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 SiO 3 N 4 / 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 k 3 f(1) k 3 f(2) k 3 f(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 Si 3 N 4 membrane LSM, TSM, Dilational, Flexural Modes

Freestanding Si 3 N 4 -PMMA bilayer nano-membranes

PMMA/SiN: dispersion

Nanowires w = 300nm, D = 100, 200, 300nm h =d P = 75, 65, 60 nm d s = 100 nm

Nano-wire Dispersion Odd parity Even parity Resonant Ultrasound Spectroscopy (Migliori)

In-plane Dispersion

Mode Profiles 2TSM Edge type 1TSM m= 0TSM q1= q x = mπ/w, q2= q y = 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 λ 2 ν 2 /4n 2 ). 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 :

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