We monitor the spectroscopic properties (absorption, scattering and extinction) of individual nano-objects

Single molecule spectroscopic detection in fluorescent microscopy is well established now. It highly relies on the fact that the fluorescence is practically background free. Extensive research pertaining to the dynamics of single molecules is based on single-molecule fluorescence spectroscopy. However, not all molecules of interest fluoresce. In many cases, the attachment of fluorescent marker molecule is required in order to investigate or monitor the required dynamics. In other cases, we interested in monitoring the spectroscopic properties of non-fluorescent molecules.

It is much more challenging to measure the absorption of a single molecule, because it involves absorption of very small fraction of the light (~10-6). Recently, techniques capable of single molecule detection via optical absorption have emerged. In our laboratory we develop a new approach in measuring the absorption of single nano objects. We use a supercontinuum laser (Fianium) and a Acousto optics tunable filter to select the wavelength. The absorption detection is then carried out by an auto-balanced photodiode-pair aimed to suppress the laser noise, and a lock-in detection of a special absorption modulation technique. This is critical to enable the detection of light absorbed by a single particle in the order of 10-4 -10-7, which is orders of magnitude smaller than the intensity fluctuations of the light source. 

One long term scientific goal is to characterize the spectroscopic properties of specially designed Si/Ge core shell nanowires (fabricated by our collaborators in Patolsky lab), which according to theoretical predictions by A. Zunger are characterized by a direct band gap.

In other projects we monitor the interaction between localized plasmons and excitons in is WS2 nanorods.

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