Bilayer amorphous carbon films synthesized by filtered cathodic vacuum arc deposition
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bilayer film deposition process for synthesizing ultrathin amorphous carbon (a-C) films with structure and properties dominated by those of the sp3-rich bulk layer was developed in this study. This was accomplished by incorporating in conventional filtered cathodic vacuum arc (FCVA) deposition a low-ion-energy pre-deposition step (no substrate biasing) leading to the formation of an ultrathin (,1 nm) carbon layer and a post-deposition step of high-energy Ar1 ion sputtering resulting in film thinning. The thickness and cross-sectional structure of hydrogen-free a-C ultrathin films synthesized by this multistep FCVA process under optimum substrate bias conditions (100 V pulsed bias voltage) were examined by high-resolution transmission electron microscopy and electron energy loss spectroscopy. The bilayer a-C films synthesized under these conditions exhibit slightly higher sp3 fractions and interface and bulk layers significantly thinner and thicker, respectively, compared with single-layer a-C films of similar thickness deposited under the same FCVA conditions.
I. INTRODUCTION
The high hardness, chemical and electrochemical inertness, and excellent wear resistance of amorphous carbon (a-C) films make them desirable overcoats for applications requiring protective ultrathin films, such as hard-disk drives, optical lenses, microelectromechanical systems, and surgical instruments. The good tribomechanical properties of a-C films originate from a relatively high content of tetrahedral (sp3) atom carbon hybridization, which controls the film density, elasticity, and hardness and is strongly depended on the film-growth conditions. Film deposition methods using energetic species as filmforming precursors, such as filtered cathodic vacuum arc (FCVA),1,2 are particularly effective in producing ultrathin a-C films rich in sp3 hybridization. This is because the kinetic energy of film-forming C1 ions can be tuned by applying a pulsed substrate bias voltage to control direct/recoil ion implantation, sputtering of weakly bonded atoms, and film growth. However, partial backscattering of C1 ions and reduced ion bombardment onto the growing film surface at the end of the film growth process leads to the formation of a multilayered film structure consisting of interface and surface layers with relatively low and varying sp3 contents and an intermediate (bulk) layer rich in sp3 hybridization.3 Current trends in most of the above mentioned technologies necessitate ultrathin a-C films. For example, in Contributing Editor: Eric Stach a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.250
contemporary hard-disk drives the physical spacing between the magnetic media of the hard disk and the read/write transducer embedded on the flying head must be ;5 nm.4,5 To achieve such a small spacing, the a-C overcoat thickness must be ;2–3 nm. However, because the structure of such ultrathin films is dominated by those of the weaker interface and surface layers, there are concerns about the uniformity, density, and protecti
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