© 2014University of Illinois Board of Trustees. All rights reserved.
Optical materials characterization
Julio Soares
Frederick Seitz Materials Research Laboratory University of Illinois at Urbana-Champaign
Why optical characterization?
2
Why optical characterization?
Optics Communications, Vol 284(9), 2376-2381 (2011)
2
Why optical characterization?
2
Why optical characterization?
2
Why optical characterization?
2
Why optical characterization?
2
Why optical characterization?
3
Why optical characterization?
4
library.thinkquest.org
Why optical characterization?
• The photoelectric effect
The Nobel Prize in Physics 1921
Albert Einstein
"for his services to Theoretical Physics, and
especially for his discovery of the law of the
photoelectric effect"
"for his work on the elementary charge of
electricity and on the photoelectric effect"
The Nobel Prize in Physics 1923
Robert A. Millikan
The Nobel Foundation
The Nobel Foundation
5
Why optical characterization?
Black body radiation, which lead to quantum physics…
The Nobel Prize in Physics 1918
Max Planck
"in recognition of the services he rendered
to the advancement of Physics by his
discovery of energy quanta"
The Nobel Foundation
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0 10,000 20,000 30,000
r(n
)
wavenumbers (1/cm) Copyright 2001 B.M. Tissue
Classical (Rayleigh-Jeans) Quantum (Planck)
6
Why optical characterization?
The Nobel Foundation
Charles Kuen Kao
Willard S. Boyle
George E. Smith
transmission of light in fibers for optical
communication and invention of the CCD
2009
contributions to the quantum theory of optical
coherence and the development of laser-based
precision spectroscopy
Roy J. Glauber
John L. Hall
Theodor W. Hänsch
2005
development of methods to
cool and trap atoms with laser
light
Steven Chu
Claude Cohen-Tannoudji
William D. Phillips
1997
1981
contribution to the development of
laser spectroscopy
Nicolaas Bloembergen
Arthur Leonard Schawlow
discovery and development of
optical methods for studying
Hertzian resonances in atoms
Alfred Kastler
1966 fundamental work in the field of
quantum electronics, which has led to
the construction of oscillators and
amplifiers based on the maser-laser
principle
Charles Hard Townes
Nicolay Gennadiyevich Basov
Aleksandr Mikhailovich Prokhorov
1964
Frits (Frederik) Zernike
demonstration of the phase contrast
method, especially for his invention of
the phase contrast microscope
1953
Sir Chandrasekhara
Venkata Raman
discovery of the
Raman effect
1930 Robert Andrews Millikan
Albert Einstein
1923 1921
the photoelectric effect
Niels Henrik David Bohr
investigation of the structure of
atoms and of the radiation
emanating from them
1922
Albert Abraham Michelson
for his optical precision
instruments and the
spectroscopic and
metrological investigations
carried out with their aid
1907
Max Karl Ernst
Ludwig Planck
discovery of
energy quanta
1918
1908
method of reproducing
colours photographically
based on the phenomenon
of interference
Gabriel Lippmann
7
Light – matter interaction
8
• Interrogating the material properties with light. – Transmission/Reflection spectroscopy (identification, structure, concentration,
speed, etc.)
• Spectrophotometry, FTIR
– Ellipsometry (dielectric function, layer thickness, carrier density, etc.)
– Raman (identification, structure, phase, crystallinity, stress, drug distribution,
diagnosis, etc.)
– PL/PLE (electronic structure, carrier life-time, defect levels, carrier concentration, size
distribution, etc.)
– SFG (surface/interface chemistry, identification, orientation, etc.)
– Modulation spectroscopy (electronic structure, carrier life-time, defect levels,
internal electric fields, thermal properties, mechanical properties, etc.)
• PR, ER, TDTR, FDTR
– Photocurrent/Photovoltage (electronic structure, energy band profile, defect
states, etc.)
• Quantum efficiency, solar cell and detector characterization
Optical methods for materials characterization
9
15 15
What is measured?
The transmission, and reflection of light as a function of the incident photon
energy.
Basic principle: The absorption, reflection
and transmission of light by
a material depends on its
electronic, atomic, chemical
and morphological
structure.
