Texturing structures of Ti films by multiple femtosecond laser pulses

Abstract

We report micrometre-sized pits structure, bump structure, and crater structure growth on a Ti film surface by multipulse femtosecond laser pulses (λ = 800nm, τ = 30 fs) irradiation in air at atmospheric pressure. All the structures are formed after 0.1s laser irradiation in our experiment. When laser power is below 20mW, there is no damage on the film. A pits structure develops in the centre of the irradiation spot after the action of laser power of 22mW, and the depth is less than 10nm. The further increase of the laser power leads gradually increasing the depth of the pits structure, which has largest depth is 70nm when laser power is 36mW. When laser power further increases, a bump structure is form in the center of the pits structure. The bump structure will gradually extend to all the irradiation zoon instead of increasing the depth of the pits structure. The forming bump’s depth does not exceed the thickness of the film. Until the laser power is larger than 90mW, a small collapse appeared in the center of the bump which leads to the crater structure. The formation processes of these structures are originated by the force under different film temperature at different laser power irradiation, including laser induced thermal stress, plasma or evaporation recoil pressure and surface tension. A simulation based on electron-lattice two-temperature model is used to evaluate the temperature and the leading force on the film at different laser fluences.We report micrometre-sized pits structure, bump structure, and crater structure growth on a Ti film surface by multipulse femtosecond laser pulses (λ = 800nm, τ = 30 fs) irradiation in air at atmospheric pressure. All the structures are formed after 0.1s laser irradiation in our experiment. When laser power is below 20mW, there is no damage on the film. A pits structure develops in the centre of the irradiation spot after the action of laser power of 22mW, and the depth is less than 10nm. The further increase of the laser power leads gradually increasing the depth of the pits structure, which has largest depth is 70nm when laser power is 36mW. When laser power further increases, a bump structure is form in the center of the pits structure. The bump structure will gradually extend to all the irradiation zoon instead of increasing the depth of the pits structure. The forming bump’s depth does not exceed the thickness of the film. Until the laser power is larger than 90mW, a small collapse appeared in the ce...