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Investigating Nanostructures to Biological Tissues Through Brillouin Scattering

Explore the impacts of nanostructures on biological tissues using Brillouin Scattering. Study includes freestanding nanomembranes, mechanical properties, and implications on heat and electron transport properties. Investigate standing wave modes, flexural and dilational modes, and their significance in biological tissues such as human and bovine lenses. Discover the potential clinical relevance of non-invasive probe techniques in corneal and lens studies.

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Investigating Nanostructures to Biological Tissues Through Brillouin Scattering

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  1. Thirty Years Ago!

  2. At the Max Planck Resonant Brillouin Scattering CdTe

  3. 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

  4. θ Longitudinal Standing Modes SiO3N4/ GaAs ZnSe/ GaAs

  5. Organ Pipe Modes d=3λ/4, f=3V/4d, Second harmonic d=λ, f=V/d Second harmonic

  6. Scattering Intensity E-O Elasto-Optic Contributions Film + Substrate Bortolani, Marvin, Nizzoli, Santoro J. Phys. C. 16, 1757 (1983)

  7. k3f(1) k3f(2) ZnSe k3f(2) k3f(1) GaAs Scattering Intensity

  8. ZnSe/GaAs: BLS Intensity

  9. 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

  10. Freestanding Si3N4 membrane LSM, TSM, Dilational, Flexural Modes

  11. Freestanding Si3N4-PMMA bilayer nano-membranes

  12. PMMA/SiN: dispersion

  13. w = 300nm, D = 100, 200, 300nm h =dP= 75, 65, 60 nm ds = 100 nm Nanowires

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

  15. In-plane Dispersion

  16. Mode Profiles q1= qx= mπ/w, q2= qy = 0 Edge type 1TSM 2TSM m= 0TSM 1TSM

  17. Mode Profiles Finite q

  18. 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 = ρλ2ν2/4n2). Heys KR, et.al Molecular Vision (2004)

  19. 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.

  20. 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

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