Self-assembly of three shapes of anatase TiO2 nanocrystals into horizontal and vertical two-dimensional superlattices

Abstract

Bone-cuboid, spindle and rhombic TiO₂ nanocrystals have been achieved by a simple solvothermal method with the oleic acid and oleylamine volume ratio at 5/5, 4/6 and 3/7, respectively. X-ray diffraction (XRD) and selected area electron diffraction (SAED) results show that all of the three shapes of TiO₂ nanocrystals are highly crystallized anatase. Furthermore, for the first time, horizontal and vertical two-dimensional superlattices have been self-assembled with all three shapes of TiO₂ nanocrystals by controlling the amount of TiO₂ nanocrystals solution and oleic acid. The self-assembly process is primarily driven by maximization of the packing density and tuning entropic depletion attraction forces. In addition, the nanodots, nanorods and nanospheres of TiO₂ nanocrystals have been obtained with various amounts of H₂O₂ (0 ml, 0.05 ml, and 0.25 ml). These ordered two-dimensional superlattices may be suitable for the fabrication of functional ultrathin films which take full advantage of the directional and shape-dependent properties for wide ranging devices.