Static and ultrafast optical response of two metal nanoparticles glued with a semiconductor quantum dot

A hot-spot of high local field can be created between two closely placed metal nanoparticles and by irradiating them with an appropriate wavelength and polarization of incident light. The strength of the field at the gap between the particles is expected to get enhanced by several orders of magnitude higher than that of the applied field. Placing a semiconductor quantum dot or an analyte molecule at the hot-spot is an essential step towards harnessing the enhanced field for various applications. This article shows that it is possible to position a CdTe quantum dot (QD) between two larger silver nanospheres in a colloidal solution. The extinction spectra measured during growth suggests that the final hybrid nanostructure have two touching Ag nanoparticles (NPs) and a CdTe QD in between them close to the point of contact. Using ultrafast transient measurements, it has been shown that the presence of CdTe QD strongly influences the dynamics when the probe excites the gap plasmon. The method demonstrated here to place the semiconductor QD in between the two Ag NPs is an important step in the area of colloidal self-assembly and for the applications of hot-spot in plasmonic sensing, optoelectronics, energy harvesting, nanolithography and optical nano-antennas.