student presentatifdons 2011
TRANSCRIPT
-
7/24/2019 Student PresentatiFDons 2011
1/102
John D. Cressler, 7/06 1
Generalized Magneto-OpticalEllipsometry
Nelson E. Lourenco
ECE 4813 - Semiconductor Materials and Device Characterization
Dr. Alan Dool itt le
School of Electrical and Computer Engineering
85 5thStreet, N.W., Georgia Institute of Technology
Atlanta, GA 30308 USA
-
7/24/2019 Student PresentatiFDons 2011
2/102
John D. Cressler, 7/06 2
Fundamentals of Polarized Light
Overview of Traditional Ellipsometry
Magneto-Optical Characterization
Generalized Magneto-Optical Ellipsometry
Vector Generalized Magneto-Optical
Ellipsometry (Vector Magnetometer)
Outline
-
7/24/2019 Student PresentatiFDons 2011
3/102
John D. Cressler, 7/06 3
Light Polarization
Light can be fully polarized, partially polarized, unpolarized
- Fully Polarized Light
Linearly Polarized
Elliptically Polarized
D.K. Schroder Semiconductor Device and Material Characterization, 3rd Ed.
-
7/24/2019 Student PresentatiFDons 2011
4/102
John D. Cressler, 7/06 4
Developed by Dr. Robert Clark Jones
- Developed between 1941-1956 at Harvard / Polaroid Corporation
- Mathematical model for describing polarized coherent light
- Randomly polarized, partially polarized, and incoherent light
cannot be modeled using Jones Calculus
Mueller Calculus (Stokes Vectors)
Jones Calculus
G.G. Fuller Optical Rheometry of Complex Fluids, 1st Ed.
-
7/24/2019 Student PresentatiFDons 2011
5/102
John D. Cressler, 7/06 5
Polarized light represented by Jones Vector
- Linearly Polarized Light
X-Direction: Y-Direction:
- Circular Polarized Light
Left-Hand (LHCP): Right-Hand (RHCP):
Linear Optical Element represented by Jones Matrix
- Horizontal Linear Polarizer:
- Vertical Linear Polarizer:
- Right Circular Polarizer:
Jones Calculus contd.
-
7/24/2019 Student PresentatiFDons 2011
6/102
John D. Cressler, 7/06 6
Interested in optical parameters of thin fi lms and/or
semiconductor substrates
- Air (n0) Semiconductor (n1 jk1) Interface
- Air (n0) Thin Film (n1) Semiconductor (n2 jk2) Interface
- Complex Index of Refraction: = n jk
n: phase velocity in mediumk: absorption loss through medium
Example: Null Ellipsometry (PCSA)
Traditional Ellipsometry
R.M. Azzam Ellipsometry and Polarized Light, 1st Ed.
-
7/24/2019 Student PresentatiFDons 2011
7/102
John D. Cressler, 7/06 7
Applications
- Optical Properties of Materials
- Film Thickness- Film Deposition / Etching
Process Control
In-situ Monitoring
GT MiRC Cleanroom
- Woollam Ellipsometer- Plas-Mos Ellipsometer
Traditional Ellipsometry
Photos courtesy of GT Microelectronics Research Center
-
7/24/2019 Student PresentatiFDons 2011
8/102
John D. Cressler, 7/06 8
Traditional Ellipsometry determine optical properties, but
there are also magneto-optical properties
- Magneto-Optical Storage Devices
Ultra thin-film magnetism
- Ferromagnetic Materials
Rare-Earth MagnetsFerrofluids
Faraday Effect
- Occurs for light propagating through magnetic fields and magneticmaterials
- Rotation of the plane of polarization
M-O Motivation
S. Mancuso `Faraday Rotation and Models (2000)
-
7/24/2019 Student PresentatiFDons 2011
9/102
John D. Cressler, 7/06 9
Full Magneto-Optical Characterization Process (2 Steps)- Optical Characterization
= n jk- Magneto-Optical Characterization
Q = Qr jQi(Complex Magneto-Coupling Constant)
Magnetization Orientation Can we simplify this setup?
