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[Display omitted] • Adopting micro-bulge textures to inhibit stick–slip behavior. • Investing stick–slip behavior in the sight of motion, friction, and wear. • Comparison of anti-stick–slip effect between micro-dimple and micro-bulge textures. • Micro-bulge textures exhibit better anti-stick–slip effect compared with others. Stick-slip behavior, a common problem of contact under severe lubrication, is closely related with surface topography. To investigate the influence of surface topography types on stick–slip behavior, micro-dimple and micro-bulge textures, typical concave and convex topographies, were fabricated by pulse picosecond laser and CW fiber, respectively. A gyroscope sensor was mounted on the pin-on-disc modular of multifunctional tribometer to conduct friction dynamics tests. The intensity of stick–slip behavior is characterized by the amplitude and duration of stick–slip behavior. The results show that, under the same starved lubrication, the micro-bulge textured disc showed the lowest intensity while the untextured one showed the highest intensity. In comparison with micro-dimple and micro-bulge textured disc exhibits higher efficiency in inhibiting stick–slip behavior as well as starting stable sliding. The mechanism of inhibiting stick–slip behavior for micro-dimple textures is generated by trapping wear debris and forming effective oil film. However, the cause of micro-bulge textures is the reduced contact area, which result in the reduction of the propensity of secondary plateaus, plastic flow, and adhesive junctions between asperities. [ABSTRACT FROM AUTHOR]

For micro/nanoscale devices, surface functionalization is essential to achieve function and performance superior to those that originate from the inherent bulk material properties. As a method of surface functionalization, we dip-coated nanometer-thick liquid lubricant films onto solid surfaces and then patterned the lubricant films with ultraviolet (UV) irradiation through a photomask. Surface topography, adhesion, and friction measurements demonstrated that the patterned films feature a concave–convex thickness distribution with thicker lubricant in the irradiated regions and a functional distribution with lower adhesion and friction in the irradiated convex regions. The pattern linewidth ranged from 100 to as fine as 0.5 μm. The surface functionalization effect of UV-patterning was investigated by measuring the water contact angles, surface energies, friction forces, and depletion of the patterned, as-dipped, and full UV-irradiated lubricant films. The full UV-irradiated lubricant film was hydrophobic with a water contact angle of 102.1°, and had lower surface energy, friction, and depletion than the as-dipped film, which was hydrophilic with a water contact angle of 80.7°. This demonstrates that UV irradiation substantially improves the surface and tribological properties of the nanometer-thick liquid lubricant films. The UV-patterned lubricant films exhibited superior surface and tribological properties than the as-dipped film. The water contact angle increased and the surface energy, friction, and depletion decreased as the pattern linewidth decreased. In particular, the 0.5-μm patterned lubricant film even showed a larger water contact angle and lower friction and depletion than the full UV-irradiated film. These indicate that UV-patterning of nanometer-thick lubricant films with a minimized linewidth has a better surface functionalization effect than full UV irradiation. Enhancement of the surface functionalization effect may be attributed to a transition in the contact state, which was indicated by the different instantaneous friction behavior of the 0.5-μm patterned lubricant film. [ABSTRACT FROM AUTHOR]

• Crystallographic orientation of MoS 2 influences its nanotribological properties. • Macroscopic coefficient of friction follows the findings on the nanoscale. • The correct growth process for the lubricant layers is crucial for applications. Tribological properties of a surface are controlled by its topography and chemical structure as suggested by theoretical studies. However, the effect of crystallographic orientation on the tribological properties is still controversial. By tuning the heating rate during sulfurization of CVD Mo films, we prepared the few-layer MoS 2 films with similar surface topography but different crystallographic c -axis orientation. This resulted in distinctly different tribological behavior both on the nanoscale and macroscale that can be attributed to different surface chemistry and surface electronic and phonon structures. In particular, horizontally aligned MoS 2 sheets with c -axis oriented along the surface normal favor the weak van der Waals forces which resulted in a twice lower coefficient of friction comparing to the vertically aligned MoS 2 sheets. These results demonstrate the possibility to optimize tribological properties by crystallographic orientation as required for the thin solid-state lubricating layers for extreme conditions. [ABSTRACT FROM AUTHOR]