Fig. 1: Heteroepitaxial nucleation and low-supply-rate kinetic control growth of 2D CaNb2O6 nanosheets.
From: 2D edge-seeded heteroepitaxy of ultrathin high-κ dielectric CaNb2O6 for 2D field-effect transistors
a Schematic synthesis diagram of 2D CaNb2O6 nanosheets by trace CaO precursor supply. b The sandwich structure precursor by stacking of Nb2O5, NaCl, and trace CaO layers, in which molten salt of NaCl could lower the sublimation temperature for top and bottom layers. (The arrows represent the volatilization direction of the powders). (c) Atomic crystal structure of non-layered CaNb2O6 unit-cell. d Optical microscopy (OM) image of 2D CaNb2O6 nanosheets on the mica substrate with uniform optical contrast. e The proposed chemical vapor deposition growth mechanism of ultrathin 2D CaNb2O6 nanosheets, including three steps of 2D edge formation in NbSe2 nucleus, edge-induced heteroepitaxial nucleation, and lateral epitaxy growth. f Atomic force microscope (AFM) image depicts the layer-by-layer growth mode of CaNb2O6 nanosheet, exhibiting a step size of approximately 1.5 nm. g The calculated surface energy results for different CaNb2O6 lattice planes and its corresponding atomic structure arrangements. h Raman spectrum and mapping image (inset, 904 cm−1) for 2D CaNb2O6 nanosheet on the mica substrate, the asterisks present the Raman peaks of CaNb2O6. i High-angle annular dark-field (HAADF) cross-section image of 2D CaNb2O6 nanosheet on mica and its energy dispersive X-ray spectrum (EDX) element mapping of Ca, Nb, and O, respectively. Scale bar: 20 nm. j Cross-sectional high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of CaNb2O6/mica interface. The inset serves as an enlarged view of their interface, emphasizing the clear visibility of the Van der Waals (vdWs) gap.
