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The field of topological mechanics has recently emerged due to the interest in robustly transporting various types of energy in a flaw and defect-insensitive fashion. While there have been a significant number of studies based on discovering and proposing topological materials and structures, very few have focused on tuning the resulting topological bandgaps, which is critical because the bandgap frequency is fixed once the structure has been fabricated. Here, we perform both lattice dynamical calculations and molecular dynamical simulations to investigate strain effects on the phononic topological bandgaps in two-dimensional monolayer hexagonal boron nitride. Our studies demonstrate that while the topologically protected phononic bandgaps are not closed even for severely deformed hexagonal boron nitride and are relatively insensitive to uniaxial tension and shear strains, the position of the frequency gap can be efficiently tuned in a wide range through the application of biaxial strains. Overall, this work thus demonstrates that topological phonons are robust against the effects of mechanical strain engineering and shed light on the tunability of the topological bandgaps in nanomaterials. [ABSTRACT FROM AUTHOR]

We investigate the strain engineering and the edge effect for mechanical properties in graphene nanoribbons. The free edges of the graphene nanoribbons are warped due to compressive edge stresses. There is a structural transformation for the free edges from the three-dimensional warping configuration to the two-dimensional planar structure at the critical strain ϵc = 0.7%, at which the applied mechanical stress is equal to the intrinsic compressive edge stress. This structural transformation leads to step-like changes in several mechanical properties studied in the present work, including the Young's modulus, the Poisson's ratio, the quality factor of nanomechanical resonators, and the phonon edge mode. [ABSTRACT FROM AUTHOR]

The topological effect on thermal conductivity is investigated through the comparison among graphene nanoribbons, carbon nanorings, and the Möbius-like graphene strips (MGS) by molecular dynamics simulation. It is found that the thermal conductivity of MGS is less than one half of that of graphene nanoribbons. The underlying mechanism whereby MGS acquire such low thermal conductivity may be attributable to the enhanced phonon-phonon scattering and localization property, which are induced by the nontrivial topology of Möbius strip. Moreover, by counting in the dimensions of MGS, a lower length/width ratio reduces its thermal conductivity, as the phonon-phonon scattering and localization within might be further elevated. [ABSTRACT FROM AUTHOR]

Structure transformation by heat treatment in single-walled carbon nanotubes (SWCNT) is investigated using molecular dynamics simulation. The critical temperature for the collapse of pure SWCNT is as high as 4655 K due to strong covalent carbon-carbon bonding. Above 2000 K, the cross section of SWCNT changes from circle to ellipse. The self-repairing capability is then investigated and two efficient processes are observed for the SWCNT to repair themselves. (1) In the first mechanism, vacancy defects aggregate to form a bigger hole, and a bottleneck junction is constructed nearby. (2) In the second mechanism, a local curvature is generated around the isolate vacancy to smooth the SWCNT. Benefit from the powerful self-repairing capability, defective SWCNT can seek a stable configuration at high temperatures; thus the critical temperature for collapse is insensitive to the vacancy defect density. [ABSTRACT FROM AUTHOR]

Thermal conductivity of graphene nanoribbons (GNR) with length 106 Å and width 4.92 Å after isotopic doping is investigated by molecular dynamics with quantum correction. Two interesting phenomena are found, (1) isotopic doping reduces thermal conductivity effectively in low doping region, and the reduction slows down in high doping region, (2) thermal conductivity increases with increasing temperature in both pure and doped GNR, but the increasing behavior is much more slow in the doped GNR than that in pure ones. Further studies reveal that the physics of these two phenomena is related to the localized phonon modes, whose number increases quickly (slowly) with increasing isotopic doping in low (high) isotopic doping region. [ABSTRACT FROM AUTHOR]

Auxetic materials (materials with negative Poisson's ratio) and nanomaterials have independently been, for many years, two of the most active research fields in material science. Recently, these formerly independent fields have begun to intersect in new and interesting ways due to the recent discovery of auxeticity in nanomaterials like graphene, metal nanoplates, black phosphorus, and others. Here, we review the research emerging at the intersection of auxeticity and nanomaterials. We first survey the atomistic mechanisms, both intrinsic and extrinsic, that have been found, primarily through atomistic simulations, to cause auxeticity in nanomaterials. We then outline the available experimental evidence for auxetic nanomaterials. In order to lay the groundwork for future work in this exciting area, we close by discussing several future prospects as well as the current challenges in this field. [ABSTRACT FROM AUTHOR]

