EAGER: Measuring near-field nanoplasmonics fields using super-resolved far-field optics

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With support from the Chemical Measurement and Imaging Program, Professors Weiss and Neuhauser at the University of California-Los Angeles are developing a new imaging tool to measure local surface plasmon field intensity near nanometer-sized structures. It is known that sometimes when the incoming light illuminates a surface immobilized with small metal features, the electrons in the metal can oscillate back and forth together and form a "wave" ? the so called "surface plasmon". Surface plasmon is an important optical phenomenon and has been widely used in many real world applications, including the dark red color in medieval stained-glass windows that are seen in an old buildings ?the color comes from the visible light interacting with gold nanoparticles embedded in the glass. In order to better utilize the surface plasmon phenomenon, it is important to understand how it is distributed around imperfect nano-structures. Modern science advancement allows scientists to estimate the distribution of surface plasmon field intensity with computer simulation programs, but direct measurements of such field intensity, especially around imperfectly prepared nano-structures, are challenging and have not been fully realized. Professors Weiss and Neuhauser are developing a way to directly measure surface plasmon intensity near a small surface structure by monitoring the blinking rate of certain types of inorganic particles. This method would allow them to map the field intensity at a very high spatial resolution. It is also very fast and inexpensive as compared with other methods currently in development. During this 18-month grant period, both groups are focusing on (1) placing the inorganic particles around nanometer-sized features on a surface and (2) studying how the placement of these particles may be used to map the local EM field intensity. They are applying this imaging technique to study how molecules move near a surface or how a reaction happens on a metal nanoparticle. The graduate students in two groups are involved in both experimental and theoretical components of research. Both professors are also actively engaged in encouraging talented high school student to be enrolled in graduate programs, in particular from underrepresented minority groups. The ability to simultaneously superresolve plasmonic field strengths over a large region is unique and desirable. Such approach will deepen the understanding of and control over plasmonic systems, and will broaden the impact of plasmonics. The novel probing technology Professors Weiss and Neuhauser are working uses the dependence of the blinking statistics in quantum dots on the electric field strength to resolve plasmonic field strengths well below the diffraction limit. The methods negate complications typical of localizing dipole emitters near a metallic nanostructure. A theoretical framework based on modeling of the quantum dots response with time-dependent density functional theory in deterministic or stochastic variants is also used to construct simplified building blocks. A computationally simplified building-blocks based modeling then allow simulations of a very large number of quantum dots and plasmonic structures simultaneously, mimicking the on-going experimental systems. By optimizing the theoretical and experimental tools developed here, the detailed electric field map of ~100x100 micrometer-squared size regions may be measured in quick succession. The imaging method, if successful, could benefit many applications that rely on the ability to measure field strengths below the diffraction limit, ranging from biology, to high speed integrated circuits, to optical computing. Additionally, the software developed for the experiments and for the theory studies provides an approachable tool for analyzing and predicting field strengths in heterogeneous regions. Professors Weiss and Neuhauser intend to disseminate the research tools developed to a broad community through freely available software packages.