INTRODUCTION TO TEM (TEM-James Hillier and Albert prebus(1938)at university of Toronto)

TEM-James Hillier and Albert prebus(1938)at university of Toronto

1. INTRODUCTION TO TEM
PRESENT BY: GUIDED BY:
CHINMAYA KUMAR SARANGI Mr. P.K. MALLICK
REGN.NO.-06011054137

2. OUTLINES
•INTRODUCTION
•BASIC PRINCIPLE
•STRUCTURE OF TEM
•SAMPLE PREPARATION
•IMAGE FORMATION
•DIFFERENT TYPES OF TEM
•APPLICATIONS
•LIMITATIONS
•CONCLUSION

3. INTRODUCTION
•TEM-James Hillier and Albert prebus(1938)at university of Toronto.
•Microscopeis an optical instrument used to increase the visual angle of
near objects which are too small to be seen by naked eye.
•Two types of microscope are found such as : simple microscope and
compound microscope.
•Generally transmitted beams of electron passes through the specimen to
detect the physical and chemical appearance.

4. BASIC PRINCIPLE
•An accelerated electron beam
produced by electron gun, move
through the vacuum tube.
•The collimated high speed electron
bombarded on thin specimen.
•Transmitted beam gets deflected and
focused on image plate.
•Beams are condensed by electric
coils.
•Generally image formation is divided
into two types: dark field image and
bright field image
•The image formed due to TEM is
erect, virtual and enlarged .

5. PARTS OF TEM

6. Contd…
•Electron gun or Source: (filament, Wehnelt cap,
Extraction anode)
•Optical part: (condenser lens ,objective lens,
projector lens, electron lenses(magnetic coil ,poles,
pole pieces))
•Vacuum System: (rotary pump, turbo pump,
10
-4
-10
-7
Pa)
•Specimen Stage: (3.05mm grid dia,(Cu, Mo, Au,
Pt),side entry &top entry)
•Apertures: (annular metallic plates)

7. SAMPLE PREPARATION
Tissue Sectioning: 1.Use glass or diamond edge for thin section .
2.Generally for inorganic samples and aluminium.
3. Generally samples need C-Coating.
Sample staining: Used for biological tissue, compounds of heavy metals
such as Os, Pb,U bounded to biological tissues.
Mechanical milling: 1.Require diamond or cubic boron nitride for polishing.
2.Used for maintaining the constant sample thickness.
Etching methods: Chemical etching: used for samples which shows optical
transparency.
Ion etching: use the sputtering technique.

8. IMAGE FORMATION
A. BRIGHT FIELD IMAGE:It is formed
directly by absorption of electrons in the
sample. Thicker regions of the sample, or
regions with a higher atomic number will
appear dark, whilst regions with no sample
in the beam path will appear bright –
hence the term "bright field".
B. DARK FIELD IMAGE : Ifthe
reflections that are selected do not include
the unscattered beam (which will appear
up at the focal point of the lens), then the
image will appear dark wherever no
sample scattering to the selected peak is
present, as such a region without a
specimen will appear dark. This is known
as a dark-field image.

9. DIFFERENT TYPES OF TEM
(A)Cryo-TEM: specimen kept at liquid nitrogen or liquid He
temperature(-120˚c to -160˚c).
(B)STEM(scanning transmission electron microscope): additional
scanning coils used to deflect the beam.
(C)LVEM(Low voltage electron microscope): operated at low
electron accelerating voltage of 5 KV.
(D)HRTEM(High resolution transmission electron microscope):
images are formed due to differences in phase of electron
waves.

10. COMPARATIVE STUDY

11. APPLICATIONS
TEM is applied on biological, metallurgical field in a vast
manner such as:
•Study of tumer cells, biologically defective cell and cellular
structures.
•To study local structure, morphology of heavy metal
specimen.
•Study dispersion of multi-component polymers and their cross
sections.
•Crystallization of metallic alloys and semiconductors.
•Study of microstructure of composite materials.
•Study of local chemistry of material by use of EDS.

12. LIMITATIONS
•Thin samples are required for the micro structural
study.
•The instrumentation is complicated and needs high
vacuum.
•Sample preparation is very time consuming.
•Some materials, especially polymers are sensitive to
electron beam.
•Quantification is possible only for elements with
atomic number ≥ 11.

13. CONCLUSION
•TEM is an optical instrument which utilises the transmitted electron
beams.
•Electric coils are used to collimate the electron beams on the
sample.
•Diffraction phenomenon helps for the imaging method.
•Sample can be prepared by tissue sectioning, sample staining,
mechanical milling and etching.
•Images are generally are of bright field and dark field images.
•Advance form of TEM are cryo-TEM,HRTEM,LVEM,STEM etc.
•Heavy metals, composites, nano-materials study are done by TEM.
•Some materials such as polymers which are sensitive to electron
beams can’t be studied.
.

14. REFERENCES
1.L.E.Murr,ElectronOpticalApplicationsinMaterialsScience,McGraw-
Hill,1970
2.J.W.Edington,PracticalElectronMicroscopyinMaterialsScience,Van-
NostrandReinhold,1976.
3.D.B.Williams,PracticalAnalyticalElectronMicroscopyinMaterials
Science,PhilipsElectronic.
4.ASMhandbook-10
5.www.brightfieldmicroscope.com

15. THANKYOU