Post on 13-Apr-2018
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
1/124
MR202Electron Microscopy in Materials Characterization
General Introduction, Resolution, Limits on resolution, Lens aberrations
Introduction to SPM/SEM, Electron Optics Electron Guns and Lenses,Probe diameter and probe current
Electron-Specimen Interactions, Interaction volume, elastic and inelasticscattering
Basics of SEM imaging, Imaging modes, Detectors, Image contrast, Imageprocessing
XEDS and WDS Principles and practice, Basics
Case studies in Materials Science Imaging and Analysis
Newer Techniques EBSD, LVSEM, ESEM
Sample Preparation and a special note about digital imaging/processing
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
2/124
Microscope
Used to see objects not visible to the human eye
Eye can resolve objects ~ 0.1mm apart
For anything closer, we need a means of magnifying
Note : BIGdifference between seeing and resolving
Seeing a car approaching (from its headlights)
Resolving the two headlights as separate sources of light
Optical System - ComponentsSource of Radiation - Visible-light
System of lenses and apertures
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
3/124
Resolution
Limit to resolution arises from the phenomenon
ofd i f f ract ion
Any system used to form an image uses lenses and
apertures that have a certain dimension
Diffraction from a single slit
Intensity ~ (sin(x)/x)2
A big maxima surrounded by smaller maxima
Point object is not mapped on to a point - spread out
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
4/124
Image of a circular slit
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
5/124
Rayleigh Criterion
Profiles from two adjacent point will overlap
To be able to resolve two points as distinct
This is the dif f ract ion- l imited resolution limit
R = sin-1(1.22/d)
To increase resolutionLarge d
Small l
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
6/124
Resolution
20/20 Vision
In the term "20/20 vision", the
numerator refers to the distance
in feet between the subject and
the chart. The denominator is the
distance at which the lines that
make up those letters would be
separated by a visual angle of 1
arc minute, which for the lowest
line that is read by an eye with no
refractive error
http://en.wikipedia.org/wiki/Fraction_%28mathematics%29http://en.wikipedia.org/wiki/Denominatorhttp://en.wikipedia.org/wiki/Visual_anglehttp://en.wikipedia.org/wiki/Arc_minutehttp://en.wikipedia.org/wiki/Arc_minutehttp://en.wikipedia.org/wiki/Visual_anglehttp://en.wikipedia.org/wiki/Denominatorhttp://en.wikipedia.org/wiki/Fraction_%28mathematics%297/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
7/124
Images at different resolution
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
8/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
9/124
Limits on Resolution
What diameter of telescope would you require to read
the numbers on a license plate from a spy satellite?
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
10/124
Lens Aberrations - Other limiting factors for resolution
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
11/124
Spherical Aberration
Zero
+
-
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
12/124
Spherical Aberration
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
13/124
Astigmatism circle becomes an ellipse
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
14/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
15/124
Chromatic Aberration
NoAberration
ChromaticAberration
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
16/124
Electron moving with a velocity v has a wavelength
associated with it
l = h/mv ~ 12.247/sqrt(E)(kV)
Electrons as Waves - The particle-wave duality
Typical wavelengths
E l
100 kV 0.037 A200 kV 0.025 A
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
17/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
18/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
19/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
20/124
First Commercial SEM
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
21/124
Old SEM
Modern day SEM
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
22/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
23/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
24/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
25/124
Basics of SEM Operation
Electron gun produces a beamThermionic/Field-emission guns
Produce a tight spot on the specimen surfaceCondenser and Objective lenses
Scanning coils raster the beam across the specimenSize of scan -> Magnification
Electron-specimen interactionsProduces a wide variety of signals
Detectors to collect the signalDifferent detectors for different signals
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
26/124
Magnification
Magnification Area on Sample Pixel Size
10x 1cmx1cm 10 mm100x 1mmx1mm 1 mm
10kx 10mmx10mm 10 nm
100kx 1mmx1mm 1 nm
Magnification = D/d
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
27/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
28/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
29/124
Electron Gun
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
30/124
h
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
31/124
Thermionic Emission
Jc= AcT2exp(-Ew/kT)
Richardson Equation
Use thermal energy to excite electrons from a metal
EF
EW
vacuum
Ew = 4.5 eV for W, atT = 2700 KJ = 3.4 A/cm2
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
32/124
Tungsten
Hairpin
FilamentWork Function = 4.5 eV
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
33/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
34/124
This is what happens when
you turn the filament knob
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
35/124
Effect of bias on the
filament emission
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
36/124
Other possible gun materials
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
37/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
38/124
LaB6
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
39/124
LaB6Filament
Work Function = 2.5 eV
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
40/124
Very high electric fields
Tip with small radius of curvature
Field Emission
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
41/124
Field EmissionGun
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
42/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
43/124
Comparison of Electron Sources
(Brightness = Current/area/solid angle)
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
44/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