Transmission, Reflection, Absorption
10
16 16 Transmission, Reflection, Absorption
UV-VIS-NIR
FTIR
11
Raman Spectroscopy
17 17
Ground state
Excited
states
Virtual state
Donnor
levels
Acceptor
levels
Vibrational states
Impurities
IR UV/VIS
Transmission, Reflection, Absorption
12
18 18
Instrumentation:
Spectrophotometry (UV-VIS-NIR)
Transmission
Specular reflectance
Diffuse reflectance
13
19 19
Instrumentation:
Spectrophotometry (UV-VIS-NIR)
14
20
-10-8 -6 -4 -2 0 2 4 6 8 10
De
tect
or
volta
ge
Time
DL = nl => constructive interference
DL = (n+1/2) l => destructive interference
Instrumentation:
The FTIR uses a Michelson interferometer with a moving mirror, in place of a diffraction grating or prism.
detector
fixed mirror
moving mirror
IR source
Beam splitter
sample
Fourier Transform IR spectroscopy (FTIR)
The Nobel Prize in Physics 1907
Albert A. Michelson
"for his optical precision instruments and the
spectroscopic and metrological
investigations carried out with their aid"
The Nobel Foundation
15
21
DL = nl => constructive interference
DL = (n+1/2) l => destructive interference
Instrumentation:
The FTIR uses a Michelson interferometer with a moving mirror, in place of a diffraction grating or prism.
-10-8 -6 -4 -2 0 2 4 6 8 10
De
tect
or
volta
ge
Timedetector
fixed mirror
moving mirror
IR source
Beam splitter
sample
Fourier Transform IR spectroscopy (FTIR)
The Nobel Prize in Physics 1907
Albert A. Michelson
"for his optical precision instruments and the
spectroscopic and metrological
investigations carried out with their aid"
The Nobel Foundation
15
22
Spectrum formation:
. dtetSI ti
nn 2)()(
-10-8 -6 -4 -2 0 2 4 6 8 10
De
tecto
r vo
lta
ge
Time0.0 0.4 0.8 1.2
Inte
nsity
Frequency
Fourier Transform IR spectroscopy (FTIR)
16
23
An example of an interferogram and its corresponding FTIR spectrum.
1000 1500 2000 2500 3000 3500 4000
0.0
0.5
1.0
1.5
2.0
Ab
sorb
ance
Wavenumber (cm-1)
Polystyrene
Frequency (Hz)
Am
plit
ude
The signal is detected as intensity
vs. time (interferogram).
The Fourier transform of the
interferogram gives the spectrum,
as intensity vs. wave number.
Fourier Transform IR spectroscopy (FTIR)
17
24 24
Instrumentation:
Spectrophotometry (UV-VIS-NIR)
18
25
Advantages:
•Multiplexing (all wavelengths
are measured simultaneously).
•No chromatic aberrations or
artifacts.
•Higher throughput.
•Improved S/N ratio.
Disadvantages:
•More complex system.
•Linearity of detectors (working
closer to saturation levels).
•Stray light scattering at low
signal level.
FT vs. Dispersive optics spectrometers
Fourier Transform IR spectroscopy (FTIR)
19
26 26
450 500 550 600 650
0.1
0.2
0.3
0.4
Absorp
tion
Wavelength (nm)
4ml Au/.1ml Hg
3ml Au/1ml Hg
2ml Au/2ml Hg
1ml Au/3ml Hg
.5mM solutions
Using absorption to determine Au/Hg
concentration in water solutions
As Au relative concentration rises, the absorption
peak shifts toward shorter wavelengths, increase in
intensity, and its FWHM decreases. The intensity
increase follows Beer-Lambert’s law.
Spectrophotometry (UV-VIS-NIR)
0.1 0.2 0.3 0.4 0.50.0
0.1
0.2
0.3
0.4
0.5
Ab
so
rptio
nAu concentration (mM)
Abs = K l c = a l
Beer-Lambert Law
20
27 27 Spectrophotometry (UV-VIS-NIR)
25000 22500 20000 17500 15000 1250054
55
56
57
58
T(%
)
n (cm-1)
14000 13000
56.0
56.5
57.0
57.5
58.0
400 500 600 700 800l (nm)
12500 13000 13500
0
10000
20000
30000
40000
50000
60000
Slope = 50.99 m
peak ind
ex / 2
n (
m
/cm
)
n (cm-1)
peak positions
linear fit
14000 16000 18000 20000 22000 240000
10000
20000
30000
peak ind
ex / 2
n (
m
/cm
)
n (cm-1)
peak positions
linear fit
Slope = 2.76 m
Using transmission interference fringes to
determine thickness
Two sets of interference fringes are present on the
spectrum, corresponding to each film that composes
the system.
