  Puckered honeycomb Sb monolayer, the structural analog of black phosphorene,
has been recently successfully grown by means of molecular beam epitaxy.
However, little is known to date about the growth mechanism for such puckered
honeycomb monolayer. In this study, by using scanning tunneling microscopy in
combination with first-principles density functional theory calculations, we
unveil that the puckered honeycomb Sb monolayer takes a kinetics-limited
two-step growth mode. As the coverage of Sb increases, the Sb atoms firstly
form the distorted hexagonal lattice as the half layer, and then the distorted
hexagonal half-layer transforms into the puckered honeycomb lattice as the full
layer. These results provide the atomic-scale insight in understanding the
growth mechanism of puckered honeycomb monolayer, and can be instructive to the
direct growth of other monolayers with the same structure.
