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To facilitate the biomedical applications of biocomposites, researchers have used different types of fillers to enhance their mechanical properties. However, the addition of fillers not only changes the mechanical performance of the biocomposites, but also affects their printability, that is, their rheological properties. With the aid of atomistic simulations, this work investigates the influence of graphene size and aggregation on the rheological properties of polycaprolactone (PCL) composites. For the same weight ratio, increasing the graphene size causes the viscosity of the PCL composite to increase until a threshold edge length equal to PCL's average radius of gyration. After this threshold value, the viscosity decreases with increasing edge length. The PCL composite with multilayered graphene exhibits a lower viscosity compared with its counterpart with monolayer graphene. Specifically, the addition of graphene is shown to augment the shear-thinning effect. The findings in this work provide a fundamental understanding of the rheological property of PCL composites with the addition of 2D nanofillers, which shed light on the ink design for bioprinting.

The arrows indicating the radius of the local bending curvature in Figure 1l should point to the neutral line instead of the outer surface of the NW. A new version of Figure 1 is included. This correction does not influence the results, discussions, and main conclusions of our original paper.

Transition-metal-doping can improve some physical properties of titanium dioxide (TiO2) nanowires (NWs), which leads to important applications in miniature devices. Here, we investigated the elastic moduli of single-crystalline pristine and Fe-doped rutile TiO2 NWs using the three-point bending method, which is taken as a case study of impacts on the elastic properties of TiO2 NWs caused by transition-metal-doping. The Young’s modulus of the pristine rutile TiO2 NWs decreases when the cross-sectional area increases (changing from 246 GPa to 93.2 GPa). However, the elastic modulus of the Fe-doped rutile NWs was found to increase with the cross-sectional area (changing from 91.8 GPa to 200 GPa). For NWs with similar geometrical size, the elastic modulus (156.8 GPa) for Fe-doped rutile NWs is 24% smaller than that (194.5 GPa) of the pristine rutile TiO2 NWs. The vacancies generated by Fe-doping are supposed to cause the reduction of elastic modulus of rutile TiO2 NWs. This work provides a fundamental understanding of the effects of transition-metal-doping on the elastic properties of TiO2 NWs.

This work summarizes the recent progress on the thermal transport properties of 3D nanostructures, with an emphasis on experimental results. Depending on the applications, different 3D nanostructures can be prepared or designed to either achieve a low thermal conductivity for thermal insulation or thermoelectric devices or a high thermal conductivity for thermal interface materials used in the continuing miniaturization of electronics. A broad range of 3D nanostructures are discussed, ranging from colloidal crystals/assemblies, array structures, holey structures, hierarchical structures, to 3D nanostructured fillers for metal matrix composites and polymer composites. Different factors that impact the thermal conductivity of these 3D structures are compared and analyzed. This work provides an overall understanding of the thermal transport properties of various 3D nanostructures, which will shed light on the thermal management at nanoscale.

Recently, ferroelectric materials have attracted considerable research attention. In particular, two dimensional (2D) ferroelectric materials have been considered as most crucial for nextgeneration circuit designs because of their application as novel electric memory devices. However, a 2D ferroelectric material is very rare. The ferroelectric materials with the form ABP2X6 (A = Ag, Cu; B = Bi, In; X = S, Se) are of interest because of their ferroelectric property maintained in their ultrathin structures. Within the ABP2X6 monolayer, the P—P bonds form the pillars that hold the top and bottom X planes, while the off-center A—B atoms between the X layers induce a spontaneous ferroelectric polarization. If the two off-center A—B sites are equally aligned, this would lead to the appearance of the paraelectric state. Such intriguing structures must impart novel mechanical properties to the materials. Until now, there has been no report on the mechanical properties of monolayer ABP2X6. Based on first-principles calculations, we studied the structural, electronic, mechanical as well as the electromechanical coupling properties of monolayer ABP2X6 (A = Ag, Cu; B = Bi, In; X = S, Se). We found that they are all semiconductors with wide bandgaps of 2.73, 2.17, 3.00, and 2.31 eV for CuInP2Se6, CuBiP2Se6, AgBiP2Se6, and AgBiP2Se6, respectively, which are calculated based on the Heyd-Scuseria-Ernzerhof (HSE) exchange correlation functional model. The conduction band minimum is mainly from p orbitals of X and B atoms, whereas the valence band maximum is due to the hybridization of the p orbital of X atoms and the d orbital of A atoms. Moreover, there are three short and three long A/B—X bonds due to the A—B offcenter displacement. Together with the d-p orbital hybridization, the main reason for the dist

