The document presents an overview of electron microscopy, detailing its types, primarily Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM), along with their principles, instrumentation, limitations, and pharmaceutical applications. Both methods provide high-resolution imaging and analysis capabilities, essential for examining materials at the nano scale. Key differences between TEM and SEM are highlighted, including their operational principles, imaging techniques, and specific applications in the pharmaceutical field.

1. ELECTRON MICROSCOPY
Prepared by: Yohannes Reda
ID: CHS/PR159681/11
Mekelle university
college of health sciences
school of pharmacy

2. Presentation outline
 Objective
 Introduction
 Types of electron microscope
 TEM (working principle, instrumentation, limitation and application)
 SEM (working principle, instrumentation, limitation and application)
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3. Objective
At the end of this presentation its expected
 To differentiate electron microscopy from light microscopy
 To grasp the working principle of TEM and SEM
 To list some of the instruments of both TEM and SEM
 The list pharmaceutical applications of SEM and TEM
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4. Introduction to electron microscopy
 Electron microscope is a type of microscope that use beam of electrons to
magnify and see in detail up to Nano meter level.
 They can see features as small as tenth of a nanometer, such as individual atoms.
 These instruments are capable of atomic scale resolution
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5. The resolution limit
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Figure 1. the resolution limit of different imaging techniques along with
radiation and the size of biological objects

6. Why electrons ?
 An atom is made up of three kinds of particles – protons, neutrons, and electrons.
 The electrons, which are about 1800 times lighter than the nuclear particles,
occupy distinct orbits, each of which can accommodate a fixed maximum
number of electrons.
 When electrons are liberated from the atom-they behave like light.
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7. Types of electron microscopes
 Generally we Can classify
EM based on the type of
electron they use in to
 Transmission electron microscope
and
 Scanning electron microscope
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SEM TEM
Figure 6: schematic drawing of scanning and transmission electron microscope
internal components

8. Interaction between electrons and matter
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Elastic interaction : No energy is transferred from the electron to the sample
Inelastic interaction :Energy is transferred from the primary electron to the specimen
Emission of electrons and radiation

9. Transmission electron microscopy (TEM)
 TEM is the direct counterpart of Light
microscope
 Involves passage of high velocity
electron beam through specimen, thin
enough to transmit 50% of the electrons
 Transmitted electrons – focused by lens
systems to form a 2 dimensional
magnified image (2D)
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Figure : schematic drawing of transmission electron
microscope internal components

10. Instrumentation
 It is convenient to divide the instrument into three/four sections
 Illumination system
 Electron gun
 Condenser
 Specimen system
 Imaging system
 Vacuum system
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11. Illumination system
Electron gun
 The electron source consists of a cathode and
an anode.
 The cathode is a tungsten filament/LaB6
which emits electrons when being heated.
 A negative cap confines the electrons into a
loosely focused beam.
 The beam is then accelerated towards the
specimen by the positive anode
Condenser
 The system allows electrons within a small
energy range to pass through, so the electrons
in the electron beam will have a well-defined
energy
 It’s a lens that help to focus the wide beams
of electrons to the specimen
 Unlike in the light microscope that uses glass
lenses the TEM uses magnetic (electro
magnetic) lenses
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12. Vacuum system
 The electron beam must be generated in and traverse through the microscope
column under a high vacuum condition.
 The presence of air molecules will result in the collision and scattering of the
electrons from their path.
 In the electron microscope the vacuum is maintained by a series of highly
efficient vacuum pumps.
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13. Imaging system
 The imaging system consists of another electromagnetic lens system and a
screen.
 The electromagnetic lens - two lens, one for refocusing the electrons after they
pass through the specimen, and the other for enlarging the image and projecting
it onto the screen.
 The screen has a phosphorescent plate which glows when being hit by electrons.
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14. Imagining formation
 The basis of image formation in the TEM is the scattering of electrons.
 The scattering results in a shadow on the viewing screen or photographic film.
 Material with high atomic numbers will cause more scattering and produce a
deep shadow.
 Such material is termed "electron dense" and has high image contrast
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15. Pharmaceutical applications of TEM
TEM can be used to analyze the internal structures of a given sample such as
 particle size, morphology, elemental composition, and crystallographic properties
 polymorph identification, mapping of crystal habit to crystal structure and crystal defect
characterization.
 Reveal changes in micro particle morphology induced by drug loading
Figure 5: micro particles before (c) and after drug loading (d)
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16. Limitations
 Sampling is difficult and very costly
 Interpreting images- 2D images need a special skill to be interpreted
 Electron beam damage and safety-particularly polymers (and most organics) or
certain minerals and ceramics.
 Specimen preparation - the specimens have to be thin if you are going to get any
information using transmitted electrons in the TEM.
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17. Scanning electron microscope(SEM)
 SEM uses a focused beam of high-energy electrons to generate a variety of
signals at the surface of solid specimens.
 Signals that derive from electron-sample interactions reveal information
including:
 Morphology, chemical composition, crystalline structure and orientation
of materials making up the sample.
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18. Cont…
The typical scanning electron microscope laboratory
contains a machine with 2 components:
 the microscope column, including the electron gun
at the top, the column, down which the electron
beam travels, and the sample chamber at the base.
 the computer that drives the microscope, with the
additional bench controls
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Figure 6: schematic drawing of scanning electron
microscope internal components

