Sharp zero-phonon lines of single organic molecules on a hexagonal boron-nitride surface

TL;DR

This study reports the first observation of sharp zero-phonon lines from single organic molecules on a surface, demonstrating potential for surface-based nanophotonics and surface physics investigations.

Contribution

It demonstrates the detection of zero-phonon lines from single molecules on a surface and compares spectral stability on different hBN surface treatments, advancing surface-based molecular photonics.

Findings

Zero-phonon lines observed on hBN surface at cryogenic temperatures.

Linewidths are about 10 times larger than the Fourier limit.

Annealing improves spectral stability of the emitters.

Abstract

Single fluorescent molecules embedded in the bulk of host crystals have proven to be excellent probes of the dynamics in their nano environment, thanks to their narrow (about 0.1 {\mu}eV) optical linewidth of the 0-0 zero-phonon line (0-0 ZPL) at cryogenic temperatures. However, the optical linewidths of the 0-0 ZPL have been found to increase dramatically as the single molecules are located closer to a surface or interface, while no 0-0 ZPL has been detected for organic molecules on any surface. Here, we study single fluorescent terrylene molecules adsorbed on the surface of hexagonal boron-nitride (hBN) substrates. Our low-temperature results show for the first time the observation of the 0-0 ZPL of fluorescent molecules on a surface. With resonant excitation, we find 0-0 ZPL linewidths down to values that are about 10 times larger than the Fourier limit of 45 +/- 3 MHz, dictated by the fluorescence lifetime. We compare our results for molecules deposited on the surfaces of annealed and non-annealed hBN flakes and we see a marked improvement in the spectral stability of the emitters after annealing. Our high-resolution spectra obtained on terrylene suggest the possibility of employing hBN in combination with a wide variety of single molecule emitters for investigation of physical phenomena at surfaces or for use in nanophotonic devices.