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MMS 8110803 - KARAKTERISASI MATERIAL + LAB
Dr. Ir. A. Herman Yuwono, M. Phil. Eng.
Departemen Metalurgi dan Material Fakultas Teknik Universitas Indonesia
Tel: +(62 21) 7863510 Fax : +(62 21) 7872350 Email: [email protected]
TRANSMISSION ELECTRON MICROSCOPY
(TEM)
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
What is Microscopy?
Microscopy: A technique for making visible images of structures or
details too small to otherwise be seen by the human eye.
How is this done?
• diffraction, reflection, or refraction of radiation incident upon the subject
of study.
• diffraction, reflection, or refraction of secondary radiation generated
within the subject of study
A microscopist must learn how are images are:
• formed
• collected
• interpreted
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
Why Use Electrons?
The primary answer is ‘resolution’
Resolution: The limit of resolution is the smallest separation at which two
points can be seen as distinct entities.
Higher magnification will not necessarily give higher resolution.
Unless a microscope is equipped to deliver higher resolution images, higher
magnification will only achieve ‘empty’ images.
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
What is TEM?
Transmission Electron Microscopy (TEM) is a method of producing
‘images’ from a sample by illuminating the sample with electrons (in a
vacuum), and detecting the electrons that are transmitted through the
sample.
Pros:
• Provides information on crystalline,
amorphous, incommensurate,
and periodic structures at fine scales
• Can gather crystallographic and
chemical data at unit cell or near
unit cell scale
• Subatomic resolution is coming
Cons:
• Requires that the sample be cut
into thin slices and placed in a
vacuum, possibly resulting in
artifacts
• High resolution TEM is
expensive, requiring high electron
voltages
• Data interpretation is time-
consuming
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
Basic Configuration
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
Basic Configuration
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
What Knowledge is Needed to Conduct TEM?
Diffraction Physics: TEM is a diffraction method, not a ‘magnifying’
method. An understanding of basic optics is essential.
Crystallography: Because TEM relies upon diffraction a grasp of
crystallography cannot be avoided if the instrument-specimen interaction
is to be meaningful and lead to interpretable data.
Patience: TEM is a difficult technique in terms of both data gathering and
data interpretation. It will normally take a graduate student 9-12 months
to obtain their first good results assuming weekly access to the
microscope.
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
Capability
Resolution:
TEM Mode < 2 Å
STEM Mode < 5 Å
Crystallographic Information:
Electron diffraction - Selected Area Electron Diffraction (SAD)
- Convergent Beam Electron Diffraction (CBED)
Imaging - Lattice Imaging
- High Resolution Electron Microscopy (HREM)
Chemical Information:
X-rays - Energy Dispersive X-ray Spectroscopy (EDS)
- Atomic Location by Channeling Enhanced
Microanalysis (ALCHEMI)
Electrons - Electron Energy Loss Spectroscopy (EELS)
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
Signals
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
Instrumentation
Basic Requirement • Intermediate voltage (200, 300, 400 keV)
• High brightness electron source
LaB6, FEG, hairpin W (possibly)
Desirable Extras • Scanning TEM
• Energy Dispersive X-ray Detector Si(Li) or Ge(Li)
• Electron Energy Loss Spectrometer (EELS)
• X-ray or EELS mapping software
• TV and CCD image capture and image
processing
• Cold stage, hot stage, tensile stage etc.
• SE & BSE Detectors
Essential Extras • Diffraction and image simulation software
• Image processing software
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
Principles of image formation:
Typically, a TEM consists of an
electron gun, a condenser lens system,
a specimen chamber, objective and
intermediate lenses, projector system
for producing images and diffraction
patterns, vacuum and computer
systems
With an electron gun, an electron
beam is formed, which is accelerated
by an electric field formed by a
voltage difference of typically
100−200 kV. By condenser lenses,
the electron beam is focused on the
sample to be investigated, where the
electrons are scattered.
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
Electron scattered in the same
direction are focused in the back focal
plane, giving rise to a diffraction
pattern, while electrons coming from
the same point of the object are
focused in the image plane. The first
image, which is formed by the
objective lens, is magnified typically
by 25 times, and the following
intermediate and projective lenses
give a final magnification of the image
in the viewing screen of more than
106 times.
Principles of image formation
(cont):
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
Image observation
A TEM image can be formed by either: the central spot of un-
scattered beam, or some or all of the scattered electrons.
Depending on beam selection, there are four common types of TEM
image:
a. Bright Field (BF) image;
b. Dark Field (DF) image;
c. Selected Area Diffraction (SAD); and
d. Lattice or High-Resolution TEM (HRTEM) image.
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
Bright Field (BF) image involves
the insertion of an aperture on
the back focal plane of the
objective lens so that only the
un-scattered electrons can pass
through and contribute to the
formation of image. As a
consequence, thick regions of
the specimen in which heavy
atoms are enriched or higher in
density such as crystalline
phase(s) will scatter more
strongly and appear as darker
areas in the resultant image. In
the absence of a specimen, a
bright background is observed.
a. Bright Field (BF) image
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
Dark Field (DF) image involves the
displacement of aperture which
allows some of the scattered
electrons to pass through the
objective aperture, while the un-
scattered electrons are blocked.
