Fluorescence spectroscopy and nanomanipulation of individual semiconductor nanocrystals

Abstract

The blinking of single nanocrystals (NCs) is investigated by means of a combined laser scanning confocal microscope and a home built nanopositioner. Artifacts of threshold analysis methods are investigated to understand the origin of the discrepancies of blinking quantification reported by different research groups. It is shown that variations of the distribution of intermediate emitting intensities are the major source of errors. The results strongly suggest that the truncation of the power law is more an artifact than a general feature of NCs. The effect of the material surrounding NCs is investigated by comparing the influence of insulating, hole conducting and electron conducting materials. It is shown that the photoluminescence is quenched in films of hole conducting materials due to the possibility of transfer of the photo-generated hole of NCs. The blinking statistic shows the existence of a correlation between the ON time and the OFF time power law exponents of given NCs and the presence of a memory between consecutive ON event, consecutive OFF events and between ON and OFF events. The necessity of an analysis method independent of the threshold separation between ON and OFF level is suggested to investigate the apparent dependence of the blinking statistic results on the matrix. The nanomanipulation experiments show that electroluminescence of areas as small as 1 µm2 can be investigated with the home built experimental setup used for this thesis. The nanomanipulation with help of a metallic tip lead to a photoluminescence quenching when charges flow in the proximity of single NCs.