Double-peak droplet mass distribution observed during sub-ps laser ablation of Si targets

The angular distribution of the ablated material was studied during sub-ps Si laser ablation deposition using a special hemicylindrical substrate holder and different laser fluences ranging between 0.4 and 1.7 J/cm(2). Scanning electron microscopy analysis of the deposited films showed that, independent of the fluence, the distribution of the deposited droplets presents two maxima. The first maximum corresponds to the average plume deflection angle value due to the local surface orientation produced by the preferential etching process. The second maximum is observed approximately at 45 degrees with respect to the normal of the target surface, and is related to the phase explosion products that expand along the incident laser beam direction. The investigation of the twofold distribution of the sub-mu m size deposited droplets is important to improve the quality of the deposited coatings.