  Atomically thin two-dimensional (2D) crystals have gained tremendous
attentions owing to their potential impacts to the future electronics
technologies, as well as the exotic phenomena emerging in these materials.
Monolayer of {\alpha} phase Sb ({\alpha}-antimonene) that shares the same
puckered structure as black phosphorous, has been predicted to be stable with
precious properties. However, the experimental realization still remains
challenging. Here, we successfully grow high-quality monolayer
{\alpha}-antimonene, with the thickness finely controlled. The
{\alpha}-antimonene exhibits great stability upon exposure to air. Combining
scanning tunneling microscope, density functional theory calculations and
transport measurement, it is found that the electron band crossing the Fermi
level exhibits a linear dispersion with a fairly small effective mass, and thus
a good electrical conductivity. All of these properties make the
{\alpha}-antimonene promising in the future electronic applications.
