[en] Highlights: • Strain-induced structural variations of GaN nanocones are estimated using in situ TEM. • Young’s modulus of GaN nanocones with a diameter of 100–350 nm are 190–290 GPa. • The E₂ peak was red-shifted, indicated increased compressive stress. - Abstract: Mechanical property measurements of single nanocones are challenging because the small scale of the nanostructures. In this study, critical-stress- and strain-induced structural variations of GaN nanocones are estimated using in situ transmission electron microscopy (TEM) compression experiments. For single GaN nanocones with a diameter of 100–350 nm, the Young’s modulus, plastic deformation energy (W_p), and elastic deformation energy (W_e) values were 190–290 GPa, 0.02–1.65 × 10⁻¹¹ J, and 0.04–3.85 × 10⁻¹¹ J, respectively. Raman spectra were used to measure GaN indentation. The E₂ peak was red-shifted, indicated increased compressive stress in the indented area

[en] The nanoindentation process of single-crystal and nanocrystalline copper is studied with molecular dynamics simulations based on the many-body tight-binding potential. The grain size effect is evaluated in terms of slip vector, atomic stress, loading force, and hardness. The inverse Hall–Petch relation is found below 7 nm. With grain size smaller than 5 nm, the equivalent stress decreases quickly and stress-induced grain growth is observed in indentation process. Grain rotation is the main cause of grain coarsening for small grain sizes. For larger grain sizes, dislocations are found at the {1 1 1} close-packed plane and {1 0 0} plane.

[en] The pattern transfer mechanism of an alkanethiol self-assembled monolayer (SAM) on various rough surfaces during the dip-pen nanolithography (DPN) process and pattern characterizations are studied using molecular dynamics (MD) simulations. The mechanisms of molecular transference, alkanethiol meniscus characteristics, surface adsorbed energy, number of molecular transfer, contact angle and pattern characteristics are evaluated during the DPN process at room temperature. The simulation results clearly show that the molecular transfer ability in DPN is optimum for deposition on a smooth surface, because surface defects create a potential diffusion barrier for the control of the spreading of excess ink molecules. The adsorbed area of SAMs, number of molecular transfer and pattern size are significantly inversely proportional to the degrees of roughness of a substrate. The adsorbed area of SAMs is increased by the pull-off process and the growth rate of adsorbed area is about 11–38%. The effect of surface roughness on the DPN process can be decreased by increasing the indentation depth of a tip

[en] In this article, the mechanical properties and dynamic responses of Cu/Ta nanofilms with a hole defect under tension process were investigated using molecular dynamics simulation. The effects of temperature, the diameter of hole defect, strain rate and growing orientation were evaluated in terms of stress–strain relationship, dislocation mechanism, structural phase transformations, interface response, and local stress concentration. The results show that the phase transformations from fcc into HCP structures, and 〈112〉, 〈110〉 dislocations were found in Cu sections. The tensile strength reduced with the increasing temperature and increasing the diameter of the hole defect. In contrast, the tensile strength increased under the strain rate increased. The greater stress concentration factor at the higher temperature, however, the smaller stress concentration factor with the larger diameter of hole defect. The void growth expanded stronger at smaller hole defect. Between the nanofilms with different growing orientations, the Cu [100]/Ta [111] nanofilms exhibited the most excellent mechanical characteristics. (paper)

[en] Single-crystal aluminium nanowires under torsion are studied using molecular dynamics simulations based on the many-body tight-binding potential. The effects of temperature, loading rate and nanowire length are evaluated in terms of atomic trajectories, potential energy, von Mises stress, a centrosymmetry parameter, torque, shear modulus and radial distribution function. Simulation results clearly show that torsional deformation begins at the surface, extends close to the two ends and finally diffuses to the middle part. The critical torsional angle which represents the beginning of plastic deformation varies with different conditions. Before the critical torsional angle is reached, the potential energy and the torque required for the deformation of a nanowire significantly increase with the torsional angle. The critical torsional angle increases with increasing nanowire length and loading rate and decreasing temperature. The torque required for the deformation decreases and the shear modulus increases with increasing nanowire length. For higher temperatures and higher loading rates, torsional buckling more easily occurs at the two ends of a nanowire, whereas it occurs towards the middle part at or below room temperature with lower loading rates. Geometry instability occurs before material instability (buckling) for a long nanowire. (paper)

