Thickness and Morphology Control in Laser-Assisted Zone Casting of Ultrathin, Polycrystalline Films

Film morphology control and adaptability of the coating process to substrate size or shape (scalability) are valid issues in thin film fabrication technologies. Overcoming technological limitations in the morphology control or the scalability stimulates development in thin film technologies and therefore drives progress in related fields of materials science. This paper demonstrates laser-assisted zone casting (LAZEC): a contactless thin-film fabrication method utilizing laser heating in a setup resembling meniscus-guided coating. LAZEC is based on thermally induced near-the-surface flows and permits the fabrication of films with thicknesses ranging from a few to several tens of nanometers on flat or curved surfaces. The film thickness can be controlled by solution viscosity, coating speed, and laser power. LAZEC enables the fabrication of polymer and small molecule films with uniform polycrystalline morphologies. Tuning the coating speed and laser power permits tailoring crystal domain sizes as well as their orientation. The latter can be translated to, e.g., planar anisotropy of field-effect charge carrier transport. Owing to its advantages, LAZEC can contribute to the development in the fields of printed electronics, photovoltaics, or thermoelectrics.