19. Interaction between matter and electrons
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20. Working Principle(Scanning process and image formation)
-After the impingement of the primary
electrons on the specimens, secondary
electrons as well as other forms of
radiation are emitted.
-But only the secondary electrons will be
collected by the signal detector.
-In the detector these electrons strike a
scintillator and the light produced is
converted to electric signals by a
photomultiplier.
-The electric signal is then amplified and
displayed on the cathode ray tube (CRT).
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Figure 6: schematic drawing of scanning electron microscope internal
components

21. Cont…
 In the SEM the electron beam is rapidly scanned back and forth in an orderly
pattern across the specimen surface.
 It is a composite of many individual image spots similar to the image formed on
the TV screen.
 The SEM has a specimen stage that allows the specimen to move freely so that
the surface of the specimen can be viewed from all angles.
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22. Limitation
 The main disadvantage of SEM is that data are collected one pixel after the
other, which leads to a longer exposure time to the electron beam when
compared to TEM
 Samples must be solid
 samples must be stable in a vacuum approximately 10-5 - 10-6 torr (samples that
tend to outgas at low pressure are not compatible with this instrument)
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23. Pharmaceutical application of SEM
 powder imaging and analysis, to gain insights into cellular interactions with new drugs,
and for applications in the most complicated cancer treatments.
 Within the field of industrial application and research, there is an increasing focus on
quality control at microscopic level, achieving high imagery level.
 Some of the uses are
 particle size distribution analysis,
 aspect ratio analysis,
 bioavailability studies and stability
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24. TEM vs SEM
TEM SEM
6 lenses – C1, C2, objective, 3
projector
3 lenses – 2 condensor, 1
objective
High accelerating voltage -
penetration
low accelerating voltage
Not complicated Specimen Stage – complicated
X & y axis X,Y,Z-axis, tilting, rotating
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Table 1: TEM vs SEM

25. Summary
 EM are useful tools for looking a range of samples.
 EM based analysis combined with other analysis techniques can assist
 Complete characterization of samples.
 They remain a very powerful analysis tool in the manufacturing of
pharmaceuticals.
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26. References
 Amelinckx, S., Van Dyck, D., van Landuyt, J. and Van Tendeloo, G. eds., 2008. Handbook of
Microscopy: Applications in Materials Science, Solid-State Physics, and Chemistry, Methods
II. John Wiley & Sons.
 Carlton, R.A., 2011. Scanning electron microscopy and energy-dispersive X-ray spectrometry.
In Pharmaceutical Microscopy (pp. 85-130). Springer, New York, NY.
 Colliex, C., 2014. Seeing and measuring with electrons: Transmission electron microscopy
today and tomorrow–An introduction. Comptes Rendus Physique, 15(2-3), pp.101-109.
 Eddleston, M.D., Bithell, E.G. and Jones, W., 2010. Transmission electron microscopy of
pharmaceutical materials. Journal of pharmaceutical sciences, 99(9), pp.4072-4083.
 Egerton, R.F., 2005. Physical principles of electron microscopy (p. 41). New York: Springer.
 Fultz, B. and Howe, J.M., 2012. Transmission electron microscopy and diffractometry of
materials. Springer Science & Business Media.
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