNRs. To elucidate these phenomena, we have calculated the phonon density of states for WS2 under different aspects. The findings of our work provide important understandings of the prospective applications of WS2 in nanoelectronic and thermoelectric devices by tailoring the thermal transport properties of WS2 nanoribbons.

Defect Engineering of MoTe2 via Thiol Treatment for Type III van der Waals Heterojunction Phototransistor.

Molybdenum ditelluride (MoTe2) nanosheets have displayed intriguing physicochemical properties and opto-electric characteristics as a result of their tunable and small band gap (Eg ∼ 1 eV), facilitating concurrent electron and hole transport. Despite the numerous efforts devoted to the development of p-type MoTe2 field-effect transistors (FETs), the presence of tellurium (Te) point vacancies has caused serious reliability issues. Here, we overcome this major limitation by treating the MoTe2 surface with thiolated molecules to heal Te vacancies. Comprehensive materials and electrical characterizations provided unambiguous evidence for the efficient chemisorption of butanethiol. Our thiol-treated MoTe2 FET exhibited a 10-fold increase in hole current and a positive threshold voltage shift of 25 V, indicative of efficient hole carrier doping. We demonstrated that our powerful molecular engineering strategy can be extended to the controlled formation of van der Waals heterostructures by developing an n-SnS2/thiol-MoTe2 junction FET (thiol-JFET). Notably, the thiol-JFET exhibited a significant negative photoresponse with a responsivity of 50 A W-1 and a fast response time of 80 ms based on band-to-band tunneling. More interestingly, the thiol-JFET displayed a gate tunable trimodal photodetection comprising two photoactive modes (positive and negative photoresponse) and one photoinactive mode. These findings underscore the potential of molecular engineering approaches in enhancing the performance and functionality of MoTe2-based nanodevices as key components in advanced 2D-based optoelectronics.

Thermal transport characterization of monolayer GaN nanoribbon doped with group IV materials: An equilibrium molecular dynamics study

Bulk gallium nitride (GaN) has been considered as one of the prominent materials for a long time in the application of laser, LED and transistors. Due to its superior electrical characteristics, its low-dimensional hexagonal counterpart is currently drawing attention like graphene. In this study, we have investigated the effect of impurity atoms on the heat energy conduction within this honeycomb nanostructure of GaN to explore its scope of applications. The room temperature thermal conductivity of zigzag GaN nanoribbon (ZGaNNR) is found to be ∼ 11 Wm−1K−1 using the molecular dynamics approach with the Green-Kubo formulation. Various group IV elements namely- carbon, silicon, germanium and tin, have been incorporated within the pristine structure in four distinct doping patterns; like- point (Type-I and Type-II), pair and delta doping, to explore the thermal transport in chemically doped nanostructures. A gradual enhancement in the thermal conductivity is observed for the increasing concentration of carbon and silicon as dopants. On the other hand, selection of germanium and tin as impurity atoms suppresses the heat conduction within the crystal due to the increased low frequency phonon scattering. In all cases, Type-I point doping affects the thermal transport of ZGaNNR significantly. The narrower ribbons impede the phonon transportation due to the strong boundary effects resulting in a lower thermal conductivity. Moreover, phonon transportation is largely suppressed, and heat energy is observed to flow at a slower rate as the temperature of the ribbon rises. We have also studied these doped structures under the influence of point, edge and pair vacancies and observed a decreasing trend in thermal conductivity for each type of vacancy defect patterns introduced in the crystal. Such a study would promote the rising interest in properly characterizing the heat transport of low dimensional nanostructures and it can be an effective technique to tune the thermal conductivity of ZGaNNR for improving thermoelectric performance and thermal management in nanoscale devices.

Atomistic simulation of the mechanical behaviors of the pristine and vacancy-induced Ti2C MXene: Effect of temperature, strain rate, and chirality