Nanoscale mechanical resonator-based nanoelectromechanical systems have been reported with ultrahigh sensitivity, which are normally acquired from an ultravacuum environment at cryostat temperature. To facilitate their practical applications for gas sensing or bio-detection, it is critical to understand how the fluid (gas or liquid) environment will impact the resonance behaviors of the nanoresonator. This work reports a first-time comprehensive investigation on the influence of the N2 gaseous environment on the resonance properties of carbon nanotube (CNT)-based mechanical resonator, through a combination of grand canonical Monte Carlo and large-scale molecular dynamics simulations. It is shown that the gaseous environment exerts a significant effect on the resonance properties of the CNT resonator through a dynamic desorption and readsorption process. Under the temperature of 100 K and the pressure of 1 bar, the displacement amplitude of the CNT resonator is found to experience a sharp reduction of about 82% within the first 90 ps vibration in the N2 gaseous environment. Further, a large initial excitation is found to result in smaller adsorption and a reduced damping effect. For instance, when the excitation velocity amplitude increases from 2 to 8 Å/ps, the damping ratio shows more than 40% reduction. It is found that higher pressure leads to a smaller resonance frequency and enhanced damping effect, while higher temperature induces an increase in the resonance frequency but a decrease in the damping ratio. This work shows that the gaseous environment has a marked impact on the vibrational properties of nanoresonators, which should shed light on the application of mechanical nanoresonators in a fluid environment.

Carbon nanothread (C-NTH) is a new ultrathin one-dimensional sp3 carbon nanostructure, which exhibits promising applications in novel carbon nanofibers and nanocomposites. Recently, researchers have successfully developed a new alternative structure - ultrathin carbon nitride nanothread (CN-NTH). In this work, we investigate the mechanical properties of CN-NTHs through large-scale molecular dynamics simulations. Comparing with their C-NTH counterparts, CN-NTHs are found to exhibit a higher tensile and bending stiffness. In particular, because of the bond redistribution, the CN-NTHs in the polymer I group and tube (3,0) group are found to possess a higher failure strain than their C-NTH counterparts. However, the CN-NTH in the polytwistane group has a smaller failure strain compared with the pristine C-NTH. According to the atomic configurations, the presence of nitrogen atoms always leads to stress/strain concentrations for the nanothreads under tensile deformation. This study provides a comprehensive understanding of the mechanical properties of CN-NTHs, which should shed light on their potential applications such as fibers or reinforcements for nanocomposites.

The discovery of high-mobility electron gas at the two-dimensional (2D) LaAlO3/SrTiO3 heterointerface [A. Ohtomo and H. Hwang, Nature (London) 427, 423 (2004)10.1038/nature02308] has attracted great research interest due to the ballistic transport of spatially confined electrons. When such kind of valence discontinuity extends to the interface of a well-chosen in-planar 2D heterostructure, a one-dimensional (1D) confined interface can be generated. Herein, through first-principles modeling, we demonstrate that Dirac-cone-like bands emerge at the 1D zigzag interface of a ZnO/MoS2 lateral heterostructure (LHS), creating a highly mobile 1D transport channel with a high Fermi velocity of 4.5×105m/s. The metallic state at the 1D heterointerface is attributed to the polar discontinuity that introduces excess charge carriers. Nontrivial polarization (excess carriers appear at boundaries) results in a large built-in electric field within the ZnO and MoS2 monolayers. Remarkably, the ultrafast 1D conducting channel is independent of the arrangements of width (m and n) in the (ZnO)m(MoS2)n LHS, which are further illustrated by tight-binding-based orbital and polarization analysis.

Inspired by recent experiments on the successful fabrication of monolayer Janus transition-metal dichalcogenides [ Lu, A.-Y.; et al. Nat. Nanotechnol. 2017, 12, (8), 744 and ferromagnetic VSe2 [ Bonilla, M.; et al. Nat. Nanotechnol. 2018, 13, (4), 289 ], we predict a highly stable room-temperature ferromagnetic Janus monolayer (VSSe) by density functional theory methods and further confirmed the stability by a global minimum search with the particle-swarm optimization method. The VSSe monolayer exhibits a large valley polarization due to the broken space- and time-reversal symmetry. Moreover, its low symmetry C3v point group results in giant in-plane piezoelectric polarization. Most interestingly, a strain-driven 90° lattice rotation is found in the magnetic VSSe monolayer with an extremely high reversal strain (73%), indicating an intrinsic ferroelasticity. The combination of piezoelectricity and valley polarization make magnetic 2D Janus VSSe a tantalizing material for potential applications in nanoelectronics, optoelectronics, and valleytronics.

This research builds up a multiphysics molecular model for nano electromechanical contact switch in a gaseous environment. To predict the device dynamic properties precisely, multiple methods have been incorporated, including: grand canonical Monte Carlo method for adsorption phenomenon, atomistic moment theory for dynamic electric field, and molecular dynamic simulation for carbon nanotube deformation. Using such a model, the charge distribution has been characterized; the adsorption influence on the frequency change and damping ratio has been investigated. The model has a great potential in the future design of nano electromechanical system.