Hypersonic Phononic Crystals* Edwin L. Thomas (MIT), DMR-0308133 by kR3B0u

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									                               Hypersonic Phononic Crystals
       Edwin L. Thomas, Massachusetts Institute of Technology, DMR 0308133
Phononic crystals are structures possessing             We fabricated hypersonic crystals with band gaps in
periodic variations in density and/or elastic           GHz frequency range using interference lithography
constants, which result in band gaps for                and measured their phonon dispersion relation with
sound and other mechanical waves. Sonic                 Brillouin light scattering (BLS). We reported the first
crystals can be used for sound and vibration            experimentally measured band gap at hypersonic
isolation, ultrasonic crystals for acoustic             frequencies in a single crystalline hypersonic
imaging. Our interest is in hypersonic                  phononic crystal.
crystals with 100nm feature sizes for the
enhancement of acousto-optical                         Fig. 2. (a) Single Crystal
                                                       Hypersonic Reflector
interactions: engineering of phonon –photon
                                                       (b) Theoretically Calculated
as well as electron-phonon interactions.               Dispersion relation of the epoxy-
                                                       air phononic crystals along[10]
                                                       (c) Experimental Phononic
Fig. 1. A sound wave is
                                                       dispersion relation along the [10]
incident on the surface of
                                                       direction showing a partial band
a two dimensional
                                                       gap between 1.21 and 1.57 GHz
phononic crystal
                                                       (in grey)
consisting of air cylinders
on a triangular lattice in a
solid film. As the sound
wave has a frequency
within the bandgap,
propagation is not allowed
and the wave is reflected
backwards.

E. Thomas et al., Nature Materials, 5(10), 773, 2006
                                                          J.-H. Jang et al., Applied Physics Letters (submitted)
                         Hypersonic phononic crystals
              Edwin L. Thomas, Massachusetts Institute of Technology, DMR 0308133


 Education                                                Outreach
This grant was used to provide support for          As a part of this investigation we have
T. Gorishnyy, a graduate student who just           established a very productive
completed his Ph.D. in Materials Science            collaboration with Prof. G. Fytas from
and Engineering (July, 2007) and provides           Max Plank Institute (MPI) for Polymer
partial support for Henry Koh, a 3rd year           Research in Mainz, Germany. T.
graduate student in Materials Science and           Gorishnyy has visited MPI twice to
Engineering and Boris Rasin a sophomore             perform Brillouin light scattering
in Materials Science and Engineering at MIT         measurements on phononic crystals.
who is working on fabricating the hypersonic        This work has resulted in several
crystals using interference lithography             publications and was presented at
during spring term 2007 and over the                number of international conferences.
summer of 2007.                                     The Interference Lithography Lab (ILL)
                                                    has offered tours and demos to
References:
                                                    Freshman Explorations as well as
•T. Gorishnyy et al., PRL, 94 115501, 2005          Parents Weekend activities.
T. Gorishnyy et al., Physics World, 18(12), 24,
2005
J.-H. Jang et al., Nano Letters, 6(4): 740, 2006
•E. Thomas et al, Nature Mat.5,10,773 (2006)
•W. Cheng, Macromolecules,39,9614(2006)

								
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