Stone-Wales Research Articles

Investigation of interfacial thermal resistance of hybrid graphene/hexagonal boron nitride

Hybrid graphene/hexagonal boron-nitride (G/h-BN) has shown significant physical properties and has been fabricated recently. Structural defects, such as Stone–Wales (SW) and vacancy, unavoidably exist in the interface of hybrid G/h-BN during the growth process. In this study, the interfacial thermal resistance (ITR) of armchair and zigzag hybrid G/h-BN with vacancy and SW defects is systematically investigated, using molecular dynamics (MD) simulations. Our results indicate that armchair edge hybrid G/h-BN possesses higher normalized ITR than the zigzag one. In addition, vacancy and SW defects introduced important influences on the ITR of hybrid G/h-BN. The ITR of hybrid G/h-BN is studied with two distinct sections. In the first section, various types of atoms, such as C, N and B, vacancy defects located throughout the interface of armchair and zigzag hybrid G/h-BN are studied. Our MD simulations results show that when the number of vacancy defect is increased, the effect of C atom vacancy defect on the normalized ITR of hybrid G/h-BN is higher than other atoms. On the other hand, the influence of B atom vacancy defect on the normalized ITR is lowest. In the second section, CC and BN types of SW defects positioned along the interface of armchair and zigzag hybrid G/h-BN are investigated. The results of this study demonstrate that CC type of SW defect shows higher normalized ITR than BN type one by increasing the SW number of defects. The obtained results in this study may open new insights for potential applications of thermal transport and control for the hybrid G/h-BN type structures.

Electronic properties of Aluminum Doped Carbon Nanotubes with Stone Wales Defects: Density Functional Theory -=SUP=-*-=/SUP=-

AbstractAl-doped single wall carbon nanotube with Stone Wales defect was theoretically analyzed, two different orientations of chiral (8, 4) carbon nanotubes was doped among the joints of defective carbon rings. Density functional theory was implemented to study structural and electronic properties of Al-doped chiral carbon nanotubes. Doping bond lengths as well as their geometrical structure were determined at the different orientations. The electronic properties were also illustrated by evaluation band of the gap energies at each possible doping site. Our results indicated that not only Al-doping tune the band structure, but also dopant site played a crucial rule on manipulating physical properties of chiral carbon nanotubes.

Tuning the electronic and magnetic properties of antimonene nanosheets via point defects and external fields: first-principles calculations.

Defects are inevitably present in materials, and their existence in a material strongly affects its fundamental physical properties. We have systematically investigated the effects of surface adsorption, substitutional impurities, defect engineering, an electric field and strain engineering on the structural, electronic and magnetic properties of antimonene nanosheets, using spin-polarized density functional calculations based on first-principles. The adsorption or substitution of atoms can locally modify the atomic and electronic structures as well as induce a variety of electronic behaviors including metal, half-metal, ferromagnetic metal, dilute magnetic semiconductor and spin-glass semiconductor. Our calculations show that the presence of typical defects (vacancies and Stone-Wales defect) in antimonene affects the geometrical symmetry as well as the band gap in the electronic band structure and induces magnetism to antimonene. Moreover, by applying an external electric field and strain (uniaxial and biaxial), the electronic structure of antimonene can be easily modified. The calculation results presented in this paper provide a fundamental insight into the tunable nature of the electronic properties of antimonene, supporting its promise for use in future applications.

Effect of Stone-Wales defects and transition-metal dopants on arsenene: a DFT study.

The structural, electronic, and magnetic properties of 3d transition metal (TM) atom (Sc, V, Cr, Mn, Co, and Cu) doped Stone–Wales (SW) defect arsenene were systematically investigated by density functional theory (DFT). The results indicated that the properties of arsenene were effectively changed by the SW-defect and TM-doping. Furthermore, chemical bonds formed between the TM-dopants and the adjacent As atoms of the SW-defect. The dopants Sc, Mn, and Cu induced an indirect-to-direct bandgap transition, and the doping of V, Cr, and Mn in SW-defect arsenene exhibited magnetic states. The magnetic moments of the systems depended on the number of spin-localized valence electrons. The functionalized electronic and magnetic properties of arsenene highlight the applications for electronics, optoelectronics, and spintronics.

