Controllable low-temperature chemical vapor deposition growth and morphology dependent field emission property of SnO₂ nanocone arrays with different morphologies

Vertically aligned SnO₂ nanocones with different morphologies have been directly grown on fluorine-doped tin oxide (FTO) glass substrates in a large area by heating a mixture of stannous chloride dihydrate (SnCl ₂·2H₂O) and anhydrous zinc chloride (ZnCl ₂) at 600 C in air. Control over the SnO₂ nanocone arrays with different morphologies is achieved by adjusting the heat treatment time. The SnO₂ nanocones are single crystalline with the tetragonal structure. A single-layer SnO₂ nanoparticle film is first formed via the vapor-solid (VS) process due to the decentralization function of ZnCl ₂ vapor, and the SnO₂ nanoparticles served as seeds and grew into nanocone arrays via the VS process. The sharp-tipped nanostructure formation may originate from a concentration gradient of reactant in the growth process. The as-obtained whiskerlike nanocone arrays exhibit enhanced field emission properties in comparison with typical nanoconelike structure arrays and other SnO₂ nanostructured materials reported previously, and the turn-on field and field-enhancement factor is 1.19 V/μm and 3110, respectively. The experimental result is consistent with the Utsumi's relative figure of merit for pillar-shaped emitters.