Phase contrast and interference microscopy with the electron microscope
Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
Transcript of Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
1/29
(an embarrassingly short description ofan embarrassingly short description of )Diffraction Contrast Imagingiffraction Contrast ImagingLecture 10ecture 10
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
2/29
Categories of imagingategories of imagingMassass-thickness contrasthickness contrast Contrast appears in the image due to differences in the inherentontrast appears in the image due to differences in the inherent
scattering from the samplecattering from the sample Z-contrast imaging (a highontrast imaging (a high-resolution version of same)esolution version of same)
Diffraction contrastiffraction contrast In crystalline materials, diffraction occurs.n crystalline materials, diffraction occurs. Utilizing the objective aperture, either the direct (tilizing the objective aperture, either the direct (unn-diffractediffracted)beam or one of the diffract beams is selected to form the imageeam or one of the diffract beams is selected to form the image
Results in crystallographic information being conveyed in the imesults in crystallographic information being conveyed in the imagegePhase contrast (hase contrast (highigh-resolutionesolution imaging)maging) Direct and diffracted beams undergo phase shifts in the materialirect and diffracted beams undergo phase shifts in the material An image if formed by recombining all beams and observing then image if formed by recombining all beams and observing the
resulting interference patternesulting interference pattern
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
3/29
BF image formedfrom the direct beam
Displaced apertureDF image formed
with off-axis
scattered beam
CTF image where theincident beam is
tilted so that the
scattered beam
remain on axis
Bright Field / Dark Field Imagingright Field / Dark Field Imaging
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
4/29
Two beam imagingwo beam imaging
Primary imaging mode is therimary imaging mode is the twowo-beameam conditiononditionAllows readily interpretable imagesllows readily interpretable images
Bright Field Image Dark Field Image Weak-Beam DarkField Image
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
5/29
Twowo-beam conditionseam conditionsExamples of twoxamples of two-beameamconditions near the 011onditions near the 011Zone Axisone Axis
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
6/29
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
7/29
Twowo-beam conditionseam conditionsExamples of twoxamples of two-beameamconditions near the 011onditions near the 011Zone Axisone Axis
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
8/29
Kinematical Diffractioninematical DiffractionAssumptionsssumptions Only two diffracted beamsnly two diffracted beams
considered, direct and oneonsidered, direct and onediffractediffracted Intensity of diffracted beam isntensity of diffracted beam issmallmall Single scattering eventingle scattering event Noo absorptionbsorption i.e.:.e.: IIdiffractediffracted
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
9/29
Kinematicinematic vs. Dynamicals. DynamicalCan be used to explain (to first approximation) the originan be used to explain (to first approximation) the originmuch of much what we see in the microscopeuch of much what we see in the microscopeHowever, cannot be used to accurately calculateowever, cannot be used to accurately calculateintensity relationshipsntensity relationshipsUse dynamical theory:se dynamical theory: Considers multiple beamsonsiders multiple beams Intensity in one or more diffracted beams can be large inntensity in one or more diffracted beams can be large incomparison with transmitted beamomparison with transmitted beam Multiple scattering allowedultiple scattering allowed Absorptionbsorption (loss of electrons) allowedloss of electrons) allowed Can explain intensity accuratelyan explain intensity accurately Very complicated to utilize practicallyery complicated to utilize practically
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
10/29
Kinematicinematic diffraction in perfectiffraction in perfectcrystalsrystalsThickness contours:hickness contours: At exact Bragg condition (s = 0),
the intensity of the direct anddiffracted beam oscillate in acomplementary way.
For a wedge specimen, theseparation of the fringes in the
image is determined by the angle
of the wedge and the extinction
distance, g.
Thus, the image may appear to
be black or white depending on
the thickness of the specimenwhere you are observing it
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
11/29
111111
hole
aa
Representative bright field (a),
and dark field (b) micrograph
showing thickness fringes
100 nm100 nm
bb 111111
Kinematicinematic diffraction in perfectiffraction in perfectcrystalsrystals
Courtesy V.R. Radmilovic
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
12/29
Kinematicinematic diffraction in perfectiffraction in perfectcrystalsrystalsThickness contours:hickness contours: At exact Bragg condition (s = 0),
the intensity of the direct anddiffracted beam oscillate in acomplementary way.
For a wedge specimen, the
separation of the fringes in the
image is determined by the angle
of the wedge and the extinction
distance, g.
