Junsuke Kiuchi

Nanoscale modification of DLC film surfaces with femtosecond laser pulses

Surface modification of thin diamond-like carbon (DLC) films deposited on stainless steel has been studied by irradiating linearly and circularly polarized femtosecond (fs), 800- and 267-nm Ti:sapphire laser pulses at laser fluence around the ablation threshold. The morphology of the DLC surfaces was observed and characterized with a field-emission scanning electron microscope and a scanning probe microscope. The linearly polarized light produced arrays of fine slender granular structure on the ablated surface, while the circularly polarized light formed a fine dot-like periodic structure. The mean spacing of these fine structures was 1/10 - 1/5 of the laser wavelength used. With an increase in the laser fluence, the size of structure was observed to increase, while the surface roughness decreased. We have analyzed the modified DLC surfaces by observing Raman spectra and found that the nanoscale modification of the DLC films is accompanied with a structural change into glassy carbon. This structural change depended on the fs laser fluence and little on the laser polarization and wavelength.

Femtosecond-laser-induced nanostructures formed on hard coatings of TiN and DLC

Linearly- and circularly-polarized femtosecond (fs) Ti:sapphire laser pulses at 800 and 267 nm were focused in air to ablate hard thin films of TiN and DLC deposited on stainless steel plates. The morphology of the thin film surfaces that were ablated by the fs laser pulses at an energy fluence slightly above the ablation threshold was observed and characterized with a field emission-scanning electron microscope. With the linearly-polarized light, arrays of fine slender granular structure were produced on the ablated surface, which were almost oriented to the direction perpendicular to the laser polarization. On the other hand, the circularly-polarized light is found to form fine dot structures on the film surface. The size of these surface structures was 1/10 ~ 1/5 of the laser wavelength used and was observed to decrease with a decrease in the laser wavelength. It should be noted that the size of surface structures observed is much smaller than that of the well-known surface ripple patterns produced by the laser-induced surface electromagnetic wave.

Periodic nanostructure formed on TiN and DLC by femtosecond laser pulses

Hard coatings of TiN and DLC were irradiated by 800- and 267-nm, femtosecond (fs) laser pulses at an energy fluence slightly above the ablation threshold. On the ablated thin-film surfaces, the linearly-polarized fs pulses produce arrays of fine periodic structures that are almost oriented to the direction perpendicular to the laser polarization, while the circularly-polarized light forms fine dot structures. The size of these surface structures is 1/10-1/5 of the laser wavelength and decreases with a decrease in the laser wavelength.