Target-plane deposition of diamond-like carbon in pulsed laser ablation of graphite

In pulsed Nd:YAG laser ablation of highly oriented pyrolytic graphite (HOPG) at 10−6 Torr, diamond-like carbon (DLC) are deposited at laser wavelengths of 1064, 532, and 355 nm on substrates placed in the target-plane. These target-plane samples are found to contain varying sp3 content and composed of nanostructures of 40–200 nm in size depending on the laser wavelength and laser fluence. The material and origin of sp3 in the target-plane samples is closely correlated to that in the laser-modified HOPG surface layer, and hardly from the backward deposition of ablated carbon plume. The surface morphology of the target-plane samples shows the columnar growth and with a tendency for agglomeration between nanograins, in particular for long laser wavelength at 1064 nm. It is also proposed that DLC formation mechanism at the laser-ablated HOPG is possibly via the laser-induced subsurface melting and resolidification.