intro to electron microscopy

1. Lecture Module #14
Introduction to Electron Microscopy
An overview
What are electron microscopes?
• Scientific instruments that use a focused beam of
electrons to examine objects on a very fine scale.
What is electron microscopy?
• Electron microscopy is the science and technology of
using an electron beam to form a magnified image.
• Advantages:
– The use of electrons rather than light provides a nearly 1000
fold increase in resolving power (i.e., ability to focus fine
details) over light.
• Disadvantages:
– High cost
– Time commitment
– Small areas of analysis
Magnification
• Refers to how large an object can be made (and still
resolved).
• Advantages:
– You get higher magnification with electron microscopes
techniques than you can with light.
– Smaller wavelength Æ higher resolving power.
object
of
size
image
of
size
ion
magnificat =

2. Resolution is:
• The closest distance between two points that can
clearly be resolved as separate entities through the
microscope.
d1
ro
Intensity
Distance
Consider light as
EM energy
transmitted as a
wave motion.
We can consider
light as a series of
ripples impinging
upon an obstacle.
Abbe relationship
NA
n
d
ro
λ
α
λ 61
.
0
sin
61
.
0
2
1
=
=
=
λ = wavelength of illuminant
α = semi-angle
n = index of refraction
NA = numerical aperature
Resolution is defined by:
↓
B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)
Depth of Field
• A measure of how much of the object that we are
looking at remains in focus at the same time.
• Advantages:
– You get higher depth of field with (many) electron
microscopy techniques than you do with light.
– WHY?
Important Terms
• Depth of Field
– Height above and below the plane of focus that an image
remains sharp.
– DOF is a function of magnification, α, and probe size
Plane of focused image
α
BEAM
Scan
Region of image
in focus
DOF

3. SEM
SEM
TEM
TEM
EPMA
EPMA
Other instruments we have or are getting
• DualBeam Focused Ion Beam (DB-FIB)
– Nano-machining platform
• X-ray photoelectron spectrometer / Auger (XPS/Auger)
• ???
What do we get out of electron
microscopes?
• Topography
– Surface features of an object. “How it looks.”
• Morphology
– Size and shape of particles making up object.
• Composition
– Relative amount of elements and compounds making up the
object.
• Structure
– Crystallography. How atoms are arranged in the object
Comparison of Selected Characteristics of Light
and Electron Microscopes
FEATURE Light Microscope SEM TEM
Uses Surface morphology
and sections (1-40 µm)
Surface morphology Sections (40-150 nm)
or small particles on
thin membranes
Source of
Illumination
Visible light High-speed electrons High-speed electrons
Best resolution 200 nm 3-6 nm 0.2 nm
Magnification range 10-1,000× 20-150,000× 500-500,000×
Depth of field 0.002-0.05 nm
(NA=1.5)
0.003-1 mm 0.004-0.006 mm
(NA=10-3
)
Lens type Glass Electromagnetic Electromagnetic
Image ray-
formation spot
On eye by lens On CRT by scanning
device
On phosphorescent
screen by lens
Information
generated
Phases
Reflectivity
Topography
Composition
Crystal orientation
Crystal structure
Crystal orientation
Defects
Composition
Limiting Factor Wavelength of light Brighness,
signal/noise ratio,
emission volume
Lens quality
Adapted from: Scanning and Transmission Electron Microscopy, S. L. Flegler, J.W. Heckman Jr., K.L. Klomparens,
Oxford University Press, New York, 1993.

4. All of this information is related to
properties.
Mechanical, Physical, Thermal, Optical, Electrical, etc…
structure
properties
processing
performance
History of electron microscopes
• Developed due to limitations of light optical
microscopes (LOMs)
– LOM: ~1000x magnification; 0.2 µm (200 nm) resolution
• Transmission Electron Microscope (TEM) was
developed first.
– M. Knoll and E. Ruska, 1931
– Patterned “exactly” like a LOM. Uses electrons rather than
light.
• Scanning Electron Microscope (SEM)
– 1942
Goodhew, Humphreys & Beanland
Electron Microscopy and Microanalysis, 3rd
Edition
Taylor & Francis, London, 2001 70X
300X
1400X
2800X
Electron microscopy
provides significant
advantages over light
optical microscopy in
terms of resolution
and depth of field
How do electron microscopes work?
• Form a stream of electrons in the electron source
(thermionic emission) and accelerate them towards
the specimen using a positive electrical potential.
• Use apertures and magnetic lenses to focus the
stream into a thin focused monochromatic beam
• Focus the beam onto the sample using another
magnetic lens.
• Interactions occur inside the irradiated area of the
sample. Collect results of interactions in a suitable
detector and transform them into an image (or
whatever you are interested in).

