3. OUTLINE
Introduction
Components, and working principles of
SEM
Salient futures of SEM
Data analysis by SEM
Textile fiber characterization by SEM
Advantages and limitations of SEM?
5. A. INTRODUCTION
Type of electron microscope that images
the sample by scanning it with high energy
beam of electrons .
What can we study in a SEM?
o Topography and morphology(texture)
o Chemistry(chemical composition)
o Crystallography
o Orientation of materials
Designed by Stinzing and Knoll in Germany in the early 25s
1965.
6. Light microscope Electro microscope
The source of illumination The ambient light source is
light for the microscope
Electrons are used to “see”
light is replaced by an
electron gun built into the
column
The lens type Glass lenses Electromagnetic lenses
Magnification
method
Magnification is changed by
moving the lens
Focal length is charged by
changing the current through
the lens
Viewing the
sample
Eyepiece (ocular) Fluorescent screen or
digital camera
Use of vacuum No vacuum Entire electron path from
gun to camera must be
under vacuum
Comparing light vs electron microscope
7.
8. TEM SEM
Electron Beam Broad, static beams
Beam focused to fine point;
sample is scanned line by
line
Voltages Needed Accelerating voltage high r
Accelerating voltage much
lower; not necessary to
penetrate the specimen
Interaction of the
beam electrons
Specimen must be very thin
Wide range of specimens
allowed; simplifies
sample preparation
Imaging
Electrons must pass through
and be transmitted by the
specimen
Information needed is
collected near the surface
of the specimen
Image Rendering
Transmitted electrons are
collectively focused by the
objective lens and magnified
to create a real image
Beam is scanned along the
surface of the sample to
build up the image
Comparing TEM vs
SEM
12. 2.
LENSES Condenser lens –determines the number of
electrons in the beam which hit the sample by
reducing the diameter of the electron beam.
Objective lenses -changes the position of the
point at which the electron are focused on the
sample.
13. 3. SCANNING COILS
Are used to raster/scan the e-beam across the sample
surface
The e-beam can be scanned in a rectangular raster
across the surface of the sample by means of a series
of “scan coils” situated above the objective lens.
4. SAMPLE CHAMBER
A place where the sample was mounted
on.
15. 6. VACUUM CHAMBER
Used to protect the electronic beam from
interference with air.
control the number of electrons which reach
the sample.
control the final convergence angle of the
electron beam onto the sample
7. Aperture
18. SIGNALS FROM THE SAMPLE
1. Secondary electrons (SE):
Low energy electrons, high resolution
Surface signal dependent on curvature
2. Backscattered electrons (BSE):
High energy electrons
“Bulk” signal dependent on atomic number
3. X-rays: chemistry
Longer recording times are needed
Absorbed e- tells the chemistry of the
sample
23. RESOLUTION IS DEPEND UP ON?
Size of the electron spot &wavelength of the
electrons .
size of the interaction volume (material
interacts with the electron beam)
24. SAMPLE PREPARATION
1) Remove all water, solvents, or
other materials that could vaporize
while in the vacuum.
2) Firmly mount all the samples.
3) Non-metallic samples, such as
plants,
and ceramics, should be coated with
electrically conductive materials.
25. Image disturbance and causes
Image
disturbance
Cause
Lack of
sharpness
Improper accelerating voltage setting
Instability of gun emission due to low heat energy
Improper setting of objective aperture
Improper focal length
Too large magnification
Specimen charge up and magnetization
Low image
quality
Improper accelerating voltage setting
Improper contrast and brightness
Improper specimen preparation process
Improper position relation between specimen and
detector
Noise Improper accelerating voltage setting
Change up of specimen surface
Mechanical vibration
Image distortion o Electron beam damage
26. C. SALIENT FUTURES OF SEM
High resolution 50 to 100 nm and magnification
ranging from 20X to approximately 30,000X
3-D Topographical imaging due to very narrow
e- beam & large depth of field yielding
Compatible with PC technologies and softwares
Fast Analysing
Store data in digital form
most powerful and popular for surface
characterization.
uses electrons to form image rather than light.
relatively easy to prepare sample.
27. Topography
The surface features of an object and its texture
(hardness, reflectivity… etc.)
Morphology
The shape and size of the particles making up the
object (strength, defects in IC and chips...etc.)
Composition
The elements and compounds that the object is
composed of and the relative amounts of them
(melting point, reactivity, hardness...etc.)
Crystallographic Information
How the grains are arranged in the object
Surface characterization of dry solid materials
29. CHARACTERIZATION OF WOOL FIBER
BY SEM
Wool have Cylindrical , irregular, rough surface,
scale like structure when we see its longitudinal
structure under SEM.
Nearly round or circular cross –sectional view
Longitudinal view Cross-sectional view
30. CHARACTERIZATION OF COTTON FIBER
BY SEM
Ribbon like with convolutions longitudinal structure
Have Elliptical been shaped stracture when we see its
cross-sectional view
Cross-sectionalLongitudinal view
31. CHARACTERIZATION OF POLYESTER
FIBER BY SEM
uniform diameter & rod like appearance of
longitudinal view
Circular cross-sectional view
Cross-sectional viewLongitudinal view
32. Limitations
Sample must fit into the microscope
chamber
Doesn't work with out vacuum
Sample should coat with electrically
conductive chemical.
Sample must be dry solid .
bulky and complex instruments as a result
needs special experts.
Ne----Advantage is listed
above( future)
