<title>Nanoscale modification of DLC film surfaces with femtosecond laser pulses</title>

Abstract

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.