Direct-current cathodic vacuum arc system with magnetic-field mechanism for plasma stabilization

Thermal stability and diffusion characteristics of ultrathin amorphous carbon films grown on crystalline and nitrogenated silicon substrates by filtered cathodic vacuum arc deposition

Amorphous carbon (a-C) films are widely used as protective overcoats in many technology sectors, principally due to their excellent thermophysical properties and chemical inertness. The growth and thermal stability of sub-5-nm-thick a-C films synthesized by filtered cathodic vacuum arc on pure (crystalline) and nitrogenated (amorphous) silicon substrate surfaces were investigated in this study. Samples of a-C/Si and a-C/SiN_x/Si stacks were thermally annealed for various durations and subsequently characterized by high-resolution transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The TEM images confirmed the continuity and uniformity of the a-C films and the 5-nm-thick SiN_x underlayer formed by silicon nitrogenation using radio-frequency sputtering. The EELS analysis of cross-sectional samples revealed the thermal stability of the a-C films and the efficacy of the SiN_x underlayer to prevent carbon migration into the silicon substrate, even after prolonged heating. The obtained results provide insight into the important attributes of an underlayer in heated multilayered media for preventing elemental intermixing with the substrate, while preserving the structural stability of the a-C film at the stack surface. An important contribution of this investigation is the establishment of an experimental framework for accurately assessing the thermal stability and elemental diffusion in layered microstructures exposed to elevated temperatures.

Nanostructure, structural stability, and diffusion characteristics of layered coatings for heat-assisted magnetic recording head media

The intense laser heating in heat-assisted magnetic recording (HAMR) has been a major hindrance to HAMR technology from becoming commercially viable. Thermal damage of the near-field transducer (NFT) and write pole (WP) embedded in the trailing edge of the magnetic head due to failure of the protective carbon overcoat after prolonged heating at an elevated temperature are major obstacles. Therefore, the main objective of this study was to develop an effective coating method for HAMR heads. This was accomplished by introducing a new class of layered coatings consisting of ultrathin amorphous carbon (a-C) overcoat, adhesion (SiN) layer, and buffer (NiCr or TaO_x) layer sequentially deposited onto Au and FeCo base layers to mimic the layer stacking of NFT and WP elements, respectively. The structural stability of the a-C overcoats and diffusion characteristics of each comprising layer under conditions of heating at 350 °C for 30 min in an Ar atmosphere were investigated by high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), and electron energy loss spectroscopy (EELS). For most stacking configurations the HRTEM/STEM and EELS results generally revealed some layer intermixing and minute carbon atom rehybridization in the heated a-C overcoats. The findings of this investigation suggest that further optimization of the developed layered coatings can provide a viable solution to thermal damage of HAMR heads.

Electrophoretic Deposition of SnFe2O4–Graphene Hybrid Films as Anodes for Lithium Ion Batteries

Binder-free SnFe2O4–submillimetre (hundreds of micrometres)-sized reduced graphene oxide (SnFe2O4–srGO) hybrid films were synthesized through electrophoretic deposition and subsequent carbonization treatment. Scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy results revealed that SnFe2O4–srGO hybrid films exhibit both horizontal and vertical channels. SnFe2O4–srGO hybrid films were used as binder-free anodes for lithium ion half-cells and revealed a high capacity of ~1018.5 mA h g−1 at 0.1 A g−1 after 200 cycles. During rate performance tests, a high capacity of 464.1 mA h g−1 (~61.2 % retention) was maintained at a current density of 4 A g−1, indicating an excellent structural stability of SnFe2O4–srGO hybrid films at high current densities.