M-O Characterization
Magneto-optical Ellipsometer
P. Q. J. Nederpel & J. W. D. Martens
January 3rd, 1985
-
7/24/2019 Student PresentatiFDons 2011
10/102
John D. Cressler, 7/06 10
Developed by Andreas Berger and Matthew Pufall at
University of California San Diego (1997)
- Complete magneto-optical characterization
- Combine two-step process into one measurement
Measurement Setup- HeNe Laser (=632.8 nm)
- Rotatable Polarizers (Glan-Taylor)
- Torroidal Ferrite Magnet
- Photodiode Detector
GMOE
A. Berger Generalized Magneto-Optical Ellipsometry, (1997)
-
7/24/2019 Student PresentatiFDons 2011
11/102
John D. Cressler, 7/06 11
Electric Field Vector at Detector
ED=P2*R*P1*EL
Glan-Taylor Polarizers defined by Jones matrix
Reflection (Jones Matrix) of sample
Light Intensity I at detector D
** Linear approximation: and switch signs at magnetization
reversal **
GMOE contd.
-
7/24/2019 Student PresentatiFDons 2011
12/102
John D. Cressler, 7/06 12
Fractional intensity change at photodetector, I/I
GMOE contd.
A. Berger Generalized Magneto-Optical Ellipsometry, (1997)
-
7/24/2019 Student PresentatiFDons 2011
13/102
John D. Cressler, 7/06 13
Example Data (from Berger & Pufall)
GMOE contd.
A. Berger Generalized Magneto-Optical Ellipsometry, (1997)
-
7/24/2019 Student PresentatiFDons 2011
14/102
John D. Cressler, 7/06 14
Generalized Magneto-Optical Ellipsometry can be used as
a vector magnetometer- Andreas Berger and Mathew Pufall
- Measurement of H vs. M dependence
Vector GMOE
A. Berger Quantitative Vector Magnetometry using Generalized Magneto-Optical Ellipsometry, (1997)
-
7/24/2019 Student PresentatiFDons 2011
15/102
John D. Cressler, 7/06 15
[1]D.K. Schroder, Optical Characterization, in Semiconductor Material and Device
Characterization, 3rd ed. 2006
[2]G.G. Fuller, Optical Rheometry of Complex Fluids, 1st ed. 1995
[3]R.M.A. Azzam,Ellipsometry and Polarized Light, 1st ed. 1988
[4]A. Berger, Generalized Magneto-Optical Ellipsometry,Appl. Phys. Lett.,
vol. 71, no. 7,pp. 965-967, August, 1997.
[5]A. Berger, Quantitaive Vector Magnetometry using Generalized Magneto-Optical
Ellipsometry,J. Appl. Phys., vol. 85, no. 8,pp. 4583-4585, April, 1999.
[1]D.K. Schroder, Optical Characterization, in Semiconductor Material and Device
Characterization , 3rd ed. 2006
References
-
7/24/2019 Student PresentatiFDons 2011
16/102December 2, 2011 [email protected]
Scanning Probe Microscopy
(SPM)
Brendan GunningECE 4813
-
7/24/2019 Student PresentatiFDons 2011
17/102December 2, 2011 [email protected]
SPM Flavors
AFM(Atomic Force Microscopy) C-AFM(Conductive Atomic Force Microscopy) BEEM (Ballistic Electron Emission Microscopy)
EFM (Electrostatic Force Microscopy) KPFM(Kelvin Probe Force Microscopy) NSOM(Near-field Scanning Optical Microscopy) SCM(Scanning Capacitance Microscopy) STM(Scanning Tunneling Microscopy) And more
-
7/24/2019 Student PresentatiFDons 2011
18/102December 2, 2011 [email protected]
Conductive Atomic Force
Microscopy(C-AFM)
-
7/24/2019 Student PresentatiFDons 2011
19/102
Like AFM but its conductive (duh)
Cantilever/tip is coated in conductive film (Pt, Pt-Ir, etc)
Apply bias to tip, ground samplecontact
Current flows
And you can still
get topography!
December 2, 2011 [email protected]
Conductive AFM
-
7/24/2019 Student PresentatiFDons 2011
20/102
December 2, 2011 [email protected]
Current Mapping
Scan across surface
Areas with different conductivity will havedifferent currents
Map currentlike you do withtopography
http://www.nrel.gov/pv/measurements/conductive_atomic.html
-
7/24/2019 Student PresentatiFDons 2011
21/102
December 2, 2011 [email protected]
Processing Characterization
as-grown CdTe/CdS Solar Cell CdTe/CdS Solar Cell
after bromine-methanol etch
Moutinho et al., Conductive Atomic Force Microscopy Applied toCdTe/CdS Solar Cells, 2004.
-
7/24/2019 Student PresentatiFDons 2011
22/102
December 2, 2011 [email protected]
More Current Mapping
Hsu et al., Direct imaging of reverse-bias leakagethrough pure screw dislocations in GaN films
grown by molecular beam epitaxy on GaN
templates, 2002.
