Hydrated ions (Li + , Na + , and K + ) are capable of achieving macroscale superlubricity under high contact pressures and high normal loads, which mainly originates from the hydration effect and tribochemical reaction related to the in situ formation of an interfacial nanostructured shear layer, namely, a silica-like tribolayer. Nevertheless, the mechanisms governing this macroscale superlubricity especially the growth activities and the specific contribution of such a silica layer formed through the tribochemical reaction to macroscale hydration superlubricity remains unclear. Here, using transmission electron microscopy and the X-ray photoelectron spectroscopy depth profile technique, we resolved the amorphous structure on the atomic scale and determined the thickness of the tribo-induced silica layer. Using atomic force microscope nanoindentation, we reveal the mechanical properties of the 6 nm-thick silica layer generated on a Si 3 N 4 ball, which has a smaller elastic modulus of 75 GPa. Through friction experiments and ζ-potential analyses, we report on two main effects of the silica layer on achieving superlubricity. First, the silica layer can significantly reduce the friction resistance between ceramic surfaces under boundary lubrication at both the macroscale and microscale. Second, the Si 3 N 4 surface exhibits a larger negative potential and better hydrophilicity due to the presence of the silica layer, thereby adsorbing more hydrated cations. The observations show that the superlubricity of hydrated ions can be obtained not only between two mica surfaces but also for ceramic surface pairs with lower surface charge density, higher elastic modulus, and even larger surface roughness. These findings demonstrate that a tribochemical pretreatment of surfaces allows the hydration effect to be effective to the macroscopic regime, thereby promoting the realization of hydration superlubricity.

The understanding on the friction properties of black phosphorus (BP) is very crucial for such applications as strain‐engineered devices and micro/nanoelectromechanical systems. Herein, the relationship between the layer number of few‐layer BP flakes and its nanoscale friction, as well as the atomic‐scale friction anisotropy, is studied. BP flakes thicker than about five layers show almost the same friction as that of the bulk value, and the friction increases with the layer number decreasing from five, due to the strengthening mechanism. Obvious friction anisotropy of BP flakes are observed in that the friction for the armchair direction is the highest, that for the zigzag direction the lowest, and that for the lattice orientation between the two directions the intermediate. Supported by the theoretical prediction with 2D Tomlinson model, the observed phenomena are explained by the anisotropies in the amplitudes of the tip‐induced flexural deformations of BP flakes.

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Spatial crowdsourcing (SC) outsources tasks to a set of workers who are required to physically move to specified locations and accomplish tasks. Recently, it is emerging as a promising tool for emergency management, as it enables efficient and cost-effective collection of critical information in emergency such as earthquakes, when search and rescue survivors in potential ares are required. However in current SC systems, task locations and worker locations are all exposed in public without any privacy protection. SC systems if attacked thus have penitential risk of privacy leakage. In this paper, we propose a protocol for protecting the privacy for both workers and task requesters while maintaining the functionality of SC systems. The proposed protocol is built on partially homomorphic encryption schemes, and can efficiently realize complex operations required during task assignment over encrypted data through a well-designed computation strategy. We prove that the proposed protocol is privacy-preserving against semi-honest adversaries. Simulation on two real-world datasets shows that the proposed protocol is more effective than

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