Accurate control of friction with nanosculptured thin coatings: Application to gripping in microscale assembly

Abstract

Chromium thin films were sputter deposited implementing the GLancing Angle Deposition (GLAD) method, which is a thin film deposition technique where the incident vapor flux – composed of atoms and molecules from gas phase – strikes onto the substrate at tilted angles a. Oriented chromium columns were produced with various column angles b (from 0 to 60°) closely linked to the sputtering pressure and incidence angle a. Three sputtering pressures of 0.11, 0.40 and 0.53 Pa were used. Incidence angle a of the sputtered particles was systematically changed from 0 to 80°. Tribological properties were investigated as a function of these operating parameters. Results reveal that the tribological behaviour is strongly correlated with the structure and especially the growth mechanism of the films, which are both linked with the operating sputtering parameters. Thus, at the lowest sputtering pressure (0.11 Pa), gradual variations of the tribological properties and wettability are observed as a function of the incidence angle a, which are interesting for tailoring surfaces displaying a gradient of wettability. In contrast, at higher sputtering pressures (>0.2 Pa), local variations of static friction coefficient, wettability and lateral contact stiffness are systematically observed as a function of the column angle b—and then the incidence angle a. Basically, these results enable to tailor tribological properties by tuning the incidence angle a in order to control the transition from sticking to sliding in micro-gripping