Optics provides us with powerful characterization techniques, allowing complex, layered structures to be imaged (confocal microscopy), the chemical composition of materials to be determined (spectroscopy), and particles to be manipulated in a non-contact manner (optical tweezers). Traditional optical methods fail for nanometer-scale structures, however, because diffraction prevents conventional lenses from focusing light to spots smaller than roughly half a wavelength. Nonetheless, the ability to apply optical methods to the nanoscale would greatly enhance our capabilities in nanotechnology and nanoscience.

The focus of the Crozier Laboratory is on developing new tools for nanotechnology based on photonics. These are largely based on surface plasmon structures, termed optical antennas, which enable light to be concentrated into spots with sub-wavelength spatial extent. The Crozier Laboratory is pursuing applications of these and related microfabricated structures in manipulation, imaging, and spectroscopy.

The incorporation of optical tweezers into microfluidic chips would provide exciting new functionalities for these systems. These include particle sorting, particle manipulation, the measurement of fluid properties, and biophysical force measurements. Professor Crozier’s group has the goal of developing microfabricated structures for optical trapping that are suitable for integration into microfluidic chips. Surface plasmon nanostructures generate optical near-fields that could be employed for the trapping of nanoparticles. For trapping microparticles, other structures, including Fresnel Zone Plates, are being investigated.

Near-field scanning optical microscopy (NSOM) extends the resolution of optical microscopes below the diffraction limit. The Crozier Laboratory is developing new probes for NSOM based on optical antenna structures. With Professor Capasso’s group, the Crozier Laboratory is also pursuing the combination of optical antennas with semiconductor lasers, in devices termed “plasmonic laser antennas.”

Raman spectroscopy is a powerful analytical technique, permitting molecules to be identified through their characteristic spectral fingerprint. A key challenge, however, is that Raman scattering cross sections are very small. In the 1970’s, it was discovered that molecules on roughened surfaces have significantly larger Raman signals. This method, known as Surface-Enhanced Raman Scattering, offers enormous potential, but its widespread adoption has been hampered by the frequently irreproducible nature of these surfaces. The Crozier Laboratory is developing surface plasmon optical antenna chips with the goal of achieving large enhancement accompanied by the reproducibility demanded by sensor applications.