C. Singh Bhatia

Hardness, elastic modulus, and structure of very hard carbon films produced by cathodic‐arc deposition with substrate pulse biasing

The hardness, elastic modulus, and structure of several amorphous carbon films on silicon prepared by cathodic‐arc deposition with substrate pulse biasing have been examined using nanoindentation, energy loss spectroscopy (EELS), and cross‐sectional transmission electron microscopy. EELS analysis shows that the highest sp3 contents (85%) and densities (3.00 g/cm3) are achieved at incident ion energies of around 120 eV. The hardness and elastic modulus of the films with the highest sp3 contents are at least 59 and 400 GPa, respectively. These values are conservative lower estimates due to substrate influences on the nanoindentation measurements. The films are predominantly amorphous with a ∼20 nm surface layer which is structurally different and softer than the bulk.

Low-temperature magnetron sputter-deposition, hardness, and electrical resistivity of amorphous and crystalline alumina thin films

Aluminum oxide films were grown by reactive magnetron sputtering. In order to maintain a stable deposition process and high deposition rate, a pulsed direct current bias was applied to the aluminum target and the substrate. An external solenoid was used to form a magnetic trap between the target and the substrate. The influence of substrate temperature, substrate bias, and the magnetic trap on film growth and properties was studied by different surface and thin-film analysis techniques and electrical measurements. Normally, amorphous alumina films were produced. However, under optimum process conditions, crystalline alumina films can be obtained at temperatures as low as 250 °C, with a hardness ∼20 GPa and excellent electrical insulating properties.

Multilayers of amorphous carbon prepared by cathodic arc deposition

Filtered cathodic arc deposition is an effective technique for preparing amorphous hard carbon films of high quality. Pulsed biasing of the substrate leads to a variation of the ion energy. Therefore the film properties, which are influenced by the ion energy, can be changed over a wide range. Using an alternating high- and low-bias voltage, we have formed multilayers of hard and soft amorphous carbon films. The structure and mechanical properties of the multilayers were investigated by transmission electron microscopy and nanoindentation. They are discussed in relation to Monte Carlo computer simulations of the deposition process. It was found that the multilayer structure formation can be well predicted by the Monte Carlo computer code.

Ultra-Thin Overcoats for the Head/Disk Interface Tribology

Areal density in magnetic storage is increasing at a blistering pace of 60% annually. Recently IBM announced its mobile product with the industry highest areal density of 2.64 Gb/In{sup 2}. The areal density demonstrations have shown up to 5 Gb/In{sup 2} possible. Reaching higher areal density targets dictate that magnetic spacing between heads and disks be reduced. For the example of a 10 Gb/In{sup 2} areal density goal, the magnetic spacing should be {approx}25 nm. In budgeting this magnetic spacing, it is required that disk and slider air bearing surface overcoats thickness be reduced to 5 nm range. Present choice of carbon overcoat in the magnetic storage hard disk drive industry is sputter deposited, hydrogenated carbon (CH{sub x}) with thickness in the range of 12-15 nm on heads and disks. Novel overcoats such as nitrogenated carbon (CN{sub x}) and cathodic arc carbon films are being developed for future applications. Cathodic arc deposition forms ultra-thin amorphous hard carbon films of high sp{sup 3} content, high hardness, and low coefficient of friction. These properties make it of great interest for head/disk interface application, in particular for contact recording. In many cases, the tribological properties of the head disk interface could be improved by factors up to ten applying cathodic arc overcoats to the slider or disk surface. This paper reviews the results of cathodic arc ultra-thin (2-10 nm) carbon overcoats for head/disk interface tribological applications.

Thermal and electron‐stimulated chemistry of Fomblin–Zdol lubricant on a magnetic disk

The thermal and electron‐induced decomposition of Fomblin–Zdol lubricant on a rigid magnetic disk with a hard carbon overcoat are studied by temperature‐programmed reaction/desorption spectroscopy and electron stimulated desorption. The thermal spectroscopy shows two desorption features peaked at 640 and 700 K resulting from decomposition of the Fomblin–Zdol molecules. The threshold temperature for dissociation of the Fomblin–Zdol molecule is at 500–550 K in accordance with the known thermal stability of the free molecule. HF originating from thermal reactions with either surface OH or surface CH groups is a prominent desorption product. Electron impact also causes Fomblin–Zdol dissociation. Two efficient mechanisms for electron impact dissociation have been resolved separately above and below the ionization threshold of ∼14 eV. The low‐energy process is likely due to the formation of negative ions followed by dissociation (dissociative electron attachment) and has a cross section of ∼2×10−16 cm2. These results show that Fomblin–Zdol as a lubricant on a magnetic disk is inherently unstable thermally and in the presence of triboelectrons.

