Manipulating light with nanostructures: controlling reflection to chemical imaging

Michael J. Gordon, Ph.D.
Associate Professor, Dept. of Chemical Engineering
University of California, Santa Barbara

This talk will highlight some of our recent work in bio-inspired photonics and plasmonics related to controlling reflection at interfaces and nanoscale chemical imaging. In the former, an easy, scalable and defect-tolerant surface modification protocol, based on colloidal lithography and plasma  etching,  was  developed  to  create  synthetic  'moth-eye'  anti-reflective  structures  on different  surfaces  for  applications  in  photon  detection  and  extraction.  Large  increases  in transmission,  bandwidth,  and  omni-directional  response  were  obtained  in  Si,  Ge,  and  GaAs platforms over the mid- and far-IR spectral regions (2-50+ mm) with performance better than commercial coatings. Moth-eye coatings were also implemented in InGaN/GaN quantum well LED structures to enhance light extraction. Effective medium theory, finite difference time domain (FDTD)  simulations,  and  quantitative  measurements  of  transmission,  reflection  and  diffuse scattering were used to understand the ‘photon balance’ of moth-eye films to investigate how   scattering phenomena are affected by moth-eye geometry.

In the materials characterization realm, we have developed hybrid atomic force microscopes that manipulate light at 'super resolutions' below the diffraction limit (l/2) to locally image surface structure and chemistry. Nanometer-scale optical fields are created at the apex of an optical antenna tip when laser light excites plasmons (i.e., collective oscillations of free electrons) in the tip material. The resulting field is then used to directly probe molecular vibrations of the surface by way of inelastic light scattering (Raman spectroscopy). Since the optical field enhancement by the tip is truly nanoscale, vibrational spectroscopy and chemically-specific surface imaging below the diffraction limit can be accomplished. All optical, structural- and chemically-specific surface imaging nanowires and organic thin films at spatial resolutions < l/60 will be discussed.

Dr. Michael J. Gordon is an Associate Professor in the Department of Chemical Engineering at UCSB. He received his BS/MS in Chemical Engineering from the Colorado School of Mines, MS (Applied Physics) and PhD (Chemical Engineering) from the California Institute of Technology, and spent two years as a post-doc in Grenoble, France at the Laboratoire des Technologies de la Microe lectronique (LTM-CNRS). Dr. Gordon joined UCSB in 2007 and is currently the head of the Undergraduate Laboratory in Chemical Engineering. Professor Gordon’s research interests include scanning probe microscopy, plasma physics, plasmonics, spectroscopy, and nanomaterials. Dr. Gordon is a Packard Fellow, received the NSF CAREER award, and was chosen as the Robert E. Vaughn Lecturer at Caltech in 2013. He has also received several department and campus-wide teaching awards.