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Overview Notebook

MSE672: Introduction to TEM

1.6. Overview Notebook#

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MSE672: Introduction to Transmission Electron Microscopy

Spring 2024

Gerd Duscher Khalid Hattar
Microscopy Facilities Tennessee Ion Beam Materials Laboratory
Materials Science & Engineering Nuclear Engineering
Institute of Advanced Materials & Manufacturing
The University of Tennessee, Knoxville

1.6.1. Import packages for figures and#

First we load the code to make figures from pyTEMlib

1.6.1.1. Check Installed Packages#

import sys
import importlib.metadata
def test_package(package_name):
    """Test if package exists and returns version or -1"""
    try:
        version = importlib.metadata.version(package_name)
    except importlib.metadata.PackageNotFoundError:
        version = '-1'
    return version

if test_package('pyTEMlib') < '0.2023.1.0':
    print('installing pyTEMlib')
    !{sys.executable} -m pip install  --upgrade pyTEMlib -q
print('done')

done

1.6.1.2. Load the plotting and figure packages#

%matplotlib widget

import matplotlib.pylab as plt
import numpy as np
import sys
if 'google.colab' in sys.modules:
    from google.colab import output
    output.enable_custom_widget_manager()

import pyTEMlib.animation as animate

You don't have igor2 installed.     If you wish to open igor files, you will need to install it     (pip install igor2) before attempting.
You don't have gwyfile installed.     If you wish to open .gwy files, you will need to      install it (pip install gwyfile) before attempting.
Symmetry functions of spglib enabled
Using kinematic_scattering library version {_version_ }  by G.Duscher

1.6.2. History#

1925

Louis de Broglie

electron has a wavelike character with a wavelength less than light

1927

Davisson and Germer

classic electron diffraction experiments

Thompson and Reed

1932

Knoll and Ruska

first electron lenses and first image (Noble Price 1986)

1936

Vickers

first commercial electron TEM

1939

Siemens and Halske

first usable and profitable TEM

1949

Heidenreich

first transparent metal foil (first materials science result)

2000

Krivanek

(STEM) first prototypes for spherical aberration

Rose/Heider

(TEM) objective-lens correctors

2007

Krivanek

(STEM) first prototypes for fifth order

Rose/Heider

(TEM) aberration objective-lens correctors

1.6.3. Available TEMs#

TEMs are now available from many sources ( for example: FEI, Hitachi, JEOL, Nion).

1.6.4. TEMs available in the UTK/ORNL area.#

  • Zeiss Libra200 MC at UTK

  • ThermoFischer Spectra300 at UTK 5th order corrected

  • Nion UltraSTEM 100 at ORNL/CNMS, 5th order corrected

  • JEOL 2100 at ORNL 3rd order corrected

  • FEI Titan at ORNL/CNMS, 3rd order corrected

  • JEOL ARM at ORNL/CNMS, 5th order corrected

  • Nion UltraSTEM 200 at ORNL, 5th order corrected

  • NionMACSTEM 100 at ORNL, 5th order corrected

  • FEI Talos F200X S/TEM at ORNL,

  • Hitachi 300 at ORNL

The dedicated STEMs are all equipped with a spherical aberration corrector by Nion. There are also four CEOS (Haider and Rose) aberration corrected TEMs (FEI Titan and JEOLs).

1.6.5. Electron Meets Matter#

To gather information about a sample the electron has to interact with this sample, otherwise it would be invisible. There is a whole zoo of interactions. The primary and most important interaction for TEM imaging is (elastic and inelastic) scattering. All the other processes are secondary (for example: X-ray emission). image.png

1.6.6. Diffraction and Imaging#

No interaction

Most electrons do not interact with a thin specimen at all.

Interaction without energy transfer

Elastic scattering is the basis for diffraction and imaging.

Interaction with energy transfer

Inelastic scattering causes a diffuse background in images and diffraction pattern, but can be used for analytical TEM.

