Subdiffraction instrumentation development and application to the elucidation of biological systems, thin films, and organic photovoltaic devices.

摘要

Fluorescence and Raman instrumentation was developed to elucidate morphology, information on local environment, and material properties of target systems. Far-field fluorescence and luminescence spectroscopic measurements were performed using a pulsed super-continuum laser source and detector with high temporal resolution. With this arrangement morphologies of structures were coupled with time-correlated data. Polymeric beads and Alexa Fluor 594-phalloidin labeled cellular actin structures of cultured cells were imaged below the diffraction limit using stimulated emission depletion to resolve structures to about 40nm. Lifetime imaging revealed a 2.0 +/- 0.1 ns lifetime for fluorescently-labeled beads in confocal and depletion imaging modes. Depletion imaging was also able to display a change of 2.2 to 2.9 ns for different regions of the cellular actin network of cultured cells with a possible difference in lifetime caused by tryptophan quenching of the dye. Subdiffraction imaging with a resolution of around 40 nm was also accomplished using luminescence depletion of photostable giant CdSe/14CdS nanocrystal quantum dots in air. Nanocrystal quantum dots, typically not prone to depletion, exhibited this phenomenon when excited with an energy of 50 pJ and 2 nJ of depletion energy. Luminescence depletion required half the energy compared to stimulated emission depletion to achieve the same resolution limit. The luminescence was depleted by as much as about 92% with no observable photobleaching. Raman measurements of polymer films were performed with 532-nm laser illumination using scanning angle and conventional 180° backscattering modes to determine chemical information. The scanning angle mode achieved an angle resolution of 0.09° and was used to probe a thin layer of polystyrene as well as a diblock copolymer of polystyrene and poly(3-hexylthiophene-2,5-diyl). Enhancements to the Raman signals at selected angles lower than the critical angle for total internal reflection, characteristic of waveguides, were measured. An additional enhancement in the Raman signal results from resonant conditions for the diblock copolymer. The epi-collection geometry was used to gain spectroscopic information regarding to the stability of heterojunction solar cells with the aid of resonance Raman spectroscopy. Raman spectral characteristics corresponding to thiophene-based functional groups were used to relate stability of the polymers under different processing conditions such as solvent and thermal annealing while undergoing laser induced photodegradation.