terahertz materials characterization in extreme environments
DESCRIPTION
Dr. David Daughton presents information about the new 8500 Series Lake Shore THz system for materials characterizationTRANSCRIPT
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Terahertz Materials Characterization in Extreme EnvironmentsEmerging Tools for Materials Research
David R. DaughtonApplications Scientist
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THz Systems
Probe Stations
Hall EffectMeasurement Systems (HMS)
Magnetometers (VSM/AGM)
Permanent Magnets
High Density Recording Media
Mineral Magnetism
Electronic thin films
Organic Electronics
Spintronics
Nanowires
Magnetoresistance
Organic electronics
Thermoelectrics
Solar Cells
HEMTS
Materials Characterization Systems Systems
Measure electrical properties of devices and materials in temperature-controlled environment
AC/DC measurements: Hall mobilities Carrier concentration Carrier type
Measure magnetic properties: Hysteresis M(H) loops FORC curves Temperature dependencies
Fully integrated for material properties: Electronic Magnetic Chemical
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Why THz?
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Equivalent Scales for THz
1012 Hz
2.5 THz ~ 10 meV
Alignment of THz energy levels with phenomena of interest– Vibrational resonances– Novel spin resonances– Free carrier motion in
semiconductors
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Materials Phenomena
The Electromagnetic Spectrum
D. N. Basov, et al. “Electrodynamics of correlated electron materials” Rev. Mod. Phys. 85(2), 471 (2011).
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Equivalent Scales for THz
THz wavelengths match the feature sizes of development-grade electronic materials– Non-contact electronic characterization– Novel magnetic materials
1012 Hz
0.6 THz ~ 0.5 mm
2”
10 mm
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Equivalent Scales for THz
Coupling to spin-based materials at THz frequencies– High speed computing
paradigms– May require large fields
1012 Hz
0.2 THz ~7 T
Nagashima, T.; Nishitani, J.; Kozuki, Kohei, "Lasers & Electro Optics & The Pacific Rim Conference on Lasers and Electro-Optics, 2009. CLEO/PACIFIC RIM '09. Conference on , vol., no., pp.1,2, 30-3 Aug. 2009
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Equivalent Scales for THz
1012 Hz
6.5 THz ~ 300 K
480 500 520 540 560 580
0.1
1
TH
z T
rans
mis
sion
Frequency (GHz)
5.8 K 75 K 150 K
a-Lactose
THz
Tran
smis
sion Cryogenic temperatures
– Homogeneous broadening of vibrational resonances
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Equivalent Scales for THz
1012 Hz
Cryogenic temperatures– Homogeneous broadening of
vibrational resonances– Temperature dependent carrier
concentration and mobility
6.5 THz ~ 300 K
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Equivalent Scales for THz
1012 Hz
10 meV7 T 300 K0.5 mm
Alignment of THz energy levels with phenomena of interest THz wavelengths match the feature sizes of development-
grade electronic materials Coupling to spin-based materials at THz frequencies Cryogenic temperatures
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THz System Product Challenges
THz performance suitable for materials characterization– Continuous tuning over bandwidth– Spectral resolution
Ability to characterize samples while exposed to variable cryogenic temperatures and magnetic fields
Affordable THz-based measurement platform Robust design Proceduralized experimental methods and reliable analysis
of the spectral results– Convenient sample insertion without complicated alignment– Enable materials developers to rapidly begin productive research
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Filling the THz Gap
The Electromagnetic Spectrum
0 10 20 30 40 50
0
Ele
ctric
F
ield
(a.u.)
Time (ps)
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THz with cryogenics & magnetics
Many materials of interest for THz require variable temperature and/or high magnetic fields
Optical cryostats are the standard approach– THz generation outside the
environment– Must pass optical energy through
windows, cutting signal power and spectral distortion
Not ideal for THz spectroscopies
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Variable Temperature and High Magnetic Field THz Platform
Cryostat Sample space
±9 T magnet
Removable sample insert
Cryo-compatibleTHz emitter with collimating optics
Rotatable sample stage(10 mm × 10 mm)
Thermally stableoptical alignment stages
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Application software for turnkey operation Experiment setup/run Analysis of spectral data Calculation of material properties
Integrated THz System Details
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Fiber-based optical platform for CW THz spectroscopy CW THz spectrometer instrument Amplitude and phase detection from
200 GHz to 1.5 THz Spectral resolution under 500 MHz Circularly polarized light
Integrated controls Model 336 cryogenic
temperature controller Model 625 superconducting
magnet power supply
Superconducting magnet High magnetic fields to ±9 Tesla
Integrated cryostat & insert Variable temperatures from 5 K to 300 K Sample size – 10 mm Measurement – THz transmission
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Photoconductive THz Emitter
Photoconductive device
-10 -5 0 5 10-40
-20
0
20
40
Cu
rre
nt (A
)
Bias (V)
Dark Fiber illuminated device
Room Temperature
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Photoconductive THz Emitter
THz-frequency transient current oscillations induced by amplitude modulated IR laser light
Current oscillations in the antenna structure radiate propagating EM waves.