In context with growing concerns regarding mechanical damage in nanoelectromechanical systems (NEMS) and energy devices, this study implemented atomistic molecular dynamics simulation to examine the mechanical performance of Ti2C MXene, a high prospectus material in the field of NEMS and energy technologies. Bond-order Tersoff potential was employed to assess the distinction in the mechanical performance of pristine and vacancy-induced Ti2C depending on different physiological conditions, including temperature, loading rate, and chirality. A competitive elastic modulus of 130.72 GPa and 129.12 GPa has been determined along the armchair and zigzag chirality. However, tensile strength along armchair chirality was found to be 30.52 GPa, 21.4% greater than its contrary direction, whereas zigzag chirality withstands 13.55% greater strain at failure than the armchair chirality, measuring 0.273. Superior tensile strength is observed in armchair chirality, whereas zigzag chirality withstands more significant strain at failure. Mechanical attributes show declining trends as the temperature rises; however, the trend is upward while loading happens rapidly. Both carbon and titanium point vacancies degrade mechanical characteristics individually, but the conjugal influence of temperature and point vacancy makes the deterioration more severe. Carbon, the central constituent element, was found to be more significant in the functionality of Ti2C MXene. Therefore, carbon vacancy shows higher formation energy and more significant deterioration in mechanical performance than titanium vacancy. This exhaustive investigation will significantly aid in the safe design of MXene-based nanoelectromechanical devices and catalyze further experimental research on the same layered materials.

First-principles study on the electronic, magnetic and optical properties of the novel squared SN2 monolayer with 3d transition metal doping and point vacancy

The SN2 monolayer with a square lattice (S-SN2) is a non-magnetic semiconductor. The lack of magnetism and the weak light absorption severely limit its further applications in spintronic and optoelectronic devices. Herein, we investigate the effects of 3d transition metal (Fe, Co and Ni) substitution doping and point vacancy engineering on the S-SN2 monolayer using first-principles calculations. The negative binding energies and the AIMD simulations indicate that all doped cases exhibit excellent structural stability. After doping, the diverse properties including ferromagnetic spin semiconducting behavior, non-magnetic semiconducting property, and significant ferromagnetic half-metallic character with 100 % spin polarization can be realized among these doped S-SN2 monolayers. Interestingly, the value of work function for S-SN2 monolayer can be regulated by doping from 6.55 eV for pure S-SN2 monolayer to a range of 5.11–6.89 eV for doped systems. Moreover, the visible light absorption of S-SN2 monolayer can be significantly enhanced by Fe doping, reaching a high value of about 1.2×105 cm−1. Additionally, a non-magnetic metal and a ferromagnetic half-metallic character with a large total magnetic moment of 5.93 μB can be induced in S-SN2 monolayer with a single N and S vacancy, respectively.

Electronic properties of SiC nanoribbon

The electronic properties of zigzag and armchair SiC nanoribbons are studied using a theoretical method. The spin-unrestricted electronic behavior of an armchair and zigzag SiC nanoribbon containing Si and C vacancy in the supercell was investigated. Spin-polarized electronic structure calculations show that armchair SiC nanoribbon was classified as a nonmagnetic semiconductor while zigzag SiC nanoribbon presents a half-metallic electronic structure. Our results suggest that SiC nanoribbon containing point vacancy may be a good candidate for spintronics due to its half-metal properties.

Mechanical Behaviors of the Single Crystal Two-Dimensional Silicon Carbide (SiC): A Molecular Dynamics Insight

This paper focuses on the two-dimensional silicon carbide (2D-SiC), which has an excellent opportunity to be used as an alternative to graphene in nanotechnologies such as in nanoelectronics, nanoelectromechanical systems (NEMS), nano-sensors, nano-energy harvesting devices, and nano-composites due to its unique structural, mechanical, electronic, and thermal properties. Their mechanical properties characterize the stability of the nanodevices. This study performs molecular dynamics (MD) simulation to examine the mechanical properties based on optimized Tersoff potential of the single crystal 2D-SiC at different temperatures, strain rates, point vacancies, and edge cracks. At room temperature (300 K), the obtained elastic modulus and fracture strength are 423 GPa and 68.89 GPa, respectively, along the armchair direction. As the temperature rises from 100 K to 800 K, the fracture stress falls by 21.96% and the fracture strain by 36.90%. An approximate linear reduction in fracture strength is noticed as the temperature rises from 100 K to 800 K. The elastic modulus also falls as the temperature rises but is not significant. Although the elastic modulus is unchanged, the fracture stress increases by 1.84% while the fracture strain increases by 5.84% for a change in strain rate from 0.0001 ps-1 to 0.005 ps-1. The fracture stress and strain are significantly reduced, primarily due to the edge crack, as the concentration of point vacancy grows from 0.1% to 0.6% and the edge crack size increases from 0.5 nm to 1.5 nm. Moreover, anisotropic behavior is also evaluated at 300 K temperature and 0.001 ps-1 strain rate. These findings would offer a deep understanding of the fracture mechanics of 2D-SiC and also help to address the mechanical instability issue with SiC-based nanodevices.

