The accurate control of the La2O3 hierarchical structure of the flower-like microspheres accompanied with vertical-standing nanopetals and the electrowetting responses with low voltage actuation

Abstract A simple hydrothermal method is successfully used to prepare the La2O3 film, and the accurate control of its surface structure is realized through the hydrothermal temperature and time from the sparsely dispersed compact microspheres to closely packed microsphere film, then from the hierarchical structure of the sparsely dispersed compact and flower-like microspheres accompanied with the discrete vertical-standing nanopetals to the hierarchical structure constituted by the closely packed compact microspheres and dense vertical-standing nanopetals. The XRD analysis shows the prepared film is mainly made of hexagonal La2O3 accompanied with some impurities of La(OH)2NO3, La(OH)3 and La2TiO5. Valuably, the prepared La2O3 film has high capacitance which can be modulated by surface structure, and achieves the maximum when the surface structure is hierarchical structure constituted by the closely packed compact microspheres and vertical-standing nanopetals. Eventually, the high capacitance leads to the electrowetting-on-dielectric (EWOD) responses with low voltage actuation below 8 V and wide contact angle modulation range of about 131°. The works are very beneficial to the design and preparation of supercapacitor and EWOD devices with high performance.