Effective Elastic Moduli of Magnetic Disks with Molecularly Thin Liquid Lubricant Films Determined Using Ar-Gas Cluster Ion Beam

Abstract

To improve the reliability of the design of hard disk drives, this study aims to determine the effective elastic properties of disks with perfluoropolyether lubricant films on the diamond-like carbon overcoats of magnetic disks. However, the determination of the effective elastic modulus of multi-layered film from molecularly thin lubricant films (1.0 nm) and diamond-like carbon overcoats is extremely difficult because these layers are ultra-thin. Therefore, the method of etching in the depth direction with an Ar-gas cluster ion beam is proposed in this study. The lubricants D-4OH and Z-tetraol, comprising different main chains, are applied to the samples at varying thicknesses. Additionally, the D-4OH is UV-treated to vary the bonded film thickness. The effective Young's modulus of disk with D-4OH is approximately 60 and 20 GPa at 1.2 and 2.9 nm film thicknesses, respectively, whereas that of Z-tetraol is approximately 16 GPa at 1.2 nm film thickness, and exhibits less dependence on the film thickness than that of D-4OH. The effective Young's modulus of D-4OH increases with increasing bonded thickness. These results suggest a significant variation in the effective Young's modulus of disks with the lubricant film based on the film thickness, molecular structure, and adsorption state.

Keywords

• magnetic disk
• perfluoropolyether
• head–disk interface
• young’s modulus
• gas cluster ion beam