Non-linear Electrodynamic Response

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Non-linear Electrodynamic Response of Dielectric
Materials
microwave applications (radar, etc) phase
shifters tuned filters voltage controlled
oscillators optical applications (wdm,
etc) amplitude modulators phase
modulators frequency shifters
PowerPoint Presentation by Professor Jim
Eckstein Department of Electrical and Computer
Engineering
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What gives rise to non-linear response?
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Dielectric polarization of a ferroelectric, which
has broken inversion symmetry.
P
P0
E
Easy to see that this is not zero in materials
with broken symmetric response.
But, two solutions or branches. c(2) diverges as
T ? Tc
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What you would like for non-linear modulators,
etc
For non-linear optical and other field tuning
applications would prefer a characteristic like
this. Stable, single solution cant
de-pole Permanently polarized dielectric with
big c(2) Use molecular nanostructuring to make
such a material (MBE) (once you figure out what
matters!)
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Artificial structures using ALL-MBE to synthesize
materials and heterostructures not found in nature
anisotropy energy surface (La0.7Ca0.3MnO3 on
SrTiO3 substrate)
Controlling material properties via epitaxial
strain
Tensile strain-induced magnetic anisotropy in
magnetic oxide
Producing new materials by modulated
heterostructure growth
Grow crystal using ferroelectric and related
phases stack with structurally broken c-axis
inversion symmetry
broken symmetry throughout film favors one
polarization permits stable operation nearer
to Curie temperature obtain larger response at
zero bias
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Introducing the actors , perovskite titanate
phases
Combine these in single crystal heterostructures
to investigate the effects of compositional
(strain) symmetry breaking ?
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Inversion symmetry?
supercell nanostructure (each rectangle is one
monolayer)
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Atomic Layer-by-Layer Molecular Beam Epitaxy
electron
hollow
photomultiplier
gun
cathode
tube
quadrupole
lamp
mass
spectrometer
Ca

• atomic absorption spectroscopy for feedback
  control
• ozone oxidation
• in-situ RHEED with digital video
• We have control over the source fluxes to better
  than 1 accuracy (AA, RHEED)

Sr
shutters
Ba
quartz
Al
crystal
monitor
La
rotating
load
substrate
lock
positioner
Y
substrate
Ti
holder
Mn
turbo
Cu
pump
RHEED
Bi
hollow
photomultiplier
cathode
tube
lamp
Oxygen
Ozone
RHEED reveals surface crystal structure
generator
Pump
ozone still
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RHEED images at different points of the super
cell growth
End of Super Cell CTO Surface
Start of Super Cell CTO Surface
After 1 ML BTO
After 1 ML STO
2 ML BTO
2 ML STO
2 ML CTO
1 ML CTO
1 ML BTO
1 ML STO
Specular Spot Oscillation from 1 Super Cell
a
a
a
a
a
a
After 0.5 ML STO
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Growth and Processing of Capacitor Devices
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(No Transcript)
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Now, add more BaTiO3 this has large c at higher
T in bulk
Both show temperature indepen-dent effect from
180 to 360 K
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Measure Obtain P0 by integrating edE Psat
should be the same size at and infinite bias
field
P0
Obtain permanently polarized material with
tunable dielectric constant