Comprehensive understanding on phosphorus precipitation in heavily phosphorus-doped Czochralski silicon

Heavily phosphorus-doped Czochralski (HP-CZ) silicon is an important substrate material for manufacturing power electronic devices. The high concentration of phosphorus impurities may be supersaturated during the crystal growth of HP-CZ silicon or device manufacturing. Thus, understanding phosphorus precipitation in HP-CZ silicon is of technological significance. Herein, a panoramic view of phosphorus precipitation in HP-CZ silicon is presented in terms of crystallography, thermodynamics, and kinetics. It is found that the orthorhombic SiP precipitates can form during the crystal growth of HP-CZ silicon and also during the post-anneals of HP-CZ silicon at 450–1050 °C. Along with increasing annealing temperature, the formed SiP precipitates tend to adopt the platelet, polyhedron, and sphere-like shapes. Moreover, the excess point defects, i.e., silicon self-interstitials and vacancies, are found to affect phosphorus precipitation occurring in the low and high temperature regimes in different ways. In light of the kinetics of phosphorus precipitation at different temperatures, it is deduced that phosphorus precipitation follows a growth law in compliant with Ham's theory to a large extent. As an important output of this work, the temperature-dependent phosphorus solubilities in the dislocation-free silicon, which have been hardly acquired previously, are derived on the basis of investigating phosphorus precipitation in a set of HP-CZ silicon wafers with different phosphorus concentrations. Moreover, the derived solvus line for the phosphorus impurities in silicon could be a beneficial supplement to the existing phase diagram of the Si–P binary system in the extremely silicon-rich corner.

First‐Principles Study of the Influences of Point Vacancies (VGa, Hi) on the Photocatalytic and Magnetic Performance of Ga2O3:Li/Na/K Systems

Under vacuum environment, an H interstitial must exist when Ga2O3 is prepared by organometallic chemical vapor deposition. However, few first‐principles systematic studies have been conducted on the influences of point vacancies (VGa, Hi) on the photocatalytic performance and magnetism of Ga2O3:(Li or Na or K) systems, and VGa is a challenge in experiments. Therefore, the first‐principles generalized gradient approximation GGA + U theory is adopted in this study. A first‐principles study is conducted on the formation energy (E f), photocatalytic performance, and magnetism of Ga30MO48 (M = Li or Na or K) and Ga30MHiO48 systems. In the results, it is shown that under Ga‐poor conditions, the Ga30MO48 and Ga30MHiO48 systems are structurally stable and prone to doping. The Ga30MHiO48 system has lower E f, more structural stability, and easier doping than the Ga30MO48 system. The Ga30KO48 system exhibits magnetism, mainly generated by the O1−‐2p spin‐polarized wandering electrons near VGa. The spin‐polarized O2−‐2p and Ga‐4s states near VGa contribute to the hybrid coupling double‐exchange interaction. Moreover, the visible spectrum of the Ga30LiHiO48 system exhibits a significant redshift, a relatively high carrier activity, carrier separation, and relative maximum lifetime. It is relatively best as a photocatalyst.

Temperature, strain rate, and point vacancy dependent anisotropic mechanical behaviors of titanium carbide (Ti3C2) MXene: A molecular dynamics study

MXenes, one of the recognizable examples of modern 2D materials, are sparking tremendous research interest because of their distinctive structural, electrical, and electrochemical properties. This study utilized classical molecular dynamics simulation to investigate temperature, strain rate, and point vacancy-dependent mechanical behaviors for both armchair and zigzag orientations of the Ti3C2 MXene using Tersoff style bond order potential. The elastic modulus of ∼155.76 GPa and fracture strain of ∼0.263 were obtained along the zigzag direction at 300 K temperature, 5.58 % and 28.29 % greater than those obtained along the armchair alignment. However, a superior tensile strength of ∼34.08 GPa was observed along the armchair orientation as opposed to ∼29.08 GPa in the zigzag direction at 300 K temperature. As the temperature rises, it was observed that fracture strength and strain both exhibit a decreasing tendency, whereas increments in strain rates cause an increasing trend. However, we observed that temperature and strain rates barely affect the elastic modulus, which agrees with the literature data. Radial distribution functions were calculated for all pair interactions to make the temperature effect more comprehensible. It was demonstrated that C, Ti, and random point vacancies have significant adverse effects on elastic modulus, fracture strength, and failure strain because of their powerful symmetry-breaking effect. With increasing concentrations of any point vacancies, rapidly declining elastic modulus, fracture strength, and failure strain were perceived. Titanium vacancies were observed to have a more significant influence on mechanical behavior, even though carbon vacancies were more likely to develop with less formation energy. The outcomes of this work deliver a clear overview of the mechanical behavior of Ti3C2 in various aspects of the environment and will shed light on the potential implementation in electrochemical sensing or energy devices.