21 𝜆𝑚 = 𝑚
𝜈 = 2𝑛𝑑 sin 𝜃
3 m
Excitations in materials
•Plasmons
22
Plasmons are quanta of collective motion
of charge-carriers in a gas with respect of
an oppositely charged background. They
play a significant role on transmission and
reflection of light.
Spectrophotometry (UV-VIS-NIR)
Phys. Today, 64, 39 (2011)
http://juluribk.com
29 29
0k
xk
Plasmonic crystal Brillouin zone from the transmission spectra measured for
many different angles of incidence.
G
X
M
G X M Optics Express 13, 5669 (2005)
200 nm
3 m
Spectrophotometry (UV-VIS-NIR)
23
30
FTIR can be used to identify
components in a mixture by
comparison with reference
spectra.
Fourier Transform IR spectroscopy (FTIR)
J. of Archaeological Sci. 39 (2012), 1227
Discovery of beeswax as binding
agent on a 6th-century BC Chinese
turquoise-inlaid bronze sword
Wugan Luo, Tao Li, Changsui Wang,
Fengchun Huang
Fingerprinting:
http://www.clockhours.com 24
31
Fingerprinting:
FTIR can be used to identify
components in a mixture by
comparison with reference
spectra.
Fourier Transform IR spectroscopy (FTIR)
Complementary characterization
techniques, like XRD can provide
conclusive evidence for the
identification.
J. of Archaeological Sci. 39 (2012), 1227
25
32 32
Strengths:
•Very little to no sample preparation.
•Simplicity of use and data interpretation.
•Short acquisition time, for most cases.
•Non destructive.
•Broad range of photon energies.
•High sensitivity (~ 0.1 wt% typical for FTIR).
Spectrophotometry (UV-VIS-NIR) and FTIR
26
33
Complementary techniques:
Raman, Electron Energy Loss Spectroscopy (EELS), Extended X-ray
Absorption Fine Structure (EXAFS), XPS, Auger, SIMS, XRD, SFG.
Spectrophotometry (UV-VIS-NIR) and FTIR
Limitations:
• Reference sample is often needed for quantitative analysis.
• Many contributions to the spectrum are small and can be buried in the background.
• Usually, unambiguous chemical
identification requires the use of
complementary techniques.
• Limited spatial resolution.
27
34
www.bobatkins.com
Guimond and Elmore - Oemagazine May 2004
Polarization
28
35 35
What is measured?
The changes in the polarization state of light upon reflection from a mirror
like surface.
Ellipsometry
29
36 36
Basic principle:
The reflected light emerges from the surface elliptically polarized, i.e. its p
and s polarization components are generally different in phase and
amplitude.
s
pi
R
Re ~
~
)tan( D
f
Ellipsometry
30
37
)(
,
,
,,,
~ isp
rspi
i
sp
r
sp
sp eE
ER
ff
ff
isp
bc
sp
ab
isp
bc
sp
absp
sp
err
errR
nn
nnr
2,,
2,,
,
22,111,2
22,111,2,
12
~~1
~~~
cos~cos~cos~cos~
~
+
+
+
iknn +~a
b
c
d fb
D
D
ir
s
p
s
pi
R
R
R
Re
~
~
)tan(~
~
)tan(
fa
fc
bbnd
fl
cos~2
2211 sin~sin~ ff nn
Ellipsometry
31
38
400 500 600 700 800
0
2
4
6
8
10
12
14
60
80
100
120
140
160
180
Model fit
Experiment
D
(
de
gre
es
)
Wavelength (nm)
D (d
eg
ree
s)
SiO2 thickness 2.19 ± 0.04 nm
c 2 4.31
SiO2 21.9 Å
Si
Ellipsometry
Applications
Film thickness
32
39 39 Ellipsometry
Composition
Surface roughness
Film thickness
Band gap energy
Applications
Ellipsometric (l) and D(l) spectra of Cd1-xZnxS thin
films deposited under the different concentration of
ammonia: 0.19, 0.38, 0.56, and 0.75 M. The solid
lines represent the best fit to the theoretical model. (a)
and (b) were measured under 68° and 72°,
respectively.
