Effects of AFM tip wear on frictional images of laser-patterned diamond-like nanocomposite films

Contact-mode atomic force microscopy (AFM) techniques (lateral force microscopy, force-distance curves) are applied to study the effects of femtosecond-laser ablation and micropatterning of diamond-like nanocomposite (DLN) films (a-C:H:Si:O films) on the friction behavior at the nano and microscale. A femtosecond laser (wavelength 515 nm, pulse duration 320 fs, pulse repetition rate 101 kHz) is used to fabricate line-like micropatterns (microgrooves) on the DLN films under ablation conditions with a scanning beam. Lateral force microscopy (LFM) studies of the laser-ablated microgrooves have revealed wearing-tip-induced nanofriction changes during AFM imaging with Si tip, characterized by much lower friction forces inside and around the microgrooves compared to the original surface (due to strong influence of the capillary forces on friction forces with increasing radius of the worn tip). Using wear-resistant diamond-coated tips, the friction contrast is found to reverse to higher friction in the laser-modified regions. The increased nanoscale roughness of the ablated DLN surface and redeposited surface layers is considered responsible for the observed nanofriction behavior of both the Si and diamond-coated tips.