Facet controlled growth mechanism of SnO₂ (101) nanosheet assembled film via cold crystallization

Cold crystallization of SnO₂ was realized in aqueous solutions, where crystal growth was controlled to form SnO₂ (101) nanosheet assembled films for devices such as chemical sensors. The nanosheets grew directly on a fluorine-doped tin oxide substrate without a seed layer or a buffer layer. The nanosheets had a thickness of 5-10 nm and an in-plane size of 100-1600 nm. Moreover, the large flat surface of the (101) facet was metastable. The thickness of the SnO₂ (101) nanosheet assembled film was approximately 800 nm, and the film had a gradient structure that contained many connected nanosheets. TEM results revealed that the predominate branch angles between any two connected nanosheets were 90° and 46.48°, corresponding to type I and type II connections, respectively. These connections were consistent with the calculations based on crystallography. Crystallographic analysis clarified the characteristic crystal growth of the SnO₂ (101) nanosheet assembled film in the aqueous solution. Furthermore, we demonstrate that the metastable (101) facet can be exploited to control the rate of crystal growth by adjusting the etching condition.