A high resistivity Si lens is attached to the emitter device to couple the THz emission to free space.
Photoconductive device
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THz Time Domain Spectroscopy
fs
I
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THz Time Domain Spectroscopy
fs
IA
0 10 20 30 40 50
0
Ele
ctric
F
ield
(a.u.)
Time (ps)
E
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THz Time Domain Spectroscopy
ps
fs
Dispersion
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THz Time Domain Spectroscopy
Dispersion Compensation
fs
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THz Time Domain Spectroscopy
Dispersion Compensation
ps
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Continuous-Wave THz Spectroscopy
DFB Laser 1
DFB Laser 2
f1
f2
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Continuous-Wave THz Spectroscopy- Generation
f1-f2
f1-f2
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Detected current No detected current
Continuous-Wave THz Spectroscopy- Detection
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Continuous-Wave THz Spectroscopy- Frequency Tuning
DFB Laser 1
DFB Laser 2
f1
f2
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DFB Laser 1
DFB Laser 2
f1
f2
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Integrated Software for Turn-key Operation
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Integrated Software for Turn-key Operation
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Integrated Software for Turn-key Operation
Sample Reference Background
BLOCK
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Integrated Software for Turn-key Operation
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Integrated Software for Turn-key Operation
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Case Study: Sr2CrReO6 Thin Films
In-plane
Double-perovskite ferrimagnet (Tc = 635 K) Ms = 1.29 mB per f.u. Predicted 90% spin polarization Large anisotropy
Stoichiometric, epitaxial, and well ordered Well ordered films on STO and LSAT
substrates
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Case Study: Sr2CrReO6 Thin Films
Stoichiometric, epitaxial, and well ordered Grown with off-axis magnetron sputtering
1 µm thickness ~ 20 hours
Low material yields 10 to 200 nm thick film on 10 × 10 mm substrate After characterization, wafer is diced & distributed for
device manufacturing
Wafer real estate is at a premium Electrical contacts for material evaluation reduce number of
devices — non contact evaluation Cryogenic characterization elucidates conduction mechanisms
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CW-THz Transmission
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0.5 1.0 1.50.0
0.5
1.0
TH
z T
rans
mis
sion
Frequency (THz)
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CW-THz Spectroscopy of Conductive Thin Films
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Thickness
Conductivity
Ga-doped ZnO on ZnO
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SCRO Film DC Conductivity
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0.0
0.2
0.4
0.6
0.8
1.0
200 400 600 800 10000.0
0.2
0.4
0.6
0.8
1.0120 m LSAT
5 K 50 K 100 K 300 K
1.4 mSCRO on 120 m LSAT
TH
z T
rans
mis
sion
Frequency (GHz)
300 K
0.0
0.2
0.4
0.6
0.8
1.0
200 400 600 800 10000.0
0.2
0.4
0.6
0.8
1.0120 m LSAT
5 K 50 K 100 K 300 K
1.4 mSCRO on 120 m LSAT
TH
z T
rans
mis
sion
Frequency (GHz)
300 K
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Variable Range Hopping Conductivity
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𝜎 (𝜔 )=𝜎𝐷𝐶
𝜎 (𝜔 )=𝐴 (𝑇 )𝜔𝑠 (𝑇 )+𝜎𝐷𝐶
Variable Range Hopping
5 K
5 K
𝐴 (5𝐾 ) 10002𝜋 𝑠 (5𝐾 ) 0.8
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What’s Next
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– Turn-key acquisition of temperature and field dependent THz spectra
Taking orders March 2014!
Model 8500 THz System for
Material Characterization
Customer applications — samples
Sponsored research program to develop turn-key analysis software for CW-THz spectra