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Siligraphene, as a composite of graphene and silicene, has attracted widespread attraction since it has many excellent properties that neither of graphene and silicene possesses. The properties of siligraphene are closely related to the distribution of Si atoms and its structure, but most of the current researches of siligraphene focus on the regular distribution of Si atoms and the planar structure with high symmetry. Therefore, we study in this work all possible Si atoms’ distributions with planar and nonplanar structures for siligraphene g-SiC7 based on density functional theory. At first, 365 kinds of inequivalent Si atoms’ distributions in g-SiC7 are selected out from the 35960 kinds of Si atoms’ distributions, and then for each inequivalent Si atoms’ distribution, a comparison of the stability between the planer and nonplanar structures is made. In terms of the Si distribution, the Si atoms tend to gather together to lower the energy. The more dispersed Si atoms’ distribution usually has appreciably higher energy. In terms of the planarity of the structures, it is found that there are many non-planar structures with significantly lower energy than the planar ones. For all possible Si atoms’ distributions, there are only 8 planar structures which are stable against out-of-plane perturbations. We further study the dynamic, thermodynamic and mechanical stability of the structures with the lowest energies and find that they are stable. The energy band calculation shows that two Dirac valleys still persist in the first Brillouin zone despite their appreciable structure deformation, and a considerable band gap is opened at the Dirac point. We calculate the Berry curvatures and find that the Berry curvatures at the inequivalent valleys are opposite, indicating that the system has valley degree of freedom. Our research shows that siligraphene is more likely to have a buckled structure and a more concentrated silicon atoms’ distribution, and the most stable structures have good electronic properties.

Objective: To investigate therapeutic effect of carotid artery stenting versus endarterectomy for patients with high-risk carotid stenosis. Methods: A total of 130 carotid stenosis patients at high-risk of stroke were randomly divided into stenting group and endarterectomy group, including 65 patients in each group. The patients in the endarterectomy group underwent endarterectomy and those in the stenting group received carotid artery stenting for treatment. Results: After operation, carotid intima-media thickness (IMT), plague areas and carotid artery resistance indexes in both groups decreased significantly, and the carotid artery peak blood flow velocities increased significantly and had significant differences with that before operation (P < 0.05). After operation, total cholesterol (TC), triglyceride (TG) and low density lipoprotein (LDL) values in two groups all significantly decreased, and intragroup and intergroup differences were statistically significant (P < 0.05). Postoperative three months of followed-up found that the mortality rate in stenting group was 1.5% and that in the endarterectomy group was 9.2%; the mortality rate in the stenting group was significantly lower than the endarterectomy group (P < 0.05). Conclusion: Compared with carotid endarterectomy, application of carotid artery stenting can effectively promote patency of blood flow in the carotid artery, and exertion of its effect is related to lowering lipid and lowering inflammatory factor expression.

We have studied the quantum diffusion in an octagonal quasiperiodic tiling. Paticular attention is paid to the analysis of long-time behavior of the autocorrelation function C(t) and the relationship between diffusion and fractal dimensions of energy spectrum. For the pure hopping model, numerical calculations show that C(t) ~ t-1, which corresponds to the case of periodic systems. For the combined model, in which the contribution of site potentials is considered, C(t) ~ t-δ with 0

The dynamical evolution process of nanoscaled film on a solid substrate depends on many factors, such as the properties of thin film, the characteristics of the substrate, and the external environment. It is essential to elucidate the influences of these factors for our understanding self-organized growth of nanoparticles and the dewetting/detachment mechanism of nanofilm on a solid substrate. In the present paper, we investigate the dynamical dewetting/detachment of metal Au and Pt nanofilm on a graphene/graphite substrate at high temperature by using the molecular dynamics simulation technique. We discuss the influences of metal-substrate interaction, temperature and thickness of film on the dewetting dynamics. Our results reveal that the Au and Pt nanofilms with the same initial thickness on graphene substrates manifest different dewetting dynamical processes at high temperatures. Some nanoscale holes are formed randomly during the dewetting of Pt nanofilm with a thickness of less than 0.6 nm because of the strong interaction between the Pt films and substrate. In contrast, no hole is observed and a nanodroplet is formed directly by high temperature dewetting for Au nanofilm with the same initial thickness as that of Pt nanofilm. The resulting Au and Pt nanodroplets move in the vertical direction due to the surface tension and the constraint of the solid substrate. A high-temperature nanodroplet will be detached from the graphene substrate surface at a constant speed. Interestingly, the values of detachment velocity (vd) of nanodroplets show different dependences on initial thickness for Au and Pt nanofilm, respectively. In a thickness range of 0.2-2.3 nm, the vd of Pt nanodroplet increases and then decreases as the thickness of nanofilm increases. However, the vd of Au nanodroplet decreases gradually and then increases steeply as the Au nanofilm turns thicker. The different thickness dependences of vd for Au and Pt nanofilms are analyzed qualitatively by considering different metal-substrate viscous dissipations. In addition, the detachment time (td) of a dewetting metal film is also related to the temperature and the thickness of substrate. Our results demonstrate that the td decreases monotonically with the decrease of film thickness and the raise of temperature. These results provide a theoretical guideline for industrial production processes, such as metal coating, flotation, and the surface cleaning.