Thus, the image may appear to
be black or white depending on
the thickness of the specimenwhere you are observing it
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
13/29
111111
hole
aa
Representative bright field (a),
and dark field (b) micrograph
showing thickness fringes
100 nm100 nm
bb 111111
Kinematicinematic diffraction in perfectiffraction in perfectcrystalsrystals
Courtesy V.R. Radmilovic
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
14/29
Translation / rotationranslation / rotationbetween two crystalsetween two crystalsyields fringes in imagesields fringes in images Stacking faultstacking faults Grain boundariesrain boundaries Translation boundariesranslation boundaries Phase boundarieshase boundaries Surfaces (if stepped)urfaces (if stepped)
Electron wave has alectron wave has adifferent amplitude &ifferent amplitude &phase in each crystalhase in each crystal Results in a fringe patternesults in a fringe pattern
Kinematicinematic diffraction in imperfectiffraction in imperfectcrystalsrystals
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
15/29
gR causes the contrast and fordislocations, R changes with z.g
b = n; if we know g and we determine n,then we know b.
Kinematicinematic diffraction in imperfectiffraction in imperfectcrystalsrystalsStrain field of dislocation causes localdiffraction differencesSeen as line of contrast in the image (iforiented correctly )
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
16/29
0.5 m
If gb = 0, then you wont see any contrast because the diffracting
planes are then parallel to R.
This is termed the invisibility criterion.
Kinematicinematic diffraction in imperfectiffraction in imperfectcrystalsrystals
Courtesy V.R. Radmilovic
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
17/29
Weak-beam dark-field imaging
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
18/29
0.5 m
If gb = 0, then you wont see any contrast because the diffracting
planes are then parallel to R.
This is termed the invisibility criterion.
Kinematicinematic diffraction in imperfectiffraction in imperfectcrystalsrystals
Courtesy V.R. Radmilovic
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
19/29
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
20/29
0.5 m
If gb = 0, then you wont see any contrast because the diffracting
planes are then parallel to R.
This is termed the invisibility criterion.
Kinematicinematic diffraction in imperfectiffraction in imperfectcrystalsrystals
Courtesy V.R. Radmilovic
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
21/29
gR causes the contrast and fordislocations, R changes with z.g
b = n; if we know g and we determine n,then we know b.
Kinematicinematic diffraction in imperfectiffraction in imperfectcrystalsrystalsStrain field of dislocation causes localdiffraction differencesSeen as line of contrast in the image (iforiented correctly )
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
22/29
100 nm100 nm100 nm100 nm
001Al
110 Al
001001AlAl
110110 AlAl
Dark field images of new Al-2at.%Cu-1at.%Si-1 at.%Ge alloy aged 1h and 3hrs
(right) at 190oC; imaged using 112 reflection.
1h1h 3h3h
Dark-field imaging
Courtesy V.R. Radmilovic
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
23/29
Diffraction condition
g
2
= t
g
2
sin2(tseff )
tseff( )2
seff = s2 + 1
g2
eff = g
w2 + 1
Weak-beam dark-field imaging
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
24/29
Weak-beam dark-field imaging
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
25/29
Kinematicinematic diffraction in imperfectiffraction in imperfectcrystalsrystals
Bright field image Dark field image
Al2O3
GaN
Weak beamdark field image
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
26/29
111111
hole
aa
Representative bright field (a),
and dark field (b) micrograph
showing thickness fringes
100 nm100 nm
bb 111111
Kinematicinematic diffraction in perfectiffraction in perfectcrystalsrystals
Courtesy V.R. Radmilovic
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
27/29
Kinematicinematic diffraction in perfectiffraction in perfectcrystalsrystals
Bend Contours
The origin of bend contours shown for
a foil symmetrically bent on either side
of the Bragg conditions. When thehkl
planes are in the Bragg condition, the
reflection G is excited.
Bend ContoursBend Contours
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
28/29
[100]
crystal
orientationEach diffracted
plane producestwo bend
contours
Kinematicinematic diffraction in perfectiffraction in perfectcrystalsrystalsBend ContoursBend Contours
[103]
crystal
orientation
-
8/8/2019 Transmission Electron Microscopy Skills:Diffraction Contrast Imaging Lecture 10
29/29
Categories of imagingategories of imagingMassass-thickness contrasthickness contrast Contrast appears in the image due to differences in the inherentontrast appears in the image due to differences in the inherentscattering from the samplecattering from the sample Z-contrast imaging (a highontrast imaging (a high-resolution version of same)esolution version of same)
Diffraction contrastiffraction contrast In crystalline materials, diffraction occurs.n crystalline materials, diffraction occurs. Utilizing the objective aperture, either the direct (tilizing the objective aperture, either the direct (unn-diffractediffracted)beam or one of the diffract beams is selected to form the imageeam or one of the diffract beams is selected to form the image
Results in crystallographic information being conveyed in the imesults in crystallographic information being conveyed in the imagegePhase contrast (hase contrast (highigh-resolutionesolution imaging)maging) Direct and diffracted beams undergo phase shifts in the materialirect and diffracted beams undergo phase shifts in the material An image if formed by recombining all beams and observing then image if formed by recombining all beams and observing the
resulting interference patternesulting interference pattern