In this study, a comparative study of a series of (MCD/NCD) bilayer films with different MCD grain sizes and NCD layer thickness deposited on cemented tungsten carbide (WC-Co) flat substrates was conducted by changing the deposition time. Tribological behaviors of these diamond films were evaluated by using a reciprocal tribometer without lubrication. In friction test against Si 3 N 4 balls, the (3hMCD/6hNCD) bilayer film showed the lowest coefficient of friction (0.059) and wear rates of counterpart balls (1.75×10 −6 mm 3 N −1 m −1 ) because of its lowest surface roughness and higher sp 2 content. This work provides a guide to choose suitable (MCD/NCD) bilayer basic structure in multilayer diamond film for getting a fine diamond film with low roughness and great tribological performance for different applications.

The switching process of ferroelectric thin films in electronic devices is one of the most important requirements for their application. Especially for the different external fields acting on the film surface, the mechanism of domain switching is more complicated. Here we observe the nanoscale domain switchings of Bi3.15Eu0.85Ti3O12 thin film under different mechanical forces at a fast scan rate. As the force increases from initial state to 247.5 nN, the original bright or grey contrasts within the selected grains are all changed into dark contrasts corresponding to the polarization vectors reversed from the up state to the down state, except for the clusters. As the mechanical force increases to 495 nN, the color contrasts in all of the selected grains further turn into grey contrasts and some are even changed into grey contrasts completely showing the typical 90° domain switching. When another stronger loading force 742.5 nN is applied, the phase image becomes unclear and it indicates that the piezoelectric signal can be suppressed under a sufficiently high force, which is coincident with previous experimental results. Furthermore, we adopt the domain switching criterion from the perspective of equilibrium state free energy of ferroelectric nanodomain to explain the mechanisms of force-generated domain switchings.