Mapping the currentcan shed light on
things like:Defects
Composition
Contamination
-
7/24/2019 Student PresentatiFDons 2011
23/102
December 2, 2011 [email protected]
More Current Mapping
Dong et al., Effects of hydrogen on the morphology and electricalproperties of GaN grown by plasma-assisted molecular-beam
epitaxy, 2005.
Top samples are GaNgrown with just N2
Bottom samples grownwith H2and N2
H2passivated dangling
bonds, reducingelectrical activity
-
7/24/2019 Student PresentatiFDons 2011
24/102
December 2, 2011 [email protected]
Scanning Current-VoltageMicroscopy (SIVM)
Tip is held at one x-y
location, contactingsurface
Sweep voltage
measure current flow
Moutinho et al., Conductive Atomic Force Microscopy Applied toCdTe/CdS Solar Cells, 2004.
I-V curve of CdTe/CdS taken byconductive AFM
-
7/24/2019 Student PresentatiFDons 2011
25/102
December 2, 2011 [email protected]
Unintended Side-Effectsof C-AFM
Scan across surface
Current shown in (b)
Dark regions
largercurrent
The current flowingactually grew an
island-like feature seenin (c)
Miller et al., Reduction of reverse-bias leakage current in Schottkydiodes on GaN grown by molecular-beam epitaxy using surface
modification with an atomic force microscope, 2002.
-
7/24/2019 Student PresentatiFDons 2011
26/102
December 2, 2011 [email protected]
Cross Sectional C-AFM
Look at cross section to probe:
Multiple layers
Interfaces
Hsu et al., Scanning Probe Studies of Defect DominatedElectronic Transport in GaN
-
7/24/2019 Student PresentatiFDons 2011
27/102
December 2, 2011 [email protected]
Scanning Tunneling Microscopy(STM)
-
7/24/2019 Student PresentatiFDons 2011
28/102
December 2, 2011 [email protected]
STM Apparatus andProcedure
Coarse control brings tip (W, Pt-Ir, or Au) close to sample
Once close enough, z-piezo brings tip within tunneling range (~5)
Z-piezo steps down until preset tunneling current is reached
As the tip rasters, changes intopography will increase/decreasecurrent
Feedback raises/lowers tip tomaintain constant current
The distance the tip wasraised/lowered forms thetopography image
-
7/24/2019 Student PresentatiFDons 2011
29/102
December 2, 2011 [email protected]
STM Images
Feenstra et al., Reconstruction of GaN and InGaN Surfaces, 2000.
Pit in N-polar GaN onSapphire
GaN on 6H-SiC
0.4off-cut
Regular(0001)
200 nm 1 m
500 nm 2 mCui et al., Suppression of Spiral Growth in Molecular Beam Epitaxyof GaN on Vicinal 6H-SiC (0001), 2001.
-
7/24/2019 Student PresentatiFDons 2011
30/102
December 2, 2011 [email protected]
Our STM Images
Me! 2010
Dirty, non-annealed Gold(726nm scan size)HOPG Highly Ordered
Pyrolytic Graphite(3nm scan size)
-
7/24/2019 Student PresentatiFDons 2011
31/102
December 2, 2011 [email protected]
Empty vs. Filled States
http://physics.usask.ca/~mitchell/facilities.html
15nm
15nm
7x7 surface reconstruction of Si (111) 1.5nA tunneling current
+2V bias = Empty states -2V bias = Filled states
-
7/24/2019 Student PresentatiFDons 2011
32/102
December 2, 2011 [email protected]
What else can we do?
Rather than just sweeping across thesurface with a set bias
STS sweeps the bias at a fixed x-y-z
position
Generates a local I-V curve,representing the integrated density ofstates at that position as a function of
energy
The derivative of this I-V curve, dI/dV,can tell us even more
-
7/24/2019 Student PresentatiFDons 2011
33/102
December 2, 2011 [email protected]
Scanning TunnelingSpectroscopy
Instead of the integrated density of states, the dI/dVspectrum shows us the actual density of states at thatlocation as a function of energy
Can use the density of statesdata to create a map acrossa sample area at a chosenenergy
-
7/24/2019 Student PresentatiFDons 2011
34/102
December 2, 2011 [email protected]
Conclusion
SPM covers a huge variety of more specificcharacterization methods
Each one of these characterization methods isuseful in and of itself
Whether its C-AFM, STM, or some other method
SPM is an extremely useful and powerfulcharacterization tool
-
7/24/2019 Student PresentatiFDons 2011
35/102
December 2, 2011 [email protected]
-
7/24/2019 Student PresentatiFDons 2011
36/102
Light Beam InducedCurrent/Voltage
Guy RazECE 4813 Dr. Alan Doolittle
Fall 2011
-
7/24/2019 Student PresentatiFDons 2011
37/102
2
Motivation
The development and production of polycrystalline solar
cells creates a necessity for analysis with high spatial
resolution
Contactless probes can be used to examine:
EBIC - has been widely applied
LBIC is more appropriate for solar cells
for study of defects
LBIV measuring VOC instead of JSC
-
7/24/2019 Student PresentatiFDons 2011
38/102
3
Solar Cell Modeling
For a short circuit current (LBIC method) where V=0
For open circuit voltage (LBIV method)
Figure and Equations from: Salinger, Benda & Machacek
p
sssPVsc
R
IR
kT
IReI
kT
IReIAJI = ]1)
2[exp(]1)[exp( 0201
)2
)(4ln(
2
01
010201
2
0202
I
AJIIIII
e
kTV
PV
oc
++++
=
-
7/24/2019 Student PresentatiFDons 2011
39/102
4
Solar Cell Modeling (cont.)
