[en] Highlights: • The dynamic conformational change of oil contaminations, at various surface coverages onto perfect α-Al_2O_3(0001) surface in aqueous solution is given. • The effect of surface coverage of oil molecules on the driving forces for the conformational change of oil contaminations is described. • The effect of interfacial water on the conformational change and even detachment of oil contaminations is considered. - Abstract: The microscopic conformational change process of oil contaminants adhered onto perfect α-Al_2O_3 (0001) surface in aqueous solution was investigated by using all-atom classic molecular dynamics simulations. The change in removal mechanism of oil contaminants induced by surface coverage (surface area per molecule) was emphatically explored. Our simulation results strongly reveal that the increase in oil surface coverage induces an evident difference in microscopic detachment processes of oil contaminants. At a low surface coverage, oil contaminants can be thoroughly detached from solid surface. The whole detachment process could be divided into multi stages, including conformational change of oil contaminants on solid surface, dynamic motion of those in bulk solution and rapid migration of those from bulk solution to air/water interface. With surface coverage increasing, water diffusion becomes the key to induce conformational change and promote the detachment of oil contaminants. When oil surface coverage exceeds a threshold value, oil contaminants also undertake an evident conformational change process exhibiting typical characteristics but an incomplete detachment process occurs. All findings of the present study are helpful for the interpretation of the removal mechanism of oil contaminants on solid surface.

[en] Graphical abstract: - Highlights: • Dynamic conformational change process of oil contaminations adhered onto Al-terminated α-Al_2O_3 surface in aqueous solution is given. • Effect of water penetration on the conformational change and even detachment of oil contaminants is considered. • Change of driving forces leading to the conformational change of oil contaminants is described. - Abstract: Microscopic conformational change of oil contaminants adhered onto perfect α-Al_2O_3 (0001) surface in the aqueous solution was simulated by means of detailed fully atomistic molecular dynamics simulations. The main driving forces of the conformation change process of the oil contaminants were explored. The simulation results indicate that with submerging of the contaminated α-Al_2O_3 (0001) surface into the aqueous solution, the oil contaminants undertake an evident conformational change process. The dynamic process can be divided into several stages, including early penetration of water molecules, formation and widening of water channel, and generation of molecularly adsorbed hydration layers. Moreover, the oil contaminants on the α-Al_2O_3 surface are not fully removed from solid surface after a 10 ns relaxation, while a relatively stable oil/water/solid three-phase interface is gradually formed. Further, the residual oil contaminants are finally divided into several new ordered molecular adsorption layers. In addition, by systemically analyzing the driving forces for the conformational change of the oil contaminants, the penetration of water molecules is found to be the most important driving force. With penetrating of the water molecules, the dominating interactions controlling the conformational change of the oil contaminants have been changing over the whole simulation.

[en] The Brenner–LJ potential is adopted to describe the interaction between C₃₆ clusters and diamond surface, and the deposition mechanism of multi-C₃₆ clusters on the diamond surface is also studied by using the method of molecular dynamics simulation. The simulation results show that the competition effects of two interactions, i.e. the interaction between cluster and cluster and the interaction between cluster and crystal plane, are studied, and then the influence of these competition effects on C₃₆ cluster deposition is analysed. The finding is that when an incident energy is appropriately chosen, C₃₆ clusters can be chemically adsorbed and deposited steadily on the diamond surface in the form of single-layer, and in the deposition process the multi-C₃₆ clusters present a phenomenon of energy transmission. The experimental result shows that at a temperature of 300K, in order to deposit C₃₆ clusters into a steady nano-structured single-layered film, the optimal incident energy is between 10 and 18 eV, if the incident energy is larger than 18 eV, the C₃₆ clusters will be deposited into an island nano-structured film. (condensed matter: structure, thermal and mechanical properties)

[en] In order to improve the lubrication of movement mechanism in final optics assembly, the plasma immersion ion implantation (PIII) technology is used to modify mechanical properties of work pieces with complex shape. The combination of suitable parameters can largely increase the hardness and wear resistance of material surfaces. The verification test was made by modifying the mechanical properties of the bearing inner race and bearing outer ring. Furthermore, the dimensional accuracy and the surface roughness of sample work pieces modified by PIII technology can maintain consistence with those of untreated pieces. The work sufficiently certificates that the PIII technology can amend the mechanical properties of work pieces and elongate the life length of movement mechanism kinematic accuracy. (authors)

[en] The formula for surface energy was modified in accordance with the slab model of molecular dynamics (MDs) simulations, and MD simulations were performed to investigate the relaxed structure and surface energy of perfect and pit rutile TiO₂(1 1 0). Simulation results indicate that the slab with a surface more than four layers away from the fixed layer expresses well the surface characteristics of rutile TiO₂ (1 1 0) surface; and the surface energy of perfect rutile TiO₂ (1 1 0) surface converges to 1.801±0.001 J m^-2. The study on perfect and pit slab models proves the effectiveness of the modified formula for surface energy. Moreover, the surface energy of pit surface is higher than that of perfect surface and exhibits an upper-concave parabolic increase and a step-like increase with increasing the number of units deleted along [0 0 1] and [1 1 0], respectively. Therefore, in order to obtain a higher surface energy, the direction along which atoms are cut out should be chosen in accordance with the pit sizes: [1-bar10] direction for a small pit size and [0 0 1] direction for a big pit size; or alternatively the odd units of atoms along [1 1 0] direction are removed

