[en] Highlights: • Mechanism of oil detachment from a glass surface in water is studied by molecular dynamics simulation. • The process of glass cleaning in water can be divided into three stages and the formation of different water channels in the oil phase is vital for the oil detachment. • The specific ring potential well structure of amorphous silica surface will hinder the detachment of oil. • One of the effective ways to clean up the oil pollution residues on the glass surface is increasing the upward lift force which acts on the hydrocarbon tail of oil molecules. - Abstract: In this paper, the mechanism of oil detachment from optical glass in water medium is studied by using molecular dynamics simulation. At the beginning, some undecane molecules are adsorbed on the amorphous silica surface to get contaminated glass. Upon addition of 6000 water molecules, most of the undecane molecules on the substrate surface can be detached from an amorphous silica surface through three stages. The formation of different directions of water channels is vital for oil detachment. The electrostatic interaction of water substrate contributes to disturbing the aggregates of undecane molecules and the H-bonding interaction between the water molecules is helpful for the oil puddle away from the substrate. However, there is still some oil molecules residue on the substrate surface after water cleaning. The simulation results showed that the specific ring potential well of amorphous silica surface will hinder the detachment of oil molecules. We also find that the formation of the specific ring potential well is related to the number of atoms and the average radius in silica atomic rings. Increasing the upward lift force, which acts on the hydrocarbon tail of oil molecules, will be benefit to clear the oil pollution residues from the glass surface.

[en] HIGHLIGHTS• Reflectivity of aluminum alloy is improved after being coated by gold film. • The optimal parameters combination of gold film are 45°C, 0.35 A, 140 s. • Adhesive force of gold film would be changed after holding at 60, −20°C. Aluminum alloys are widely applied in optical turrets after coating and super-finishing. Gold films prepared on aluminum alloy substrates via electron beam (e-beam) evaporation are considered to be effective way to realize close to total reflection of incident light. Here, we investigated the optimization of the reflectivity parameters of e-beam evaporated gold films; then, the influence of different deposition parameters on the surface quality, adhesive force and reflectivity (incident light in the 650–1700 nm range) of the film at −20, 25 and 60°C were systematically studied. The results demonstrated that the reflectivity and adhesion of the gold films both increased after high temperature holding and decreased slightly after low temperature holding. However, the surface morphology of the gold film did not change substantially. After holding at 60 and −20°C, the adhesive force decreased, which indicated that the adhesion strength between the reflective membrane and the substrate decreased.

[en] Highlights: • 3D Model was used to predict the laser ablation of AA 6061 before and after SiO₂ film. • Laser was utilized to redistribute to smooth the material pits and improve its performance. • The protective way of SiO₂ film reflected in the ablation depths and irradiation times. -- Abstract: In this work, the process of laser ablation of aluminum alloy 6061 (AA 6061) before and after silicon dioxide (SiO₂) coating was studied both experimentally and by numerical simulation. Four different laser fluences (0.5 J/cm², 1 J/cm², 1.5 J/cm² and 2 J/cm²) were applied to investigate laser ablation of AA 6061 before and after coated by SiO₂ film. It was founded that the thermal diffusion and ablation depth of AA 6061 had been directly influenced by both laser fluence and SiO₂ coating. At relatively low laser fluence (0.5 J/cm²), ablation deformation and damage of AA 6061 were not observed. While the laser fluence reached to 1 J/cm², vaporization took place in AA 6061. With increased laser fluence, the ablation range and depth expanded. The vaporization of SiO₂ films happened in the first laser fluence, however, the area of the zone affected were much less than AA 6061, that demonstrates the SiO₂ film has a positive effect on AA 6061. A 3-dimensional computational model was used to compute the temperature variation in a solid material over time. The results of the model (depth to width ratio versus laser ablation) exhibited well with the experimental results in some ways.

[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] Graphical abstract: In this paper, molecular dynamics simulation is performed to study the distribution of dislocation defects and local atomic crystal structure of single crystal copper. The stress distribution is investigated which is calculated by virial stress and analyzed by static pressure. The results are shown in (a)–(d). It is indicated that the compressive stress mainly spreads over the shear-slip zone, and the tensile stress is consisted in flank friction zone, shown in (a). The high tensile stress in subsurface is the source of stress, shown in (b). By the driven action of the stress source, the initial stair-rod dislocation nucleates. Then the dislocation climbs along four {1 1 1} planes under the stress driven action, shown in (d). Finally, the SFT is formed by the interaction of the compressive stress and the tensile stress which come from the shear-slip zone and friction zone, respectively. Besides, stair-rod dislocation, stacking faults and dislocation loop are also nucleated in the subsurface, shown in (c). Dislocation distribution, local atomic crystal structure state and stress-induced formation process of SFT by atomic. - Highlights: • A novel defect structure “stress-induced stacking fault tetrahedra” is revealed. • Atomic structural evolution and stress state distribution of the SFT are studied. • The stress-induced formation mechanism of the SFT is proposed. - Abstract: Stacking fault tetrahedra commonly existed in subsurface of deformed face center cubic metals, has great influence on machining precision and surface roughness in nano-cutting. Here we report, a stacking fault tetrahedra is formed in subsurface of workpiece during nano-cutting. The variation of cutting force and subsurface defects distribution are studied by using molecular dynamics simulation. The stress distribution is investigated which is calculated by virial stress and analyzed by static compression. The result shows that the cutting force has a rapidly increase in the initial stage and fluctuates at their equilibrium position at stable cutting stage, which is because of the energy accumulation and release leading to the dislocation emission. A typically stacking fault tetrahedra is nucleated in the subsurface defect layer, which is induced by the complex tension and compression stress. The stress-induced mechanism of stacking fault tetrahedra formation is investigated by atomic scale evolution and local stress distribution.

[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

[en] The volume change of liquid and solid gallium has been studied as a function of pressure and temperature up to 3.02 GPa at 300 K and up to 3.63 GPa at 330 K using synchrotron x-ray microtomography combined with energy dispersive x-ray diffraction techniques. Two sets of directly measured P-V data at 300 K and 330 K were obtained from 3D tomography reconstruction data, and the corresponding isothermal bulk moduli were determined as 23.6 (0.5) GPa and 24.6 (0.4) GPa, respectively. The existence of a liquid-liquid phase transition region is proposed based on the abnormal compressibility of Ga melt at about 2.44 GPa and 330 K conditions.