Nanoscale optical microscopy.

Enabling higher spatial resolution and surface specificity.

Although the past decade has seen rapid developments in the application of nanosized materials such as biological sensors, flexible solar cells, drug delivery carriers, or bit elements in computers, the potential nanoscience holds has yet to be fulfilled. In this context, the characterization of these nano-objects or functionalized surfaces using optical spectroscopy combined with advanced microscopy techniques offers information far beyond that provided by pure imaging techniques as it allows the molecular properties of these materials to be correlated with their molecular structures, sizes and compositions. The possibility to investigate nanomaterials with a spatial resolution much better than 1 micron is a major topic of significance for a better understanding of their optical-mechanical-electrical properties, their interactions and their responsiveness to an external stimuli or perturbation. Similarly, it is important to probe biological processes and chemical exchanges in biological systems. A better spatial resolution or time resolution of the biochemical exchanges would lead to a more precise understanding of the fundamentals of biological processes. Our program focuses on the study of materials and biomaterials organized at the nano- and microscale using a combination of scanning probe microscopy together with a variety of optical microscopy techniques (Raman, Fluorescence). Such an ensemble of complementary methods will be used to (i) determine the confinement effects in semi-conductor nanowires, (ii) develop ultrasensitive vibrational measurements in conjunction with plasmonic platforms and (iii) evaluate chemical exchanges between cells organized on modified surfaces.
Project 1: Tip Raman Enhanced Spectroscopy of Nanomaterials A limitation of optical microscopy is intrinsic to the diffraction limit of light, as stated by the Rayleigh criterion which states that a spatial resolution of lambda/2 can be achieved in the best conditions, lambda being the wavelength of the light. However, this spatial resolution (0.5-1 micron) excludes the precise characterization of individual nanoobjects or domains that are much smaller than the diffraction limit. In this context, tip-enhanced Raman spectroscopy (TERS) employs a metallic tip that scans the near-field of the probed object. The sharp metal tip concentrates the EM field. The optical enhancement is confined at the apex of the metallic tip and allows one to correlate vibrational Raman information with the topography of the object. Using TERS We are investigating a variety of nanomaterials (semiconductors) as well as biomaterials in order to reveal intimate properties at the nanoscale. This work in done in our groups and/or in collaboration with other groups on the material part.

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