Jpn. J. Appl. Phys. 49 (2010) 081202
33
40 40 Ellipsometry
Composition
Surface roughness
Film thickness
Band gap energy
Applications
Parameters of the Cd1xZnxS thin films as a function of
different ammonia concentrations obtained from SE analysis.
[NH4OH] (M)
Thickness (nm)
Roughness (nm)
ZnS (%) Band-gap (eV)
0.19 42.12 23.77 99.7 3.49
0.38 73.79 7.15 45.5 2.52
0.56 50.89 5.94 32.3 2.45
0.75 18.59 4.54 5.2 2.43
Jpn. J. Appl. Phys. 49 (2010) 081202
34
41 41 Ellipsometry
Composition
Surface roughness
Film thickness
Band gap energy
Optical constants
(dielectric function)
Applications
Jpn. J. Appl. Phys. 49 (2010) 081202
Refractive index (n) and extinction coefficient (k) as a function
of wavelength of Cd1-xZnxS thin films under different ammonia
concentrations.
Plots of (αhν)2 versus photon energy
h for Cd1-xZnxS thin films under
different ammonia concentration.
35
42 Ellipsometry
Optical Hall Effect 36
43 43 Ellipsometry
Applications
Electrical properties
From the fit for the C-face sample:
Two graphene layers with distinctly different properties:
a bottom p-type channel with Ns=(5.5±0.4)x1013 cm-2 and
=1521±52 cm2 V-1 s-1
a top p-type channel with Ns=(3.4±0.6)x1014 cm-2 and
=18±4 cm2 V-1 s-1
From electrical dc Hall effect measurement:
p-type conductivity with Ns=(3.0±0.5) x1013 cm-2 and
=3407±250 cm2 V-1 s-1
37
44 44 Ellipsometry
Applications
Electrical properties
From the fit for the Si-face sample:
A p-type channel with Ns=(1.2±0.3)x1012 cm-2 and =794±80
cm2 V-1 s-1
From electrical dc Hall effect measurement:
p-type conductivity with Ns=(1.9±0.2) x1012 cm-2 and
=891±250 cm2 V-1 s-1
The correspondence between electrical
and OHE data is very good.
38
45 45 Ellipsometry
Applications
Electrical properties
m* = (0.19−0.08√B) m0
m* = 0.035 m0
Top layer:
Bottom layer:
m* = 0.03 m0
C-face:
Si-face:
39
46 46 Ellipsometry
Stregths: – Fast.
– Measures a ratio of two intensity values and a phase.
• Highly accurate and reproducible (even in low light levels).
• No reference sample necessary.
• Not as susceptible to scatter, lamp or purge fluctuations.
• Increased sensitivity, especially to ultrathin films (<10nm).
– Can be used in-situ.
DC Comics
40
47 47
Limitations:
– Flat and parallel surface and
interfaces with measurable
reflectivity.
– A realistic physical model of the
sample is usually required to obtain
useful information.
Complementary techniques:
PL, Modulation spectroscopies, X-Ray Photoelectron Spectroscopy,
Secondary Ion Mass Spectroscopy, XRD.
Ellipsometry
Neil Miller
41
Raman Spectroscopy Sir Chandrasekhara Venkata Raman
The Nobel Prize in Physics 1930 was awarded to Sir
Venkata Raman "for his work on the scattering of light and
for the discovery of the effect named after him".
The Nobel Foundation
48 48 Raman spectroscopy
42
Raman Spectroscopy
49 49 Raman spectroscopy
Ground state
Excited state
Virtual states
Vibrational states
Resonance
Raman
Ra
yle
igh
sca
tterin
g
An
ti-S
tokes
Sto
ke
s
An
ti-S
tokes
Sto
ke
s
Photon energy
Scattere
d inte
nsity
Raman shift
What is measured?
The light inelastically scattered by the
material.
Basic principle:
The impinging light couples
with the lattice vibrations
(phonons) of the material,
and a small portion of it is
inelastically scattered. The
difference between the
energy of the scattered light
and the incident beam is the
energy absorbed or
released by the phonons.
