Imaging the defect distribution in 2D hexagonal boron nitride by tracing photogenerated electron dynamics

Hexagonal boron nitride (hBN) has become a prominent material for nanophotonic and quantum technology studies. Its wide bandgap can accommodate room temperature radiative optical transitions originating from defect states in different atomic structures. Here, we report the engineering of visible defects in chemical vapor deposited monolayer hBN irradiated by femtosecond pulses (0.1-0.5 W) at room temperature. Photoluminescence and transient photoluminescence measurements reveal the presence of a sharp emission at 630 nm with a time constant of approximately 3 ns randomly distributed around the irradiated region. We imaged the distribution of the photogenerated electrons by time-resolved photoemission electron microscopy in the picosecond and nanosecond timescales with 100 nm spatial resolution. We determined the precise location of the defects within the region of interest corresponding to an optical transition between 1.95 eV and 3.90 eV above the valence band maximum of hBN, ascribed to NBVN color centers.