Number density and size distribution of droplets in KrF excimer laser deposited boron carbide films

This paper contributes to the old problem of droplet formation by providing detailed quantitative data on the population statistics of particulates deteriorating the surface of boron carbide films produced by PLD. Films of 180 ± 30 nm thicknesses have been fabricated by KrF excimer laser ablation of a sintered B4C target in high vacuum. Number densities and size distributions of the particulates are given for 14 films, deposited at laser fluences tuned between 2 and 14 J cm−2, as a result of evaluating SEM images of the same magnification taken from minimum five different areas (altogether (2-4) × 10−2 mm2) of each film. The overwhelming majority of the droplets is small with diameters, d ≤ 1 μm. The number density of those with d ≤ 0.5 μm ranges from (1 to 7) × 104 mm−2. The effect of gradual deterioration of the target surface as a result of prolonged irradiation screens practically totally the effect of changing fluence. The number of droplets of diameters in excess of 1 μm increases linearly with increasing number of shots/site resulting in maximum surface coverage values as high as 36%.