Substrate-free, self-standing ZnO thin films

Substrate-free ZnO thin films have been obtained by metal organic chemical vapor deposition. Mild heating (37-51 degrees C) of the Zn(C5F6HO2)(2)center dot 2H(2)O center dot CH3(OCH2CH2)(n)OCH3 (n = 2, 3, 4) adduct precursors produced thermally stable liquid compounds that were easily evaporated. Rapid quenching to room temperature of the reactor quartz tube caused self-exfoliation of ZnO films deposited on the walls, thus giving flexible films having a few hundred nanometer thickness. No exfoliation was observed from films grown on flat silica Substrates, even in the case of rapid quenching to room temperature. The obtained films were characterized by X-ray diffraction, UV-vis spectra, secondary electron microscopy, and transmission electron microscopy. The film thickness was evaluated by SEM cross-sections. Present ZnO films are semiconducting with an allowed direct transition at 3.3 eV.