Structure and surface morphology evolution of amorphous carbon surfaces during transformation by 0.2-20 ps laser pulses

Different kinds of amorphous materials are used in industry and science for various purposes: they serve as protecting materials, solar cell base materials, biocompatible coatings for implants, etc. The surface texture of these materials modified by laser pulses below or above the ablation threshold plays an important role in different applications: the surface area can be increased, cell adhesion can be modified etc. The laser induced processes are strongly influenced by the ambient and laser pulse parameters: wavelength, fluence, and pulse number. In our earlier experiments the surface texture formation processes were studied on different type of crystalline materials as function of the pulse number and laser fluence. Based on these results a possible scheme for the formation processes was sketched, but further examination is needed to reveal the processes being most significant from point of view of surface texturing. A further parameter of which variation can help to determine the main processes of surface texturing is the duration of the laser pulse. Its variation in the 100 fs to several tens of ps range allows investigating the effect of processes of different characteristic times (electron thermalization, electron phonon interaction, rearranging the bonding system, phonon relaxation, fixation of bonding structure). Increasing the pulse duration causes decreasing cooling rate in the laser heated material which can lead to increase the size of the ordered domains in the amorphous material, effecting the bonding structure besides surface morphology. In this paper our results concerning the pulse duration and pulse number dependence of the surface texture formation and bonding structure modification of different carbon surfaces just below the ablation threshold are presented. (author)