| Description |
This work studies the optical interactions between single emitters, mainly quantum dots (QD) and a sharp tip. The fluorescence intensity, quantum yield and angular emission of a single emitter can be strongly modifi ed by near- field coupling with the sharp tip. Gold, silicon, and carbon nanotube (CNT) tips are employed in order to understand the physical mechanisms which are responsible for the various near- field eff ects. Each of these materials carries diff erent properties, which modify the optical properties of QDs in unique ways. In order to maximize the amount of information accessible by our near- field scanning microscope (NSOM), a novel near-f ield tomography technique is implemented. This technique facilitates the revelation of a number of interesting three-dimensional near- field features and is instrumental in the study of the di fferent near- field mechanisms. The flexibility in the data acquisition (DAC) technique allows us to study the influence of fluorescence intermittency (blinking) in QDs on the near- field coupling with the probes. The fluorescence emission from states with high quantum yield is more sensitive to quenching due to energy transfer, while in the low-yield states, near- field signal enhancement is more pronounced. The emission fluctuations of the QDs are progressively suppressed upon approach of a gold tip due to strong near- field coupling of gold tips to the QDs. Moreover, the angular emission of QDs in proximity to gold tips is very sensitive to the exact tip-QD position but does not depend on the intrinsic quantum yield of the QD. Energy transfer dominates the interactions of single CNTs with the QDs. Precision measurements of the energy transfer exhibit unique features as a result of the one-dimensional nature of CNTs. In particular, the energy transfer efficiency saturates at ~96% for all CNTs tried, even though the CNTs are expected to have a distribution of chiralities. |
