Facile Phase-Selectable Chemical Synthesis of Tin Selenide Nanosheets toward Nanostructured Materials for Energy-Related Applications

Here, we present a facile, phase-selectable, size-controllable chemical method for the synthesis of Sn-Se nanosheets (NSs). The resultant NSs were characterized using XRD, SEM, TEM, STEM, and EDS. Phase control was achieved by changing the input molar ratio of Sn:Se. At ratios of 1:1 and 1:2, pure-phase, rectangular SnSe NSs; at ratios of 1:6 and 1:10, pure-phase, hexagonal SnSe2 NSs; and at a ratio of 1:4, a mix of the two NSs were produced. The produced NSs were large (a few hundred nm in diameter) and thin (10–20 nm), although there was no significant increase in the optical band gap calculated from UV–vis–NIR spectroscopy, indicating an absence of quantum confinement effects. Size control of both phases was achieved by changing the amount of the ligand, trioctylphosphine oxide (TOPO). Increasing the amount of TOPO decreased the size of the SnSe NSs and increased the size of the SnSe2 NSs. Finally, the formation mechanism was investigated and it was found that the formation of metal-ion complexes, namely, Sn-TOPO and Se-oleylamine, played an important role in the phase selectivity and size distribution of the NSs by changing the effective ratio of Sn:Se and slowing the nucleation of the NSs.