Line defects in graphene: How doping affects the electronic and mechanical properties

A number of past studies have focused on point and line defects in graphene epitaxially grown on SiC substrates. However, few studies have investigated closed-ring defects formed within grain boundary loops. The present study addresses this issue by applying low-temperature scanning tunneling microscopy/spectroscopy to investigate the atomic structures of closed-ring defects in graphene epitaxially grown on 4H-SiC, and to evaluate their effects on the electron state density. The results indicate that the orientations of the graphene lattice inside and outside of grain boundary loop structures are rotated uniformly by an angle of 30° relative to each other, suggesting that closed-ring defects are highly ordered and are mainly composed of clusters of pentagon-heptagon carbon rings and highly ordered pentagon-heptagon chains. In addition, the spectroscopy results reveal for the first time that the density of electron states inside a closed-ring defect is strongly localized and position-dependent. Moreover, these closed-ring defects can eliminate intervalley scattering while maintaining intravalley scattering. These findings are not only helpful for contributing to a deeper understanding of the effects of closed-ring defects in graphene, but also present a potentially useful valley-filtering mechanism for charge carries that can be applied to the practical development of all-electric valley-based devices.

The density functional tight binding approach (DFTB) is well adapted for the study of point and line defects in graphene based systems. After briefly reviewing the use of DFTB in this area, we present a comparative study of defect structures, energies, and dynamics between DFTB results obtained using the dftb+ code, and density functional results using the localized Gaussian orbital code, AIMPRO. DFTB accurately reproduces structures and energies for a range of point defect structures such as vacancies and Stone–Wales defects in graphene, as well as various unfunctionalized and hydroxylated graphene sheet edges. Migration barriers for the vacancy and Stone–Wales defect formation barriers are accurately reproduced using a nudged elastic band approach. Finally we explore the potential for dynamic defect simulations using DFTB, taking as an example electron irradiation damage in graphene.magnified image DFTB‐MD derived sputtering energy threshold map for a carbon atom in a graphene plane.

We present a systematic study of 3d transition-metal (TM) atomic chains adsorbed on a line defect consisting of octagonal and pentagonal carbon rings embedded in a perfect graphene sheet. The results suggest that Sc, Ti, V, Cr and Mn atoms can be spontaneously adsorbed at octagonal sites and form an atomic chain along the line defect in graphene, while Fe, Co and Ni atomic chains are adsorbed at pentagonal sites. Moreover, the Sc, Ti, V, Cr, Mn and Fe chains embedded in line defect of graphene structures show half-metallic characters. These results propose a new route to explore the potential applications of the system in spintronic devices.

Global air quality has deteriorated significantly in recent years due to large emissions from the transformation industry and combustion vehicles. This issue requires the development of portable, highly sensitive, and selective gas sensors. Nanostructured materials, including defective graphene, have emerged as promising candidates for such applications. In this work, we investigated the B-doped topological line defect in graphene as a sensing material for various gas molecules (CO, CO2, NO, and NH3) based on a combination of density functional theory and the non-equilibrium Green's function method. The electronic transport calculations reveal that the electric current can be confined to the line defect region by gate voltage control, revealing highly reactive sites. The B-doped topological line defect is metallic, favoring the adsorption of NO and NH3 over CO and CO2 molecules. We notice changes in the conductance after gas molecule adsorption, producing a sensitivity of 50% (16%) for NO (NH3). In addition, the recovery time for nitride gases was calculated for different temperatures and radiation frequencies. At 300 K the ultraviolet (UV) has a fast recovery time compared to the visible (VIS) one by about two orders of magnitude. This study gives an understanding of how engineering transport properties at the microscopic level (by topological line defect and chemical B-doping) leads to promising nanosensors for detecting nitride gas.

A DFT study of CO adsorption on the pristine, defective, In-doped and Sb-doped graphene and the effect of applied electric field

We have investigated the electronic, optical, and mechanical properties of six structures belonging to the Tubulanes-cross-linked carbon nanotube family, using Density Functional Theory (DFT) with the Generalized Gradient Approximation (GGA) and the Perdew–Burke–Ernzerhof (PBE) functional. Our results highlight the remarkable anisotropic mechanical behavior of these materials, distinguishing them from isotropic structures, such as diamond. Notably, the 8-tetra-22 structure has a higher Young’s modulus (YM) along the z-direction compared to diamond. Unlike diamonds, the mechanical properties of Tubulanes are direction-dependent, exhibiting significant variations in Young’s Modulus (2.3 times). Additionally, the Poisson’s ratio is highly anisotropic, with at least one direction exhibiting a value close to zero. The inherent anisotropy of these materials enables tunable mechanical properties that depend on the direction of applied stress. Regarding their electronic properties, all Tubulane structures studied possess indirect electronic band gaps, dominated by 2p orbitals. The band dispersion is relatively high, with band gaps ranging from 0.46 to 2.74 eV, all of which are smaller than that of diamond. Notably, the 16-tetra-22 structure exhibits the smallest bandgap (0.46 eV), making it particularly interesting for electronic applications. Additionally, these structures exhibit porosity, which offers advantages over denser materials, such as diamond. Given recent advances in the synthesis of 3D carbon-based materials, the synthesis of tubulane-like structures is within current technological capabilities.

