Reuben J. Yeo

Understanding the Role of Nitrogen in Plasma-Assisted Surface Modification of Magnetic Recording Media with and without Ultrathin Carbon Overcoats

A novel scheme of pre-surface modification of media using mixed argon-nitrogen plasma is proposed to improve the protection performance of 1.5 nm carbon overcoats (COC) on media produced by a facile pulsed DC sputtering technique. We observe stable and lower friction, higher wear resistance, higher oxidation resistance, and lower surface polarity for the media sample modified in 70%Ar + 30%N2 plasma and possessing 1.5 nm COC as compared to samples prepared using gaseous compositions of 100%Ar and 50%Ar + 50%N2 with 1.5 nm COC. Raman and X-ray photoelectron spectroscopy results suggest that the surface modification process does not affect the microstructure of the grown COC. Instead, the improved tribological, corrosion-resistant and oxidation-resistant characteristics after 70%Ar + 30%N2 plasma-assisted modification can be attributed to, firstly, the enrichment in surface and interfacial bonding, leading to interfacial strength, and secondly, more effective removal of ambient oxygen from the media surface, leading to stronger adhesion of the COC with media, reduction of media corrosion and oxidation, and surface polarity. Moreover, the tribological, corrosion and surface properties of mixed Ar + N2 plasma treated media with 1.5 nm COCs are found to be comparable or better than ~2.7 nm thick conventional COC in commercial media.

Probing the Role of an Atomically Thin SiNx Interlayer on the Structure of Ultrathin Carbon Films

Filtered cathodic vacuum arc (FCVA) processed carbon films are being considered as a promising protective media overcoat material for future hard disk drives (HDDs). However, at ultrathin film levels, FCVA-deposited carbon films show a dramatic change in their structure in terms of loss of sp3 bonding, density, wear resistance etc., compared to their bulk counterpart. We report for the first time how an atomically thin (0.4 nm) silicon nitride (SiNx) interlayer helps in maintaining/improving the sp3 carbon bonding, enhancing interfacial strength/bonding, improving oxidation/corrosion resistance, and strengthening the tribological properties of FCVA-deposited carbon films, even at ultrathin levels (1.2 nm). We propose the role of the SiNx interlayer in preventing the catalytic activity of Co and Pt in media, leading to enhanced sp3C bonding (relative enhancement ~40%). These findings are extremely important in view of the atomic level understanding of structural modification and the development of high density HDDs.

Probing the role of carbon microstructure on the thermal stability and performance of ultrathin (<2 nm) overcoats on L10 FePt media for heat-assisted magnetic recording.

An understanding of the factors influencing the thermal stability of ultrathin carbon overcoats (COCs) is crucial for their application in heat-assisted magnetic recording (HAMR) at densities ≥ 1 Tb/in(2). Two types of non-hydrogenated ultrathin (∼1.5 nm) COCs were investigated after being subjected to laser-induced localized heating (at temperatures > 700 K) as envisaged in HAMR. Filtered cathodic vacuum arc (FCVA)-processed carbon with tuned C(+) ion energies of 350 eV followed by 90 eV provides significantly higher sp(3) C-C hybridization than magnetron sputter deposition even at very low thicknesses of ∼1.5 nm. As a result, the FCVA-deposited ultrathin carbon overcoats displayed excellent thermal stability along with improved wear and corrosion resistance. On the other hand, the sputtered carbon exhibited carbon loss and topographical and structural changes after laser irradiation owing to lower sp(3) hybridization. Therefore, this study highlights the pivotal role of carbon microstructure, primarily sp(3) hybridization, in non-hydrogenated carbon overcoats to maintain excellent thermal stability during the recurring high-temperature cycles in a HAMR process.

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

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.

Enhanced Tribological, Corrosion, and Microstructural Properties of an Ultrathin (<2 nm) Silicon Nitride/Carbon Bilayer Overcoat for High Density Magnetic Storage

An ultrathin bilayer overcoat of silicon nitride and carbon (SiNx/C) providing low friction, high wear resistance, and high corrosion resistance is proposed for future generation hard disk media. The 16 Å thick SiNx/C overcoat consists of an atomically thin SiNx underlayer (4 Å) and a carbon layer (12 Å), fabricated by reactive magnetron sputtering and filtered cathodic vacuum arc (FCVA), respectively. When compared with monolithic overcoats of FCVA-deposited carbon (16 Å) and sputtered SiNx (16 Å), the SiNx/C bilayer overcoat demonstrated the best tribological performance with a coefficient of friction < 0.2. Despite showing marginally less electrochemical corrosion protection than monolithic SiNx, its ability to protect the magnetic media from corrosion/oxidation was better than that of an ∼27 Å thick commercial hard disk overcoat and 16 Å thick monolithic FCVA-deposited carbon. From X-ray photoelectron spectroscopy and Raman spectroscopy analyses, it was found that the introduction of the 4 Å SiNx underlayer facilitated higher sp(3) hybridization within the carbon layer by acting as a barrier and promoted the formation of strong bonds at the SiNx/C and the SiNx/media interfaces by acting as an adhesion layer. The higher sp(3) carbon content is expected to improve the thermal stability of the overcoat, which is extremely important for future hard disk drives employing heat assisted magnetic recording (HAMR).

