Photoinduced deprotection and ZnO patterning of hydroxyl-terminated siloxane-based monolayers

Trimethoxy-[11-(2-nitrobenzyloxy)undecyl]silane (1) and trimethoxy-[17-(2-nitrobenzyloxy)heptadecyl]silane (2) have been used for the covalent assembly of siloxane-based photopatternable monolayers. Exposing the monolayers to UV light (312 ± 10 nm) results in the generation of reactive hydroxyl-terminated monolayers without affecting the film quality. The new monolayers, deprotection chemistry, and the effect of photoinduced headgroup lift-off on the monolayer microstructure have been studied in detail by a full complement of physicochemical techniques, including optical (UV-vis) spectroscopy, ellipsometry, aqueous contact angle (CA) measurements, X-ray photoelectron spectroscopy (XPS), synchrotron X-ray reflectivity (XRR), and atomic force microscopy (AFM and AFM-force spectroscopy). AFM-force spectroscopy was used to analyze hydrogen-bond interactions as a function of the nature of the solid-liquid interface. AFM-force spectroscopy indicates a hydrogen-bond energy for photodeprotected monolayers of 8.2 kJ mol ^-1 (∼2 kcal mol ^-1). Scanning electron microscopy (SEM) revealed that treatment of photopatterned monolayers with ZnEt ₂ solutions resulted in well-defined ∼2 μm × 2 μm features of 10 Å thick ZnO layers.