1. Micro structural Characterization
By
Harsha Kamatagi
Usn 1ms10mse08

2. Scanning Electron Microscope (SEM)
• The SEM is an instrument that produces a largely magnified image by using
electrons instead of light to form an image.
• A beam of electrons is produced at the top of the microscope by an electron
gun.
• The electron beam follows a vertical path through the microscope, which is held
within a vacuum.
• The beam travels through electromagnetic fields and lenses, which focus the
beam down toward the sample.
• Once the beam hits the sample, electrons and X-rays are ejected from the
sample.
• Detectors collect these X-rays, backscattered electrons, and secondary
electrons and convert them into a signal that is sent to a screen similar to a
television screen. This produces the final image.

5. Specimen chamber

6. Beam-Specimen Interactions

7. signals
 The beam electron can interact with electric charge field of both
specimen nucleus and electrons
 These interactions are responsible for a multitude of signal types:
backscattered electrons, secondary electrons, X-Rays, Auger
electrons, cathadoluminescence.
 When a beam of electrons interacts with electric charge of a
specimen atom electron The result is a transfer of energy to the
specimen atom and a potential expulsion of an electron from that
atom as a secondary electron (SE).
 If the vacancy due to the creation of a
secondary electron is filled from a higher
level orbital, an X-Ray characteristic of that
energy transition is produced.

8. Hitachi S-4700.

9. Optical microscope

10. Comparison between SEM and
optical microscope

11. optical sem
Illumination Light beam Electron
beam
Wave length 2000-7000 .05A
A
Resolution Visible 50A
region on
2000A
Magnification 10x-20x 10x-2,00,00
0x
Depth of .1microns 30
focus mircometer
at 1000x

12. Transmission Electron Microscope (TEM)

13. Working
 TEMs work the same way except that they shine a beam of electrons (like
the light) through the specimen(like the slide).
 Whatever part is transmitted is projected onto a phosphor screen for the
user to see.
 The "Virtual Source" at the top represents the electron gun, producing a
stream of monochromatic electrons.
 This stream is focused to a small, thin, coherent beam by the use of
condenser lenses 1 and 2. The first lens largely determines the "spot size";
the general size range of the final spot that strikes the sample.
 The second lens actually changes the size of the spot on the sample;
changing it from a wide dispersed spot to a pinpoint beam.

14. Conti…..
 The beam is restricted by the condenser aperture (usually user selectable),
knocking out high angle electrons (those far from the optic axis, the dotted
line down the center)
 The beam strikes the specimen and parts of it are transmitted
 This transmitted portion is focused by the objective lens into an image
 Optional Objective and Selected Area metal apertures can restrict the
beam; the Objective aperture enhancing contrast by blocking out high-angle
diffracted electrons
 The image is passed down the column through the intermediate and
projector lenses, being enlarged all the way

15. Contd….
 The image strikes the phosphor image screen and light is generated,
allowing the user to see the image.
 The darker areas of the image represent those areas of the sample that
fewer electrons were transmitted through (they are thicker or denser).
 The lighter areas of the image represent those areas of the sample that
more electrons were transmitted through (they are thinner or less dense)

16. Differences

17. Auger Electron Spectroscopy
 When an electron beam bombards a solid surface; secondary electrons,
backscattered electrons, Auger electrons, and characteristic X-rays are
produced.

18. Auger Electron Spectroscopy

19. Auger process
 The basic Auger process starts with the removal of an inner shell
atomic electron to form a vacancy.
 Several processes are capable of producing the vacancy, but the
bombardment with an electron beam is the most common one.
 The inner shell vacancy is then filled by a second electron from a
higher shell. Energy will be simultaneously released.
 A third electron, the Auger electron, is ionized. The excessive
energy in this process is dissipated as kinetic energy of the Auger
electron.
 This process of an excited ion decaying into a doubly charged ion
by the ejection of an electron is called the Auger process.

20. A typical AES spectrum in the form of d N(E)/dE vs E.
Reference:
J. C. Vickerman, Surface
analysis – the principal
techniques, John Wiley & Sons

21. Contd…..
 electron spectroscopy is one of the most frequent analytical
methods for surfaces, thin-films, and interface compositions.
 This wide applicability arises from the combination of surface
sensitivity (0.5 to 10 nm), good lateral surface resolution (as little as
10 nm), periodic table coverage (except hydrogen and helium),

22. References
 FE-SEM Training Manual, Hitachi Scientific Instruments
 http://www.microscopy.ethz.ch/lens.htm
 Joseph Goldstein et al. “Scanning Electron Microscopy
 JEOL 6700 SEM User Manual
 http://www.cas.muohio.edu/~emfweb/EMTheory
/OH_Index.html
 http://www.gel.usherbrooke.ca/casino/What.html
 http://emalwww.engin.umich.edu/courses/semlectures/semlec.
 anchor659909 David C. Joy. “Low Voltage Scanning Electron
Microscopy”,

23. THANK YOU