Design and Dynamics of Flying Height Control Slider With Piezoelectric Nanoactuator in Hard Disk Drives

To achieve the areal density goal in hard disk drives of 1 Tbit/in. 2 the minimum physical spacing or flying height (FH) between the read/write element and disk must be reduced to 2n m. A brief review of several FH adjustment schemes is first presented and discussed. Previous research showed that the actuation efficiency (defined as the ratio of the FH reduction to the stroke) was low due to the significant air bearing coupling. In this paper, an air bearing surface design, Slider B, for a FH control slider with a piezoelectric nanoactuator is proposed to achieve virtually 100% efficiency and to increase dynamics stability by minimizing the nanoscale adhesion forces. A numerical study was conducted to investigate both the static and dynamic performances of the Slider B, such as uniformity of gap FH with near-zero roll over the entire disk, ultrahigh roll stiffness and damping, low nanoscale adhesion forces, uniform FH track-seeking motion, dynamic load/unload, and FH modulation. Slider B was found to exhibit an overall enhancement in performance, stability, and reliability in ultrahigh density magnetic recording. DOI: 10.1115/1.2401208

Ultrathin CNx overcoats for 1 Tb/in.2 hard disk drive systems

Carbon nitride films were grown on silicon and hard disk substrates using pulsed dc magnetron sputtering in a single-cathode deposition system. Substrates were mounted on a specially designed holder that allowed 45° tilt angle and substrate rotation about the surface normal up to 20 rpm. The influence of substrate bias, substrate tilt, and rotation on film growth and properties was studied. Films with the lowest rms surface roughness and corrosion performance were obtained at −100 V substrate bias with substrate tilt and rotation. Atomic force microscope scans over 10×10 μm2 sampling areas showed that 50 nm thick CNx films prepared under these conditions have roughness almost four times lower than those prepared without substrate tilt and rotation. We observed a twofold reduction in corrosion damage for hard disk substrates with 1 nm thick CNx overcoats deposited with substrate tilt and rotation. This improved performance is likely a result of more efficient and uniform momentum transfer parallel to the s...

Hardness and tribochemical evaluation of ultra-thin CH/sub x/ and CN/sub x/ overcoats

In this paper we present the results of nanoindentation hardness measurements, nano-wear measurements as well as tribochemical wear tests on a series of hydrogenated and nitrogenated carbon films. It is shown that the mechanical properties, such as hardness and abrasive wear resistance, while important, are not the primary determining factors in the wear durability of the head disk interface in magnetic hard disk drives.

Gaseous wear products from perfluoropolyether lubricant films

Abstract Degradation products of perfluoropolyether lubricants are observed during friction tests on thin film magnetic recording disks using a mass spectrometer. The friction tests are conducted in high vacuum using thin film read-write heads as sliders. Fomblin Z-dol and Krytox 143AX are used as lubricant. Observed removal rates are significant compared with the lubricant film thickness used. The data suggest that the degradation reaction is activated by low energy electrons produced at the tribological interface.

The decomposition mechanisms of a perfluoropolyether at the head/disk interface of hard disk drives

The decomposition mechanisms of a perfluoropolyether (ZDOL) at the head/disk interface under sliding friction conditions were studied using an ultra‐high vacuum tribometer equipped with a mass spectrometer. Chemical bonding theory was applied to analyze the decomposition process. For a carbon coated slider/CNx disk interface, the primary decomposed fragments are CFO and CF2O, caused by the friction decomposition and electron bombardment in the mass spectrometer. For an uncoated Al2O3–TiC slider/CNx contact, CF3 and C2F3 fragments appear in addition to CFO and CF2O, resulting from the catalytic reactions and friction decomposition, indicating that the decomposition mechanism associated with friction leads to the breaking of the main chain of ZDOL and forms CF2=O, which reacts with Al2O3 to produce AlF3, and the rapid catalytic decomposition of ZDOL on the AlF3 surface follows. Moreover, the effects of frictional heat, tribocharge, mechanical scission and Lewis acid catalytic action, generated in friction process, on the decomposition of ZDOL are discussed.