LBIC measurements are made around V=0
Slope is low, current changes slowly
LBIV made around I = 0
Figure and Equations from: Salinger, Benda & Machacek
-
7/24/2019 Student PresentatiFDons 2011
40/102
5
Introduction
When a light beam strikes a semiconductor, it will
generate electron-hole pairs (EHPs) within the beams
interaction volume.
These EHPs will be separated by drift due to the internal
electric field. The E/Hs can be collected at the contacts of the object.
Amplifying and analyzing these measurements show
variations in generation, drift and recombination which
can be measured and displayed.
-
7/24/2019 Student PresentatiFDons 2011
41/102
6
Apparatus
Figure from: Hiltner & Sires
-
7/24/2019 Student PresentatiFDons 2011
42/102
7
Quantum Efficiency
QE is the ratio of the number of charge carriers collected
by the solar cell to the number of photons shinning on
the solar cell.
EQE
ISC is dependent on the amount of absorbed light
Corrected by first factor
)//(
/
1
1
chP
eI
RIQE
L
sc
=
-
7/24/2019 Student PresentatiFDons 2011
43/102
8
Photon Penetration/Absorption
Energy of a photon depend only on its wavelength by
The depth of penetration depend on Energy (KeV) and
material. (silicon example)
http://micro.magnet.fsu.edu/primer/java/digitalimaging/ccd/quantum/
chE
=
Wavelength (nm) Penetration Depth (m)
400 0.19
500 2.3
600 5.0
700 8.5
800 23
900 62
1000 470
http://micro.magnet.fsu.edu/primer/java/digitalimaging/ccd/quantum/http://micro.magnet.fsu.edu/primer/java/digitalimaging/ccd/quantum/ -
7/24/2019 Student PresentatiFDons 2011
44/102
9
Diffusion Length
Photo-induced current decay is dependant on the
relative thickness of sample
It is necessary to consider two cases when analyzing LBIC
intensity :
Thick Sample Cases (W> 4Lb) Thin Sample cases (W< 4Lb)
-
7/24/2019 Student PresentatiFDons 2011
45/102
10
Sample Cases
Thick Sample Cases (W> 4Lb)
EBIC intensity as a function of distance x from the barrier,
in a semiconductor of semi-infinite thickness and far from
the collector edge (x>> Lb)
Thin Sample Cases (W < 4Lb)
In thin samples, the influence of the front and rear surfacerecombination becomes very important
Equations from: Sayad, Kaminski, Blanc, Nouiri & Lemiti
n
b
xLxCxI = )exp()(
)exp()( 0effL
xIxI =
-
7/24/2019 Student PresentatiFDons 2011
46/102
11
Surface Recombination Velocity
-
7/24/2019 Student PresentatiFDons 2011
47/102
12
LBIC topography
Imaging carried out using 100 line with 100 points each
at a step of 10m
Solar cell area is 1mm2
Minority carrier recombination is clearly evident
Photocurrent reduced by 25% near grain boundary
Figure from: Masri, Boyeaux, Kumar, Mayet & Laugier
-
7/24/2019 Student PresentatiFDons 2011
48/102
13
LBIC topography (cont.)
