Collision Sliding Contact of Silicon-Based Nanodevices Considering the Influence of Microgravity Environment

With the development of nanotechnology, nano/micro-electromechanical systems (NEMS/MEMS) have also made significant progress. Because of their small size, low power consumption, and low cost, they are widely used in micro-nano satellites, pico-satellites and various high-precision instruments. Due to the severe size effects, the surface adhesion and friction force are more prominent compared to the volume force in traditional machinery, which greatly affect the performance, stability and service life of NEMS/MEMS devices. In space environment, the microgravity environment induces irregular collisions when components are disturbed, which causes collision friction and further influences their friction performance. Single crystal silicon is widely used in NEMS/MEMS, while its collision friction properties are still unknown. Therefore, studies on collision sliding contact of silicon-based nanodevices considering the influence of microgravity environment are of great significance for the wide application of NEMS/MEMS in the aerospace field. Based on the movement characteristics of random collisions of space mechanisms in microgravity environment, this paper proposed a molecular dynamics model to describe the collision and sliding contact between a rigid diamond indenter and an elastic silicon substrate, and the collision was represented by applying the coupled vibrations in Y and Z directions to the indenter. Besides, a spring was applied at the bottom of the substrate to simulate the response of the substrate to the vibrations of the indenter. The effects of vibration frequencies and amplitudes on the average friction forces were studied. The results showed that the average friction force of collision sliding contact exhibited obvious frequency dependence. When the vibration frequency of the indenter was lower than the natural frequency of the substrate, the average friction force showed little variation with the increase of the vibration frequency of the indenter. When the vibration frequency of the indenter was higher than the natural frequency, there was severe vibration between the indenter and substrate, and the average friction force decreased at the initial stage and then tended to a stable level with the increase of the vibration frequency. Severe vibration led to an increase in the surface temperature of the substrate and the failure of a large number of atomic lattice structure, which made the surface material of the substrate soft and reduced the shear modulus of the substrate. Increasing of the amplitude led to severe collisions between the indenter and the substrate. The increase of the amplitude led to the destruction of the lattice structure of more atoms on the surface of the substrate. As a result, the number of failure atoms increased and the temperature of the substrate surface became higher, which reduced the average friction force significantly. In addition, a large number of studies proved that textured surface with specific structural characteristics exhibited excellent tribological properties. Texture was introduced on the surface of the substrate, and the friction properties of the textured surface and a smooth surface under different working conditions were compared. The results showed that the textured surface reduced the real contact area between the indenter and the substrate. As the vibration frequency increased, the collision caused a great temperature rise in the contact area, which made the substrate material become soft, and the resistance of the indenter was reduced during the sliding process. As a result, the textured surface can reduce the average friction force effectively. In this work, molecular dynamics simulation was used to study the friction mechanism of collision sliding contacts and the anti-friction effects of textured surface, which provided a theoretical basis and scientific guidance for the anti-stick and anti-friction design of micro-nano devices.