Synergy of tellurium and defects in control of activity of phosphorene for oxygen evolution and reduction reactions.

Developing low-cost and metal-free electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is desirable for renewable energy technologies. Recent experiments show that tellurium (Te) atoms can be effectively doped into black phosphorus (BP) nanosheets, and they greatly improve its OER catalytic performance. However, the specific active sites and microscopic configurations in the atomic-scale are still ambiguous. Here, we show that the doped Te atoms prefer to bond with each other to form clusters in phosphorene and they can be further stabilized by various intrinsic defects (Stone-Wales, single vacancy defects and zigzag nanoribbon). Benefiting from the reduced binding strength of O*, Te dopants and intrinsic defects synergistically boost the catalytic activity of phosphorene. The best OER catalytic activity could be realized in the cluster SW2-Te1p (Stone-Wales defect decorated by one Te atom). For ORR, the cluster Pri-Te3p (pristine phosphorene decorated by three Te atoms) exhibits optimal catalytic activity. Calculated ORR/OER potential gaps indicate that the SW2-Te3p cluster most likely acts as the efficient bifunctional catalytic site for both ORR and OER.

Effect and Characterization of Stone–Wales Defects on Graphene Quantum Dot: A First-Principles Study

A first principles based density functional theory (DFT) has been employed to identify the signature of Stone–Wales (SW) defects in semiconducting graphene quantum dot (GQD). Results show that the G mode in the Raman spectra of GQD has been red shifted to 1544.21 cm − 1 in the presence of 2.08% SW defect concentration. In addition, the intensity ratio between a robust low intense contraction–elongation mode and G mode is found to be reduced for the defected structure. We have also observed a Raman mode at 1674.04 cm − 1 due to the solo contribution of the defected bond. The increase in defect concentration, however, reduces the stability of the structures. As a consequence, the systems undergo structural buckling due to the presence of SW defect generated additional stresses. We have further explored that the 1615.45 cm − 1 Raman mode and 1619.29 cm − 1 infra-red mode are due to the collective stretching of two distinct SW defects separated at a distance 7.98 Å. Therefore, this is the smallest separation between the SW defects for their distinct existence. The pristine structure possesses maximum electrical conductivity and the same reduces to 0.37 times for 2.08% SW defect. On the other hand, the work function is reduced in the presence of defects except for the structure with SW defects separated at 7.98 Å. All these results will serve as an important reference to facilitate the potential applications of GQD based nano-devices with inherent topological SW defects.

Defects guided wrinkling in graphene on copper substrate

Pristine graphene depositing on metallic substrates often wrinkles when the film-substrate system undergoes a temperature drop from the chemical vapor deposition (CVD) chamber to ambient environment. The pattern of wrinkles is governed by the crystallographic planes of the substrates and the defects in the film. In this paper, we report how commonly seen Stone-Wales defects and grain boundaries (GBs) influence the morphology of graphene on different planes of single crystalline copper substrate. Stone-Wales defects weaken the bending stiffness in graphene, and result in wrinkling along the defect direction. In the presence of GBs, primary wrinkles are always parallel to the GB direction, and there are also secondary wrinkles perpendicular to the GB. In combination with planes of the substrate and the orientation of defects, we demonstrate that we may manipulate wrinkling patterns for possible engineering applications.

Bandgap opening in graphene using alkali ions by first principles

Recently, bandgap opening at the Dirac point in graphene, formed on SiC(0001) surfaces, has been reported in different experiments, by deposition of positively charged alkali ions. This is clearly of great relevance for the countless practical applications of graphene in nano-electronic devices. By first principles calculations, based on the Density Functional Theory, the electronic band structure and the energetic properties are obtained for Na+, K+, and Cs+ ions interacting with graphene on SiC. We show that simple adsorption of alkali ions on intact graphene cannot give rise to a significant energy gap. An appreciable bandgap opening, similar to that observed in actual experiments, occurs instead due to the formation of Stone-Wales defects and substitutional defects (where positively charged alkali ions replace carbon atoms) that lead to a significant breaking of the charge symmetry among the carbon atoms of pristine graphene.

