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SUMMARY:Chameleon Metals: from nanostructures  for plasmon engineering to 
 molecular detection - Professor Jeremy Baumberg\, Department of Physics\, 
 University of Southampton
DTSTART:20060503T151500Z
DTEND:20060503T161500Z
UID:TALK4691@talks.cam.ac.uk
CONTACT:Duncan Simpson
DESCRIPTION:The interaction of light with metallic surfaces is strongly en
 hanced when the surface is patterned on the wavelength scale.  Arrays of s
 ub-wavelength holes exhibit many interesting properties mediated by the pl
 asmonic surfaces. Here we demonstrate spectral and angular dispersion meas
 urements of both surface and localised plasmons on nano-structured surface
 s composed of spherical voids. We reveal a new strong coupling between the
  plasmonic-crystal modes and the localised plasmons\, which allows plasmon
 ic atoms to communicate. We show that such nanostructured plasmonic substr
 ates have widespread application in molecular sensing.\nNano-structured su
 rfaces are formed by electrochemical deposition through an ordered templat
 e of self-assembled latex spheres.[1\,2]  The technique of casting intrica
 te 3D objects was invented five thousand years ago in Mesopotamia. We have
  found a way to re-invigorate this technique on scales of billionths of a 
 metre\, to help us make nanostructures with extremely unusual optical prop
 erties.[3] Control over the charge while plating allows precise control of
  the thickness of the metallic mesh.  This process is used to grade the th
 ickness of the sample from shallow dishes to almost entirely encapsulated 
 spherical voids.\nSurface plasmons are efficiently excited due to the regu
 lar array of close-packed dishes\; localised plasmons on the other hand re
 side in the deep cavities at larger sample thicknesses. We show there exis
 ts a critical geometry which induces full localisation\, corresponding to 
 a Mott transition for surface plasmons.  By measuring the spectral respons
 e of the samples at different thickness and incident angles the full dispe
 rsion is revealed.  Of particular interest is the strong mixing and anticr
 ossing of surface and localised plasmons at intermediate thicknesses.  The
 se new mixed states correspond to the crossover to hopping plasmonic trans
 port.[4]\nUnderstanding the mixing of plasmon states leads to an in-depth 
 knowledge of the electric-field distribution on the nano-structured surfac
 es allowing the optimisation of efficient plasmonic devices\, such as SERS
  sensors [5\,6].\n[1] S. Coyle et al.\, Phys. Rev. Lett. 87\, 176801 (2001
 ) \n[2] P.N. Bartlett et al.\, Faraday Discussions 125\, 117 (2003) \n[3] 
 J.J. Baumberg\, commentary\, Nature Materials 5\, 2 (2006)\n[4] T.A. Kelf 
 et al.\, Phys. Rev. Lett. 95 116802 (2005)\n[5] J.J. Baumberg et al.\, Nan
 o. Lett. 5\, 2262 (2005)\n[6] http://www.mesophotonics.com/news/index.htm#
 klarite\n[7] S. Cintra et al.\, Faraday Discussions\, 136\, 16 (2005)
LOCATION:Pippard Lecture Theatre\, Cavendish Laboratory
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