IR
43
http://www.physik.tu-berlin.de/institute/IFFP/richter/new/research/surface-phonons.shtml
Excitations in materials
•Phonons
•Molecular vibrations
44
Phonons are the quanta of Collective
lattice vibrations
Raman spectroscopy
51
Raman Spectroscopy
51 51 Raman spectroscopy
1000 1500 2000 2500 3000
1000 1500 2000 2500 3000
FTIR
Raman
Wavenumber (cm-1)
Inte
nsity
Raman shift (cm-1)
PolyetherurethaneLike the FTIR, Raman
spectroscopy measures the
interaction of photons with
the vibration modes of
materials, but the physical
processes behind the two
techniques are fundamentally
different and so are the
selection rules that apply to
each.
The two techniques are
complementary, rather than
equivalent.
45
52
Raman Spectroscopy
Molecular and crystalline structure characterization
52 52 Raman spectroscopy
1000 2000 3000
Ra
ma
n in
ten
sity
(a
rb. u
nits
)
Raman Shift (cm-1)
Diamond
C Nanotube
Coal (Rock)-norm
Graphite
coal (wood)
Raman is sensitive to the
atomic structure of the
material.
Physics Reports, 409 (2005), 47
46
53
Raman Spectroscopy
The AAPS Journal 2004; 6 (4),
32
Distribution of ingredients in a pharmaceutical
tablet
Renishaw, Inc.
Chemical composition & component identification
Components distribution at micron & sub-micron scale
53 53 Raman spectroscopy
47
< C
> C
Presence of N vacancies
yields poor crystallinity
Substitutional C fills N
vacancies improving the
crystallinity
C incorporates interstitially
causing a degradation of
the crystal lattice
54
Raman Spectroscopy
Molecular and crystalline structure characterisation
54 54 Raman spectroscopy
48
55
Raman Spectroscopy
Phase transition monitoring
Stress measurements
Mapping the Raman peak position of a
micro indentation in a silicon wafer.
Renishaw, Inc.
55 55 Raman spectroscopy
49
A complete Raman mapping of phase transitions in Si under indentation C. R. Das, H. C. Hsu, S. Dhara, A. K. Bhaduri, B. Raj, L. C. Chen, K. H. Chen, S. K. Albert, A. Raye and Y. Tzengc
Raman spectroscopy
50
Raman spectroscopy is able to clearly distinguish areas of
differing numbers of layers in thin graphene sheets.
Graphene monolayer, bilayer and other multiple-layer regions
identified
57
Raman Spectroscopy
57 57 Raman spectroscopy
K.S. Novoselov et al., Science 306, 666 (2004).
51
FS-MRL
Oriented CNT between two
electrodes
58
Raman Spectroscopy
58 58 Raman spectroscopy
52
Primary Strengths:
• Very little sample preparation.
• Structural characterization.
• Non destructive technique.
• Chemical information.
• Complementary to FTIR.
Super Optical Powers
59
Raman Spectroscopy
59 59 Raman spectroscopy
53
Primary Limitations:
• Expensive apparatus (for high
spectral/spatial resolution and
sensitivity).
• Weak signal, compared to fluorescence.
• Limited spatial resolution.
Kryptonite DC
Comics
Complementary techniques:
FTIR, EELS, Mass spectroscopy, EXAFS, XPS, AES, SIMS, XRD, SFG.
60
Raman Spectroscopy
60 60 Raman spectroscopy
54
Raman Spectroscopy
61 61 Raman spectroscopy
Ground state
Excited
states
Virtual states
Donnor
levels
Acceptor
levels
Vibrational states
Impurities
Luminescence Raman scattering
Excitation
55
Acceptor
levels
Raman Spectroscopy
62 62 Raman spectroscopy
Ground state
Excited
states
Virtual states
Vibrational states
Impurities
Luminescence Raman scattering
Excitation
55
Donnor
levels
63
Lifetime: Phosphorescence, fluorescence
Mechanism: Photoluminescence, bioluminescence,
chemoluminescence, thermoluminescence,
piezoluminescence, etc.
Trevor Morris
Luminescence
56
Radim Schreiber
64 64 Photoluminescence
http://uclagettyprogram.wordpress.com
Charles Hedgcock © University of Arizona, Tucson, AZ
http://www.evidentcrimescene.com
http://kevincollinsphoto.smugmug.com
57
65 65
What is measured?