Total Structure, Electronic Structure and Catalytic Hydrogenation Activity of Metal-Deficient Chiral Polyhydride Cu57 Nanoclusters.

Accurate identifying and in-depth understanding of the defect sites in a working nanomaterial could hinge on establishing specific defect-activity relationships. Yet, atomically precise coinage-metal nanoclusters (NCs) possessing surface vacancy defects are scarce primarily owing to challenges in the synthesis and isolation of such defective NCs. We report a mixed-ligand strategy to synthesizing an intrinsically chiral and metal-deficient copper hydride-rich NC [Cu57H20(PET)36(TPP)4]+ (Cu57H20). Its total structure (including hydrides) and electronic structure are established by combined experimental and computational results. Crystal structure reveals Cu57H20 features a cube-like Cu8 kernel embedded in a corner-missing metal-ligand shell of Cu49(PET)36(TPP)4. Single Cu vacancy defect occurs at one corner of the shell, evocative of mono-lacunary polyoxometalates. Theoretical calculations demonstrate that the above-mentioned point vacancy causes one surface hydride exposed as an interfacial capping μ3-H-, which is accessible in chemical reaction, as proved by deuterated experiment. Moreover, Cu57H20 shows catalytic activity in the hydrogenation of nitroarene. The success of this work opens the way for the research on well-defined chiral metal-deficient Cu and other metal NCs, including exploring their application in asymmetrical catalysis.

Total Structure, Electronic Structure and Catalytic Hydrogenation Activity of Metal‐Deficient Chiral Polyhydride Cu57 Nanoclusters

AbstractAccurate identifying and in‐depth understanding of the defect sites in a working nanomaterial could hinge on establishing specific defect‐activity relationships. Yet, atomically precise coinage‐metal nanoclusters (NCs) possessing surface vacancy defects are scarce primarily owing to challenges in the synthesis and isolation of such defective NCs. Herein we report a mixed‐ligand strategy to synthesizing an intrinsically chiral and metal‐deficient copper hydride‐rich NC [Cu57H20(PET)36(TPP)4]+ (Cu57H20). Its total structure (including hydrides) and electronic structure are well established by combined experimental and computational results. Crystal structure reveals Cu57H20 features a cube‐like Cu8 kernel embedded in a corner‐missing metal‐ligand shell of Cu49(PET)36(TPP)4. Single Cu vacancy defect site occurs at one corner of the shell, evocative of mono‐lacunary polyoxometalates. Theoretical calculations demonstrate that the above‐mentioned point vacancy causes one surface hydride exposed as an interfacial capping μ3‐H−, which is accessible in chemical reaction, as proved by deuterated experiment. Moreover, Cu57H20 shows catalytic activity in the hydrogenation of nitroarene. The success of this work opens the way for the research on well‐defined chiral metal‐deficient Cu and other metal NCs, including exploring their application in asymmetrical catalysis.

The effect of antisite defects on the mechanical and dynamic stability of Nb3Al

The A15-type conventional superconductor Nb3Al alloys has been considered as an ideal candidate for next generation high field magnets due to its higher superconducting properties and less sensitivity to stain than that of industrialized Nb3Sn superconductor. First-principles methods are employed to study the potential point defects, vacancy and antisite defects in deviating stoichiometric Nb3Al alloys and their effect on structure and mechanical properties. Our results show that antisite defects are easier to be produced than vacancy defects, and Nb antisite defects can keep the tetragonal structure of Nb3Al. Furthermore, the influence of antisite defects on dynamic stability of Nb3Al is investigated together with Nb defects. With the increase of Nb antisite defect content and the formation of orderly arrangement, we found the phonon spectrum yields no more soft phonon modes, which is in contradiction with the dynamical instability of stoichiometric Nb3Al with no defects. Our calculations indicate Nb antisite defects play a crucial role on the dynamic stability of Nb3Al compounds.

