electron tomography -a study of electron

2. ATalk On
ELECTRON
TOMOGRAPHY

3. Imaging by sections or sectioning, through the use of any
kind of penetrating wave
• Tomograph
• Tomogram
• Tomographic reconstruction

4. Superposition of
free tomographic
cross sections S1
and S2 compared
with the projected
image P.

5. Physical phenomenon Type of tomogram
X-rays CT hyperlinkct.docx
Radio-frequency waves MRI hyperlinkmri.docx
Muons Muon tomography hyperlinkmt.docx
Magnetic particles Magnetic particle imaging
hyperlinkmpi.docx
Gamma rays SPECT
Electron-position annihilation PET hyperlinkpet.docx
 archaeology
 Geophysics
 Oceanography
 Radiology
 Biology
 Materials science
 Astrophysics
 Quantum
 Information
 and other sciences…

6. ELECTRON TOMOGRAPHY

7.  Wave nature of electrons
 λ=h/mvλ=h/mv
 ½ mv½ mv22
=eV=eV
 λλ=h/=h/√2meV√2meV

11.  Electron beam hits the sample
 Producing electron and photon signals
 Collected by detectors and converted to a
voltage and amplified.
 Applied to grid of CRT
 Image is formed

12. Figures of Merit
-higher resolving power~0.1nm
-higher magnification~10,00,000X
-higher depth of field

17. Allows for the imaging of the surfaces of metals and semiconductors at
the atomic level.
Developed by Gerd Binnig and Heinrich Rohrer at the IBM Zurich
Research Laboratory in 1982.
The two shared half of the 1986 Nobel Prize in physics for developing
STM.
Binnig Rohrer

18.  In classical physics e flows are not possible without a direct connection
 On an atomic scale a quantum mechanical particle behaves in its wave
function.
 An electron will “jump” from one surface to the other of lower potential.
How tunnelling works?????
"... I think I can safely say that nobody
understands Quantum Mechanics"
Richard P. Feynman
L

19. Basic Principles of STM
Electrons tunnel between the tip and sample, a small current I is
generated (10 pA to 1 nA).
d ~ 6 Å
Bias voltage:
mV – V range
Transmission Probability: T ≈ 16ε(1 – ε)e-2κL

20. Two Modes of Scanning
Constant
Height Mode
Constant
Current
Mode
Usually, constant current mode is superior.

21. Instrumental Design: Controlling the
Tip
Raster scanning
Precise tip control is achieved with
Piezoelectrics
Displacement accurate to ± .05 Å

22.  Raster the tip across the
surface
 The tip-surface
separation is controlled
to be constant by
keeping the tunneling
current at a constant
value.
 The voltage necessary
to keep the tip at a
constant separation is
used to produce a
computer image of the
surface.

23. Advantages
No damage to the sample
Vertical resolution superior to SEM
Spectroscopy of individual atoms
Relatively Low Cost
Disadvantages
Samples limited to conductors and
semiconductors
Limited Biological Applications
Generally a difficult technique to
perform
Figures of Merit
Maximum Field of View: 100 μm
Maximum Lateral
Resolution: 1 Å
Maximum Vertical
Resolution: .1 Å

24. An STM representation of the surface of
silicon at the atomic level

25. Copper Surface

26. Iron on Copper

27. Iron on Copper

28. Carbon Monoxide Man: CO on Platinum

29. Xenon on Nickel

30. Wikipedia
 Google
 Scanning Tunneling Microscopy.” National Center for Photovoltaic at the National
Renewable Energy Laboratory. http://nrel.gov/measurements/tunnel.html
“The Nobel Prize in Physics 1986.” Nobel e Museum. http://www.
nobel.se/physics/laureates/1986/index.html
 STM Image Gallery. http://www.almaden.ibm.com/vis/stm/gallery.html