Tuning Electronic Transport Properties of Zigzag Graphene Nanoribbons with Stone-Wales Defect

Influences of the symmetric Stone-Wales (SW) defect on the electronic transport properties of the zigzag graphene nanoribbons (ZGNRs) has been studied using $\it{ab}$ $\it{ initio}$ simulation based on density functional theory (DFT) combined with non-equilibrium Green's function (NEGF) technique. The calculated transmission spectra T(E) at various bias windows, device densities of states (DDOS), current characteristics as well as local density of states (LDOS) of the defective asymmetric and symmetric ZGNRs are presented in comparison of those for the pristine ZGNRs. It has been established the metallic character of the electronic transport in asymmetric ZGNRs, and in symmetric ones, the current has a semiconductor behavior, with negative differential resistance (NDR) effect. Symmetric SW defect, as a most unfavorable SW defect type for electric conductance, remarkably decreases the current values, but does not change the character of conductivity in both the asymmetric and symmetric ZGNRs. NDR has been explained by the altering by SW defect the number of frontier molecular orbitals entering bias windows.

Oxidation effect on the shear strength of graphene on aluminum and titanium surfaces

We report the interfacial shear strength of graphene on pure and oxidized Ti and Al metal surfaces using density functional theory calculations. Our results show significant changes to the graphene-metal bonding properties in the presence of an oxide phase. In particular, the strongly chemisorbed interface between graphene and pure Ti is drastically weakened by the formation of a metal-oxide phase, while the weakly physisorbed interface between graphene and pure Al is significantly strengthened through the metal oxide formation. These oxidation effects can be modulated to some extent by the presence of vacancy or Stone-Wales defects which increases the binding interactions of weaker graphene-metal interfaces. These dramatic changes to the interfacial properties by surface oxidation explain the results of recent carbon nanotube pull-out experiments from Al and Ti metal-matrix nanocomposites.

Effect of Center Crack on Mechanical Properties of Graphene

Graphene is a thin sheet with special properties and complicated mechanical behavior. It’s important to study graphene experimentally and theoretically. Stone–Wales defects, cracks and atom vacancy are popular defects in carbon allotropes especially in graphene. In this paper, effect of center cracks on graphene was discussed. At first, mechanical properties of non-defected graphene sheet was obtained using molecular dynamics simulation. Comparing result with theoretical and experimental studies showing good agreements and proofing the results. Then, 8 different cracks were considered in center of graphene sheets. Stress-strain curves of defected graphene sheets with different tension strain rates were plotted. The results showed that increasing crack length lead to decreasing Young’s modulus of graphene from 870GPa to 670GPa. Also, fracture occurred in less tensile strain. In the following, structural molecular mechanics method was used to simulate cracked graphene sheets. The results showed good agreement between two methods.

Atomistic insights into mechanical and thermal properties of stanene with defects

Stanene, two-dimensional, graphene-like buckled honeycomb structure, has been deemed as a potential material for the next generation nano-electronics application. In electronic applications, the materials are subjected to both thermal and mechanical loadings. In addition, structural defects are inevitable during synthesis of nanomaterials. Therefore, it is essential to study the mechanical and thermal properties of stanene with various structural defects. We investigated the effects of point vacancy, bivacancy and Stone-Wales defects on tensile response and thermal transport of single-layer bulk stanene sheets using classical molecular dynamics (MD) simulations. MEAM potential is used to describe the inter-atomic forces in order to predict the properties of the stanene adequately. We probed the deformation process of defective bulk stanene by applying uniaxial tensile loading. Our study suggests that tensile strength and elastic modulus of stanene decrease with the increment of defect concentrations. Moreover, stanene sheet with Stone-Wales defect shows less in-plane stiffness to the loading. Using non-equilibrium molecular dynamics (NEMD) method, we found that, the phonon thermal conductivity of stanene is highly sensitive to defect concentrations. Only 0.1% of defect concentrations result in about 40% reduction in thermal conductivity. To elucidate the underlying mechanism responsible for this reduction, vibrational density of states (vDOS) are calculated. Overall, our reported results provide an insight into the effect of defects in mechanical and thermal properties of defective bulk stanene and will facilitate further tailoring of the design of stanene based nanoelectronics device.

