Material transport during excimer-laser nitriding of iron

The surface topology and nitrogen concentration profiles of iron irradiated with pulses of an excimer laser in a nitrogen atmosphere were studied by means of optical and scanning electron microscopy, surface profilometry, energy-dispersive x-ray spectroscopy, and resonant nuclear reaction analysis. The observations are combined to distinguish several mechanisms contributing to the material transport: ablation, redeposition of nitride from the plasma and pressure-induced lateral flow of the molten iron towards the edges of the laser spot (piston mechanism). Numerical estimates of the time and spatial evolution of temperature and pressure at the surface led to average rates of the material transport in good agreement with the experiment.