Molecular Dynamics Modeling Of Ultrathin Amorphous Carbon Films

Increasing demands for high magnetic storage capacity have led to the increase of the recording area density by more than 100,000 times over the past 30 years. Among all the approaches considered to increase the area density, reducing the magnetic spacing is an effective solution that directly impacts the thickness and quality of the carbon overcoat. One of the methods of carbon overcoat deposition is chemical vapor deposition, which uses carbon-containing precursor gases as the source of carbon radicals and atoms to form the carbon overcoat. The produced carbon film is characterized by high hydrogen content (20%-50%), depending on the carbon-to-hydrogen ratio of the precursor gas and process parameters. Because of the hydrogen content, CVD-deposited hydrogenated amorphous carbon (a-C:H) deposited by CVD exhibit density of 1.7-2.2 g/cm3, which is much lower than the density (~3 g/cm3) of hydrogen-free amorphous carbon (a-C) films deposited by filtered cathodic vacuum arc (FCVA). The superior nanomechanical/tribological properties of FCVA-deposited a-C films have been widely-reported; however, most studies have examined relatively thick (tens of nanometers) a-C films, while current demands require much thinner films of thickness in the range of 1-4 nm. FCVA-deposited a-C films overcoats are desirable protective overcoats for HDDs provided they can maintain their demonstrated high quality even for thickness as low as 1 nm. In this dissertation, an in-depth study of the structure of FCVA-deposited a-C films deposited on silicon was carried out using high-resolution transmission electron microscopy (HRTEM) and analytical electron energy loss spectroscopy (EELS). Both low- and high (core)-loss EELS spectra of Si and C were analyzed to determine the elemental content and through-thickness structure of ~20-nm-thick a-C films. Calculations of atomic carbon hybridization based on EELS spectra were used to track the film structure evolution. The average content of carbon hybridization in the top few nanometers of the a-C film, determined from EELS analysis, was found to be ~50%, much less than 73% of the bulk film. This multilayer structure was also validated by X-ray photoelectron spectroscopy (XPS). Results indicate that the minimum thickness of a-C films deposited by the FCVA method under conditions of optimum substrate bias ( -100 V) should be equal to 3-3.5 nm, which is the total thickness of the buffer and surface layers. The effects of other important FCVA process parameters on film growth were also investigated to explore the prospect of further decreasing the a-C film thickness. The incidence angle effect of energetic C+ ions bombarding onto the growing film surface was studied in terms of the deposition rate, topography, and film structure. Cross-section TEM measurements combined with Monte Carlo (T-DYN) simulations revealed that the deposition yield (rate) is independent of the ion fluence but varies with the incidence angle according to a relationship derived from sputtering theory. XPS and atomic force microscopy (AFM) studies were also performed to examine carbon hybridization and film topography. The optimum incidence angle for FCVA deposition was found equal to 45o. A relatively new technology that shows potential for further breakthroughs in magnetic recording is heat-assisted magnetic recording (HAMR). This technology utilizes a tightly focused laser beam to heat and temporarily reduce the coercivity of magnetic nanodomains below that of the magnetic field applied by the magnetic head. Impulsive laser heating (typically

Molecular dynamics computer simulations are used to study the effect of substrate temperature on microstructure of deposited amorphous hydrogenated carbon (a:CH) films. A transition from dense diamond- like films to porous graphite-like films is observed between substrate temperatures of 400 and 600 K for a deposition energy of 20 eV. The dense a:CH film grown at 300 K and 20 eV has a hardness ((approximately)50 GPa) about half that of a pure carbon (a:C) film grown under the same conditions.

Proceedings of the NATO Advanced Study Institute, held in Kaunas, Lithuania, from 3-14 September 2001

This book presents the status quo of the structure, preparation, properties and applications of tetrahedrally bonded amorphous carbon (ta-C) films and compares them with related film systems. Tetrahedrally bonded amorphous carbon films (ta-C) combine some of the outstanding properties of diamond with the versatility of amorphous materials. The book compares experimental results with the predictions of theoretical analyses, condensing them to practicable rules. It is strictly application oriented, emphasizing the exceptional potential of ta-C for tribological coatings of tools and components.