-
7/24/2019 Student PresentatiFDons 2011
49/102
14
Light Sweep
-
7/24/2019 Student PresentatiFDons 2011
50/102
15
Resolution
Figures from: Sites & Nagle
-
7/24/2019 Student PresentatiFDons 2011
51/102
16
Defect Detection
Figures from: Sites & Nagle
-
7/24/2019 Student PresentatiFDons 2011
52/102
17
LBIC Variations
Wavelength Variation
Figures from: Sites & Nagle
Bias Variation
i
-
7/24/2019 Student PresentatiFDons 2011
53/102
18
Quiz
1. What does LBIC stand for?
2. How is light generated for the LBIC apparatus?
3. What is the limit for defining a thick/thin sample?
(W >/< ___)
4. Which would have a greater affect on the Isc? Rsor Rp
5. What is the highest resolution that can be seen with LBIC?
-
7/24/2019 Student PresentatiFDons 2011
54/102
Vibrating SampleMagnetometer
Brooks TellekampECE 4813
November 2011
O li
-
7/24/2019 Student PresentatiFDons 2011
55/102
2
Outline
Overview of Magnetic Properties
Units
Basic Magnetic Relations
History
VSM Basics
Mechanical Design
Properties of VSM
O i f M i P i
-
7/24/2019 Student PresentatiFDons 2011
56/102
3
Overview of Magnetic Properties
B = Magnetic Flux Density or Magnetic Induction
H = Magnetic Field (typically applied to a sample)
m = Magnetic Dipole Moment
M = Magnetization
= Magnetic Permeability
Permeability of free space 0= 4 107
(SI)
= Magnetic Susceptibility
U it
-
7/24/2019 Student PresentatiFDons 2011
57/102
4
Units
Gaussian units a physical system for electromagnetic
units based in CGS (centimeter-gram-second) base units
Unit SI CGS Conversion
B Tesla Gauss 1T=10,000G
H
Oersted (Oe)
=
1000Oe
m (
)
= 1000
M
=
3
= .001
Unitless 0
=
Unitless Unitless
= 4
O i f M ti R l ti
-
7/24/2019 Student PresentatiFDons 2011
58/102
5
Overview of Magnetic Relations
Where
==relative permeability (material dependant)
And = where =
(number of acting moments per unit volume)
SI CGS
==0(+ )
=
=0(1 +)
==+ 4
=
= 1 + 4
H t i
-
7/24/2019 Student PresentatiFDons 2011
59/102
6
Hysteresis
Ferromagnetic materials retain magnetic orientation
Ferromagnetic materials exhibit different curves for
directional field sweeps (+ to -, or - to +)
Hi t
-
7/24/2019 Student PresentatiFDons 2011
60/102
7
History
Developed in the late 1950s
No good way to measure magnetic moments without
considerable prior knowledge of material properties
Force methods are very sensitive and require a field
gradient Other specific techniques existed, but were not
adaptable to many material classes
Vibrating coil technique used a coil with the detectionaxis parallel to the applied field
Idea modified by Dr. Simon Foner of MIT to vibrate the
sample and use a coil perpendicular to the applied field
VSM B i
-
7/24/2019 Student PresentatiFDons 2011
61/102
8
VSM Basics
In a uniform magnetic field, a
ferromagnetic sample is vibrated
along the z axis
The dipole field induces a current
in the pickup coils, which isproportional to the magnetic
moment
Susceptibility is obtained as the
slope of the M-H Curve
Permeability is obtained as the
slope of the B-H Curve
x
yz
Mechanical Design
-
7/24/2019 Student PresentatiFDons 2011
62/102
9
Mechanical Design
1) Loudspeaker Transducer2) Paper Cup Support
3) Sample Holder Straw
4) Reference Sample5) Sample
6) Reference Coils
7) Pickup Coils8) Magnets
9) Housing
Frequency Invariance
-
7/24/2019 Student PresentatiFDons 2011
63/102
10
Frequency Invariance
Reference sample attached to sample holder
High coercivity material
Identical coil arrangement to pickup coils
Loudspeaker vibrates the sample and reference sample
at the same frequency
Phase and Amplitude of coil voltages are directly related
via the magnetic moment of the sample
Time Varying Dipole Field
-
7/24/2019 Student PresentatiFDons 2011
64/102
11
Time-Varying Dipole Field
Fixed Dipole Scalar Potential
=
3
Time variant field
1where
1=
=
5
Where the flux pattern is
1
The pattern allows for a variety of coil arrangements where the coil
axis is along a flux line.
Circuitry
-
7/24/2019 Student PresentatiFDons 2011
65/102
12
Circuitry
Many options for output signal measurement
Always a temperature controlled resistor in series with
the pickup coils
Voltage drop is proportional to magnetic moment, m Lock-in Amplifier to compare reference signal and sample
signal.
