This document discusses four main types of electron microscopes: transmission electron microscope (TEM), scanning electron microscope (SEM), reflection electron microscope (REM), and low-voltage electron microscope (LVEM). It provides details on the components, imaging mechanisms, advantages, limitations, and typical voltages used for each microscope type. The TEM is noted as the original and most powerful microscope for high resolution imaging, but requires thin sample preparation. The SEM can image thicker bulk samples but provides 3D surface images rather than internal structure. The REM uses elastically scattered electrons for raster scanning. The LVEM provides high contrast images at lower voltages than TEMs, with improved thickness limits over conventional TEM.

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