T he P rinciple of M icroscopy : SEM, TEM, AFM
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The Principle of Microscopy : SEM, TEM, AFM 2014.02.25 So-Yeon Park [email protected] Tuesday seminar
description
Tuesday seminar. T he P rinciple of M icroscopy : SEM, TEM, AFM. 2014.02.25 So- Yeon Park [email protected]. Contents. Introduction : Motivation for Microscopy Electron Microscopy - interaction with matter - SEM : S canning E lectron M icroscopy - PowerPoint PPT Presentation
Transcript of T he P rinciple of M icroscopy : SEM, TEM, AFM
The Principle of Mi-croscopy : SEM, TEM, AFM
2014.02.25So-Yeon Park
Tuesday seminar
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 imageElectron beam Electron beam
Electrons for SEM imageThe intensity of emitted secondary electron for a line scan over some different surface features
Edge ef -fect
Functional principle
Functional principle
Functional principle
Functional principle
Functional principle
Electron detec-tor
Main concern of SEM
High vacuum : to avoid crashing into air
Edge effect
Main concern of SEM
Charging effect ▶ non-conductive mate-rial ▶ no electrons escaping
from specimen ▶ Gold coating
Au, Pd, Pt
More electronDiffraction
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
Position-sensitive photodetector
Laser diode
Cantilever spring
Tip
by measuring forces between a sharp probe (<10 nm) and surface at very short distance
Tip
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/de-form 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 AFMUsed 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 AFMFor water droplet(물방울 )
Example
Lung cell
Collagen matricesEBT2 film
Thank you for attention :D