5. The Electron Gun
• The electron gun provides an intense beam of high
energy electrons.
• There are two main types of gun. The thermionic
gun, which is the most commonly used, and the field
emission gun.
• Electrons are generated and emitted from a filament
by thermionic emission (W or LaB6) or from a sharp
tip by field emission (single crystal of W).
• The electrons are accelerated through a potential
difference.
Electron Source
(i.e., electron gun)
Thermionic electron gun
most widely used (~$70K-$150K)
Electrons are emitted
from a heated
filament and
accelerated towards
an anode
Wehnelt cap
(negative potential)
W Filament
Anode Plate
(positive potential)
Electron
Beam
Space charge
Crossover
–
10-1000 kV
+
Ground
Bias
resistor
Wehnelt cap
(negative potential)
W Filament
Anode Plate
(positive potential)
Electron
Beam
Space charge
Crossover
–
10-1000 kV
+
Ground
Bias
resistor
Filament
Made from a high Tmp material
with a low work function (φ) in
order to emit as many electrons
as possible. The work function
is the energy needed by an
electron to overcome the barrier
that prevents it from leaking out
of the atom. φW = 4.5 eV, φLaB6 =
3.0 eV.
Wehnelt
A biased grid with a potential that is
a few hundred volts different than
the filament (cathode). This helps
to accelerate the electrons and
causes their paths to cross over.
Crossover
The effective source of
illumination for the
microscope. The size
is critical for high
resolution
applications.
Anode
Positively charged metal plate
at earth potential with a hole in
it. It accelerates the electron
beam to the high tension
potential.
Operation of thermionic gun
• Apply a positive electrical potential to the anode
• Heat the cathode (filament) until a stream of electrons is
produced
– >2700 K for W
• Apply a negative electric potential to the Wehnelt
– electrons are repelled by the Wehnelt towards the optic axis
• Electrons accumulate within the region between the filament tip
and the Wehnelt. This is known as the space charge.
• Electrons near the hole exit the gun and move down the column
to the target (in this case the sample) for imaging.

6. Other Types of Electron Sources
(i.e., electron guns)
Lanthanum hexaboride (LaB6)
Higher brightness than W. More $$$ (~$500K)
Field emission source
Highest brightness. Even more $$$ (~$750K)
ADVANTAGES
Provide higher current density → Higher brightness
http://www.matter.org.uk/tem/electron_gun/electron_sources.htm
Brightness, B, is the beam
current density per unit solid
angle.
B = jcπβ2
jc = current density
β = convergence angle
The function of the electron gun is:
To provide an intense beam of high
energy electrons
There are two main types of gun. The
thermionic gun, which is the most
commonly used, and the field emission
gun.
• This is what makes electron microscopy possible.
• Electrons strike the sample leading to a variety of reactions.
• Use results of reactions to form image or generate other
information.
Beam-Specimen Interaction
Incident high kV beam of
electrons
Secondary e-
(SE)
Characteristic
x-rays
Visible light
Backscattered
e- (BSE)
Auger e-
Inelastically
scattered e-
Elastically
scattered e-
Bremsstrahlung
x-rays
(noise)
Direct
(transmitted)
beam
Absorbed e- e- - hole pairs
Bulk (SEM)
Foil (TEM)
Interaction Volume
Interaction Volume
• Represents the region penetrated by electrons
– Signals must escape the sample to be detected
Secondary electrons
Backscattered electrons
X-rays
Incident electron beam

