Abstract
This thesis introduces a simple, yet controllable scheme to pick up a single 13 nm Au nanoparticle (Au-NP) using the tip of an atomic force microscope (AFM) probe through the application of electrical biases between the tip and the Au-NP. Comparison to conventional methods for particle-attached probes, this method provides the following benefits: (1) the AFM probes do not require surface pre-treatment (not in solution); (2) Au-NPs of various sizes can be attached; and (3) the entire process can be completed within 10~15 min. Transmission electron microscope (TEM) images were acquired to verify that a single Au-NP was attached to the AFM probe. We postulate that the mechanism underlying the ability to manipulate individual Au-NPs at the apex of the AFM probe tip is Coulomb interaction induced by tip bias. The AFM tip with the attached Au-NP was then used to study the interaction between a single quantum dots (QDs) and the Au-NP. The blinking behavior of single colloidal CdSe/ZnS core/shell QDs was significantly suppressed with the approach of the 13 nm Au-NP attached to the AFM tip. The fluorescence lifespan of a single QD when approaching to the tip with Au-NP was one order-of-magnitude shorter than that without an Au-NP (From 7.74 ns to 0.41 ns). Photon anti-bunching analysis are used prove the existence of hybrid nanostructures (single QDs and Au-NP attached AFM probe). The bi-exciton (BX) states of single colloidal QDs would undergo efficient non-radiative Auger relaxation (AR), thus leading to pure single-photon emission arising from single-exciton (X) decay even at room temperature. The AR process should play an important role in maintaining pure single-photon emission, which is the main advantage for colloidal QDs serving as room-temperature single-photon light sources. In order to investigate the influence of AR on the single-QD emission behavior (the purity of single-photon emission), we intentionally introduced non-radiative processes by placing QDs onto the conductive substrate (ITO and metal) to compete with inherent AR. Upon externally introducing such non-radiative processes, we found that original single-photon emission characters would be degraded or even disappeared accompanied with blinking suppression. By carefully analyzing our experimental data, the reason can be attributed to different extent of non-radiative influence on BX and X emission owing to their distinct radiative lifetime. This leads to the increase of the quantum yield ratio between BX and X emission, thus lowering the purity of single-photon emission. This understanding can facilitate the researchers in this field to further design high-performance single-photon sources based on low-cost colloidal QDs operating at room temperature.