This is termed as dark field
imaging because the background
appears dark, in the absence of a
specimen, providing a reverse
contrast to the bright field image.
By this technique, the diffracted
beam can have strong interaction
with the sample; enabling some
useful information be obtained,
such as planar defects, stacking
faults or crystallite size
b. Dark Field (DF) image
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
Comparison of BF and DF Images
30-fold quasi crystalline Al-Mn film grown by sequential deposition of Mn on a (111)-
oriented Al film at 260oC.
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
c. Selected area diffraction (SAD)
Selected Area Diffraction (SAD) is
obtained when a special aperture namely
SAD aperture is inserted. It encloses a
small area through which both un-
scattered and diffracted electrons
contribute to the image formation. The
diffraction pattern obtained on the back
focal plane of the objective lens
represents an image of reciprocal lattice
and therefore contains information about
crystal structure.
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
For the purpose of analysis, the Bragg’s law can be applied with only the
first order diffraction (i.e. n =1) is considered. This is assumed so since
the Bragg’s angle is very small due to the very short wavelength of the
electron beam used in TEM. Therefore the simplified Bragg’s law can be
written as:
l = 2dq
For electrons which are diffracted through an angle q by the crystal
planes of spacing d and hit the screen or film which is a distance L from
the specimen, the resulting distance r from the un-diffracted spot at the
center can related by a simple geometry:
q2L
r
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
Combining the previous two equations results in:
or
Ll is called camera constant since the camera length L and the electron
wavelength l are independent of the specimen, and thus a constant.
The distance of a diffraction spot from the un-diffracted spot r, is therefore
inversely proportional to the d-spacing of the diffracting planes.
Given the camera constant, d can be determined simply by measuring r on
the pattern accurately.
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
Types of SAD Patterns
Diffraction type depends on the size of
the electron probe, as well as the crystallite size.
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
TEM image and corresponding SAD pattern of amorphous TiO2
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
TEM image and corresponding SAD pattern of crystalline TiO2
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
Crystalline diffraction pattern
from a twinned grain of FCC
Austenitic steel
Transmission Electron Micrograph of
Dislocations, which are faults in the
structure of the crystal lattice at the
atomic scale
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
d. Lattice or high-resolution TEM (HRTEM) image.
A lattice or High-Resolution TEM
(HRTEM) image is formed by the
interference between the diffraction
beam and un-scattered beam. In
practice, a larger objective aperture
is selected to allow both types of
beam to pass.
The incident parallel electrons
interact elastically when passing
through the sample, and the
resulting modulation of phase and
amplitude are present in the
electron wave leaving the sample.
This type of wave thus contains the
information about the object
structure.
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
d. Lattice or high-resolution TEM (HRTEM) image (cont)
Furthermore, all the diffracted beam and un-scattered beam are brought together
again in the objective lens and the Fourier transform (analysis) creates a
diffraction pattern of the object in the back focal plane.
The inverse Fourier transform (synthesis) is performed subsequently, making the
interference of diffracted beams back to a real space image in the image plane as
a lattice image.
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
Preparation of TEM
Specimen
In a TEM, the specimen you want to
look at must be of such a low density
that it allows electrons to travel
through the tissue.
There are different ways to prepare
your material for that purpose. You
can cut very thin slices of your
specimen from a piece of tissue
either by:
fixing it in plastic or working with it as
frozen material.
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
Negative Staining of Isolated
Material
The isolated material (can be a
solution with bacteria or a solution with
isolated molecules) is spread on a
support grid coated with plastic. A
solution of heavy metal salt is added.
The metal salt solution does not bind
to the material but forms a "shadow"
around it on the grid. The specimen
will appear as a negative picture when
viewing it in the TEM.
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
How do they look under microscope?
Hexagonal
Grid
Square Grid
•200 mesh
•55% open area,
•28 µm bar width
•Thick:17.8 µm
3 mm
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
TEM Grid Preparation
There are two sides in carbon coated ultra-thin grid:
1. Formvar side - lighter side (less hydrophobic than
the carbon film)
2. Carbon film is on the darker side.
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
TEM Grid Preparation
• Hold the grid with tweezers.
• Do not touch/contaminate the grid.
• Do not bend the grid.
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
Tem Grid Preparation
• Take a micropipette and put a droplet on top the grid. Let the
solution sit on the grid.
• After 10-12 min, wick away the rest of the solution with filter paper.
Do not touch the grid!
• Finally let it sit until the grid dries off.
MMS 8110803- KARAKTERISASI MATERIAL + LAB [email protected]
DEPARTEMEN METALURGI DAN MATERIAL FAKULTAS TEKNIK UNIVERSITAS INDONESIA
TEM is a diffraction technique requiring a knowledge of optics and
crystallography to operate in a meaningful way.
TEM can collect signals from elastic and inelastic electron-matter
interactions to derive crystallographic and chemical information at atomic
or near-atomic scales.
The capability of TEM can be expanded by using hot stages, cold stages
and so on.
Image and/or spectral simulation are usually required for serious data
interpretation.
Summary