Exciton-trion dynamics of a single molecule in a radio-frequency cavity

TL;DR

This study investigates the ultrafast exciton-trion dynamics in single molecules using phase fluorometry combined with radio-frequency scanning tunnelling luminescence, revealing mechanisms of trion formation at atomic and picosecond scales.

Contribution

It introduces a novel method combining radio-frequency modulated scanning tunnelling luminescence with time-resolved detection to study exciton-trion dynamics at the single-molecule level.

Findings

Determined exciton and trion lifetimes in single ZnPc molecules.

Showed dependence of lifetimes on bias voltage.

Proposed charge capture as the primary mechanism for trion formation.

Abstract

Charged optical excitations (trions) generated by charge carrier injection are crucial for emerging optoelectronic technologies as they can be produced and manipulated by electric fields. Trions and neutral excitons can be efficiently induced in single molecules by means of tip-enhanced spectromicroscopic techniques. However, little is known of the exciton-trion dynamics at single molecule level as this requires methods permitting simultaneous sub-nanometer and sub-nanosecond characterization. Here, we investigate exciton-trion dynamics by phase fluorometry, combining radio-frequency modulated scanning tunnelling luminescence with time-resolved single photon detection. We generate excitons and trions in single Zinc Phthalocyanine (ZnPc) molecules on NaCl/Ag(111), determine their dynamics and trace the evolution of the system in the picosecond range with atomic resolution. In addition, we explore dependence of effective lifetimes on bias voltage and propose a conversion of neutral excitons into trions via charge capture as the primary mechanism of trion formation.