Target morphology dependence of the particulate generation during excimer laser ablation of polytetrafluoroethylene

Particulate ejection accompanying the excimer laser ablation is a permanent disadvantage in the pulsed laser deposition of thin films, since the quality of films is lowered by the presence of these grains. Dependence of the particulate generation on the target surface morphology during single shot excimer laser ablation of polytetrafluoroethylene foil was investigated. An ArF excimer laser was used for ablation, the applied fluence was varied between 2 and 6 J/cm2. The particulates emitted from the ablated surface were deposited onto a quartz plate placed above the target surface. Before the measurements, the roughness of the target surface was modified with low fluence excimer laser radiation. The surface was scanned with an atomic force microscope and its roughness was characterized by an Ra mean roughness number. After each shot, the number of the deposited grains and the area covered by them were determined. Dynamics of the particulate ejection was also studied with a fast photographic arrangement. The particulate generation was found to strongly depend on the microscopic roughness of the sample surface, the rougher the surface is the higher particulate number is.