1. Asad Rasheed
11-ARID-433

2. Type of Electron
Microscope
 Transmission Electron Microscope
 Scanning Electron Microscope
 Reflection Electron Microscope
 Low-Voltage Electron Microscope

3. Transmission Electron
Microscope
 The Original Form of EM that uses the
high voltage Beam of Electrons to create
an image.
 Its has Resolution power up to
0.5 angstrom (50 picometres).
 Most Powerful for observing
minute objects

4. Components

5. Mechanism
 Electron Gun Produces Beam of 100 keV.
 Anode and Cathode accelerate Beam.
 Focusing occur by Electrostatic and
electromagnetic lenses
 Beam strikes the sample and pass through
it.
 After emerging out it carries information
about Sample and magnify it by objective
lens
 Information can be analyzed by Screen or
Film or CCD Cameras on LCD or monitor.

6. Advantages
 TEMs offer the most powerful
magnification, potentially over one million
times or more
 TEMs provide information on element and
compound structure
 Images are high-quality and detailed
 TEMs are able to yield information of
surface features, shape, size and structure
 They are easy to operate with proper
training

7. Limits of TEM
 Spherical Aberration.
 High Voltage can damage Sample.
 Sample should be xtremely thin upto 100
nm.
 Bio Samples are Dehydrated , chemically
fixed, embedded in polymer resin to
stabilize them.
 Staining is required to highlight in order to
achieve require image contrast.
 Thinning of sample should be done upto
100 nm

8. Scanning Electron Microscope
 SEM produces the image by scanning it
with focus beam of electron.
 Electrons interact with electrons in
sample and convey information in form
of signals to detectors. E.g. topography
& sample surface.
 SEM can achieve resolution better than
1 nanometer
 Raster image focusing is used

9. Mechanism
 When High energy Electrons strikes the
surface, it lose energy by diff.
mechanisms like heat, emission of low
energy secondary electrons and high
energy backscattered electrons.
 X-ray or light emerges from sample that
carries information on it.

10. Advantages
 Its basically used for biological samples
 It can scan the processes occurring on
surface and tells about topography and
composition.
 Enable us to view without thinning
dehydrating fixing the sample
 Can scan bulk samples upto 2-3 cm which
can not be examined by TEM.
 View obtained is in 3D.
 ESEM produce image of Wet, gas &
Vacuumed Samples and biological samples.

11. Reflection Electron Mcroscope
 Its is the fixation of Transmission and
Scanning Electron Microscope.
 Uses the Elastically Scattered Electrons
for focusing the electron beam into a
narrow spot which is scanned over the
sample in a raster.
 Raster is the rectangular pattern of
image capture and reconstruction in
television.

12.  TEM Sample forming processes are involved
like thinning.
 Highly contrasted mage is produces with
higher focusing
Difference
 Rastering of beam occurs by focusing on
rectangular area.
 In REM Focusing action occurs before the
beam strikes the sample but in TEM focusing
action occurs after the striking
 Also data is obtained in series image rather
in parallel image form.

14. Low-Voltage Electron
Mcroscope Microscope
 As the Name suggests that it uses low
voltage for scanning i.e. up to 5 KeV.
 Higher Contrasting focus and good quality
image are produces with good magnifying
power better then TEM.
 Pinpoint image are obtained on CCD
Camera.
 This type can be used as
TEM, SEM, STEM.
 No Staining Required

15. Comparison of LVEM & TEM of
Rat Heart (Specific part)
 LEVM @ 5 Kev TEM @ 80 Kev

16. Cont…
 Present low voltage electron
microscopes are capable of spatial
resolutions of about 2.5 nm in TEM
2.0 nm in STEM and 3.0 nm in SEM.
 Low voltage limits the maximum
thickness of samples
 It is about 100–200 nm in conventional
TEM.
 It decreases to around 20–65
nanometers for LVEM.

17. Thanks for being Patience