Attachment of CO to a (6, 6) CNT with a Sc adsorbate atom

We have comparatively investigated the adsorption behaviors of Sc atom on the external and internal surfaces of the pristine, Stone-Wales (SW), and single-vacancy (SV) defect nanotubes based on the density functional theory. Our results reveal that the stability of Sc atom onto the external and internal surfaces of the carbon nanotubes is in following orders by defect: SV>SW1>SW2>pristine (external surfaces), SV>SW2>SW1>pristine (internal surfaces). To explore the reactivity of Sc@CNT/SW/SV complexes which can serve as a gas sensor or a catalyst in direct methanol fuel cell (DMFC), the interaction between a CO molecule and Sc@CNT/SW/SV is also examined. The SV defect in carbon nanotubes can make the confined Sc atom with good CO adsorption property, while the confined Sc in the SW defect carbon nanotube has good anti-CO poisoning. By our studies, it plays an important guidance role in improving the activity of metal catalyst and the sensitivity and stability of metal particles to functional molecules, and provides the theoretical basis for designing new carbon nanotube-based metal catalyst.

Residual strain in graphene: study of temperature and crack effect

Graphene is a thin sheet with special properties and complicated mechanical behavior. It’s important to study graphene experimentally and theoretically. Stone–Wales defects, cracks and atom vacancy are popular defects in carbon allotropes especially in graphene. In this paper, residual strain in graphene was discussed. At first, stress-strain curve of non-defected graphene sheet was obtained using molecular dynamics simulation and effect of temperature on mechanical properties of graphene was obtained. Then, four different cracks were considered in center of graphene sheets. Stress-strain curves of defected graphene sheets with different tension strain rates were plotted. The results showed that cracks lead to the graphene to fracture sooner. Also, increasing temperature lead to the Young’s modulus of graphene decreases and graphene fractured at lower strain. On the other hand, residual strain of non-defected and cracked graphene increased by increasing temperature from 200 K to 1200 K. It means that graphene had more plasticity behavior by increasing temperature.

Vibrational Signatures of Carboxylated Graphene: A First-Principles Study

Raman and infrared (IR) spectroscopies are fast, efficient, and nondestructive techniques commonly used for structural characterization of nanoscale materials. The complimentary characters of the Raman and IR spectroscopies make them ideally suited for experimental studies of carbon nanostructures. Using first-principles computational methods based on density functional perturbation theory, we computed nonresonant Raman and IR absorption spectra of carboxylated graphene containing no surface defects, containing Stone–Wales defects, and containing divacancies. Our calculations demonstrated that the presence of point defects near the functionalization sites significantly altered the Raman and IR spectra of carboxylated graphene. In all cases, we observed the emergence of new Raman and IR absorption bands in the range of low and high vibration frequencies. The calculated Raman and IR spectra showed clearly distinguishable spectroscopic signatures associated to different types of structural defects present in...

Stone-Wales like defects formation, stability and reactivity in black phosphorene

During the synthesis of ultra-thin materials with a hexagonal lattice structure, Stone-Wales (SW) type of defects are quite likely to be formed that can result in dramatic changes in their electronic and mechanical properties. Here we investigated the formation and reactivity of SW-like defects in Phosphorene. Our calculations show that the energy barrier for the formation of SW-like defects in phosphorene is significantly lower than in graphene. Moreover, the nature of phosphorene provides a large energy barrier for the healing of the SWL defect, therefore defective phosphorene is stable. SWL-defect phosphorene are semiconductors with bandgap wider than pristine phosphorene that depends on the density of defects. Furthermore, nitrogen substitution in SWL defected phosphorene shows that defect lattice sites are the least preferable substitution locations for the N atoms. Easy formation of SWL defects in phosphorene provides a guideline for bandgap engineering in phosphorene based materials through such defects.