The emission spectra of materials due to radiative recombination following
photo-excitation.
Basic principle:
The impinging light promote electrons from the less energetic levels to
excited levels, forming electron-hole pairs. As the electrons and holes
recombine, they may release some of the energy as photons. The emitted
light is called luminescence.
direct band gap indirect band gap
Conduction
band
Valence band
Photoluminescence
58
Peter Abbamonte et al., Proc. Nat. Acad. Sci. 105 (34)
Photoluminescence
59
Exciton describes the bound state of an electron-
hole pair due their mutual Coulomb attraction
Excitations in materials
•Excitons •Bound excitons
•Excitonic complexes
67 67 Photoluminescence
Davydov et al. Phys. Stat. Solidi (b) 230 (2002b), R4
Photoluminescence spectra of
InN layers with different carrier
concentrations.
1 - n = 6x1018 cm-3 (MOCVD);
2 - n = 9x1018 cm-3 (MOMBE);
3 - n = 1.1x1019 cm-3 (MOMBE);
4 - n = 4.2x1019 cm-3 (PAMBE).
Solid lines show the theoretical
fitting cures based on a model of
interband recombination in
degenerated semiconductors. As
a result, the true value of InN band
gap Eg~0.7 eV was established.
60
68 68 Photoluminescence
InxGa1-xN alloys. Luminescence peak positions of catodoluminescence and
photoluminescence spectra vs. concentration x.
The plots of luminescence peak positions can be fitted to the curve
Eg(x)=3.48 - 2.70x - bx(1-x) with a bowing parameter of b=2.3 eV
Ref.1 - Wetzel., Appl. Phys. Lett. 73, 73 (1998).
Ref.2 - V. Yu. Davydov., Phys. Stat. Sol. (b) 230, R4 (2002).
Ref.3 - O’Donnel., J. Phys .Condens. Matt. 13, 1994 (1998).
Hori et al. Phys. Stat. Sol. (b) 234 (2002) 750
61
69
Conduction band
Valence band
FE D
A (Ao,X)
(Do,X)
GaAs
(D+,X)
Photoluminescence Photoluminescence
62
70 70
Using PL to determine the width and quality of InGaAsN/GaAs quantum wells.
3nm InGaAsN QW
5nm InGaAsN QW
9nm InGaAsN QW
Photoluminescence
63
71
Strengths:
• Very little to none sample
preparation.
• Non destructive technique.
• Very informative spectrum.
Photoluminescence Photoluminescence
64
72
Limitations:
• Often requires low temperature.
• Data analysis may be complex.
• Many materials luminescence
weakly.
Complementary techniques:
Ellipsometry, Modulation
spectroscopies,
Spectrophotometry, Raman.
Photoluminescence Photoluminescence
65
73 73
What is measured?
The reflectance variation with temperature.
hn0 hn0
Basic principle:
The dielectric function of a material, and thus its reflectance, is a function of
temperature. By modulating the material’s temperature, we can measure the
variation in its reflectivity, caused by that modulation. With time resolved
measurements, we can calculate the thermal conductivity of the sample.
Time-domain thermoreflectance
66
74 74
Instrumentation:
• fs Ti:Sapphire laser operating in the
range 700-800 nm.
• A variable delay line in the pump
beam path for time resolution.
• Scanning sample stage.
• Cryostats.
• Magnetic field.
Applications of TDTR include:
Spatially resolved thermal and elastic
properties of materials:
•Thermal effusivity (LC) and conductivity.
•Mechanical properties (by determination of
the speed of sound).
J. Appl. Phys., Vol. 93, 793 (2003).
Time-domain thermoreflectance
67
75 75
The lowest thermal conductivity so far observed
for a fully dense solid. (48 mWm-1K-1)
Time-domain thermoreflectance
68
76 76
The lowest thermal conductivity so far observed
for a fully dense solid. (48 mWm-1K-1)
Time-domain thermoreflectance
68
77 Time-domain thermoreflectance
69
78 Time-domain thermoreflectance
69
79 79
Strengths:
– Thermoconductivity over a broad range can be measured.
– Can measure interface thermal conductance.
– Spatial resolution.
– Measurements can be made over a wide range of
temperatures.
– Fast.
Time-domain thermoreflectance
70
Science 315, 342 (2007)
80 80
Limitations:
– Samples need coating with an Al
thin film.
