Minimization of nano-scale friction force of DLC films with the periodic structiues processed by a femto-seoond laser

2004 Fiscal Year Final Research Report Summary

• Project/Area Number: 15560115
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Design engineering/Machine functional elements/Tribology
• Research Institution: University of Fukui
• Principal Investigator: HONDA Tomomi University of Fukui, Dept.of Mechanical Engineering, Associate Professor, 工学部機械工学科, 助教授 (80251982)
• Co-Investigator(Kenkyū-buntansha): YASUMARU Naoki Fukui National College of Tehcnology, Dept.of Mechanical Engineering, Professor, 機械工学科, 教授 (90158006)
• Project Period (FY): 2003 – 2004
• Keywords: Nano-tribology / DLC films / Femto-second laser / Nano-texturing / Low friction / Atomic force microscope / Adhesive force / Contact angle

Research Abstract

It is known that the optimum surface roughness is capable of reducing lateral force. The pull-off force and lateral force were measured by using a scanning probe microscope (SPM) with various curvature radius of a spherical tip in air under the relative humidity controlled.
(1)The frictional properties of the diamond-like carbon (DLC) films with the periodic structures were investigated in nano-scale using SPM. DLC films were prepared by an unbalanced magnetron sputtering method. The periodic structures have been generated on the surface of DLC films by polarized femto-second laser (τ=40fs, λ=800nm, F=10Hz) of energies nearby ablation threshold. The influence of normal load and relative humidity on the lateral forces was confirmed by the SPM. We used a silicon nitride rectangular cantilever with sharpened pyramidal tip or a spherical glass tip. Using the sharpened pyramidal tip, the lateral force of the DLC film with the periodic structures was higher than that of the film without the periodic structures. On the other hand, the lateral force of the DLC film with the periodic structures was lower than that of the film without the periodic structures using a spherical glass tip at low normal load and low relative humidity.
(2)The tests were performed with two kinds of super-water-repellent coating films, which are the porous Al_2O_3+FAS and the flower-like Al_2O_3+FAS. The lateral force increases with the increase in the inclination of surface asperities in case of the SiN tip whose radius of curvature is too small. On the contrary, the lateral force hardly takes the influence of the inclination of surface asperities, and almost becomes constant value with the glass sphere tip whose radius of curvature is big.
From these results, it is found that for the control of the friction force in nano-scale, the control of the surface roughness is effective and we can reduce the friction force using this method.