45/124
Source Brightness
(A/cm2
sr)
SourceSize
Lifetime(h)
VacuumLevel
Tungstenfilament
(4.5 eV)
105 30-100 mm 40-100 10-5Torr
LaB6 (2.5 ev)
105
5-50mm 200-1000 10
-7
Torr
Cold FE 108 < 5nm > 1000 10-10Torr
Thermal FE 108 < 5 nm > 1000 10-9Torr
Schottky 108 15-30 nm > 1000
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
46/124
C f S
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
47/124
Comparison of Electron Sources
Note that a very small FE probe carries a much larger currentcompared to a W filament.
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
48/124
Lenses in the Electron Microscope
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
49/124
Electromagnetic Lens
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
50/124
Two types of
Objective Lenses
Large working distance
Very small working
distance
(
a) Pin-hole lens variable working distance, no size limitation of sample,good depth of field
(b) Small focal length => High Resolution
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
51/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
52/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
53/124
aberrations
Asymmetric
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
54/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
55/124
Demagnification
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
56/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
57/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
58/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
59/124
aberrations
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
60/124
Weak
condenser
lens
Strong
condenser
lens
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
61/124
Small
working
distance
Large
workingdistance
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
62/124
Three important parameters for image formation
Probe Size -Smaller the probe size, higher the resolution
Smaller the probe size, lower the brightness
Probe Current/Brightness -
Imaging requires large currents
Convergence Angle
Depth of field increases as angle decreases
Aberrations decrease as angle decreasesBrightness decreases as angle decreases
Probe Size dp diameter of beam as it falls on the specimenBrightness b Current density/solid angleProbe convergence a
p angle made by the cone of electrons with the central axis at the sample surface
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
63/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
64/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
65/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
66/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
67/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
68/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
69/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
70/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
71/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
72/124
Astigmatism
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
73/124
Astigmatism
A ti ti
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
74/124
Astigmatism
Astigmatism
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
75/124
Astigmatism
Astigmatism
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
76/124
g
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
77/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
78/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
79/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
80/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
81/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
82/124
El S i I i
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
83/124
Electron-Specimen Interactions
Beam-Sample Interactions
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
84/124
Beam-Sample Interactions
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
85/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
86/124
We need to understand..
Elastic Scattering
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
87/124
Elastic Scattering
Inelastic Scattering
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
88/124
Inelastic Scattering
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
89/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
90/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
91/124
Scattering of Electrons
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
92/124
Scattering of Electrons
Mean Free Path
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
93/124
Mean Free Path
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
94/124
Elastic Scattering
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
95/124
Elastic Scattering
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
96/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
97/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
98/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
99/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
100/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
101/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
102/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
103/124
Inelastic Scattering
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
104/124
Inelastic Scattering
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
105/124
Inelastic Scattering Bethe Approximation
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
106/124
g pp
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
107/124
Energy Loss
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
108/124
Energy Loss
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
109/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
110/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
111/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
112/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
113/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
114/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
115/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
116/124
Experimental Measurement
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
117/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
118/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
119/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
120/124
Monte Carlo Simulations
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
121/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
122/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
123/124
7/27/2019 IMAGING ABERRATIONS IN SCANNING ELECTRON MICROSCOPY
124/124