Charge-Induced Formation and Field-Driven Directional Motion of Vacancies in a Two-Dimensional Halide

Controlling defect evolution in two-dimensional (2D) materials is essential for reliable nanoelectronic functionalities, yet selectively inducing defect formation and externally driven migration remains a key challenge. Here, we demonstrate two distinct mechanisms governing halogen vacancy formation and migration in a PbBr2 monolayer on highly ordered pyrolytic graphite using low-temperature scanning tunneling microscopy combined with density functional theory calculations. We show that halogen vacancies reshape the local density of states and electrostatic potential beyond the immediate defect site. Crucially, electric fields and charge injection mediate distinct atomic-scale responses: tip-induced electric fields drive directional vacancy migration and coalescence, whereas charge injection from the tunneling current induces vacancy formation, with enhanced efficiency when coupling to shallow defect states. These results demonstrate that direct electrical stimuli can drive both vacancy motion and creation in a two-dimensional, predominantly ionic material system. Our findings establish a framework linking defect-induced electronic structure, local electrostatics, and externally driven atomic rearrangement under conditions relevant to device operation.