Kaixiong Gao

Recent advances in the mechanical and tribological properties of fluorine-containing DLC films

Fluorine easily substitutes hydrogen in DLC films due to its monovalence and high electronegativity. The peculiarities of fluorine bestow low surface energy, low inner stress, good thermal stability, preeminent tribological properties and biocompatibility on fluorine-containing, diamond-like carbon (F-DLC) films. Although there are some reviews that introduce the important advances in DLC films, they are not particularly focused on the promising F-DLC films. In this review, we mainly concentrate on the mechanical and tribological properties of F-DLC films. The mechanical properties, including hardness, modulus, and inner stress, will be discussed thoroughly. More importantly, the eminent tribological properties of F-DLC films would be emphasized based on the surface passivation and repulsive forces induced by fluorine atoms from the surface chemical and micro-mechanical viewpoints. Finally, some existing challenges and promising breakthroughs about F-DLC films are also proposed. It is expected that these films would be produced on a large scale and applied extensively in industrial applications such as micro-electro-mechanical systems, ultra-large scale integrated circuits, thin film transistor liquid crystal displays and biomedical devices.

Monitoring the nanostructure of a hydrogenated fullerene-like film by pulse bias duty cycle

The fullerene-like (FL) nanostructure is extremely important for fullerene-like hydrogenated carbon (FL-C:H) films that exhibit excellent mechanical properties and ultralow friction in ambient air, but the details of the contributing nanostructures are not well understood. We have prepared FL-C:H films with different morphologies and contents of FL nanostructures through tailoring the pulse bias duty cycle, and have investigated the contribution of the FL nanostructures. It is found that the straighter graphitic nanostructures in FL-C:H films could form under a high pulse bias duty cycle, and the low pulse bias duty cycle could increase the five-membered ring fractions, which results in more curved FL nanostructures with a larger curvature radius. Further investigation proved that the FL nanostructures with the more curved morphology could increase the mechanical properties and improve the tribological performance of the FL-C:H films. This work established a convenient controlling method to prepare FL-C:H films with tailored structures and performance.