Thirty Years Ago!. At the Max Planck CdTe Resonant Brillouin Scattering.
-
Upload
emma-bates -
Category
Documents
-
view
229 -
download
1
Transcript of Thirty Years Ago!. At the Max Planck CdTe Resonant Brillouin Scattering.
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