1. Hypersonic Phononic Crystals
Edwin L. Thomas, Massachusetts Institute of Technology, DMR 0308133
Fig. 2. (a) Single Crystal
Hypersonic Reflector
(b) Theoretically Calculated
Dispersion relation of the epoxy-
air phononic crystals along[10]
(c) Experimental Phononic
dispersion relation along the [10]
direction showing a partial band
gap between 1.21 and 1.57 GHz
(in grey)
Fig. 1. A sound wave is
incident on the surface of
a two dimensional
phononic crystal
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.
J.-H. Jang et al., Applied Physics Letters (submitted)
Phononic crystals are structures possessing
periodic variations in density and/or elastic
constants, which result in band gaps for
sound and other mechanical waves. Sonic
crystals can be used for sound and vibration
isolation, ultrasonic crystals for acoustic
imaging. Our interest is in hypersonic
crystals with 100nm feature sizes for the
enhancement of acousto-optical
interactions: engineering of phonon –
photon as well as electron-phonon
interactions.
E. Thomas et al., Nature Materials, 5(10), 773, 2006
We fabricated hypersonic crystals with band gaps in
GHz frequency range using interference lithography
and measured their phonon dispersion relation with
Brillouin light scattering (BLS). We reported the first
experimentally measured band gap at hypersonic
frequencies in a single crystalline hypersonic
phononic crystal.

2. Hypersonic phononic crystals
Edwin L. Thomas, Massachusetts Institute of Technology, DMR 0308133
Education
This grant was used to provide support for
T. Gorishnyy, a graduate student who just
completed his Ph.D. in Materials Science
and Engineering (July, 2007) and provides
partial support for Henry Koh, a 3rd year
graduate student in Materials Science and
Engineering and Boris Rasin a sophomore
in Materials Science and Engineering at MIT
who is working on fabricating the hypersonic
crystals using interference lithography
during spring term 2007 and over the
summer of 2007.
References:
•T. Gorishnyy et al., PRL, 94 115501, 2005
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)
Outreach
As a part of this investigation we have
established a very productive
collaboration with Prof. G. Fytas from
Max Plank Institute (MPI) for Polymer
Research in Mainz, Germany. T.
Gorishnyy has visited MPI twice to
perform Brillouin light scattering
measurements on phononic crystals.
This work has resulted in several
publications and was presented at
number of international conferences.
The Interference Lithography Lab (ILL)
has offered tours and demos to
Freshman Explorations as well as
Parents Weekend activities.