Transcript Electrons for SEM image

Tuesday seminar
The Principle of Microscopy :
SEM, TEM, AFM
2014.02.25
So-Yeon Park
[email protected]
Contents
• Introduction : Motivation for Microscopy
• Electron Microscopy
- interaction with matter
- SEM : Scanning Electron Microscopy
- TEM : Transmission Electron Microscopy
• AFM : Atomic Force Microscopy
Motivation of microscopy
Resolution of light microscope is limited
▶ possible magnification : ~ 2 000
Different approach : use electrons instead of light
▶ access to much smaller wavelengths
▶ electrostatic lenses instead of glass lenses
▶ possible magnification : ~ 2 000 000
Interaction with matter
Interaction with matter
SEM
Scanning
Electron
Microscopy
Electrons for SEM image
Secondary electrons (SE)
Backscattered electrons (BSE)
Electrons for SEM image
Electron beam
Electron beam
Electrons for SEM image
The intensity of emitted secondary electron for a line scan over some
different surface features
Edge effect
Functional principle
Functional principle
Functional principle
Functional principle
Functional principle
Electron detector
Main concern of SEM
High vacuum : to avoid crashing into air
Edge effect
Main concern of SEM
Charging effect
▶ non-conductive material
▶ no electrons escaping
from specimen
▶ Gold coating
Au, Pd, Pt
More electron
Diffraction
Gold coating
EBT2 with Au coating
Graduate School of Convergence Science and Technology. Seoul
National University
Example
EBT2
TEM
Transmission
Electron
Microscopy
Functional principle
Functional principle
Functional principle
Functional principle
Example
Lung cell
AFM
Atomic
Force
Microscopy
Principle
Tip
Position-sensitive
photodetector
Laser diode
Cantilever spring
Tip
by measuring forces between a sharp probe (<10 nm) and surface at very
short distance
Mode of operation
(1) Contact AFM
< 0.5 nm probe-surface separation
(2) Intermittent contact (tapping mode AFM)
0.5-2 nm
(3) Non-contact AFM
0.1-10 nm
Contact mode
The force on the tip is repulsive.
Advantage: fast scanning, good for rough samples
Disadvantage : at time forces can damage/deform
soft samples
Intermittent mode(Tapping)
The cantilever is oscillated at this resonant
Frequency.
Advantage: high resolution of samples that are
easily damaged, good for biological samples
Disadvantage : more challenging to image in
liquids, slower scan speeds needed
Non-contact mode
The force on the tip is attractive.
Advantage: VERY low force exerted on the sample,
extended probe lifetime
Disadvantage : lower resolution, usually need ultra
high vacuum to have best imaging
Limitations of AFM
Used to study a wide variety of samples.
The physical probe is not ideally sharp.
An AFM image dose not reflect the true sample
topography.
Limitations of AFM
For water droplet(물방울)
Example
Lung cell
Collagen matrices
EBT2 film
Thank you for attention :D