7. ~1 nm – Auger electrons
~5–50 nm
Secondary electrons
~300 nm
Backscattered
electrons
~50 nm
TEM
specimen
thickness
~1.5 µm
X-rays
~1.0 µm
X-ray
resolution
Z = 29 (Cu), Accelerating voltage = 20kV
INCIDENT BEAM
Different signals come from
different depths in the target
(sample)
• X-rays:
– most escape
– sampling volume ≈ interaction volume
• Backscattered electrons:
– originate further from the incident beam (some fraction of a µm)
• Secondary electrons:
– escape from a region slightly larger than the incident beam
(several µm)
– yield the best spatial resolution
Interaction Volume
Backscattered electrons (BSE)
• Formation
– Caused when incident electrons collide with an atom in a specimen
that is nearly normal to the path of the incident beam.
– Incident electron is scattered backward (“reflected”).
• Use
– Imaging and diffraction analysis in the SEM.
– Production varies with atomic number (Z).
– Higher Z elements appear brighter than lower Z elements.
– Differentiate parts of specimen having different atomic number
Backscattered electrons are not as numerous as others. However,
they generally carry higher energies than other types of electrons.
Secondary Electrons (SE)
• Formation
– Caused when an incident electron “knocks” and inner shell
electron (e.g., k-shell) out of its site.
– This causes a slight energy loss and path change in the
incident electron and ionization of the electron in the
specimen.
– The ionized electron leaves the atom with a small kinetic
energy (~5 eV)
• Use
– IMAGING!
– Production is related to topography. Due to low energy, only
SE near the surface can exit the sample.
– Any change in topography that is larger than the sampling
depth will change the yield of SE.
More abundant than other types of electrons. They are electrons
that escape the specimen with energies below ~50eV

8. Auger Electrons (AE)
• Formation
– De-energization of the atom after a secondary electron is
produced.
– During SE production, an inner shell electron is emitted from
the atom leaving a vacancy.
– Higher energy electrons from the same atom can fall into the
lower energy hole. This creates an energy surplus in the
atom which is corrected by emission of an outer shell (low
energy) electron
• Use
– AE have characteristic energies that are unique to each
element from which they are emitted.
– Collect and sort AE according to energy to determine
composition.
– AE have very low energy and are emitted from near surface
regions.
X-rays
• Formation
– Same as AE. Difference is that the electron that fills the
inner shell emits energy to balance the total energy of the
atom.
• Use
– X-rays will have characteristic energies that are unique to
the element(s) from which it originated.
– Collect and sort signals according to energy to yield
compositional information.
– Energy Dispersive X-ray Spectroscopy (EDS)
Foundation of XPS (X-ray photoelectron spectroscopy). XPS can
be used to determine the “state” of an atom and to identify chemical
compounds.
Transmitted electrons
• Can be used to determine:
– thickness
– crystallographic orientation
– atomic arrangements
– phases present
– etc.
• Foundation for Transmission Electron Microscopy (TEM)
Specimen Interaction Volume
• Volume where electron beam - specimen interactions
occur.
• Depends upon:
– Z of material being examined
• higher Z materials absorb more electrons and have smaller
interaction volume
– Accelerating Voltage
• higher voltages penetrate further into the specimen and
generate larger interaction volumes
– Angle of incidence of electron beam
• larger angle leads to a smaller interaction volume

9. ~1 nm – Auger electrons
~5–50 nm
Secondary electrons
~300 nm
Backscattered
electrons
~50 nm
TEM
specimen
thickness
~1.5 µm
X-rays
???
X-ray resolution
Z = 29 (Cu), Accelerating voltage = 20kV
INCIDENT BEAM
10 Å - 30 Å – Auger electrons
~100 Å
Secondary electrons
<1µm - 2µm
Backscattered
electrons
~5 µm
X-rays
~1.0 µm
X-ray resolution
Z = 28 (Ni), Accelerating voltage = 20kV
INCIDENT BEAM
~50 nm
TEM
specimen
thickness
• Interaction volume is larger for materials that have
lower atomic numbers and for higher incident beam
energies!
~50 nm
Increasing atomic number (Z)
Increasing incident energy (E0)
Z1
Z2
Z3
Z1 < Z2 < Z3
“Instruments of the trade”
• Primary Instruments
– Transmission Electron Microscope (TEM)
– Scanning Electron Microscope (SEM)
• Variants
– Electron Probe Microanalyzer (EPMA)
– Scanning Transmission Electron Microscope (STEM)
– Environmental SEM (ESEM)
– High Resolution TEM (HRTEM)
– High Voltage TEM (HVTEM)
– etc...

