Fig. 1: Sample fabrication.

Schematic of 2D superlattice fabrication in the Langmuir-Schaefer trough: (a), the colloidal solution of PbS QD is drop-casted at the centre of the bath on the EG surface; (b), after solvent evaporation, the compression is started and the film is compacted until the desired starting surface pressure is reached; (c), the ligand exchange solution is injected in the trough from both sides underneath the barriers while compression is continued; (d), once the desired final surface pressure is reached, the SLs are transferred to the substrate of choice with the Langmuir-Schaefer method. e Exemplary surface pressure isotherms as a function of the area available per single QD. The dashed arrows indicate the points of solution injection and film pick-up on the ligand exchange curve. The coloured regions indicate the approximate timespan of ligand exchange injection. f STEM-HAADF micrograph of the OA sample fabricated at high surface pressure. The FFT is relative to the area indicated by the white square (scale bars: 200 nm, 0.5 nm⁻¹).