Growth of few-layer molecular crystals of PTCDI on hexagonal boron nitride by microspacing air-gap sublimation

TL;DR

This paper demonstrates a simplified method for growing few-layer PTCDI molecular crystals on hexagonal boron nitride using microspacing air-gap sublimation, with confirmed molecular order and theoretical insights into their morphology.

Contribution

It introduces a novel, vacuum-free technique for fabricating 2D organic dye crystals on hBN, advancing the production methods for 2D molecular materials.

Findings

Successful growth of PTCDI layers with atomic step terraces

Observation of polarization anisotropy confirming molecular order

Identification of canted molecules as key to morphology

Abstract

Extended two-dimensional (2D) crystals of dye molecules adsorbed on 2D material substrates like 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 vacuum. We demonstrate that few-layer crystalline films of the organic dye molecule PTCDI on boron nitride can be produced by microspacing in-air sublimation, a radically simplified technique, not requiring 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 motive is identified as the most likely building block for the morphology of a PTDCI monolayer on the hBN substrate.