Electronic properties of tetragonal MoSi2 thin films are studied by the first-principles method. The results show that the MoSi2 film is always metallic, and its density of states and electronic structure are gradually close to their bulk counterpart as the film thickness increases. We further show that the three-atomic-layer film with the lowest energy is magnetic and has a magnetic moment of 0.33 B for its unit cell, and the film becomes non-magnetic when its thickness is more than three atomic layers. Moreover, we investigate the electronic properties of the three-atomic-layer MoSi2 films under unilateral and bilateral hydrogenation and find that the film with unilateral hydrogenation is magnetic and has a magnetic moment of 0.26 B, while the film with bilateral hydrogenation is non-magnetic. The spin polarizations for the films without hydrogenation and unilateral hydrogenation are 30% and 33%, respectively. These results suggest that three-atomic-layer MoSi2 film is metallic or magnetic when it is under suspension or grown on substrate, indicating its potential applications in nanoscale electronic and spintronic devices.

By using the classical molecular dynamics and the simulated annealing techniques, the evolutions of the rippled morphology in single atomic graphenes placed on the Si (100), Si (111) and Si (211) surfaces respectively are performed at an atomic level. Our results show that the monolayer graphene sheets on the different Si surfaces form atomic scale rippled structures. A graphene monolayer prepared on Si surface forms rippled structure due to the relative lattice mismatch between graphene and Si substrate. The rippled morphology of graphene sheet on Si surface is strongly dependent on the annealing temperature. Such ripples will directly affect the adhesion strength between graphene and Si substrate. These findings are useful for understanding the structural morphology and stability of graphene on the semiconductor Si substrate, which will provide an analysis reference for further applications of graphene.

By using first-principles method, we study the stacking effects on the electronic structure, topological phase and spin splitting in the bulk and film of topological insulator Bi2Se3. It is found that the different stackings can lead to different interlayer interactions and change the centrosymmetry of Bi2Se3. The centrosymmetric ABC and AAA stackings in bulk Bi2Se3 have similar band structures. ABA stacking breaks the centrosymmetry, giving rise to considerable changes of the band structure and large spin splitting. We further study the stacking effects in the film of Bi2Se3 and find that the non-centrosymmetric ABA stacking can induce large spin splitting in Bi2Se3 film. It is proposed and illustrated that the strain can tune the spin splitting effectively.

Using Green's function method, we investigate the spin transport properties of armchair graphene nanoribbons (AGNRs) under magnetic field and uniaxial strain. Our results show that it is very difficult to transform narrow AGNRs directly from semiconductor to spin gapless semiconductors (SGS) by applying magnetic fields. However, as a uniaxial strain is exerted on the nanoribbons, the AGNRs can transform to SGS by a small magnetic field. The combination mode between magnetic field and uniaxial strain displays a nonmonotonic arch-pattern relationship. In addition, we find that the combination mode is associated with the widths of nanoribbons, which exhibits group behaviors.

In practical applications of graphene-based electronic devices, they may have some pore defects under energetic particle bombardment, or chemical corrosion, which will inevitably affect their electrical properties. These problems have recently aroused great concern and interest. In this paper, we systematically study the influence of shape (tripartite, tetragonal and hexagonal) of hole defect on the electrical property of zigzag graphene nanoribbon (ZGNR). The results show that the influence of the shape of the pore defects on the conductance and current characteristics of ZGNRs is significant, whicl may result from electron scattering for the different shapes of the poredefect boundary. In addition, due to defects in suspension adsorbed hydrogen or nitrogen atoms, caused by defects of the pore shape changes, it also affects the electrical properties of ZGNRs. This study will supply valuable theoretical guidances for graphene-based electronic device failure analysis and the design of the graphene pore structure.

Using classical molecular dynamics and a simulated annealing technique, we show that microscopic corrugations occur in monolayer and bilayer graphene on 6H?SiC substrates. From an analysis of the atomic configurations, two types of microscopic corrugations are identified, namely periodic ripples at room temperature and random ripples at high temperature. Two different kinds of ripple morphologies, each with a periodic structure, occur in the monolayer graphene due to the existence of a coincidence lattice between graphene and the SiC terminated surface (Si- or C-terminated surface). The effect of temperature on microscopic ripple morphology is shown through analysing the roughness of the graphene. A temperature-dependent multiple bonding conjugation is also shown by the broad distribution of the carbon-carbon bond length and the bond angle in the rippled graphene on the SiC surface. These results provide atomic-level information about the rippled graphene layers on the two polar faces of the 6H?SiC substrate, which is useful not only for a better understanding of the stability and structural properties of graphene, but also for the study of the electronic properties of graphene-based devices.