Null Amplifier from a calibrated diode bridge
Reference signal is controlled with a potentiometer for
precise voltage division to balance with the sample output
Sensitivity
-
7/24/2019 Student PresentatiFDons 2011
66/102
13
Sensitivity
Sensitivity depends on coil geometry
With a 2 vertical coil method
Susceptibility changes of 5x10-10can be measured
Magnetic moment changes of 5x10-6emu
Average stability of balanced signals is 1 part in 10,000
Calibration
-
7/24/2019 Student PresentatiFDons 2011
67/102
14
Calibration
Can be calibrated by 2 methods
Using a sample of known magnetic properties and mass
Usually 8mg of pure Nickel (high coercivity)
For weakly magnetic samples of obscure shape First measure the sample in vacuum
Then measure in pure O2 gas (well known susceptibility)
The difference of the two gives the susceptibility of the
sample, which is used to calibrate that specific shape
Demagnitizing Factor
-
7/24/2019 Student PresentatiFDons 2011
68/102
15
Demagnitizing Factor
Calibration is used to determine the Demagnitizing
Factor,
Once and m are determined, the BH curve can be
extracted
Note: SI equations only, CGS equations vary
= 4
= 4
=+ 4=+ 4(1 )
Sample values
Sphere: = 3
,
Infinite plane: = 4,
Cylinder: = 2
Other shapes are well
documented
Measurements
-
7/24/2019 Student PresentatiFDons 2011
69/102
16
Measurements
Low-Conductivity Materials
Spherical or ellipsoid samples are preferred
Cubic crystals should be oriented 110 perpendicular to
the z-axis
High Conductivity Materials Demagnetization corrections are not necessary
Paramagnetic Samples
VSM can measure the magnetic field created byparamagnetic materials by the average value over the
sample volume
Sample Data
-
7/24/2019 Student PresentatiFDons 2011
70/102
17
Sample Data
Actually emu
Sources
-
7/24/2019 Student PresentatiFDons 2011
71/102
18
Sources
FONER, S. "Versatile and Sensitive Vibrating-sample
Magnetometer." Review of Scientific Instruments, 30.7 (1959):548-557.
http://stephenmullens.co.uk/projectwork/Vibrating%20Sample%
20Magnetometer.pdf
http://www.lakeshore.com/pdf_files/systems/vsm/Permanent%20Magnet%20Paper.pdf
http://magician.ucsd.edu/essentials/WebBookse7.html
http://bohr.physics.berkeley.edu/classes/221/0708/notes/emunit
s.pdf
http://stephenmullens.co.uk/projectwork/Vibrating%20Sample%20Magnetometer.pdfhttp://stephenmullens.co.uk/projectwork/Vibrating%20Sample%20Magnetometer.pdfhttp://www.lakeshore.com/pdf_files/systems/vsm/Permanent%20Magnet%20Paper.pdfhttp://www.lakeshore.com/pdf_files/systems/vsm/Permanent%20Magnet%20Paper.pdfhttp://magician.ucsd.edu/essentials/WebBookse7.htmlhttp://magician.ucsd.edu/essentials/WebBookse7.htmlhttp://bohr.physics.berkeley.edu/classes/221/0708/notes/emunits.pdfhttp://bohr.physics.berkeley.edu/classes/221/0708/notes/emunits.pdfhttp://bohr.physics.berkeley.edu/classes/221/0708/notes/emunits.pdfhttp://bohr.physics.berkeley.edu/classes/221/0708/notes/emunits.pdfhttp://magician.ucsd.edu/essentials/WebBookse7.htmlhttp://magician.ucsd.edu/essentials/WebBookse7.htmlhttp://www.lakeshore.com/pdf_files/systems/vsm/Permanent%20Magnet%20Paper.pdfhttp://www.lakeshore.com/pdf_files/systems/vsm/Permanent%20Magnet%20Paper.pdfhttp://stephenmullens.co.uk/projectwork/Vibrating%20Sample%20Magnetometer.pdfhttp://stephenmullens.co.uk/projectwork/Vibrating%20Sample%20Magnetometer.pdf -
7/24/2019 Student PresentatiFDons 2011
72/102
Transmission ElectronMicroscopy (TEM)
Jevon RaghubirECE-4813
Fall 2011
Dr. Alan Doolittle
Why TEM?
-
7/24/2019 Student PresentatiFDons 2011
73/102
2
Why TEM?