10. TEM
• Patterned after transmission light optical microscopes
• Yield Following Information:
– Morphology
• Size shape and arrangement of particles, precipitates, etc.
– Crystallographic information
• Atomic arrangement
– Compositional Information
• If proper detector is present
The TEM is analogous to the transmission LOM
Source
Condenser
system
Stage
Objective
lens
Final imaging
system
Observation and
recording system
x
y
z
+ Tilt & rotation
Vacuum
column
Apertures
x
y
z
1 in 1020 electrons
are collected
<1 in 106 photons are
collected
TEM LOM
Phosphor
screen; film;
digital recording
system
Eyepiece or TV
screen; film;
digital recording
system
Light source
Electron gun
Components of the TEM
• Source – filament plus anode plates with
applied accelerating voltage.
• Condenser Lenses – electromagnetic lenses
adjusted by lens currents not position.
• Specimen Stage – allows translations and tilts.
• Objective Lens – usually <50X.
• Imaging System – multiple electromagnetic
lenses below the objective: set magnification,
focal plane (image vs. diffraction pattern).
• Observation – fluorescent screen, plate film,
CCD camera.
x
y
z
+ Tilt & rotation
Vacuum
column
1 in 1020 electrons
are collected
Phosphor
screen; film;
digital recording
system
Electron gun
Adapted from
B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)
Condensor Lenses
ELECTROMAGNETIC
lenses focus the
electron beam to as
small a spot as is
possible. They are
equivalent to convex
lenses in optical lens
systems.
Light Source
OPTICAL LENS
Cu coils
Soft Fe
pole
pieces
N
S
N
S
Electron Source
MAGNETIC LENS
Adapted from
B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)

11. Electron Lenses
• Use electrostatic or electromagnetic fields to focus
beams of charged electrons.
• ELECTROMAGNETIC – Most lenses are of this type.
Consist of Cu wire coils around soft Fe cores.
Sometimes an Fe pole-piece is used to “shape” the
field.
• ELECTROSTATIC – Unusual. Only common
example is the Wehnelt aperture in the electron gun.
Electrons in Magnetic Fields
A. Electrons moving through a perpendicular magnetic field experience
perpendicular forces.
B. Electrons moving parallel to a magnetic field are unaffected.
C. Electrons moving nearly parallel to a magnetic field take a helical
path around the magnetic field direction (i.e., the microscope axis).
electron
Magnetic
field
Force on
electron is
out of plane
No Force
Electrons
follow a
helical path
unaffected
Nearly
aligned
electron
A B C
Adapted from
B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)
Trajectories in Electromagnetic Lenses
• When you adjust the magnification (and the focal length),
you modify the lens strength by adjusting the current in the
electromagnetic lens coils.
• Since the magnetic field is changed,
so are the helical trajectories.
• This ultimately leads to image
rotation which must be corrected
for or calibrated.
Rotated
image
Object
Cu coils
Soft Fe pole
pieces
N
S
N
S
Image is inverted
and rotated
Electron Source
MAGNETIC LENS
Beam Tilting and Translation
• The electron beam can be positioned for fine
measurements (spot modes) or scanning (SEM, STEM)
BEAM TRANSLATION
BEAM TILTING
APPARENT
ORIGIN
APPARENT
ORIGIN
Upper scan
coil
Lower scan
coil

12. Condenser Alignment
• In TEM it is important to center the condenser aperture about
the optical axis.
• If the aperture is off center, the beam is displaced away from
the axis when the condenser lens is focused.
• You can try condenser alignment at:
http://www.matter.org.uk/tem/condenser_alignment.htm
Condenser Astigmatism
• Astigmatism in the condenser lenses distorts the beam to an
elliptical shape either side of focus and prevents the beam
being fully focused. It is corrected by applying two
orthogonal correction fields in the x and y directions.
• You can try stigmator adjustment at:
http://www.matter.org.uk/tem/condenser_astigmatism.htm
Objective Aperture
• Depending upon where you position the objective aperture
and whether or not you tilt the beam, a bright field image, a
dark field (i.e., scattered) image, or a diffraction pattern can
be collected.
• You can look at this in more detail at:
http://www.matter.org.uk/tem/dark_field.htm
B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005) AND http://www.matter.org.uk/tem/stem_images.htm

