1. Outline
• History(TEM)
• Background
• Components
• Specimen Preparation
• Imaging method
• Contrast formation
• Modifications
• STEM
• References

2. Scanning Transmission Electron
Microscope

13. Specimen Preparation
• Prepare a specimen with at least part of its
thickness at about 100 nm, depending on the
atomic weight of specimen materials.
• Pre-Thinning:
1st specimen less than 1mm thick is prepared
 Reducing the thickness to about 0.1mm before
final thinning to 100 nm thickness
• Final Thinning: involve
Ion Milling
Electrolytic Thinning
Ultramicrotomy

14. Ion Milling
• Uses a beam of energetic
ions to bombard
specimen surfaces to
reduce the thickness by
knocking atoms out of a
specimen
• General procedure
a) Dimple grinding
b) ion milling
 ion beam of 1–10 keV
bombarded
 specimen is placed in
the center at an angle of

15. Electrolytic Thinning
• Reducing specimen
thickness to 100nm
• General procedure
A specimen placed in
an electrochemical
cell as anode
A suitable reduce
specimen thickness
Common technique is
jet polishing
Electrolytic thinning
completed in 3–15
minutes.

16. Ultramicrotomy
• Reducing specimen
thickness to 100nm
• General procedure
A specimen is
mounted in a holder
against the cutting tool
The specimen should
be trimmed to have a
tip held against the
knife
The holder gradually
moves toward the
knife while it

21. STEM
• The basic principle of
image formation
fundamentally different
from static beam TEM
• small spot size is formed
on the sample surface
with the condenser
lenses
• This probe is scanned on
the sample surface
• the signal is detected by
an electron detector,
amplified and

22. Cont…
• DETECTOR
1. Small disk on the column axis which detects
the transmitted beam (BF STEM image) or
diffracted beam (DF STEM image)
2. Annular detector (a plate with a hole) which
detects all the diffracted beams except the
transmitted one (ADF STEM)
• Resolution
 limited by the spot size
have poorer resolution but better contrast

24. MATERIALS CHARACTERIZATION Introduction to Microscopic and
Spectroscopic Methods by Yang Leng -ISBN 978-0-470-82298-2