Limited image resolution in light microscopes
Smallest distance that can be resolved by VLM:
=0.61
Around 300nm for green light (=550nm) w/ NA=1
That is 1000 atom diameters
Need to image details all the way down to the atomic level
Solution: TEM
Electron Wavelength
-
7/24/2019 Student PresentatiFDons 2011
74/102
3
Electron Wavelength
=
20(1 +
202
/2
At high energies electrons approach the speed of light
Relativistic effect must be taken into account
Schematic of TEM
-
7/24/2019 Student PresentatiFDons 2011
75/102
4
Schematic of TEM
Illumination system
Illumination System (Electron Emission)
-
7/24/2019 Student PresentatiFDons 2011
76/102
5
Illumination System (Electron Emission)
Field Emission
Uses large electric fields at sharp points
Electrons tunnel out of source
Source: tungsten wire
Thermionic Emission
Uses heat
Electrons gain enough energy to overcome natural barrier
Sources:
Tungsten filaments LaB6 crystals
Electron Sources
-
7/24/2019 Student PresentatiFDons 2011
77/102
6
Electron Sources
Thermionic emission source Field emission source
LaB6 crystal
Tungsten needle
Illumination System (Electron Gun)
-
7/24/2019 Student PresentatiFDons 2011
78/102
7
Illumination System (Electron Gun)
Thermionic electron gun
Illumination System (Condenser Lenses)
-
7/24/2019 Student PresentatiFDons 2011
79/102
8
Illumination System (Condenser Lenses)
Parallel electron beam
TEM imaging
Selected-area diffraction (SAD)
Convergent beam
STEM
AEM
Dependent on mode of operation
Schematic of TEM
-
7/24/2019 Student PresentatiFDons 2011
80/102
9
Schematic of TEM
The objective lens &
stage
Objective Lens (Cs Correction)
-
7/24/2019 Student PresentatiFDons 2011
81/102
10
Objective Lens (Cs Correction)
Instrumental resolution is limited primarily by spherical
aberration of the objective lens
Image w/o Cs correction Image w/ Cs correction
HRTEM Images
Schematic of TEM
-
7/24/2019 Student PresentatiFDons 2011
82/102
11
Schematic of TEM
Imaging system
Imaging System
-
7/24/2019 Student PresentatiFDons 2011
83/102
12
Imaging System
Post-specimen lenses
Magnify signal transferred by objective lens
Diffraction pattern
Image
Viewing images and DPs
Fluorescent screen
Photographic film
CCD camera
TEM Modes of Operation
-
7/24/2019 Student PresentatiFDons 2011
84/102
13
TEM Modes of Operation
Diffraction mode
Image mode
Bright-field microscopy
Block all diffracted beams and pass only transmitted
electron beam Dark-field microscopy
Allows diffracted beams and block transmitted electron
beam
High-resolution electron microscopy Admits transmitted beam and at least one diffracted beam
Example Images
-
7/24/2019 Student PresentatiFDons 2011
85/102
14
Example Images
DP from a single crystal Fe thin film
BF TEM image of a specimen
TEM Uses
-
7/24/2019 Student PresentatiFDons 2011
86/102
15
Crystal structure
Lattice repeat distance
Specimen shape
Analytical measurements
Chemical information
Study of defects
Failure analysis
Advantages
-
7/24/2019 Student PresentatiFDons 2011
87/102
16
g
High lateral spatial resolution compared to other type of
microscopes
High quality and detailed images
Can produce wide range of secondary signals
Backscattered electrons, auger electrons, characteristicsx-rays, elastically and inelastically electrons, etc.
Wide range of applications that can be utilized in a
variety of different scientific, educational and industrial
fields
Disadvantages
-
7/24/2019 Student PresentatiFDons 2011
88/102
17
g
Limited depth resolution
Gives 2D images for 3D specimens
Specimen preparation
Thinning procedure can affect both their structure and
chemistry of specimen Time consuming
Cost
About $5 for each eV
Types of Transmission Electron Microscopes
-
7/24/2019 Student PresentatiFDons 2011
89/102
18
yp p
HRTEM (High-resolution)
HVTEM (High-voltage)
Can be damaging to specimen
Huge
IVTEM (Intermediate voltage)
STEM (Scanning)
AEM (Analytic)
Example TEMs
-
7/24/2019 Student PresentatiFDons 2011
90/102
19
p
HVTEM HRTEM
References
-
7/24/2019 Student PresentatiFDons 2011
91/102
20
[1] D. Williams and B. Carter, Transmission Electron Microscopy A
Textbook for Materials Science, Springer, 2004.
[2] D. K. Schroder, Semiconductor Material and Device
Characterization, Wiley & Sons, 2006.
[3] C. Evans and R. Brundle, Encyclopedia of Materials
Characterization, Butterworth-Heinemann, 1992.
[4] W. R. Runyan, Semiconductor Measurements and
Instrumentation, McGraw-Hill, 1998.