13. B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)
B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)
B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)
B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)

14. B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)
B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)
B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)
BF TEM Micrograph and SADP
Grain structure
Crystallographic information
[111] zone axis
NiAl-1.0Hf

15. 250 nm
1hr
NiAl-1.0Hf
BF TEM Micrographs
Precipitate distribution
Defect structures
4hr
NiAl-1.0Hf
100 nm
β′
Defect Structures
Dislocations imaged in NiAl-0.5Zr single crystals deformed at elevated temperatures.
Nano-scale X-ray Analysis
β′ -NiAl
EDX spectrum
β′ -precipitate
β′
HAADF (Z-contrast imaging) analysis
2
1
Ni2AlHf
Hf rich region
• Hf segregates to GB’s in as-deposited & annealed coatings.
• Hf precipitates as β´-Ni2AlHf phase after annealing.
NiAl-1.0Hf
NiAl-1.0Hf
As-deposited Annealed 1000°C/1h
20 nm
200 nm

16. How does a TEM work?
• Pass a focussed beam of electrons through a thin foil
• As beam passes through sample, it is scattered
• Project the transmitted (scattered) beam onto a
phosphor screen to form an enlarged image
• Modes:
– Bright Field/Dark Field modes for visualization of structure
and defects
– Selected Area Diffraction/Convergent Beam Diffraction
for crystallographic information
Electron Beam
Thin Foil
< 500 nm thick
Electron Gun
Anode Plate
First Condenser Lens (C1)
Second Condenser Lens (C2)
Condenser Aperture
Sample
Objective Lens
Objective Aperture
Selected Area Aperture
First Intermediate Lens
Second Intermediate Lens
Projector Lens
Phosphor Screen
Used to
magnify image.
Schematic
Representation
of optics in a
TEM
Technical Details
• Produce a stream of monochromatic electrons in the electron gun
• Focus the stream into a small coherent beam using C1 and C2
– C1 determines the “spot size” (i.e., size of electron probe)
– C2 changes intensity or brightness
• Use condenser aperture to restrict the beam
• Part of the beam is transmitted through the sample
• Focus transmitted portion using the objective lens to form an image
• Objective and selected area apertures are used to restrict the beam further
– allows examination of diffraction from specific atoms, crystals, features…
– SAD, CBD
• Enlarge image with intermediate and projector lenses

17. SEM
• Patterned after reflecting light optical microscopes
• Yield Following Information:
– Topography
• Surface features of an object. Detectable features limited to a
few nanometers depth.
– Morphology
• Size shape and arrangement of particles, precipitates, etc
– Compositional Information
• Elements and compounds the sample is composed of
– Crystallographic information
• Possible using new techniques (OIM/BKD)
x
y
z
Vacuum
column
x
y
z
TEM SEM
Electron gun
Condenser system
Stage
Objective lens
Final imaging system
Observation
and recording
system
Probe lens
Stage
Scan coils
Time
base
Signal
amplifier
CRT
Condenser lens
Also tilts and rotates
Also tilts and rotates
In the SEM you use secondary signals to acquire images.
Electron gun
Detector and
processing
system
Components of an SEM
• Source:
– same as TEM but lower V
• Condenser:
– same as TEM
• Scan Coils:
– raster the probe
• Probe Lens:
– lens that forms a spot at the
specimen surface
• Detector & Processing System:
– collects signals such as X-rays and
electrons as a function of time and
position.
– Provides digital images for real-time
viewing, processing, and storage.
x
y
z
Probe lens
Stage
Scan coils
Time
base
Signal
amplifier
CRT
Condenser lens
Also tilts and rotates
Electron gun
Detector and
processing
system
Schematic
Representation
of the optics in
an SEM
Electron Gun
Anode Plate
First Condenser Lens (C1)
Second Condenser Lens (C2)
Condenser Aperture
Sample
Objective (probe) Lens
Objective Aperture
Scan Coils
Detector

