Controlled Formation of Highly Crystallized Cubic and Hexagonal Mesoporous SnO₂ Thin Films

Highly organized and crystallized cubic and hexagonal mesoporous SnO 2 thin films were selectively synthesized via an evaporation-induced self-assembly (EISA) process with SnCl 4 as the precursor and a triblock copolymer (pluronic F127) as the template. The as-spin-coated films were treated in two separate aging steps. Initial aging in a relative humidity (RH) of 75−85% at 25 °C was essential for obtaining the transparent and highly organized mesoporous films. The introduction of 1-BuOH instead of EtOH in the Sn−sol solution induced the formation of a robust hexagonal mesophase. X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and UV−visible spectroscopy revealed the mesopore structures of the SnO 2 thin films to be periodically organized with uniform surfaces, highly crystallized in the cassiterite phase, and thermally stable up to 600 °C. The optical transparencies were greater than 97% in the visible-light range. The sheet resistances of the prepared cubic and hexagonal mesoporous SnO 2 thin films were also analyzed.