Aromatic molecular emitters in a hexagonal boron nitride stack

This study investigates whether polycyclic aromatic hydrocarbon (PAH) molecules, specifically perylene, can be deterministically integrated into hexagonal boron nitride (hBN) stacks to function as stable, narrow-linewidth quantum emitters. The researchers aim to determine if these molecules can be embedded without the need for organic nanocrystal hosts and to understand the physical mechanisms that govern their binding and stability within the hBN lattice.

The authors utilized a thermal evaporation technique to deposit perylene molecules onto exfoliated hBN flakes, which were subsequently encapsulated by a second hBN layer. The resulting heterostructures were analyzed at cryogenic temperatures (below 4 K) using confocal fluorescence microscopy and hyperspectral imaging. To verify the origin of the emission, the team compared the measured vibronic spectra against reference data from perylene in organic hosts and performed ab initio quantum chemistry calculations to model the vibrational energy landscape. They also employed atomic force microscopy (AFM) to correlate emission intensity with the structural morphology of the hBN stacks.

The study successfully demonstrated gigahertz-narrow zero-phonon-line (ZPL) transitions from perylene molecules embedded in hBN. Vibronic analysis confirmed that the emission originates from the perylene molecules, which exhibit a slight softening of vibrational modes due to the hBN environment. The researchers found that pristine hBN layers tend to expel the molecules; instead, stable binding is facilitated by morphological defects, hydroxyl groups, and unpassivated atomic sites. Furthermore, thermal annealing of the stacks was shown to significantly improve spectral stability by removing trapped volatile adsorbates like water and oxygen, which otherwise contribute to spectral diffusion and photobleaching.