t he p rinciple of m icroscopy : sem, tem, afm

The Principle of Mi-croscopy : SEM, TEM, AFM

2014.02.25So-Yeon Park

vsoyounv@gmail.com

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