Lecture 6: Microscopy II

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Lecture 6 Microscopy II

• PHYS 430/603 material
• Laszlo Takacs
• UMBC Department of Physics

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Light microscopyThe principle and a commercial
scope
Useful sites http//www.microscopyu.com/articles
/optics/components.html http//em-outreach.ucsd.ed
u/web-course/toccontents.html
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Optical microscope (OM) and transmission electron
microscope (TEM)
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TEM modesComposite image, bright field image,
dark field image, selected area diffraction
Transmitted and diffracted beams
Diffraction pattern
First image
Bright field Bright field, transmitted electrons
only Dark field Selected area
diffraction pattern
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Comparing imaging and diffraction in a TEM.
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Electron diffraction from amonocrystal polycrys
tal glass
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How do scanning microscopies work?

• Measurement generates a value for every location
• Reflectivity of light (scanner)
• Ejected electrons (SEM)
• Current between tip and surface (STM)
• Force between tip and surface (AFM)
• Any quantity of interest

0 2 1 2 2 1 1 1
1 9 7 2 1 8 7 0
2 8 6 1 2 9 8 1
0 8 8 1 8 7 0 1
1 9 7 9 6 0 1 1
1 7 8 8 7 1 1 0
2 9 8 8 6 1 2 1
1 8 9 2 9 7 1 1
0 8 7 1 1 8 3 1
2 1 1 0 2 1 0 1
Interpret numbers as intensities for display or
printer. Digital image processing.
Image table of numbers
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The principle of STM
What exactly is measured? Tunneling current
probability of an electron tunneling out from
the surface electron density. Largest where
the atoms are, thus we see the atoms - kind of.
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48 Fe atoms forming a quantum collar on a Cu (1
1 1) surface. The inner rings are not from atoms
at the location.
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STM of Si (1 1 1) 7x7 reconstructed surface
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Surface structure

• Relaxation change of distance between the first
  few lattice planes. Typically, 10 change in the
  first, 1 in the second distance.
• Reconstruction change of the arrangement/
  symmetry of the arrangement of atoms.
• Reactive, usually picks up other atoms, e.g. O.

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• Notice that smaller circles represent atoms
  farther from the top layer.

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Low Energy Electron Diffraction

• Cu (1 0 0) ZnO (1 0 -1 0)

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Typical surface features after cleaving close to
a lattice plane or building up a crystal from the
gas phase
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• FeSi2 on a Si (111) surface
• Notice
• Reconstruction of Si
• Relationship between the orientations of
  substrate and coating
• Steps and kinks in the FeSi2 layers

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Contact-mode AFM It is a miniature profilometer,
directly measures height. Best for larger-scale
(at least a few nm) features.
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The principle of field ion microscopy
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Images taken by field ion microscope

• Ir (1 1 0) Pt (0 1 2)

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E. W. Müller, Platinum Metal Rev. 9 (1965) 84-89
Vacancies Dislocations on platinum tips