Monitoring the Formation of Thin Films by Photothermal Technique

Evaporation is a widely used technique for developing thin films. In this study the formation of a film on top of a substrate is investigated using a photothermal technique. The configuration implies the illumination of an opaque substrate by modulated laser radiation and the detection of the heat at the illuminated zone. The system is considered as a two-layer system in which the non-illuminated layer presents a dynamic response, the thickness and thermophysical properties, which change as a function of time. Results of modeling such a system, which depend on the evaporation rate and concentration changes are preseInted. It was found that for the process in which evaporation constitutes a dominant contribution, one observes a stable long time process, and at a certain instant, the amplitude of the photothermal signal suddenly grows. On the other hand, additional contributions (such as the increase of concentration) involve processes that cause the amplitude of the photothermal signal to grow smoothly with time. The contributions of different mechanisms involved during the film formation are discussed