Erratum to: Quantum-Chemical Study of Structural Stone–Wales Defect in Functionalized Fullerene C20

The first author should have the second affiliation and affiliations should read: M. A. Salem a,b,** , K. S. Grishakov a,* , M. A. Gimaldinova a a National Research Nuclear University “MEPhI”, Kashirskoe sh. 31, Moscow, 115409 Russia; * e-mail: ksgrishakov@yahoo.com b Department of Physics, Faculty of Science, Zagazig University, Zagazig 44519, Egypt; ** e-mail: mahmod_ali735@yahoo.com, masalm@zu.edu.eg Received July 4, 2018

Macromolecular evolution and structural defects in tectonically deformed coals

Here, the differential macromolecular evolutions and the structural defects in various TDCs (tectonically deformed coals) were profoundly investigated utilizing the 13C NMR, FTIR, Raman, and DFT (density function theory) calculations. The increasing aromatics provides evidences for advance evolution for aromatic clusters induced by dynamic metamorphism. The variations of fal∗ (non-protonated carbons) and falH (CH or CH2) indicates that the brittle could promote the aliphatic carbon diversifications while ductile deformation could significantly promote the loss of aliphatic carbons. The I2 (=A900–700/A3000–2800) gradually increases while the I3 (=A1703+1745/A1618) decreases. The comparisons of the D1 peak in TDCs with those in perfect- and defective graphene indicated the existences of the structural defects in TDCs. The ductile TDCs have the lowest D1 peak positions, indicating that ductile deformation can promote the macromolecular disorder degrees to the maximum extent. The gradual increase of ID1/IG and the good linear relationship (R2 = 0.90) between ID1/IG and AD1/AG indicated the gradual increasing content of structural defects with the enhancement of the tectonic deformation. The geological conditions and the Raman results indicated the existences of the Stone-Wales defect (SW) and vacancy-like defects, including the single vacancy (SV), double vacancies (DV), and multi vacancies (MV1 and MV2) in TDCs. The evolution paths of DV (formation energy, Ef: 11.68 eV) → MV1 (Ef: 9.74 eV) → MV2 (Ef: 18.34 eV) and initial structures → SW defects have witnessed the increasing defects and disorder degrees with the enhancement of the tectonic deformation without damaging the continuity of coal matrix structures, which macroscopically manifests as ductile deformation. However, the evolution paths of initial structure → DV (Ef: 11.68 eV) and initial structure → SV (Ef: 9.08 eV) have damaged the continuity by missing carbons, which are consistent with the brittle TDCs.

Direct electric field imaging of graphene defects

Material properties are sensitive to atomistic structure defects such as vacancies or impurities, and it is therefore important to determine not only the local atomic configuration but also their chemical bonding state. Annular dark-field scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy has been utilized to investigate the local electronic structures of such defects down to the level of single atoms. However, it is still challenging to two-dimensionally map the local bonding states, because the electronic fine-structure signal from a single atom is extremely weak. Here, we show that atomic-resolution differential phase-contrast STEM imaging can directly visualize the anisotropy of single Si atomic electric fields in monolayer graphene. We also visualize the atomic electric fields of Stone–Wales defects and nanopores in graphene. Our results open the way to directly examine the local chemistry of the defective structures in materials at atomistic dimensions.

Effect of electric field on the electrical conductivity of defected carbon nanotube: Multifractal properties of the wavefunctions

A theoretical analysis of controllable metal–insulator transition is performed by carrying out a quantum chaos analysis for a single-walled carbon nanotube which is affected by topological Stone–Wales defect. Nanotubes have recently attracted attention as promising materials for flexible nanoelectronic devices. Individual topological Stone–Wales defects have been identified experimentally in carbon nanotubes (CNTs) and graphene. The findings reveal that defected CNT displays a gradual crossover from metal to insulator phase in a longitudinal electric field. By determining the threshold value of the electric field for metal–insulator transition, CNT may be used as a switch in electronic devices. Our results are obtained by calculating the singularity spectrum of a nearest-neighbor tight-binding model. Also, quantum chaos theory is used for obtaining a detailed understanding of a dynamic phase transition from delocalized states (chaotic) to localized states (Poisson). More interestingly, the appearance of negative differential resistance for pure CNT suggests potential applications in nanoelectronic devices.