Improved Langmuir−Blodgett titanate films via in situ exfoliation study and optimization of deposition parameters

The exfoliation and deposition of large (10–100 μm) Ti0.87O2 and small (0.1–1 μm) Ti0.91O2 nanosheets from lepidocrocite-type protonated titanates was investigated for getting high quality films. Exfoliation was carried out with different tetra-alkyl ammonium ions (TAA+) and varying TAA+/H+ ratios, and the colloidal solutions were characterized by small-angle X-ray scattering (SAXS) and ultraviolet–visible (UV–vis) spectroscopy. Using Langmuir-Blodgett deposition the titanate nanosheets were directly transferred onto a Si substrate. The resulting films were characterized by atomic force microscopy (AFM).The results indicate that the H1.07Ti1.73O4 titanate exfoliated at very low ratios of TAA+/H+; no lower threshold for exfoliation was observed for the TAA+ concentration. Nanosheets exfoliated at very low ratios of TAA+/H+ typically showed a small size and porous surface. Subsequent exfoliation of the remaining layered titanate particles yielded much higher quality nanosheets. The optimized deposition parameters for Langmuir-Blodgett films suggest that the surface pressure is a key parameter to control the coverage of the film. The bulk concentration of nanosheets was found to be a less important deposition parameter in the LB deposition process. It only influenced whether the desired surface pressure could be reached at a given maximum degree of compression.