Carbon nanotubes (CNTs) have gained considerable attention in drug delivery applications due to their high surface area and exceptional electronic and mechanical properties. Doping CNTs with metals like aluminum (Al) and gallium (Ga) can modify their electronic, chemical, and stability characteristics, enhancing their suitability for drug delivery. This study investigates the interaction of the drug molecule 5-fluorouracil (5-FU) with pristine and doped (8,8) CNTs using density functional theory (DFT) calculations with the B3LYP functional and the 6-31 G basis set. The results reveal significant changes in the electronic properties after doping. Aluminum doping increases the energy gap, reducing system reactivity, while gallium doping decreases the energy gap, promoting stronger interactions with the drug. Aluminum doping improves the structural stability of CNTs with 5-FU, whereas gallium enhances the chemical potential and hardness, favoring interactions with the drug molecule. In conclusion, aluminum- and gallium-doped CNTs exhibit different behaviors in drug interactions, allowing for optimization of targeted drug delivery systems. Based on energy gap, chemical potential, and chemical hardness values, both doping types can enhance drug delivery properties, with the specific doping choice dependent on the therapeutic application.

Carbon nanotubes (NTs) exhibit a wealth of fascinating structural, mechanical, and electronic properties. As an ideal one-dimensional structure, their properties are highly anisotropic. For example, mechanically the NTs are extraordinarily hard in the axial direction but soft in the radial direction; the compressibility anisotropy in the two directions exceeds orders of magnitude. As the NTs are virtually incompressible in the axial direction, much attention has been paid to their structural and mechanical behavior in the radial direction. 1‐8 The radial deformation (i.e., the change of cross-section shape) of single-walled carbon nanotubes (SWNTs) in turn influences their mechanical 1‐5 and electronic properties. 7‐9 The hardness, as one of the most important parameters characterizing the mechanical properties of SWNTS, has been intensively studied. 10‐12 However, so far, most studies have focused only on the ground-state hardness of SWNTs at ambient conditions. In this Paper, we investigate the mechanical properties, especially the hardness, of a single SWNT under hydrostatic pressure, using constant-pressure molecular-dynamics (MD) simulations and linear elastic analysis. We discover a pressure-induced hard-to-soft transition at which the radial modulus of the SWNT decreases by as much as two orders of magnitude. We show that this mechanical (hardness) transition is caused by a pressureinduced structural (shape) transition of SWNT characterized by a transformation of its cross section from a circular to elliptical shape. The critical transition pressure decreases with increasing tube radius. We use a constant-pressure MD method especially suited

The electronic and structural properties and elastic constants of the wurtzite phase of GaN, was investigated by computer simulation at Density Functional Theory level, with B3LYP and B3PW hybrid functional. The electronic properties were investigated through the analysis of the band structures and density of states, and the mechanical properties were studied through the calculus of the elastic constants: C11, C33, C44, C12, and C13. The results show that the maximum of the valence band and the minimum of the conduction band are both located at the Γ point, indicating that GaN is a direct band gap semiconductor. The following constants were obtained for B3LYP and B3PW (in brackets): C11 = 366.9 [372.4], C33 = 390.9 [393.4], C44 = 99.1 [96.9], C12 = 143.6 [155.2], and C13 = 107.6 [121.4]. Keywords: GaN, elastic constant, B3LYP, B3PW, periodic calculations.

Carbon based nanostructures such as graphene and carbon nanotubes have received widespread attention due to their unique mechanical and electronic properties. This paper describes a quantum mechanics based study of the electronic band structures and transport properties of one-dimensional (1D) carbon chains, the thinnest nanowires available in nature. The study is based on the application of density functional theory and non-equilibrium Green's function where maximally localized Wannier functions and Landauer formalism are combined to compute the electronic band structures and quantum conductance of the 1D carbon chains. The simulation result indicates that the peak quantum conductance of 1D carbon chains is about five times smaller than that of carbon nanotubes. However, the quantum conductance is also a function of the length and chemical bonds of the carbon chains. When the carbon chains are mechanically strained at 3%, the quantum conductance is reduced by about 50%. This result suggests 1D carbon chains can provide ultra high-resolution electromechanical measurements of important biomolecules such as DNA.