We derive analytical expressions for the Young's modulus and the Poisson's ratio of the graphene nanoribbon, in which free edges are warped by the compressive edge stress. Our analytical formulas explicitly illustrate the reduction of the Young's modulus by the warped free edges, leading to the obvious width dependence for the Young's modulus of the graphene nanoribbon. The Poisson's ratio is also reduced by the warped free edges, and negative Poisson's ratio can be achieved in the graphene nanoribbon with an ultra-narrow width. These results are comparable with previous theoretical works. [ABSTRACT FROM AUTHOR]

We perform classical molecular dynamics simulations to demonstrate the application of kinked silicon nanowires (KSiNWs) as nanoscale springs. The spring-like oscillation in gigahertz frequency range is successfully actuated using a similar procedure as the actuation of a classical mass spring oscillator. We detect the spring-like mechanical oscillation and some other low-frequency oscillations by the energy spectrum analysis, where a dimensional crossover phenomenon is observed for the transverse mode in KSiNWs with decreasing aspect ratio. Our findings shed light on the elastic properties of the KSiNW and open a way for its application in nanomechanical devices. [ABSTRACT FROM AUTHOR]

We study thermal transport in folded graphene nanoribbons using molecular dynamics simulations and the non-equilibrium Green's function method. It is found that the thermal conductivity of flat graphene nanoribbons can be modulated by folding and changing interlayer couplings. The analysis of transmission reveals that the reduction of thermal conductivity is due to scattering of low frequency phonons by the folds. Our results suggest that folding can be utilized in the modulation of thermal transport properties in graphene and other two dimensional materials. [ABSTRACT FROM AUTHOR]

Due to the similar chemical properties to the inorganic component in calcified tissues, synthetic calcium phosphate has been considered as ideal biomaterials with excellent biocompatibility. Nanostructured calcium phosphate materials play an important role in the formation of hard tissues in nature. It is reported that calcium phosphates materials in nano-size can mimic the dimensions of constituent components of calcified tissues. Recently, the synthesis and application of nanostructured calcium phosphate materials have become a very hot field. Lots of methods have been reported to prepare nanostructured calcium phosphate, and various morphologies including nanoparticles, plate-like nanocrystals, nano-needles, whiskers/fibres/ wires, mesoporous, nanotubes, nano-blades, and powders with three-dimensional (3-D) structures have been obtained. More studies of nanostructured calcium phosphates are expected in biomedical area, such as tissue engineering scaffolds, drug/gene delivery systems and multifunctional systems. In this article, the synthesis and application of nanostructured calcium phosphates are reviewed and discussed. [ABSTRACT FROM AUTHOR]

Photoconduction studies have been carried out with single crystal GaN nanowires. The nanowire transistors exhibited a substantial increase in conductance upon UV light exposure. Besides the selectivity to different light wavelengths, extremely short response and recovery time have also been obtained, as well as the great reversibility of the nanowire between the high and low conductivity states. In addition, a polarization anisotropy effect was demonstrated and studied for GaN nanowires working as polarized UV detectors. The nanowire conductance varied periodically with the polarization angle of the incident light (θ), which can be well fitted into a function of cos2θ. [Copyright &y& Elsevier]

A novel method was developed for synthesizing SnO2 zigzag nanobelts on a silicon substrate with the assistance of CuO powder. The crystalline structure and morphology of SnO2 zigzag nanobelts were characterized using x-ray diffraction, scanning electron microscopy and transmission electron microscopy. The growth habits and formation mechanism of the obtained SnO2 zigzag nanobelts were discussed in detail based on a series of experimental results. The optical property was evaluated by room temperature photoluminescence spectra. Field emission properties of SnO2 zigzag nanobelts was measured for the first time leading to good performance with a turn-on field of 1.9 V µm[?]1 and a threshold field of 5.1 V µm[?]1. [ABSTRACT FROM AUTHOR]

Abstract: Nanocrystalline NbC has been prepared via a convenient route by the reaction of metallic magnesium powders with niobium pentoxide and basic magnesium carbonate in an autoclave at 550°C. X-ray powder diffraction pattern indicated that the product was cubic niobium carbide, and the cell constant was a =4.461Å. Transmission electron microscopy (TEM) image showed that it consisted of particles with an average size of about 30nm in diameter. The product was also studied by BET and TGA. It had good thermal stability and oxidation resistance below 400°C in air. [Copyright &y& Elsevier]