Dynamic properties of nanoresonators based on three-walled carbon nanotubes and influence of atomic vacancies and pin hole defects

The presence of point vacancies and pin holes are the most common flaws found in the lattice structure of carbon nanotubes (CNTs). Additionally, impact of mention defects on the vibrational properties of three-walled carbon nanotubes (TWCNTs) remains unknown. Aim of study, to address these gaps by introducing a novel method for identifying defects in TWCNTs through vibrational analysis. The research employed a molecular structural mechanics technique to simulate 648 samples of TWCNTs, followed by finite element studies to determine their modes of vibration. The natural frequency of the basic vibration of flawed TWCNTs was then determined. It was observed that the natural frequency is inversely proportional to (i) the number of point vacancies and (ii) the diameter of the TWCNTs. Furthermore, the natural frequency exhibited an exponential increase after reaching a mass of 10−20gm in armchair and zigzag TWCNTs, while in chiral TWCNTs, the exponential increase occurred after reaching a mass of10−19gm. Notably, in TWCNTs with 0% and 0.5% vacancy defects, the natural frequency results were very close for chiral TWCNTs when compared to zigzag and armchair TWCNTs.

Hexagonal Boron Nitride/Reduced Graphene Oxide Heterostructures as Promising Metal‐Free Electrocatalysts for Oxygen Evolution Reaction Driven by Boron Radicals

Developing highly efficient earth‐abundant alternatives to traditional noble metal catalysts is essential for clean and sustainable energy‐conversion and energy‐storage technologies, yet still challenging in limited active sites and weak resistance to electrochemical corrosion. Herein, density‐functional theory calculations demonstrate that hexagonal boron nitride (h‐BN), albeit often being considered inert, can generate boron‐active radicals at defective sites by forming heterogeneous structures with graphene‐containing point vacancies, leading to a substantial electron delocalization and charge transfer, indicating a superior catalytic activity. Experimentally, the van der Waals heterostructure is rationally designed with h‐BN nanosheets (BNNs) anchored on reduced graphene oxide (rGO) as strongly coupled composite catalysts. Despite the poor conductivity in BN and lower catalytic activity in rGO, the created heterostructures demonstrate unexpected, improved oxygen evolution reaction (OER) activity with excellent stability in alkaline electrolyte. Qualitative analysis of the valence band offset and theoretical calculation reveal that the formation of heterostructures can significantly drive the electron transfer between C and B atoms near the vacancies across the interface and cause a half‐metallic property of BN, decreasing the free energy barrier of four‐electron OER kinetics. Herein, the synthetic schemes of h‐BNNs are guided as highly active metal‐free OER electrocatalysts.

Impact of point vacancy defects on vibrational behaviour of three-walled carbon nanotubes.

Through experimental observations and reports, various challenges have been identified in carbon nanotubes (CNT), including Stone Wales (SW) flaws and position flaws. Among these imperfections, point vacancies are the most prevalent in the CNT lattice. However, there is currently no established method for detecting these issues, and the influence of these flaws on the vibrational properties of three-walled carbon nanotubes (TWCNTs) remains uncertain. This research paper introduces a novel approach that utilizes vibrational analysis to detect flaws in TWCNTs. By conducting the first investigation into the impact of point vacancies on the vibrational modal frequencies of TWCNTs, our study bridges these knowledge gaps. This study examines the impact of defect quantity on various types of TWCNTs and investigates the vibrational properties of TWCNTs with point vacancies using a molecular structural mechanics technique. A total of 432 TWCNT models were simulated using molecular structural mechanics (MSM), and their modes were identified through finite element (FE) analysis. The fundamental vibration's natural frequency in TWCNTs with defects was then determined. The findings indicate that the depth of the mode shape is influenced by the TWCNTs' diameter, the extent of point vacancy defects, and the boundary condition. It was observed that as the number of vacancy defects increases from 0 to 4%, the natural frequency decreases. The study also establishes the order of TWCNTs with the highest natural vibrational frequency at 0%-point vacancy and [Formula: see text] a given attached mass, which follows the sequence of chiral, armchair, and zigzag TWCNTs.