-
7/24/2019 Student PresentatiFDons 2011
92/102
Alex Walker
Raman Spectroscopy
-
7/24/2019 Student PresentatiFDons 2011
93/102
Raman Spectroscopy
Based on the effects of Raman effect, firstreported in 1928
This is a vibrational spectroscopic techniquethat can detect both organic and inorganicspecies and measure the crystallinity ofsolids
Advantages:
Free from charging effects
Sensitive to strain
Raman Spectroscopy
-
7/24/2019 Student PresentatiFDons 2011
94/102
Raman Spectroscopy
-
7/24/2019 Student PresentatiFDons 2011
95/102
Types of Scattering
-
7/24/2019 Student PresentatiFDons 2011
96/102
Types of Scattering
Raman Shift
-
7/24/2019 Student PresentatiFDons 2011
97/102
Raman Shift
=
o = excitation wavelength1 = Raman spectrum wavelength
Raman Spectrum of cyclohexanone
Raman Spectroscopy
-
7/24/2019 Student PresentatiFDons 2011
98/102
Raman Spectroscopy
Variations of Raman Spectroscopy
-
7/24/2019 Student PresentatiFDons 2011
99/102
Variations of Raman Spectroscopy
Surface Enhanced RamanSpectroscopy
surface-sensitive technique
that enhances Ramanscattering by moleculesabsorbed on rough metalsurfaces .
Variations of Raman Spectroscopy
http://..///upload.wikimedia.org/wikipedia/commons/5/51/Sers.jpg -
7/24/2019 Student PresentatiFDons 2011
100/102
Variations of Raman Spectroscopy
Resonance Raman Spectroscopy Uses IR spectrum to identify unknown
substances, measure the energy required tochange the vibrational state of a chemical
compound, and bioinorganic materials.
Ultraviolet Resonance Raman Spectroscopy
Variations of Raman Spectroscopy
-
7/24/2019 Student PresentatiFDons 2011
101/102
Raman Optical Activity reliant on the difference in intensity of
Raman scattered right and left circularlypolarised light due to molecular chirality.
Variations of Raman Spectroscopy
Resources
http://..///upload.wikimedia.org/wikipedia/commons/5/5a/ROA_pinene.PNG -
7/24/2019 Student PresentatiFDons 2011
102/102
Resources
http://www.fdmspectra.com/fdm_raman_organics.htm http://en.wikipedia.org/wiki/Raman_spectroscopy http://en.wikipedia.org/wiki/Surface_Enhanced_Rama
n_Spectroscopy
http://en.wikipedia.org/wiki/Resonance_Raman_spectroscopy http://en.wikipedia.org/wiki/Raman_optical_activity http://en.wikipedia.org/wiki/Raman_optical_activity http://www.nano.org.uk/news/1368/
http://www.andor.com/learning/applications/Raman_Spectroscopy/
http://www.fdmspectra.com/fdm_raman_organics.htmhttp://www.fdmspectra.com/fdm_raman_organics.htmhttp://en.wikipedia.org/wiki/Raman_spectroscopyhttp://en.wikipedia.org/wiki/Surface_Enhanced_Raman_Spectroscopyhttp://en.wikipedia.org/wiki/Surface_Enhanced_Raman_Spectroscopyhttp://en.wikipedia.org/wiki/Resonance_Raman_spectroscopyhttp://en.wikipedia.org/wiki/Resonance_Raman_spectroscopyhttp://en.wikipedia.org/wiki/Raman_optical_activityhttp://en.wikipedia.org/wiki/Raman_optical_activityhttp://www.nano.org.uk/news/1368/http://www.andor.com/learning/applications/Raman_Spectroscopy/http://www.andor.com/learning/applications/Raman_Spectroscopy/http://www.andor.com/learning/applications/Raman_Spectroscopy/http://www.andor.com/learning/applications/Raman_Spectroscopy/http://www.nano.org.uk/news/1368/http://en.wikipedia.org/wiki/Raman_optical_activityhttp://en.wikipedia.org/wiki/Raman_optical_activityhttp://en.wikipedia.org/wiki/Resonance_Raman_spectroscopyhttp://en.wikipedia.org/wiki/Resonance_Raman_spectroscopyhttp://en.wikipedia.org/wiki/Surface_Enhanced_Raman_Spectroscopyhttp://en.wikipedia.org/wiki/Surface_Enhanced_Raman_Spectroscopyhttp://en.wikipedia.org/wiki/Raman_spectroscopyhttp://www.fdmspectra.com/fdm_raman_organics.htmhttp://www.fdmspectra.com/fdm_raman_organics.htm