Surface modification of ITO layers by AFM-based electrooxidative lithography

Transparent conductive oxides like indium tin oxide (ITO) are fundamental components in manifold technological applications. The modulation of ITO surface properties, such as wettability, adhesion, and conductivity, is crucial to its integration in complex frameworks. Silane-based self-assembled monolayers (SAMs) have proved reliable systems to tailor the oxide surface properties.1 The site-selective oxidation of SAMs by electro-oxidative probe lithography enables the assembly of nanoscale structures by supramolecular chemistry.2 Here, we report for the first time the nanoscale oxidation of octadecyltrichlorosilane (OTS) monolayers onto ITO films by electro-oxidative probe lithography. The lithographic process results in a local overoxidation of the substrate, as confirmed by tests onto bare ITO. Moreover, the monolayer oxidation causes the conversion of –CH3 groups into hydrophilic functionalities. This phenomenon was exploited to further modify the surface by site-selective growth of Ag nanoparticles. The oxidation process was studied by Scanning Kelvin Probe Microscopy (SKPM) and compared to the oxidation of the non-coated oxide and of the “reference” OTS-Si. Marked difference related to the oxidized monolayer are appreciable in SKPM images, which are not observable in topography or lateral force images. SKPM thus represents a powerful tool to investigate the monolayer oxidation.