– Alignment can be tedious.
– Thermal conductivity cannot be
measured for films much thinner
than the thermal penetration
depth.
Complementary techniques:
3w method, Raman spectroscopy, Nanoindentation.
Time-domain thermoreflectance
71
Optical microscopy
72
Optical microscopy
"Classical" Optical Microscopy
Image Formation
•In the optical microscope, light from the microscope
lamp passes through the condenser and then through
the specimen (assuming the specimen is a light
absorbing specimen).
• Some of the light passes both around and through the
specimen undisturbed in its path (direct light or
undeviated light).
•The direct or undeviated light is projected by the
objective and spread evenly across the entire
image plane at the diaphragm of the eyepiece.
•Some of the light passing through the specimen is
deviated when it encounters parts of the specimen
(deviated light or diffracted light).
73
Optical microscopy
74
Optical microscopy
Objective Type
Spherical Aberration
Chromatic Aberration
Field Curvature
Achromat 1 Color 2 Colors No
Plan Achromat 1 Color 2 Colors Yes
Fluorite 2-3 Colors 2-3 Colors No
Plan Fluorite 3-4 Colors 2-4 Colors Yes
Plan Apochromat 3-4 Colors 4-5 Colors Yes
75
Optical microscopy
Bright field Phase contrast Dark field Polarizing 76
Optical microscopy
Difference interference contrast 77
Optical microscopy
Bright field Phase contrast Dark field Polarizing
Fibers in bright field and dark field
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Optical microscopy
Fluorescence 79
Optical microscopy
Specimen Type
Imaging Technique
Transmitted Light Transparent Specimens
Phase Objects Bacteria, Spermatozoa,
Cells in Glass Containers, Protozoa, Mites, Fibers, etc.
Phase Contrast Differential Interference Contrast (DIC)
Hoffman Modulation Contrast Oblique Illumination
Light Scattering Objects Diatoms, Fibers, Hairs,
Fresh Water Microorganisms, Radiolarians, etc.
Rheinberg Illumination Darkfield Illumination
Phase Contrast and DIC
Light Refracting Specimens Colloidal Suspensions powders and minerals
Liquids
Phase Contrast Dispersion Staining
DIC
Amplitude Specimens Stained Tissue
Naturally Colored Specimens Hair and Fibers
Insects and Marine Algae
Brightfield Illumination
Fluorescent Specimens Cells in Tissue Culture
Fluorochrome-Stained Sections Smears and Spreads
Fluorescence Illumination
Birefringent Specimens Mineral Thin Sections
Liquid Crystals Melted and Recrystallized Chemicals
Hairs and Fibers Bones and Feathers
Polarized Illumination
Contrast-Enhancing Techniques for Optical Microscopy
http://micro.magnet.fsu.edu
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Optical microscopy
Reflected Light
Specular (Reflecting) Surface Thin Films, Mirrors
Polished Metallurgical Samples Integrated Circuits
Brightfield Illumination Phase Contrast, DIC
Darkfield Illumination
Diffuse (Non-Reflecting) Surface Thin and Thick Films Rocks and Minerals
Hairs, Fibers, and Bone Insects
Brightfield Illumination Phase Contrast, DIC
Darkfield Illumination
Amplitude Surface Features Dyed Fibers
Diffuse Metallic Specimens Composite Materials
Polymers
Brightfield Illumination Darkfield Illumination
Birefringent Specimens Mineral Thin Sections
Hairs and Fibers Bones and Feathers
Single Crystals Oriented Films
Polarized Illumination
Fluorescent Specimens Mounted Cells
Fluorochrome-Stained Sections Smears and Spreads
Fluorescence Illumination
http://micro.magnet.fsu.edu
Contrast-Enhancing Techniques for Optical Microscopy
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Resolution
He defined the resolving power of an optical instrument as the distance
between two point sources for which the center of one Airy disk coincides
with the first zero of the other:
d 0.61lNA
Rayleigh criterion (light emitting particle)
Based on the Airy discs formation Abbé
derived a theoretical limit to an optical
instrument resolution.
