Thirty Years Ago!

At the Max Planck

CdTe

Resonant Brillouin Scattering

Membrane Acoustics: Nanostructures to biological tissues

• Supported layers – standing resonances– SiON/GaAs; ZnSe/GaAs

• Freestanding Nanomembranes– SiN– SiN/Polymer– Patterned nanowires

• Cornea and eye lens

Longitudinal Standing Modes

SiO3N4/ GaAs ZnSe/ GaAs

θ

Organ Pipe Modes

d=3λ/4, f=3V/4d,Second harmonic d=λ, f=V/d

Second harmonic

Scattering Intensity

Elasto-Optic Contributions Film + Substrate

Bortolani, Marvin, Nizzoli, Santoro J. Phys. C. 16, 1757 (1983)

E-O

Scattering Intensity

ZnSe

GaAs

k3f(1) k3

f(2)

k3f(2)

k3f(1)

ZnSe/GaAs: BLS Intensity

Freestanding membranes• Ultra-light weight

– Robust, pliable, flexible electronics– Mechanical/ elastic properties

• Proximity of surfaces ~ phonon wavelengths– Lattice vibrations modified– Increased phonon relaxation rates– Nano-scale heat transport; Quantized thermal conductance– Consequence on electron transport

• Composite hard-soft (inorganic-polymer) membranes– Phonon isolation

• Lithography on soft layer– Nano-wires/ lines

Freestanding Si3N4 membrane

LSM, TSM, Dilational, Flexural Modes

Freestanding Si3N4-PMMA bilayer nano-membranes

PMMA/SiN: dispersion

Nanowires

-20 -15 -10 -5 0 5 10 15 20

D=300nm

w=200nm

q||

=200

=400

=540

Frequency (GHz)

D=300nmw=200nm

q T

=540

=400

=200

w = 300nm,D = 100, 200, 300nmh =dP= 75, 65, 60 nmds = 100 nm

Nano-wire Dispersion

Odd parity

Even parity

Resonant Ultrasound Spectroscopy (Migliori)

In-plane Dispersion

Mode Profiles

2TSM

Edge type1TSM

1TSMm= 0TSM

q1= qx = mπ/w,q2= qy = 0

Mode Profiles

Finite q

Human Lens Soft outer cortex, stiff inner nucleus

Transition between stiff nucleus to soft cortex results in mode doublet

No change in frequency and bulk modulus with age (B = ρ λ2 ν2/4n2).

Heys KR, et.al Molecular Vision (2004)

Bovine Lens and Cornea

Probe intact bovine eye globe, power ~5mW.

Frequency (bulk modulus) profile mapped through axial depth of eye globe.

Corneal modulus (BLS) excellent agreement with ultrasonics on same location

Cortex-nucleus transition in bovine lens not seen.

Corneal and lenticular thickness, distance between cornea and lens measured.

Probe fibril structure in cornea?

Bulk Modulus:

Human Lens: 3.7 GPa,

Bovine Lens: 4.1 GPa,

Bovine Cornea: 2.6 GPa

Mission, G. Ophthal. Physiol. Opt. 2007 27: 256-264.

Conclusions

• BLS of elasticity on nanoscale structures• Standing wave modes (LSM, TSM) distinct role

of ripple and e-o contributions• Flexural and Dilational modes• Mode confinement across width and height of

rectangular wires – role of sidewalls in trench structures

• Corneal and Lens studies – non-invasive probe with potential clinical relevance