Vacuum vapor deposition of PFPE molecules on CHxNy and CHxFy amorphous carbon surfaces

Abstract

According to the demand of increasing storage density for the magnetic data storage, a contact recording system is proposed, in which the head constantly makes contact with the disk surface during read/write cycles. In this system a stronger lubricant film for head disk interface (HDI) is required. In a conventional dip-coating method, which is carried out under atmospheric conditions, however, a fresh diamond like carbon (DLC) surface adsorbs several contaminations from the air and a strong lubricant layer is difficult to form on the DLC surface. In this study, a DLC layer is coated on a Si substrate by a plasma chemical vapor deposition (PCVD) method, then the DLCcoated Si sample is transferred to another vacuum chamber without being exposed to the atmosphere, and a perfluoropolyether (PFPE) lubricant film is vapor-deposited on the sample. The sample is analyzed by XPS and compared to the surface on which the PFPE lubricant is dip-coated. It is noted that both samples are rinsed after the coatings and the loose PFPE molecules are washed away. A thicker bonded layer of PFPE is formed on the DLC surface treated by vapor deposition. A tribological wear test is also carried out using a pin-on-disk tribotester. Both results show that the tribological characteristics are improved by the vapor deposition of PFPE molecules compared to the dip-coating method.

Effect of Heat Treatment Temperature on PFPE Molecules Bonded on DLC Surface

“…One of the features of bonding will be PFPE bonding which occurs when a hydrogen atom is transferred from the hydroxyl end to a dangling bond on the DLC surface 13) . In addition to bonding, hydrogen bonding between the hydroxyl end of the PFPE and an amine terminated sites on the DLC surface may occur because the desorption energy between the hydroxyl end and an amine terminated sites is higher than that between the hydroxyl end and an oxidized site on the DLC surface 5,6) . In this study, the amount of covalent bonding and hydrogen bonding were not quantitatively determined, therefore, a quantitative analysis for the covalent bonds and the hydrogen bonding must be a future study in order to clarify these features.…”

“…In addition, a thicker bonded layer of the PFPE molecules invites a higher wear resistance against the intermittent or continuous contact between the head and disk 4) . Vacuum vapor deposition of the PFPE film can effectively produce the thickest bonded PFPE film layer, which will be a monolayer, because some pollution of the DLC surface originating from the atmosphere can be avoided 5) . For vacuum vapor deposition, the PFPE film can be lubricated on the DLC surface without exposure to the atmosphere, therefore, contamination from the atmosphere does not affect the adsorption between the PFPE molecules and the active sites of the DLC surface during the lubrication process.…”