K. S. S. Christie1, 2, J. K. Young3, Y. Mukai4, W. S. Rockward1 , K. Tanaka4, T. A. Searles1, T. Arikawa4
1Department of Physics, Morehouse
College , Atlanta ,
Georgia 30314, USA
2 NanoJapan Program, Rice
University , Houston , Texas 77005 , USA
3 Department of Electrical & Computer Engineering, Rice University ,
Houston , Texas
77005 , USA
4 Department of Physics, Kyoto University ,
Kyoto , 606-8502, Japan
Nanoparticles have distinct electrical and vibrational properties from
bulk materials originating from the quantum confinement and surface effect.
Bioengineers are currently able to exploit these properties for applications in
biosensing, using the surface plasmon resonance wavelength of gold nanorods to
monitor changes in their local environment. THz-TDS provides scientists with
new opportunities to study low frequency phonons, and low frequency phonons in
gold nanoparticles are explicatory of their morphology. Here, terahertz
time-domain spectroscopy (THz-TDS) was used to study the vibrational behavior
of gold nanorods embedded in a poly(vinyl alcohol) matrix. The nanorods’ aspect
ratios (diameter x length) of 30.7 x 81.6 nm, 30.7 x 84.0 nm, 16.2 x 39.5 nm,
18.7 x 52.2 nm, and 18.5 x 56.5 nm are confirmed by visible/near-infrared
absorption spectroscopy and transmission electron microscopy. The frequencies
of the phonon modes are expected to be proportional to the longitudinal and
transverse sound velocity in the material and inversely proportional to the
size of the Au nanorods. We discuss how THz-TDS offers a solid method to
determine nanoparticle morphology
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