Arch. Microskop. Anat. 9, 413 (1873)
Near-field Scanning Optical microscopy Optical microscopy
Abbé criterion (illuminated particle) 𝑑 ≈𝜆
𝑁𝐴𝑐𝑜𝑙 + 𝑁𝐴𝑜𝑏𝑗≈
𝜆
2 𝑁𝐴
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Optical microscopy
Rayleigh criterion (light emitting particle)
Abbé criterion (illuminated particle) 𝑑 ≈𝜆
2 𝑛 sin 𝜇
𝑑 ≈0.61 𝜆
𝑛 sin 𝜇
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Confocal microscopy
• In confocal microscopy, due to the
constrained light path provides an
increased contrast, allowing for resolving
objects with intensity differences of up to
200:1.
• The in plane resolution, in confocal
microscopy, is also slightly increased (1.5
times) while the resolution along the
optical axis is high.
•These improvements are obtained at the
expense of the utilization of mechanisms
for scanning either by moving a specimen
or by readjustment of an optical system.
Scanning application allows to increase
field of view as compared with conventional
microscopes.
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Confocal microscopy
The relation of the first ring maximum amplitude to the amplitude in the
center is 2% in case of conventional point spreading function (PSF) in a
focal plane while in case of a confocal microscope this relation is 0.04%.
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Confocal microscopy
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Confocal microscopy
Anna-Katerina Hadjantonakis; Virginia E Papaioannou
BMC Biotechnology 2004, 4:33
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Confocal microscopy
Strengths:
– Optical sectioning (0.5 m).
– three-dimensional images.
– Improved contrast (200:1).
– Better resolution (1.5x).
– Field of view defined by the
scanning range.
Limitations:
– Image is scanned, resulting in slower
data acquisition.
– High intensity laser radiation can
damage some samples.
– Cost (typically 10x more than a
comparable wide-field system).
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Beyond confocal microscopy
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Beyond confocal microscopy
Nature Reviews Genetics 4, 613 (2003)
(courtesy of Brad Amos MRC, Cambridge)
Biophysical J. 75, 2015 (1998)
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Beyond confocal microscopy
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Beyond confocal microscopy
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Beyond confocal microscopy
• Sample is illuminated with a
patterned light source.
• The pattern interact with
structures finer than the
diffraction limit;
• The pattern projection itself is
diffraction limited.
• The big advantage of HR-SIM is
again its ease of-use.
• Uses common
• Fixation and labeling
procedures are similar to normal
fluorescence microscopy,.
• Dye labeling must be stable
enough to survive the
acquisition of multiple images.
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Beyond confocal microscopy
PALM (photo-activated localization microscopy)
Widefield PALM Widefield PALM
Biophysical Journal 91, 4258 (2006)
Nature Methods 6, 689 (2009)
Nature Protocols 4, 291 (2009)
Other similar echniques:
STORM (Stochastic optical
reconstruction microscopy)
FIONA (Fluorescence Imaging with
One Nanometer Accuracy)
SHReC (Single Molecule High
Resolution Colocalization)
SPDM (Spectral Precision Distance
Microscopy)
And many variants.
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Near-field microscopy: resolution beyond the diffraction limit!
The near field microscope resolves objects much smaller than the
wavelength of light by measuring at very short distances from the sample
surface, through sub-wavelength apertures.
Basic principle:
The principle of operation of the NSOM
was devised by Synge in 1928 †.
•The sample is kept in the near-field
regime of a sub-wavelength source.
•If z<<l, the resolution is determined
by the aperture, not wavelength.
•The image is constructed by scanning
the aperture across the sample and
recording the optical response.
† Philos.Mag. 6, 356 (1928).
Near-field Scanning Optical microscopy Near-field scanning optical microscopy (NSOM)
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Instrumentation:
Near-field Scanning Optical microscopy Near-field scanning optical microscopy (NSOM)
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Strengths:
– Powerful, very attractive.
– No sample preparation.
– Non destructive technique.
– Sub diffraction limit
resolution (50 nm).
Near-field scanning optical microscopy (NSOM)
CBS Broadcasting Inc.
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Requirements and limitations:
– Careful alignment required.
– Very low throughput.
– Slow data acquisition.
– Limited to fairly flat samples (20 m).
– Interaction between tip and sample
may make analysis difficult.
Complementary techniques:
AFM, SEM,TEM, Confocal microscopy.
Near-field scanning optical microscopy (NSOM)
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It is Important to use complementary techniques!
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