SEM and TEM SEM and TEM

El t Electron Microscopy  Mi SEM and TEM SEM and TEM

Content 1. Introduction: Motivation for electron microscopy 2 Interaction with matter 2. Interaction with matter 3. SEM: Scanning Electron Microscopy  3.1 Functional Principle 3.2 Examples 3.3 EDX (Energy‐Dispersive X‐ray spectroscopy) 4 TEM: Transmission Electron Microscopy 4. TEM: Transmission Electron Microscopy 4.1 Functional Principle 4.2 Examples 4.3 Comparing SEM and TEM           d 4.4 HAADF (High Angle Annular Dark‐Field Imaging)

1 Motivation for EM 1. Motivation for EM Resolution of light microscope is limited: λ sin Θ = 1.22 ⋅

D

• wavelenght of visible light wavelenght of visible light • less diffraction for smaller wavelenghts

¾ possible magnification: ~ 2 000 [ ] [1]

1 Motivation for EM 1. Motivation for EM Different approach: use electrons instead of light • Access Access to much smaller wavelengths to much smaller wavelengths h λ= (3.7 pm for 100 keV) p • electrostatic/electromagnetic  lenses    l t t ti / l t ti l instead of glass lenses

¾ possible magnification: ~ 2 000 000

[2]

2 Interaction with matter 2. Interaction with matter Backscattered electrons Secondary electrons y Auger electrons Transmitted electrons Transmitted electrons X‐Rays

specimen

phonons

2 Interaction with matter 2. Interaction with matter Topography and composition  Topography p g p y Structure and composition Structure and composition Composition

Backscattered electrons Secondary electrons y Transmitted electrons Transmitted electrons X‐Rays

2 Interaction with matter 2. Interaction with matter 2 different approaches: Backscattered and  B k d d secondary electrons

SEM

T Transmitted electrons i d l

TEM

3 SEM 3. SEM

Scanningg Electron Microscopy

3 1 Functional Principle 3.1 Functional Principle Electron source Condenser lens Scan coil Objective lens Specimen  + Detectors

2‐25 kV

e‐

3 1 Functional Principle 3.1 Functional Principle e‐

Electron gun Condenser lens Scan coil Objective lens Specimen  + Detectors

coils N N

S

coils

3 1 Functional Principle 3.1 Functional Principle Electron gun

e‐

Condenser lens Scan coil Objective lens Specimen  + Detectors

Waveform  generator Detector signal

3 1 Functional Principle 3.1 Functional Principle Electron gun

e‐

Condenser lens Scan coil Objective lens Specimen  + Detectors

coils

coils

f

3 1 Functional Principle 3.1 Functional Principle Electron gun Condenser lens Scan coil Objective lens Specimen  + Detectors

e‐

El t Electron‐ and d Lightdetectors

3 2 Examples 3.2 Examples Photonic crystal in silicon substrate

WSI, D. Dorfner

Nanowires in silicon substrate 

WSI, D. Pedone

3 3 Energy Dispersive Systems (EDX) 3.3 Energy Dispersive Systems (EDX) e‐

e‐ Bremsstrahlung

→ X‐ray Continuum

Electron filling holes

→ Characteristic X‐rays Information about  chemical composition p

3 3 Energy Dispersive Systems (EDX) 3.3 Energy Dispersive Systems (EDX) Solid state X‐ray Solid state X ray Detector Detector

N2

Si(Li) coldfinger X‐ray

‐X‐ray creates hole/electron pairs (3.8 eV necessary per pair) ‐Number Number of pairs and current are a measure for X of pairs and current are a measure for X‐ray ray energy energy

3 3 Energy Dispersive Systems (EDX) 3.3 Energy Dispersive Systems (EDX) Alloy of aluminum and  tungsten

[3]

reminder 2 different approaches: Backscattered and  B k d d secondary electrons

SEM

T Transmitted electrons i d l

TEM

4 TEM 4. TEM

Transmission Electron Microscopy

4 1 Functional principles 4.1 Functional principles Electron gun Condenser lenses Object Objective lens  + intermediate lens  + projective lense l

50‐ 400 kV

e‐

4 1 Functional principles 4.1 Functional principles Electron gun Condenser lenses Object Objective lens  + intermediate lens  + projective lense l

e‐

4 1 Functional principles 4.1 Functional principles e‐

Electron gun Condenser lenses ~100nm

specimen p

Object Objective lens  + intermediate lens  + projective lense l

scattered

direct beam

4 1 Functional principles 4.1 Functional principles Electron gun Condenser lenses Object Objective lens  + intermediate lens  + projective lense l

4 2 Example 4.2 Example Crossectional analysis of a  conductor nanogap device

WSI, S. Strobel

WSI, D. Pedone

4 3 Comparison of SEM and TEM 4.3 Comparison of SEM and TEM SEM: scans with a  focused point

TEM: illumantes whole  sample

4.4 High Angle Annular Dark‐Field   4 4 High Angle Annular Dark Field Imaging (HAADF) g g( ) ‐ used in STEM (scanning transmission electron microscopy) ‐ rayleigh scattering at high angles rayleigh scattering at high angles ‐Angle depends on the atomic number Z:  ‐electron intesity: I ∝ Z 2

¾ by messuring the electron intensity, while scanning over  the sample, information about the chemical compositio  can be aquired can be aquired

Thanks for your attention.

reference ‐ TUM chemie department:  http://www.ch.tum.de/em/emlabor/methoden/rem.htm http://www ch tum de/em/emlabor/methoden/tem htm http://www.ch.tum.de/em/emlabor/methoden/tem.htm ‐wikipedia: http://en.wikipedia.org/wiki/Electron_microscopy http://en wikipedia org/wiki/Transmission electron microscope http://en.wikipedia.org/wiki/Transmission_electron_microscope http://en.wikipedia.org/wiki/Scanning_Electron_Microscope http://en.wikipedia.org/wiki/Energy‐dispersive_X‐ray_spectroscopy http://en wikipedia org/wiki/HAADF http://en.wikipedia.org/wiki/HAADF http://en.wikipedia.org/wiki/EELS ‐ Transmission Electron Microscopy, D. B. Williams and C. B. Carter ‐ Scanning electron microscopy and X‐ray Microanalysis, G. Lowes g py y y , ‐ electron microscopy in solid state physics, H. Bethge and J. Heydenreich

reference [1] http://en.wikipedia.org/wiki/Optical_microscope [2] http://de.wikipedia.org/wiki/Elektronenmikroskop [3] http://www ch tum de/em/emlabor/methoden/rem edx htm [3] http://www.ch.tum.de/em/emlabor/methoden/rem‐edx.htm