Atomic Scale Interface Manipulation, Structural Engineering, and Their Impact on Ultrathin Carbon Films in Controlling Wear, Friction, and Corrosion

Reducing friction, wear, and corrosion of diverse materials/devices using <2 nm thick protective carbon films remains challenging, which limits the developments of many technologies, such as magnetic data storage systems. Here, we present a novel approach based on atomic scale interface manipulation to engineer and control the friction, wear, corrosion, and structural characteristics of 0.7-1.7 nm carbon-based films on CoCrPt:oxide-based magnetic media. We demonstrate that when an atomically thin (∼0.5 nm) chromium nitride (CrNx) layer is sandwiched between the magnetic media and an ultrathin carbon overlayer (1.2 nm), it modifies the film-substrate interface, creates various types of interfacial bonding, increases the interfacial adhesion, and tunes the structure of carbon in terms of its sp(3) bonding. These contribute to its remarkable functional properties, such as stable and lowest coefficient of friction (∼0.15-0.2), highest wear resistance and better corrosion resistance despite being only ∼1.7 nm thick, surpassing those of ∼2.7 nm thick current commercial carbon overcoat (COC) and other overcoats in this work. While this approach has direct implications for advancing current magnetic storage technology with its ultralow thickness, it can also be applied to advance the protective and barrier capabilities of other ultrathin materials for associated technologies.

Durable ultrathin silicon nitride/carbon bilayer overcoats for magnetic heads: The role of enhanced interfacial bonding

Pole tip recession (PTR) is one of the major issues faced in magnetic tape storage technology, which causes an increase in the magnetic spacing and hence signal loss during data readback. Despite efforts to reduce the magnetic spacing, PTR, and surface wear on the heads by using protective overcoats, most of them either employ complex fabrication processes and approaches do not provide adequate protection to the head or are too thick (∼10–20 nm), especially for future high density tape storage. In this work, we discuss an approach to reduce the PTR and surface wear at the head by developing an ultrathin ∼7 nm bilayer overcoat of silicon/silicon nitride (Si/SiNx) and carbon (C), which is totally fabricated by a cost-effective and industrial-friendly magnetron sputtering process. When compared with a monolithic C overcoat of similar thickness, the electrically insulating Si/SiNx/C bilayer overcoat was found to provide better wear protection for commercial tape heads, as demonstrated by Auger electron spectr...

Excellent wear life of silicon nitride/tetrahedral amorphous carbon bilayer overcoat on functional tape heads

Developing ultrathin and highly wear-resistant overcoats for magnetic tape heads is one of the current research areas of interest, because of its potential to delay pole tip recession and increase the operational lifetime of high areal density tape drives. Using optimized process conditions and an appropriate overcoat design, we report on the development of a ∼20 nm thick silicon nitride/tetrahedral amorphous carbon (Si/SiNx/ta-C) bilayer overcoat, where the ta-C film was deposited by a filtered cathodic vacuum arc process. The bilayer overcoat deposited on a functional tape head survived 40–50 × 106 m of testing with commercial tape media under standard industrial testing conditions. The excellent wear resistance of the overcoat was attributed to the generation of high (∼72%) sp3 carbon content and the formation of strong interfacial bonds, such as Si-C, C=N, nitrile, and (Al, Ti)N at the interfaces, as confirmed by various spectroscopic techniques. This study demonstrates the pivotal role of high sp3 ca...

Comparison of Corrosion and Tribological Properties of Ultrathin (<2 nm) Carbon Films on Hard-Disk Media by DC Sputtering and FCVA Processes

Ultrathin carbon overcoats (COCs) are of great interest for future hard-disk media. In view of future requirements, the key research focus lies in investigating/maintaining tribological and oxidation resistance properties of different types of COCs with thicknesses <;2nm. We report on the tribological and oxidation resistance properties of sputtering and filtered cathodic vacuum arc (FCVA) processed ultrathin COCs of thicknesses in the range of ~1.2-1.6nm. FCVA-deposited 1.6nm COC exhibits excellent properties in terms of lower coefficient of friction (COF, 0.2-0.25), higher wear resistance and greater oxidation resistance. In contrast, sputtered 1.2 and 1.5nm COCs show higher COF (~0.4-0.5), poor wear and oxidation resistance properties. The tribological and oxidation resistance performance of 1.2 and 1.6nm thick FCVA-processed COCs are found to be comparable with, or even better than, significantly thicker ~2.7nm commercial COC, demonstrating the effectiveness of the FCVA processed ultrathin protective magnetic media overcoats.

Silicon nitride/tetrahedral amorphous carbon bilayer overcoat for exceptional wear life of functional tape heads

In this study, we developed a novel bilayer overcoat on a functional tape head which exhibits long-term wear durability with commercial tape in an actual tape drive environment. The overcoat used in this work is a ~ 20 nm bilayer overcoat structure comprising a composite interlayer of amorphous silicon/silicon nitride (Si/SiNx) after bombardment with high energy C+ ions, followed by a ta-C layer deposited atop .