Younan Xia (NSF Award Number: DMR-0451788)

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Shape-Controlled Nanostructures of Metals
Younan Xia (NSF Award Number DMR-0451788) Departm
ent of Chemistry, University of Washington
Silver nanostructures are containers for surface
plasmons the collective oscillation of
conduction electrons in phase with incident
light. By controlling the shape of the container,
one can control the ways in which electrons
oscillate, and in turn how the nanostructure
scatters light, absorbs light, and enhances local
electric fields. With a series of discrete dipole
approximation calculations, each of a distinctive
morphology, we illustrate how shape control can
tune the optical properties of silver
nanostructures. Calculated predictions are
validated by experimental measurements performed
on nanocubes with controllable corner truncation,
right bipyramids, and pentagonal nanowires. Such
a control of nanostructure shape allows one to
optimize surface plasmon resonance for improved
molecular detection and spectroscopy. Both
synthetic and computational studies were recently
highlighted as a cover feature article in J.
Phys. Chem. B., 2006, 110, 15666. In addition to
silver, we have also extended the synthetic
methodology to other noble metals including
palladium, platinum, and rhodium.
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Shape-Controlled Nanostructures of Metals
Younan Xia (NSF Award Number DMR-0451788) Departm
ent of Chemistry, University of Washington
(left) Illustration of the reaction paths leading
to well-defined silver nanostructures. Ethylene
glycol reduces silver ions to atoms, which form
clusters of fluctuating structure. Fluctuation
decreases as the cluster grows, until it evolves
into a single-crystal, single twinned, or
multiple twinned seed. Further growth of seeds
can selectively enlarge (100) facets at the
expense of (111) facets, resulting in formation
of nanocubes, bipyramids, or pentagonal
nanowires. (middle) SEM image of Pt nanorods
grown on the surfaces of spherical aggregates of
Pt nanoparticles that were formed through a
surfactant-directed self-assembly process.
(right) TEM image of Pt nanorods after they had
been released from the surfaces by brief
sonication. The inset in (D) gives a typical
selected-area electron diffraction pattern of the
Pt nanorods, with the four rings indexed to the
111, 200, 220, and 311 diffraction of
face-centered cubic Pt, respectively. Note that
several nanorods could grown from the same seed
of Pt nanoparticle, resulting in a branched
morphology.
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Other Accomplishments

• Supervision of 6 undergraduates enrolled for
  the independent study (with a total of
• 21 credits) and 1 REU summer student. Two of
  them co-authored 3 articles recently
• published in Adv. Mater. (2005) Nano Lett.
  (2005), and Chem. Soc. Rev. (2006)
• Supervision of 2 junior students from the
  Redmond High School in the summer of
• 2005
• Giving invited lectures at MRS and ACS national
  meetings, as well as more than 40
• universities (chemistry, chemical
  engineering, and materials science engineering)
  
• around the world
• Giving lectures at the Sandia National
  Laboratories and the 3rd ASME Nano Training
• Boot Camp
• Serving as a committee member of the Inorganic
  Nanostructures Facility at the DOE
• Molecular Foundry
• Serving as the associate editor of Nano Letters
• Serving as a member of the advisory board for
  Nano Today, Langmuir, Chemistry of
• Materials, International J. of
  Nanotechnology, and International J. of
  Nanoscience.
• Serving as symposium co-organizers and session
  chairs for MRS, ACS, and SPIE
• Serving as the guest editor for a special issue
  on metal nanostructures and surface
• plasmon resonance published in Mater. Res.
  Roc. Bull. (May, 2005)
• Preparation of three education articles, which
  have been accepted for publication in