Controlled formation of highly crystallized cubic and hexagonal mesoporous SnO2 thin films

Highly organized and crystallized cubic and hexagonal mesoporous SnO2 thin films were selectively synthesized via an evaporation-induced self-assembly (EISA) process with SnCl4 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 degrees 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 SnO2 thin films to be periodically organized with uniform surfaces, highly crystallized in the cassiterite phase, and thermally stable up to 600 degrees C. The optical transparencies were greater than 97% in the visible-light range. The sheet resistances of the prepared cubic and hexagonal mesoporous SnO2 thin films were also analyzed.