Reversible Light-Induced Surface Superwetting of Atomic/Molecular Layer-Deposited TiO₂:Organic Superlattices for...

Atomic layer deposition (ALD) is a prominent technique for the precise fabrication of high-quality thin films of various inorganic materials with substantial applications in optoelectronics and semiconductor industries. However, continuous advances are required in materials design to develop next-generation thin-film architectures with multiple functionalities to meet consumer demands. Here, we combine the potential of inorganic ALD with its organic counterpart, molecular layer deposition (MLD), to fabricate TiO₂-based inorganic:organic superlattice (SL) structures with enhanced mechanical flexibility and tailored optical properties. The sequential deposition of TiO₂ and monomolecular organic layers through the combined ALD/MLD technique yielded a series of TiO₂:organic SL thin films with predefined TiO₂-layer thicknesses ranging between 1 and 10 nm, as confirmed with X-ray reflectivity measurements. We investigate four different organic components, hydroquinone, terephthalic acid, 2-amino-terephthalic acid, and 3,5-pyridinedicarboxylic acid, for their impact on the structural, mechanical, and optical properties of the resultant SL structures. We demonstrate the effects of the different functional groups of the organic precursors on the type of chemical bonding between titanium and the organic moiety and, consequently, on the optical and mechanical properties of the thin films. The TiO₂:organic SLs outperform the pristine TiO₂ thin films by presenting excellent resistance to strain-induced fragmentation, increased film flexibility, improved adhesion to the substrate, and exceptional surface wettability, in combination with the possibility of modulating the refractive indexa key feature for their potential application as antireflective coatings. Moreover, we demonstrate reversible light-induced superhydrophilic surface behavior for the TiO₂:organic SL structures. The TiO₂-based inorganic:organic SLs we present in this work are expected to open attractive pathways for antireflective coatings with added functionalities such as self-cleaning and antifogging surfaces.