We report a new patterning method using photocatalytic lithography of alkylsiloxane self-assembled monolayers and selective atomic layer deposition of thin films. The photocatalytic lithography is based on the fact that the decomposition rate of the alkylsiloxane monolayers in contact with TiO2 is much faster than that with SiO2 under UV irradiation in air. The photocatalytic lithography, using a quartz plate coated with patterned TiO2 thin films, was done to prepare patterned monolayers of the alkylsiloxane on Si substrates. A ZrO2 thin film was selectively deposited onto the monolayer-patterned Si substrate by atomic layer deposition.

Mixed self‐assembled monolayers (SAMs) with different ratios of –OH to –CH3 groups were used to modify the surface free energies of the Si substrates from 64 to 29 mN m–1. The TiO2 thin films were grown on the mixed SAM‐coated Si substrates by atomic layer deposition (ALD) from titanium isopropoxide and water. A two‐dimensional growth mode is observed on the SAMs‐coated substrates possessing high surface free energies. As the surface free energy decreases, a three‐dimensional growth mode begins to dominate. These observations indicate that the mixed SAMs can control the growth modes of the atomic layer deposition by modifying of the surface free energies of the substrates.

The photocatalytic decomposition of octadecyltrichlorosilane (OTS) based self-assembled monolayer formed on TiO2 has been studied using atomic force microscopy(AFM), X-ray photoelectron spectroscopy (XPS), and contact angle analysis. The TiO2 thin films were grown on Si(100) substrates by atomic layer deposition from titanium isopropoxide and water. Densely packed alkylsiloxane monolayers similar in quality to those on SiO2 are formed on TiO2. It is found that the monolayers on TiO2 are decomposed much faster than those on SiO2 under UV irradiation of 254 nm in air. The OTS-based SAMs on TiO2 are decomposed through the photocatalytic oxidation of the alkyl chains with a gradual and homogeneous reduction in chain length. After the complete photodecomposition of the OTS−SAMs, the siloxane headgroups remain on the TiO2 surface. The observation indicates that the titanium oxide, a well-known photocatalyst for organic pollutant treatment, efficiently decomposes the alkylsiloxane monolayers under UV irradiation in air.

The thermal decomposition of alkylsiloxane self-assembled monolayers in air has been studied using atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle analysis. It is found that the monolayers are stable in air up to about 200 °C. Above 220 °C the monolayers primarily decompose through C-C bond cleavage, with a gradual reduction in chain length. The siloxane headgroups remain on the surface following the decomposition of hydrocarbon fragments in the monolayers.