Local deposition of diamond-like carbon films on tungsten tips by KRF excimer laser

Diamond-like carbon (DLC) films were deposited on tungsten tips under KrF excimer laser irradiation in benzene solution. The influence of laser fluence and tip geometry were studied. The deposition process was found to be highly dependent on tip sharpness. Tips with larger curvature radii and smaller aspect ratios could not be coated with DLC films under the same condition as that for sharp tips. Raman spectra showed that more sp³ tetrahedral structures were present in the DLC films on a tip with a smaller curvature radius. Simulation results showed that the tip sharpness dependent local optical enhancement played an important role in the DLC deposition process. An optical field gradient from apex to tip body was also found in the simulation. We suggest that there are two modes in the process of DLC deposition on nanotips under different laser fluences, i.e. local apex DLC deposition under low laser fluences and phase-graded DLC deposition under high laser fluences.