TiO₂ Thin Films Obtained via Two-Phase Dip-Coating: Impact on Surface Roughness and Application to Heterostructures

An innovative biphasic dip-coating process is introduced for the deposition of TiO₂ thin films using a heterogeneous fluid system where an immiscible floating phase modifies the deposition dynamics. By controlling the height of the buoyant phase (ΔH), the method may reduce the agglomerate size during the gelation process, tending to shift the draining regime toward a capillary-dominated flow, a behavior typically observed only at lower withdrawal speeds. Numerical simulations based on Navier-Stokes equations suggest that increasing ΔH narrows and shifts the interface downward, which is consistent with the alteration in the stagnation point and deposition profile, supporting the role of pressure-driven flow and surface tension in deposition parameters. This controlled deposition mechanism may reduce the adhered precursor volume, leading to films with locally thinner deposited regions and decreased surface roughness. The proposed method suggests a direct correlation between floating phase height and film morphology, where an increase in ΔH is associated with smoother and more uniform thin films. This approach was applied to the development of a TiO₂/SnO₂ heterostructure, revealing via electrical characterization that heterostructures assembled with a thicker floating phase (ΔH = 0.6 cm) may exhibit higher homogeneity and reduced surface roughness, consistent with the behavior expected for a type-II heterojunction. The proposed biphasic dip-coating method presents a novel layering mechanism that may enhance film quality and provides a new parameter for adjusting thin-film properties, offering a promising alternative for advanced material processing in optoelectronics, sensors, and coatings.