Fabrication of anatase thin film with perfect c-axis orientation on glass substrate promoted by a two-dimensional perovskite nanosheet seed layer

摘要

Nanointerface engineering using unique two-dimensional (2D) crystals of nanosheets overcomes the difficulty in controlling crystal growth processes on amorphous substrates. Fabrication of highly oriented anatase (001) films on widely used glass substrates has been achieved for the first time utilizing a monolayer film of Ca_2Nb_3O_(10) nanosheets. The nanosheet has a 2D-perovskite structure, and the cell parameter (0.386 nm) is very similar to the a-axis of anatase (0.379 nm). The orientation degree and crystallinity of the films are examined by X-ray diffraction (XRD). The Ξ-rocking curve for the anatase 004 peak reveals a full width at half-maximum of 1.2°, which is virtually the same as that on single-crystal substrate of SrTiO_3 (001) (fwhm = 1.0°) deposited under the same conditions. The epitaxial relationship between the anatase layer and the underlying nanosheet is confirmed by cross-sectional high-resolution transmission electron microscopy observations. Synchrotron radiation in-plane XRD measurement is used to directly observe structural changes of the films. Slight but evident lattice shrinkage of the nanosheet occurs in synchrony with the relaxation of lattice distortion in the growing anatase layer. The flexible nature of the nanosheet associated with the 2D crystal structure may be responsible for this unique self-relaxing behavior of the nanosheet seed layer.