Semiconductor nanostructures such as nanocrystals and nanowires show a fluctuating fluorescence when they are irradiated. This effect is called blinking as the fluorescence intensity of nanocrystals changes between two states, a radiative and a non-radiative. For nanowires a fluctuation between a fluorescence intensity maximum and minimum is observed. Additional charge carriers in the core of the nanostructure are thought to be responsible for the quenching or reduction of the fluorescence intensity in both cases.
The investigations on CdSe nanowires conducted during this thesis were performed with a microscope consisting of two components. A confocal laser scanning microscope is used for optical investigations. An atomic force microscope placed on top of the optical microscope allows for a simultaneous measurement on the same sample. With this atomic force microscope it is not only possible to image the topography but also the charge state of the sample. Therefore, it is possible to investigate the charge under optical manipulation and the optical properties under electrical manipulation through the biased atomic force microscope tip. The conducted experiments will be introduced briefly in the following.
The charge state of single CdSe nanowires was investigated under local illumination. The part of the nanowire that was irradiated with a diffraction limited spot charges positively while the ends charge negatively. This can be explained with the different mobilities of the positively and negatively charged charge carriers. The results furthermore allow an insight in the dynamics of the charge carriers in a CdSe nanowire.