Electron Microscopy SEM and TEM

Electron Microscopy SEM and TEM

Content 1. Introduction: Motivation for electron microscopy 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 4.1 Functional Principle 4.2 Examples 4.3 Comparing SEM and TEM 4.4 HAADF (High Angle Annular Dark Field Imaging)

1. Motivation for EM Resolution of light microscope is limited: λ sin Θ = 1. 22 D wavelenght of visible light less diffraction for smaller wavelenghts possible magnification: ~ 2 000 [1]

1. Motivation for EM Different approach: use electrons instead of light Access to much smaller wavelengths h λ = (3.7 pm for 100 kev) p electrostatic/electromagnetic t ti l t ti lenses instead of glass lenses possible magnification: ~ 2 000 000 [2]

2. Interaction with matter Backscattered electrons Secondary electrons Auger electrons Transmitted electrons specimen X Rays phonons

2. Interaction with matter Topography and composition Topography p Backscattered electrons Secondary electrons Structure and composition Composition Transmitted electrons X Rays

2. Interaction with matter 2 different approaches: Backscattered and Transmitted electrons secondary electrons SEM TEM

3. SEM Scanning Electron Microscopy

31Functional 3.1 Principle Electron source Condenser lens Scan coil Objective lens Specimen + Detectors 2 25 kv e

31Functional 3.1 Principle Electron gun e Condenser lens Scan coil Objective lens coils N coils Specimen + Detectors S N

31Functional 3.1 Principle Electron gun e Condenser lens Scan coil Objective lens Waveform generator Specimen + Detectors Detector signal

31Functional 3.1 Principle Electron gun Condenser lens e Scan coil coils coils Objective lens Specimen + Detectors f

31Functional 3.1 Principle Electron gun Condenser lens e Electron and Lightdetectors Scan coil Objective lens Specimen + Detectors

32Examples 3.2 Photonic crystal in silicon substrate Nanowires in silicon substrate WSI, D. Dorfner WSI, D. Pedone

33Energy 3.3 Dispersive Systems (EDX) e e Bremsstrahlung X ray Continuum Electron filling holes Characteristic X rays Information about chemical composition

33Energy 3.3 Dispersive Systems (EDX) Solidstate X ray Detector N 2 Si(Li) X ray coldfinger X ray creates hole/electron pairs (3.8 ev necessary per pair) Number of pairs and current are a measure for X ray energy

33Energy 3.3 Dispersive Systems (EDX) Alloy of aluminum and tungsten [3]

reminder 2 different approaches: Backscattered and Transmitted electrons secondary electrons SEM TEM

4. TEM Transmission Electron Microscopy

41Functional 4.1 principles Electron gun Condenser lenses Object Objective lens + intermediate lens + projective lense 50 400 kv e

41Functional 4.1 principles Electron gun Condenser lenses e Object Objective lens + intermediate lens + projective lense

41Functional 4.1 principles Electron gun e Condenser lenses Object ~100nm specimen Objective lens + intermediate lens + projective lense scattered direct beam

41Functional 4.1 principles Electron gun Condenser lenses Object Objective lens + intermediate lens + projective lense

42Example 4.2 Crossectional analysis of a conductor nanogap device WSI, S. Strobel WSI, D. Pedone

43Comparison 4.3 of SEM and TEM SEM: scans with a focused point TEM: illumantes whole sample

44High 4.4 Angle Annular Dark Field Imaging g( (HAADF) used in STEM (scanning transmission electron microscopy) rayleigh scattering at high angles Angle depends on the atomic number Z: 2 electron intesity: I Z by messuring the electron intensity, while scanning over the sample, information about the chemical compositio 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 tum htm wikipedia: http://en.wikipedia.org/wiki/electron_microscopy http://en.wikipedia.org/wiki/transmission_electron_microscope 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/eels Transmission Electron Microscopy, D. B. Williams and C. B. Carter Scanning electron microscopy and X ray Microanalysis, G. Lowes 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 tum edx htm