Spectroscopic techniques for studying atoms, molecules, and solids

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Spectroscopic techniquesfor studying (atoms,
molecules, and) solids
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MAX-lab visit

• Suggested date
• 2nd October, 17.00
• Meeting place Department of Physics, Reception

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Regalskeppet Vasa The Vasa warship

• Discuss and try to understand your
  experimental method!
• Each group should explain their method to the
  other students, using the whiteboard and/or
  overhead transparencies. You should also outline
  what has been achieved using the method in
  conjunction with the Vasa research project.
• Hints
• What is/do you think is the principle of the
  method?
• How does the method work (practically)? (if you
  dont know make a suggestion)
• What kind of information do you obtain using the
  method?
• What kind of data do you get out?
• Why did one choose the particular method?
• What are the methods advantages and
  disadvantages?

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Photoemission spectroscopy
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Photoemission spectroscopy (Photoelectron
spectroscopy)
PES Photoemission Spectroscopy Photoelectron
Spectroscopy XPS X-ray Photoelectron
Spectrocopy UPS Ultraviolet Photoelectron
Spectroscopy
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Reminder characteristic x-rays in PIXE
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Electron binding energies
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Photoemission spectroscopy an example
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Vasa XPS results
XPS Elemental and chemical analysis, primarily
of surfaces, but at high primary energies also of
the bulk.
Sandström et al., Nature 415 (2002) 893.
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X-ray absorption spectroscopy
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X-ray absorption spectroscopy
XANES X-ray Absorption Near Edge Structure
NEXAFS Near Edge X-ray Absorption Fine
Structure ( XAS X-ray Absorption Spectroscopy)
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How to measure x-ray absorption spectra
True absorption measurement
Electron yield or fluorescence yield measurement
(b)
(a)
Measure I1(hn)-I0(hn).
The number of decays (as a function of photon
energy) is (exactly) proportional to the number
of excitations (as a function of photon energy)!
Wood from the Vasa warship, G. Almkvist, Dissertat
ion SLU, 2008
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Reminder characteristic x-rays in PIXE
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Probability of fluorescence and Auger decays
Fluorescence decay probability wf
Auger decay probability wa
Sum rule for Auger and fluorescence decay wf
and wf
wf wa 1
X-ray Data Booklet, Thompson and Vaughan
(Eds.), Lawrence Berkely National
Laboratory, available from http//xdb.lbl.gov
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X-ray emission spectroscopy
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Reminder characteristic x-rays in PIXE
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X-ray emission spectroscopy
XRF X-ray fluorescence spectroscopy XES
X-ray emission spectroscopy
M. Hollas, Modern Spectroscopy, John Wiley
Sons, New York 2004.
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X-ray emission spectraComparison of different
ways of exciting
PIXE excitation by protons or particles in the
MeV range
advantages
particles/protons easy to focus, even down to
small beam sizes
low bremsstrahlung background
disadvantages
very low sensitivity to low-Z elements
accelerator necessary
XRF/XES excitation by electrons in the keV range
advantages
electron easy to focus, even down to small beam
sizes
most surface sensitive
lab source
disadvantages
very low sensitivity to low-Z elements
high bremsstrahlung background
XRF/XES excitation by photons (typically from
soft x-rays to g-rays)
advantages
lab source possible
low background
disadvantages
very low sensitivity to low-Z elements
photons hard to focus down to small beam sizes
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Regalskeppet Vasa The Vasa warshipRecent
results

• Iron rather than sulphuric acid seems to be the
  real problem
• Iron ions catalyse the degradation of the
  cellulosis
• Two recent PhD theses, both available on the
  internet
• Gunnar Almkvist, Sveriges lantbruksuniversitet,
  Uppsala, 2008
• Yvonne Fors, Stockholms universitet, 2008