Supplement Number 2

FIG. S2. Vacancy voids formation and self-healing in the monolayer P during the consecutive STM scanning. (a) An intact monolayer P island on the Cd(0001) surface (U = 2.5 V, I = 30 pA). (b) Vacancy voids formation in the monolayer P island during low-bias scanning (U = 0.5 V, I = 30 pA), as marked by the white and black circles. (c) Self-healing of the large vacancy void within the white circle after scanning at high bias voltage (U = 2.5 V, I = 30 pA). A big notch was created at the right edge of monolayer island as marked by the yellow arrow.