[en] Highlights: • m′ of paired twins distributes in a wide range (− 0.5 to 1) for extruded Mg alloys. • But about 60% of paired twins have the first rank m′ indicating the importance of local strain compatibility. • Simultaneously high SF and high m′ is favorable for twin pair formation in extruded Mg alloys. - Abstract: Recently, geometrical compatibility factor (m′) has been used to characterize local strain compatibility between paired twins formed in rolled Mg alloys with basal texture. High m′ and m′ rank were present in most cases, suggesting that m′ plays an important role in twin pair formation. The present study aims to extend the understanding of the effects of m′ and grain boundary (GB) misorientation angle on twin pair formation in an extruded Mg alloy with basal fiber texture. 106 sets of paired twins were extracted from electron backscatter diffraction (EBSD) data and were analyzed. The results show that m′ of paired twins distributes in a wide range (− 0.5 to 1) in extruded Mg alloys due to the presence of a large fraction of high angle GBs. About 60% of twin pairs have the first m′ rank, implying that m′ is still an important factor for variant selection of paired twins in extruded Mg alloys. The distribution of m′ with SF rank was also analyzed, showing that more than half of twin pairs are located in the left-top corner with m′ > 0.6 and SF either rank one or two, which confirms that simultaneously high SF and high m′ is favorable for twin pair formation in extruded Mg alloys.

[en] Highlights: • High processing capacity of nanoscale multi-tip diamond tools in terms of the dimensional accuracy of machined nanostructures is demonstrated. • A minimum designed ratio of tip distance to tip base width (L/W_f) should be met when designing the nanoscale multi-tip tool. • The overlap of the work-affected layers significantly affects the shaping capacity of nanoscale multi-tip tools. • The multi-tip tool with a tool tip angle (>11.8°) can improve the form accuracy of nanostructures. - Abstract: In this article, the shape transferability of using nanoscale multi-tip diamond tools in the diamond turning for scale-up manufacturing of nanostructures has been demonstrated. Atomistic multi-tip diamond tool models were built with different tool geometries in terms of the difference in the tip cross-sectional shape, tip angle, and the feature of tool tip configuration, to determine their effect on the applied forces and the machined nano-groove geometries. The quality of machined nanostructures was characterized by the thickness of the deformed layers and the dimensional accuracy achieved. Simulation results show that diamond turning using nanoscale multi-tip tools offers tremendous shape transferability in machining nanostructures. Both periodic and non-periodic nano-grooves with different cross-sectional shapes can be successfully fabricated using the multi-tip tools. A hypothesis of minimum designed ratio of tool tip distance to tip base width (L/W_f) of the nanoscale multi-tip diamond tool for the high precision machining of nanostructures was proposed based on the analytical study of the quality of the nanostructures fabricated using different types of the multi-tip tools. Nanometric cutting trials using nanoscale multi-tip diamond tools (different in L/W_f) fabricated by focused ion beam (FIB) were then conducted to verify the hypothesis. The investigations done in this work imply the potential of using the nanoscale multi-tip diamond tool for the deterministic fabrication of period and non-periodic nanostructures, which opens up the feasibility of using the process as a versatile manufacturing technique in nanotechnology

[en] A simple relocation technique for atomic force microscopy (AFM), which takes advantage of multi-wall carbon nanotube (MWCNT), is used for investigating repeatedly the imaging of some specific species on the whole substrate with a high relocation accuracy of tens of nanometers. As an example of the application of this technique, TappingMode AFM ex situ study of the morphology transition induced by solvent treatment in a triblock copolymer thin film has been carried out

[en] This study proposes a tungsten grating structure with SiO₂–W–SiO₂ multilayer films on a tungsten substrate as a thermal emitter for transverse-magnetic waves in a broad spectral region. The rigorous coupled-wave analysis method is employed to analyze the spectral emittance. Three close-to-unity peaks on the emittance spectrum lift the emittance in the wavelength range from 0.7 μm to 2.0 μm for the proposed thermal emitter. To quantify the applicability of the proposed emitter, parametric studies are performed regarding the effects of grating geometrical parameters, emission angle, metallic/dielectric layer thicknesses, and mismachining tolerance. The normal emittance of the proposed emitter is shown to be wavelength-selective and direction-insensitive. The mechanisms of excitations of surface plasmon polariton (SPP), gap plasmon polariton (GPP), and magnetic polariton (MP) in the multilayer structure are elucidated to evaluate their contributions on the emittance under different conditions. The results provide a useful reference to design and optimize selective thermal emitters with excellent performance. -- Highlights: • A thermal emitter with high emittance in a broad spectral region is proposed. • The polariton excitations are elucidated to evaluate their contributions. • The normal emittance is wavelength-selective and direction-insensitive. • The 0th order diffraction is the absolute contributor on the emission peaks

[en] Highlights: • An innovative analysis method is adopted to analyze nano-cutting process accurately. • A characteristic SFT and stair-rod dislocation are found in subsurface defect layer. • The formation mechanism of stair-rod dislocation is investigated. • The local atomic structure of subsurface defects is introduced. - Abstract: In this work, molecular dynamics simulation is performed to study the subsurface defects structural distribution and its evolution during nano-cutting process of single crystal copper. The formation mechanism of chip and machined surface is interviewed by analyzing the dislocation evolution and atomic migration. The centro-symmetry parameter and spherical harmonics method are adopted to characterize the distribution and evolution of the subsurface defect structures and local atomic structures. The results show that stacking faults, dislocation loops, “V-shaped” dislocation loops, and plenty of point defects are formed during the machined surface being formed in shear-slip zone. In subsurface damage layers, stair-rod dislocation, stacking fault tetrahedra, atomic cluster defect, and vacancy defect are formed. And the formation mechanism of stair-rod dislocation is investigated by atomic-scale structure evolution. The local atomic structures of subsurface defects are icosahedrons, hexagonal close packed, body-centered cubic, and defect face center cubic, and the variations of local atomic structures are investigated