The line defect of graphene has significant applications in valleytronics, which has received extensive attention in recent years. It is found experimentally that there exists local deformation around the line defect. Current studies generally believe that the influence of local deformation on the valley transport properties can be negligible, because the modifications to the nearest neighbour hopping energy is less than 5% under the small deformation. Based on the first-principles calculations and the non-equilibrium Green’s function method, we investigated the effect of local deformation on the valley transport properties of two different kinds of line defects, the 58 ring line defect and the 57 ring line defect. It is found that for the 58 ring line defect, the effect of local deformation on the valley transmission coefficient is not evident at lower energies. However, at higher energies, the impact of local deformation is obvious, and the maximum valley transmission coefficient does not decrease with increasing energy, but can be maintained 1 within a large energy range. In contrast, the influence of local deformation on the valley transmission coefficient of the 57 ring line defect indeed can be negligible, regardless of the level of energy. Further investigation indicates that the change of the C—C bond length connected to the two defect atoms in the 58 ring plays a key role in the transmission of the valley states across the line defect. If this part of the influence is not taken into account, the valley transmission coefficient is nearly unaffected by the local deformation. The valley state enters the right side of the line defect directly through the bond connected to the line defect, so the change in bond length connected to the line defect has a significant impact on the valley transmission. This special structure does not exist in the 57 ring, where the valley states will have to pass through a narrow region containing 57 ring to enter the right side of the line defect, resulting in different valley scattering phenomena. By constructing two parallel line defects, the 100% valley polarization can be achieved in a large angular range with the 58 ring line defect. The finding has important implications for the design of graphene line defect based valley filters.

The effect of metal transition dopant on electronic and mechanical properties of titanium nitride: First principle method

Self healing mechanisms of vacancy defects in graphene and silicene are studied using first principles calculations. We investigated host adatom adsorption, diffusion, vacancy formation and revealed atomistic mechanisms in the healing of single, double and triple vacancies of single layer graphene and silicene. Silicon adatom, which is adsorbed to silicene at the top site forms a dumbbell like structure by pushing one Si atom underneath. The asymmetric reconstruction of the single vacancy in graphene is induced by the magnetization through the rebonding of two dangling bonds and acquiring a significant magnetic moment through remaining unsaturated dangling bond. In silicene, three two-fold coordinated atoms surrounding the single vacancy become four-fold coordinated and nonmagnetic through rebonding. The energy gained through new bond formation becomes the driving force for the reconstruction. Under the external supply of host atoms, while the vacancy defects of graphene heal perfectly, Stone-Wales defect can form in the course of healing of silicene vacancy. The electronic and magnetic properties of suspended, single layer graphene and silicene are modified by reconstructed vacancy defects.

Defects in graphene are important nanoscale pathways for metal atoms to enter the interface between epitaxial graphene and SiC in order to form stable ultrathin metal layers with new exotic physical properties. However, the atomic-scale details of defects that mainly govern the intercalation process remain modest. In this work, we present the first atomic investigation of point defects generated by oxygen plasma treatment on epitaxial graphene grown on SiC using low-temperature scanning tunneling microscopy, corroborated by density functional theory calculations. We found a broad spectrum of point defects that varies in size, shape, and symmetry and is dominated by triangular species. Tunneling spectroscopy identified defect-induced states in the vicinity of the Fermi level that significantly perturb the graphene electronic properties at the defect site. Based on the well-defined defect symmetry, we simulated the local density of states of the triangular defects and their corresponding scanning tunneling microscopy images which further helped us to identify the exact atomic configurations of monovacancy defects. The combination of atomic-scale scanning tunneling microscopy experiments and reliable density functional theory simulations provides ultimate microscopic details and opens a new way to identify the atomic configurations of defects in oxygen plasma-treated graphene. Our work might shed light on precise control of defect engineering in graphene for metal intercalation by controlling the defect types based on a deep understanding of each configuration.

Carbon nanotube is excellent material for hydrogen storage and molecular sensory applications thanks to its quasi-one dimensional geometry and unique structure-property relationship. In this paper, hydrogenation of carbon nanotubes is discussed in the extent of binding geometry and mechanochemical coupling under structural deformation. Our first-principles calculations show that the atomic structures, mechanical and electronic properties of carbon nanotubes can be significantly modified by hydrogenation. Moreover, the hydrogenation process is controlled by strain loading. Under an axial compressive or tensile strain of 10 %, the binding energies of hydrogen on carbon nanotubes can be changed up to -0.24 and 0.74 eV respectively. Analysis on electronic structure, mechanical properties and charge density reveals the underline mechanisms. The results reported here offer a way not only to tune the binding strength of hydrogen on carbon nanotubes in a controllable and reversible manner, but also to engineer the properties of carbon nanotubes through a synergistic control on hydrogen binding and mechanical loading.