Fig. 4: Characterizing a bleached emitter with ADF-STEM.

False-color optical micrograph (a) and wide-field photoluminescence imaging (b) of monolayer CVD hBN, suspended on a holey carbon film of TEM grid. Scale bars in (a) and (b) correspond to 20 μm. c Confocal photoluminescence spectrum, showing a zero-phonon line (+) near 1.98 eV (P₃) and one-phonon sideband (*) from the suspended hBN monolayer, and a Raman response (o) from the carbon film of the grid. Light-colored and dark-colored lines correspond to the raw and smoothed data, respectively. P₃ emission is in red, and the background spectrum in black. In (a) and (b), the circle denotes the position of the background measurement, and the dotted square represents the position of the P₃ spectrum. Note that only P₃ emission is observed in the hBN covering this TEM grid. d Zoomed-out ADF-STEM image of a hole in the grid, which is the same position as the dotted square in (a) and (b). Scale bar corresponds to 1 µm. e ADF-STEM image of a typical clean region of hBN. The green circle indicates a point defect. Scale bar corresponds to 2 nm. f Representative ADF-STEM analysis of monovacancies missing boron with atomic-scale resolution, showing experimental images (left column), simulated images (middle column) and their corresponding atomic structures (right column). The top row presents a monovacancy with NNN innermost edge atoms, while the bottom row shows OCC replacing NNN. g Averaged intensity of two consecutive frames under high magnification, showing a monovacancy missing boron, which has two O replacing inner most edge N, with higher uniformity in the image by noise reduction. Scale bar corresponds to 2 Å in (f) and 5 Å in (g), respectively. h A representative image of vacancy-free region under high magnification, the white arrow indicates the direction of line 1, 2 and 3. i Line profile analysis corresponding to line 1, 2, 3 in (h). The y-axis values indicate the intensity. j, ADF-STEM image from (h) with annotations, from the analysis in (i). Scale bars correspond to 5 Å in (h) and (j).