[en] The deformation behaviour and mechanical properties of three-dimensional (3D) pillared graphene are investigated using molecular dynamics simulations. The Tersoff–Brenner many-body potential model is employed to evaluate the interactions between 3D pillared-graphene carbon atoms and nanotube carbons. The Lennard-Jones potential model is used to compute the interactions between a conical indenter and 3D pillared-graphene carbon atoms. The effects of the size and geometric structure of 3D pillared-graphene are evaluated in terms of the indentation force and contact stiffness. The simulation results for an armchair nanotube of 3D pillared graphene show that the contact stiffness increases with increasing chiral vector of the 3D-pillared graphene. However, the adhesive force sharply decreases with increasing chiral vector of the 3D-pillared graphene. A zigzag nanotube of 3D-pillared graphene exhibits better mechanical properties compared with those of the armchair nanotube. (paper)

[en] This study investigated the mechanical properties and crack propagation behavior of polycrystalline copper using a molecular dynamics simulation. The effects of temperature, grain size, and crack length were evaluated in terms of atomic trajectories, slip vectors, common neighbor analysis, the material’s stress–strain diagram and Young’s modulus. The simulation results show that the grain boundary of the material is more easily damaged at high temperatures and that grain boundaries will combine at the crack tip. From the stress–strain diagram, it was observed that the maximum stress increased as the temperature decreased. In contrast, the maximum stress was reduced by increasing the temperature. With regard to the effect of the grain size, when the grain size was too small, the structure of the sample deformed due to the effect of atomic interactions, which caused the grain boundary structure to be disordered in general. However, when the grain size was larger, dislocations appeared and began to move from the tip of the crack, which led to a new dislocation phenomenon. With regards to the effect of the crack length, the tip of the crack did not affect the sample’s material when the crack length was less than 5 nm. However, when the crack length was above 7.5 nm, the grain boundary was damaged, and twinning structures and dislocations appeared on both sides of the crack tip. This is because the tip of the crack was blunt at first before sharpening due to the dislocation effect. (paper)

[en] In this study, an indentation simulation is employed to study the anisotropic crack propagation and re-forming mechanism of freestanding black phosphorus (FBP) nanosheets by molecular dynamics simulation. The results indicate that the size of the FBP nanosheet decides the crack direction as well as the von Mises stress concentration. It is found that crack directions are not influenced by temperature. With increasing specimen size, the crack propagation rate is nearly the same as at the first stage of crack formation, while in the later stage, cracking develops very quickly in larger specimens. Especially, small FBP nanosheets almost re-form in a short time at ambient temperature. However, after being destroyed, the larger specimen has no possibility of recovery. Besides, when increasing the number of layers of FBP, the energy stored by the top layer and the system undergoing deformation increases. In addition, the specimen with two fixed edges is less stable, leading to increased stress and decreased Young’s modulus compared with the specimen with four fixed edges. (paper)

[en] In this study, we investigate the mechanical properties of single-crystal copper (Cu) nanopillars. Critical deformation variations of Cu-nanopillared structures are estimated using in situ transmission electron microscopy compression tests and molecular dynamics simulations. The Young’s moduli of Cu nanopillars with diameters of 2–6 nm were 90.20–124.47 GPa. The contact stiffnesses of the Cu nanopillars with diameters of 400 and 500 nm were 1.33 and 3.86 N m⁻¹, respectively; the Poisson’s ratios for these nanopillars were 0.32 and 0.33. The yield strength of the nanopillars varied from 0.25 GPa at 500 nm to 0.42 GPa at 400 nm; the yield strength of single-crystal Cu nanopillars decreased with increasing diameter. The values of the indented hardness of the Cu block were 0.27 and 1.06 GPa, respectively. Through experimental work and molecular dynamics simulations, we demonstrate that Cu nanopillars exhibit internal stress transmission during compression. When compression reaches the maximum strain, it can be observed that Cu slips. Our results are useful for understanding the mechanical properties, contact, and local deformation of Cu nanopillars. (paper)

[en] In this study, fluorescent Eu³⁺-doped ZnLiNbO₄ materials were prepared via a vibrating milled solid-state reaction method. The objective was to develop new fluorescent oxide materials and study their fluorescent properties. The ZnLiNbO₄ tetragonal spinel structure was formed with a single phase at a sintering temperature of 800 °C and with a regular shape at 1000 °C. The main exciton band was at 466 nm (⁷F₀ → ⁵D₂), and the main emission band was at 615 nm (⁵D₀ → ⁷F₂), which was an orange–red light band. The emission intensity was approximately 5% when the doping concentration reached 7%. The decay time was 2.96 ms. (paper)