Si-doped carbon nanostructured films by pulsed laser deposition from a liquid target

摘要

Ablation of a silicone oil, Dow Coming's DC-705 with laser pulses of sub-ps duration in high vacuum is a novel approach to fabrication of Si-doped carbon nanocomposite films. Gently focused, temporally clean 700 fs pulses @ 248 nm of a hybrid dye/excimer laser system produce power densities of the order of 10~(11)-10~(12) Wcm~(-2) on the target surface. The evolution of the chemical structure of film material is followed by comparing Fourier Transformed Infrared and X-ray Photoelectron spectra of films deposited at temperatures between room temperature and 250 deg C. Despite the low thermal budget technique, in the spectrum of films deposited at room temperature the fingerprint of the silicone oil can clearly be identified. With increasing substrate temperature the contribution of the features characteristic of the oil gradually diminishes, but does not completely disappear even at 250 deg C. This result is intriguing since the chance of oil droplets to survive in their original liquid form on the hot surface should be minimal. The results of the X-ray Photoelectron Spectroscopy suggest that the chemical structure of the film material resembles that of the oil. Both reflection mode optical microscopy and low magnification Scanning Electron Microscopy reveal that the films are inhomogeneous: areas of lateral dimensions ranging from a few to tens of micrometers, characterized by different contrasts can be identified. On the other hand, surface mapping by Scanning Electron and Atomic Force Microscopy unambiguously proves that all films possess a solid surface consisting of nanoparticles of less than 100 nm dimension, without the presence of any drop of oil. Possible explanations of the puzzling results can be that the films are polymers consisting mainly of the molecules of the target material, or composites of solid C:Si nanoparticles and oil residues.