Kinetic model for scanning laser-induced deposition from the liquid phase

The effect of precursor concentration (0.005–0.05M) and scanning speed (0.20–0.96 mm/s) on the volume of the deposited material, determined with a circumstantial procedure using the cross-sectional data measured by a DEKTAK profilometer, in pyrolytic laser writing from aqueous solutions of ammonium heptamolybdate has been studied. From the detailed investigation we have given evidences that the structures of the deposits and their concentration and scanning speed dependencies can be consequently interpreted on the basis of material supply speeds, i.e. short illumination times, minutes deposition rates are observed indicating that material transport takes place via short-range diffusion. On decreasing the writing speed, i.e. increasing the dwell time, the slope of the volume versus dwell time function is higher because of forced (convectional) material supply due to local stirring in the liquid phase in close proximity to the heated surface area. With a further increase of the dwell time a saturation effect was also observed due to material depletion from the vortex affected liquid volume which can only be eliminated by less effective long-range diffusion. The main result of this work is a semi-quantitative description of the kinetics of the deposition process which gives an explanation for the large variety of morphologies and changes in deposition rates in terms of material transport.