Based on the Anderson tight-binding model, the electronic properties of disordered bilayer hexagonal boron nitride quantum films are investigated. Our numerical results show that the electrons in a disordered bilayer hexagonal boron nitride quantum film are localized, presenting an insulating property. However, for the monolayer disordered bilayer hexagonal boron nitride quantum film, the energy spectrum has persistent mobility edges which are independent of the disorder strength. This indicates that a metal-insulator transition occurs in the monolayer disorder structure. This is similar to the case in an order-disorder separated quantum film. The results could offer useful information for understanding and manipulating the electronic properties of bilayer hexagonal boron nitride quantum films.

By using nonequilibrium Green’s function method, the thermal transport properties of L-shaped graphene nano-junctions consisting of a semi-infinite armchair-edged nanoribbon and a semi-infinite zigzag-edged nanoribbon were studied. It is shown that the thermal conductance of the L-shaped graphene nano-junctions depends on the included angles and the widths of the graphene nanoribbons. As the angle of L-shaped graphene nano-junctions increases from 30° to 90° and further to 150°, the thermal conductance obviously increases. For the right-angle L-shape graphene nano-junction, the thermal conductance undergoes a transition with the increasing of the widths of the armchair nanoribbons. The thermal conductance decreases at low temperature region and increases at high temperature region. Meanwhile the thermal conductance of L-shape graphene nano-junction with included angle 150° decreases by increasing the widths of zigzag-edged nanoribbons in both low and high temperature regions. These thermal transport phenomena can be reasonably explained by analyzing the phonon transmission coefficient. We illustrate the mechanisms of thermal transport for different L-shaped graphene nano-junctions. The results provide significant physical models and theoretical basis for designing the thermal devices based on the graphene nano-junctions.

The effect of stacked graphene flakes (GFs) on the electronic transport property of zigzag-edged graphene nanoribbon (ZGNR) is investigated. By using the Greens function method, we calculate the conductances of ZGNRs with two different stacked-type GFs. It is found that the coupling effect between ZGNRs and GFs can induce dips at the conductance profiles in two different stacked-types. For both stacked-types, the dips far away from the Fermi level are nearly overlapped. However, the position of conductance dip near the Fermi level depends on the stacked-type. In addition, we discuss the effect of geometric size of GF on the electronic transport property. The results show that with the increase of the size of GF, the dips far away the Fermi level in two stacked-types gradually move toward the Fermi level, while the discrepancy of the dips near the Fermi level is much evident. Our results indicate that the stacked GFs can effectively tune the electronic transport of ZGNR.

The transport properties of hexagonal boron–nitride nanoribbons under the uniaxial strain are investigated by the Green's function method. We find that the transport properties of armchair boron–nitride nanoribbon strongly depend on the strain. In particular, the features of the conductance steps such as position and width are significantly changed by strain. As a strong tensile strain is exerted on the nanoribbon, the highest conductance step disappears and subsequently a dip emerges instead. The energy band structure and the local current density of armchair boron–nitride nanoribbon under strain are calculated and analysed in detail to explain these characteristics. In addition, the effect of strain on the conductance of zigzag boron–nitride nanoribbon is weaker than that of armchair boron nitride nanoribbon.

We investigate the strain effects on the electronic properties of boron nitride nanoribbons (BNNRs) by using first-principles calculations. The results show that the energy gap of BNNRs with both armchair edges (A-BNNRs) and zigzag edges (Z-BNNRs) decreases as the strain increases. As strain increases, the energy gaps of Z-BNNRs decrease rapidly as the width increases and reduce significantly to small values, which makes Z-BNNRs change from wide-gap to narrow-gap semiconductors.

We have used molecular dynamics (MD) simulation to investigate the evaporation of the surface wall of multi-wall carbon nanotubes (MWCNTs) at high temperature，using the environment dependent interatomic potential (EDIP) to describe the C—C interaction in carbon nanotube. The simulation results show that the Stone-Wales defect in the surface wall of a multi-wall carbon nanotube vibrates violently，which causes C—C bond breaking and evaporation of atoms along the circumferential directions of the nanotube. The formation of Stone-Wales defect is attributed to the atomic thermal motion or tensile strain. Using the Lindemann index as a criterion，we found that the surface wall of MWCNT evaporates around 2290 K. Our simulation results agree very well with the observation of the surface wall evaporation of the MWCNT at 2000 ℃.

Using the first-principles method, we have studied the structure transition of two-dimensional hexagonal boron nitride (2D h-BN) under large uniaxial strain. The strain is applied by changing the values of Lx and Ly, which correspond to the lengths of primitive cell in the directions perpendicular and parallel to B—N bonds, respectively. For the large asymmetrical tensile strain perpendicular to B—N bonds, the rhombic structure is stable when Lx≤0.3388 nm. As the strain increases, the system transforms from the rhombic structure to a rectangular structure consisting of interlaced interacting BN chains, which becomes stable when Lx≥0.3488 nm. When the strain further increases, the system finally changes into the one comprised of isolated BN chains. For the 2D h-BN with large asymmetrical tensile strain distribution parallel to B—N bonds, there is no stable rectangular structure and the system becomes the one composed of isolated BN chains when Ly>0.571 nm.