Ultrathin Carbon with Interspersed Graphene/Fullerene-like Nanostructures: A Durable Protective Overcoat for High Density Magnetic Storage.

Neeraj Dwivedi,Hai Xu,Kian Ping Loh,Sudhiranjan Tripathy,Reuben J Yeo,Nalam Satyanarayana,Charanjit S Bhatia

doi:10.1038/srep11607

Abstract

One of the key issues for future hard disk drive technology is to design and develop ultrathin (<2 nm) overcoats with excellent wear- and corrosion protection and high thermal stability. Forming carbon overcoats (COCs) having interspersed nanostructures by the filtered cathodic vacuum arc (FCVA) process can be an effective approach to achieve the desired target. In this work, by employing a novel bi-level surface modification approach using FCVA, the formation of a high sp3 bonded ultrathin (~1.7 nm) amorphous carbon overcoat with interspersed graphene/fullerene-like nanostructures, grown on magnetic hard disk media, is reported. The in-depth spectroscopic and microscopic analyses by high resolution transmission electron microscopy, scanning tunneling microscopy, time-of-flight secondary ion mass spectrometry, and Raman spectroscopy support the observed findings. Despite a reduction of ~37 % in COC thickness, the FCVA-processed thinner COC (~1.7 nm) shows promising functional performance in terms of lower coefficient of friction (~0.25), higher wear resistance, lower surface energy, excellent hydrophobicity and similar/better oxidation corrosion resistance than current commercial COCs of thickness ~2.7 nm. The surface and tribological properties of FCVA-deposited COC was further improved after deposition of lubricant layer.

Highlights

With the growing usage and demand for digital data storage in recent years, the magnetic hard disk drive (HDD) industry is working towards finding solutions to achieve higher data storage densities
This has spurred immense interest to search and explore alternative processes to tailor the microstructure of carbon overcoats (COCs) such that the desirable functional performance can be realized at a thickness of < 2 nm for future media overcoats
Amaratunga et al.[14] and Alexandrou et al.[16] confirmed the presence of graphene/fullerene-like nanocrystallites in amorphous carbon matrix by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS), while Chhowalla et al.[15] have employed mass spectrometry to investigate the generation of fullerene-like carbon structures in the plasma phase and later by TEM in the condensed state

Summary

Introduction

With the growing usage and demand for digital data storage in recent years, the magnetic hard disk drive (HDD) industry is working towards finding solutions to achieve higher data storage densities. This indicates that FCVA-processed COCs have great potential to be used in future magnetic recording technologies such as heat assisted magnetic recording (HAMR) Advanced carbon nanomaterials such as fullerene-like carbon and graphene nanostructures show remarkable properties such as high hardness, low friction, high elasticity, high wear- and corrosion resistance[11,12,13]. While the presence of high sp[3] carbon bonding helps to acheive high thermal stability as well as high corrosion- and wear resistance, the presence of these graphene/fullerene-like carbon nanostructures can contribute to further improvement of the wear- and corrosion resistance of the COC as well as to attain low friction Due to their synergetic effect the presence of graphene/fullerene carbon nanostructures in a highly sp[3] bonded a-C ultrathin film may show improved functional performance for for future media overcoats. The perfluoropolyether (PFPE)-based lubricated (lube) was applied on FCVA-deposited COC to compare the tribological and surface properties of media with our COC and lube and full commercial media with commercial COC and commercial lube

Methods

Results

Conclusion