Deposition of Metal Oxide Films at Liquid−Liquid Interface by the Liquid Phase Deposition Method

The liquid phase deposition (LPD) of metal oxide thin films at the liquid−liquid interface was investigated. Just after the start of the LPD reaction, depositions were observed continually at the liquid−liquid interface. The deposition grew two-dimensionally into a self-standing film with thickness of 1 μm and domain size of up to ca. 1 mm without any solid substrates. The self-standing film was formed with asymmetrical morphology, which consisted of flat surface on the side of the liquid−liquid interface and relatively rough surface on the side of the bulk solution. The structure was characterized by Raman spectroscopy, confirming that metastable ammonium titanium oxide fluoride (NH 4 TiOF 3 ) was first deposited at the liquid−liquid interface, on which anatase-type titanium oxide (TiO 2 ) was deposited second to forming the asymmetrical bilayer structure. It was suggested that the metal fluoride complex of the precursor was concentrated in the vicinity of the liquid−liquid interface compared with the solid−liquid interface due to the difference of the interfacial free energy, which could cause formation of the asymmetrical structure. The liquid−liquid interface could be confirmed as the specific reaction field for the LPD reaction. Also, the other metal oxide self-standing films such as tin oxide (SnO 2 ) and iron hydroxide oxide (β-FeOOH) were obtained in this process. The process also has great potential not only for basic science but also in the engineering field such as a soft solution process for template-free synthesis.