18. SEM: Technical Details
• Produce a stream of monochromatic electrons in the electron gun
• Focus the stream using the first condenser lens
– Coarse probe current knob
• The beam is constricted by the condenser aperture (eliminates high-angle electrons)
• Second condenser lens is used to form electrons into a thin, tight, coherent beam.
– Use fine probe current knob
• Use objective aperture to limit beam (i.e., eliminate high-angle electrons)
• Scan coils raster the beam across the sample, dwelling on the points for a
predetermined period of time (selected using scan speed)
• Final objective lens focuses beam on desired region.
• When beam strikes the sample, interactions occur. We detect what comes out of the
sample.
Secondary electron mode
Could get
additional
information in
backscattered or
mixed mode
10 µm
Substrate IDZ Coating
γ′
γ γ+γ′
γ+γ′
40
50
60
70
80
0
10
20
30
40
0
10
20
30
40
-15 -10 -5 0 5 10 15 20 25
0.0
0.2
0.4
0.6
0.8
1.0
γ'
Substrate γ + γ'
Composition
(at%)
Ni-AD
Ni-Annealed
Ni
Al-AD
Al-Annealed
Al
Pt-AD
Pt-Annealed
Pt
Hf-AD
Hf-Annealed
Hf
Distance (µm)
Figure 4.8. Composition profiles of the major elements
measured by WDS in an EPMA.

19. X-ray Analysis in the SEM
EDS or WDS
Elemental diffusion profile NiAlPtHf coatings on CMSX-4 substrates
for a temperature of 1150°C and times from (a) 20 hrs and (b) 100 hrs.
Al O
Ni
Pt
Hf
Al Ni
O
Pt
Hf
Al2O3 + ???
???
• Change magnification by changing the scan area
• Focus by changing the objective lens current
• The probe current/spot size are controlled by the
condenser lens current
Useful things to remember about
SEM operation
B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)
B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)

20. B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005) B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)
Microanalysis in Electron Microscopy
• Characteristic X-rays are always generated by
interactions between the incident electron beam and
the sample. They constitute a fingerprint of the local
chemistry.
• Collect X-ray signal to determine local chemistry
• Common Techniques:
– Wavelength-Dispersive Spectrometry/Spectroscopy (WDS)
– Energy-Dispersive Spectrometry/Spectroscopy (EDS)
WDS
• Yields best discrimination of emitted X-ray signal
• Use a series of bent crystals to cover the range of
wavelengths of interest
• Scan wavelengths within each range by rotating the
crystal and moving the detector while keeping the
position of the crystal fixed.
• X-rays are collected from the sample at a fixed angle.
The angle at the collecting crystal will vary with 2θ
and the diameter of the focusing circle will change

21. Specimen
X-ray Detector
Receiving slits
Bent crystal
Radius = 2R
R
Focusing Circle
WDS
WDS continued
• All peaks are scanned sequentially. You cannot
record more than one characteristic line at once
unless there are multiple spectrometers available.
• EPMA!
• Data is collected sequentially. Takes more time but
the results are much more precise than EDS.
Resolution of M lines in a WDS spectrum of a superalloy
(Oxford Instruments)
EDS vs. WDS
• Pulse height is recorded by the detector. It is related
to the energy of the photon responsible for the pulse.
• Solid-state detectors are generally used.
• EDS is faster than WDS
• Problems with EDS:
– Poor discrimination or energy resolution. WDS systems are
much better, particularly when characteristic lines from
different elements overlap.
– Need a windowless or thin window detector to pick up light
elements.
– WDS is more quantitative

22. The BSE sampling volume is large which limits resolution
Multiple elements of BSE
detector
“Overlapping shadows”
Reduced resolution
SE image
Single segment of BSE
detector
Can use BSE signal in conjunction with SE signal to yield enhanced topographical
information Images
• Topography and atomic number influence signal.
• Backscatter coefficient:
– η = -0.254 + 0.016Z - 1.86x10-4Z2 + 8.3x10-7Z3
• Atomic number contrast:
– C = (η1 - η2)/ η1
TOPOGRAPHIC
CONTRAST
TOPOGRAPHIC
CONTRAST
Signals from 2
detectors
B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)

23. B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005) B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)
B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)
B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)

24. B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)
B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)
B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)
B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)

25. B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005) B.D. Huey, MMAT322 Lecture Notes, University of Connecticut (2005)