Nanoscale Transport of Surface Excitons at the Interface between ZnO and a Molecular Monolayer

Abstract

Excitons play a key role for the optoelectronic properties of hybrid systems. We apply near-field scanning optical microscopy (NSOM) with a $100\text{-nm}$ spatial resolution to study the photoluminescence of surface excitons (SX) in a $20\text{nm}$ thick ZnO film capped with a monolayer of stearic acid molecules. Emission from SX, donor-bound (DX), and - at sample temperatures $T>20\text{K}$ - free (FX) excitons is separated in steady-state and time-resolved photoluminescence spectra. The $4\text{meV}$ broad smooth envelope of SX emission at $T<10\text{K}$ points to an inhomogeneous distribution of SX transition energies and spectral diffusion caused by diffusive SX transport on a $50\text{nm}$ scale with a SX diffusion coefficient of $D(T<10 K)=0.30\,\text{cm$^2$/s}$.

14 pages, 3 figures

References in corpus (1)

• Ultrafast exciton formation at the ZnO(10$\overline{\text{1}}$0) surface