Growth of Few-Layer Molecular Crystals of PTCDI on Hexagonal Boron Nitride by Microspacing Air-Gap Sublimation

Extended two-dimensional (2D) crystals of dye molecules adsorbed on 2D material substrates such as boron nitride have recently become a subject of intense study, with potential applications ranging from quantum technology to optoelectronics. The most established technique for the production of these films is physical vapor transport in a vacuum. We demonstrate that few-layer crystalline films of the organic dye molecule perylenetetracarboxylic diimide (PTCDI) on boron nitride can be produced by microspacing in-air sublimation, a radically simplified technique that does not require complicated vacuum systems. The resulting layers display clearly resolved atomic step terraces in atomic force microscopy and a clear polarization anisotropy in their fluorescence, confirming molecular alignment and long-range order. Using density functional theory and classical molecular dynamics simulations, the canted motif is identified as the most likely building block for the morphology of a PTDCI monolayer on the hBN substrate.