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

## TL;DR

A new dip-coating method using a two-phase system improves TiO2 thin film quality by reducing surface roughness and enhancing uniformity.

## Contribution

The study introduces a biphasic dip-coating process that controls film morphology through a floating phase height parameter.

## Key findings

- Increasing the floating phase height (ΔH) leads to smoother and more uniform TiO2 thin films.
- The method reduces surface roughness by altering the deposition dynamics toward capillary-dominated flow.
- TiO2/SnO2 heterostructures made with this method show higher homogeneity and reduced roughness.

## Abstract

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.