Inspired by recent experiments on the successful fabrication of monolayer Janus transition metal dichalcogenides [Nat. Nanotechnol. 12 (2017) 744] and ferromagnetic VSe 2 [Nat. Nanotechnol. 13 (2018) 289], here we for the first time predict a highly stable room temperature ferromagnetic Janus monolayer (VSSe) by ab initio evolutionary and density functional theory methods. Monolayer VSSe exhibits a large valley polarization due to the broken space and timereversal symmetry. Moreover, the low symmetry C3v point group of VSSe monolayer results in giant in-plane piezoelectric polarization. Most interestingly, a strain-driven 90° lattice rotation is occurred in magnetic VSSe monolayer with an extremely high reversal strain (73%), indicating an intrinsic ferroelasticity. The combination of multiferroic, piezoelectricity, and valley polarization will render magnetic 2D Janus VSSe for potential applications in nanoelectronics, optoelectronics and valleytronics.

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.

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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, AgBiP2S6, 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 distorted ferroelectric structure in ABP2X6 monolayers is the Jahn-Teller effect. ABP2X6 monolayers are predicted to be a new class of auxetic materials with an out-of-plane negative Poisson's ratio, i.e., the values of the negative Poisson's ratio are in the order AgBiP2S6 (−0.805) < AgBiP2Se6 (−0.778) < CuBiP2Se6 (−0.670) < CuInP2S6 (−0.060). This is mainly due to the tensile strain applied in the x/y direction enlarging the angle between P-P bonds and top layer X atoms, thereby enhancing the bucking height of monolayer ABP2X6. Moreover, external strain has a significant impact on the A-B off-center displacement, rendering an out-of-plane piezoelectric polarization. The values of e13 for CuInP2S6, CuBiP2Se6, AgBiP2S6, AgBiP2Se6 monolayers are calculated to be −3.95 × 10 −12 , −5.68 × 10 −12 , −3.94 × 10 −12 , −2.71 × 10 −12 C•m −1 , respectively, which are comparable to the only experimentally confirmed 2D out-of-plane piezoelectric Janus system (piezoelectric coefficient = −3.8 × 10 −12 C•m −1 ). This unusual auxetic behavior, ferroelectric polarization, and the electromechanical coupling in monolayer ABP2X6 could potentially lead to enormous technologically important applications in nanoelectronics, nanomechanics, and piezoelect...

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.

Gold nanoparticles (AuNPs) are promising materials for many bioapplications. However, upon contacting with biological media, AuNPs undergo changes. The interaction with proteins results in the so‐called protein corona (PC) around AuNPs, leading to the new bioidentity and optical properties. Understanding the mechanisms of PC formation and its functions can help us to utilise its benefits and avoid its drawbacks. To date, most of the previous works aimed to understand the mechanisms governing PC formation and focused on the spherical nanoparticles, although non‐spherical nanoparticles are designed for a wide range of applications in biosensing. In this work, we investigated the differences in PC formation on spherical and anisotropic AuNPs (nanostars in particular) from the joint experimental (extinction spectroscopy, zeta potential and surface‐enhanced Raman scattering [SERS]) and computational methods (the finite element method and molecular dynamics [MD] simulations). We discovered that protein does not fully cover the surface of anisotropic nanoparticles, leaving SERS hot‐spots at the tips and high curvature edges ‘available’ for analyte binding (no SERS signal after pre‐incubation with protein) while providing protein‐induced stabilization (indicated by extinction spectroscopy) of the AuNPs by providing a protein layer around the particle's core. The findings are confirmed from our MD simulations, the adsorption energy significantly decreases with the increased radius of curvature, so that tips (adsorption energy: 2762.334 kJ/mol) would be the least preferential binding site compared to core (adsorption energy: 11819.263 kJ/mol). These observations will help the development of new nanostructures with improved sensing and targeting ability.

Titanium dioxide (TiO 2 ) nanowires (NWs) are usually considered to be brittle semiconductor materials, which limits their use in strain-related applications, even though they are already widely applied in various fields. Based on observations using an in situ transmission electron microscopy method, we find, for the first time, that individual crystalline TiO 2 NWs with a bronze phase (TiO 2 −B) can exhibit an ultralarge elastic bending strain of up to 18.7%. Using an in situ atomic-scale study, the underlying mechanisms of the ultralarge bending deformation of TiO 2 −B NWs under the ⟨111⟩{100} system are revealed to be governed by lattice shear and rich dislocation movements; the lattice shearing is supported by numerical simulations. Locally, large-scale sheared lattices with a shear strain of up to 10.7% can be observed in a bent NW. It is believed that the large-scale lattice shearing deformation offers the NW the ability to absorb a large bending energy so that fast dislocation aggregation and propagation are avoided. Therefore, the TiO 2 −B NWs can endure an ultralarge bending strain without crack formation or amorphization. However, it is found that the lattice shear-governed bending mechanism is not applied in the ⟨010⟩{100} system. These results are able to provide more opportunities for the strain engineering of TiO 2 NWs and also help promote the potential applications of TiO 2 NW-based flexible devices.

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