Structure and morphology of laser-ablated Pb thin films

The growth of polycrystalline Pb thin films on Si substrates at room temperature by near infrared laser ablation of pure Pb target is presented. Several diagnostic techniques were used to deduce the structure, the morphology and the thickness of the deposited films. We investigated the above properties as a function of laser fluence (1–8 J/cm2). Detailed morphological studies were also carried out on the irradiated target surface to deduce the laser ablation process. According to our results, the increase of laser fluence improves the crystallinity of the deposited films but not the deposition rate and the droplet density. The measured deposition rate was extremely low and varied between 0.04 and 0.09 Å per pulse. The final goal of this research activity is the realization of photocathodes based on Pb-thin-film to be used in superconducting Nb radio-frequency cavity.

► Crystallinity and adherence improve with laser fluence.
► Low laser fluences provide the lowest droplet density.
► Phase explosion at medium laser fluence increases mass removal and droplet density.
► Plume deflection and plasma absorption reduce deposition rate at the highest fluence.