1.6.7. Modes of a TEM#

Some techniques:

SAED

selected area electron diffraction

CBED

convergent beam electron diffraction

Kikuchi

Kikuchi diffraction

Fresnel

Fresnel diffraction

CTEM

conventional transmission electron microscopy

BF

bright field imaging

DF

dark field imaging

HRTEM

high resolution (phase contrast)

SE

secondary electron imaging

BE

backscatter electron imaging

Lorentz

Lorentz microscopy

HAADF

high angle annular dark field imaging (Z-contrast)

1.6.8. Modes of a TEM/STEM#

illumination

objective

projective

I projective II

TEM

TEM

Mag

Image

ESI

Nanoprobe

Spot

Mag

Image

ESI

LowMag

TEM

LowMag

Image

ESI

Microprobe

Spot

LowMag

Image

ESI

SAED

TEM

Mag

Diffr

ESI

Low angle diffraction

TEM

LowMag

Diffr

ESI

CBED

Spot

Mag

Diffr

ESI

LACBED

Spot

LowMag

Diffr

ESI

Spectroscopy

TEM

Mag

Image

EELS

Spectroscopy

Spot

Mag

Diffr

EELS

STEM

Spot

Mag

Diffr

ESI

STEM-LM

Spot

LowMag

Diffr

ESI

STEM-SI

Spot

Mag

Diffr

EELS

image.png

The main ingredients in an TEM method are how is the sample illuminated (condenser) and how are the electrons sorted and selected (projector and spectrometer).

1.6.9. Diffraction and Imaging#

Even though we are dealing with relativistic and quantum mechanical principles the geometric ray diagrams are essential for an understanding of how to set up a TEM mode.

# ---INPUT------ #
focal_length = 1.3
# -------------- #

animate.geometric_ray_diagram(focal_length, magnification=True)

1.6.10. Basics of Diffraction#

  • Diffraction is the direct result of the interaction (without energy transfer) of electrons and matter.

  • Kinematic diffraction theory describes only the Bragg angles (the position) but not the intensity in a real electron diffraction pattern.

  • Dynamic theory is responsible for the intensity distribution in an electron diffraction pattern

1.6.11. Diffraction and Imaging#

  • To form an image from a diffraction pattern only a Fourier transformation of parts of the diffraction pattern is needed.

  • Any image in a TEM can be described as Fourier filtering, because we select beams. The knowledge of which and how many diffracted beams contribute to the image formation is crucial for interpretation.

  • Because the intensity of selected diffracted beams is necessary to calculate image intensities, dynamic theory is necessary.

  • Understanding diffraction theory of electrons is the core of the analysis of TEM data.

1.6.12. Electron Energy-Loss Spectroscopy#

image.png

No Energy Transfer

The zero-loss peak is caused by electrons of the acceleration energy which apparently did not loose any energy.

Little Energy Transfer: 1-70 eV

The valence-loss region shows intraband, interband, and plasmon transitions.

High Energy Transfer: above 70eV

The core-loss region contains excitation from the atom core levels into the conduction band appear as saw tooth like edges.

1.6.13. Secondary Processes#

After excitation through the incident electrons, the atoms will fall back to their ground state and emit the gained energies as photons (in the light and X-ray region) or (Auger-) electrons. These secondary processes are also used for analytical analysis such as:

  • Energy Dispersive X-Ray Spectroscopy (EDS)

  • Auger-Spectroscopy

  • Cathodoluminescence

1.6.14. Drawbacks of Transmission Electron Microscopy#

  • Sample preparation is tedious and can induce artifacts.

  • Sampling: Only a small area is getting investigated.

  • Electron beam damage

  • Sample contamination

  • Image/data interpretation is not easy:

  • A micrograph is a projection only, and high resolution images must be simulated.

  • The instruments are under vacuum and are generally fragile, which results in long experimental times.

1.6.15. Summary#

  • The TEM enables many powerful techniques.

  • The TEM is only useful to solve problems needing spatially resolved information

  • The TEM is most powerful with complementary (less spatially resolved) techniques

1.6.15.1. Outlook#

  • The interpretation of selective area diffraction.

  • Next: Geometric Ray Optics.

1.6.15.2. Read your Assignment#

Carter and Williams: Chapter 6

Contents