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Spectroscopic techniques for studying (atoms, molecules, and) solids.

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Presentation on theme: "Spectroscopic techniques for studying (atoms, molecules, and) solids."— Presentation transcript:

1 Spectroscopic techniques for studying (atoms, molecules, and) solids

2 Lunds universitet / Fysiska institutionen Fysikexperiment i forskning och samhälle HT 2008 MAX-lab visit Suggested date: 2nd October, Meeting place: Department of Physics, Reception

3 Lunds universitet / Fysiska institutionen Fysikexperiment i forskning och samhälle HT 2008 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 don’t 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 method’s advantages and disadvantages? Regalskeppet Vasa – The Vasa warship

4 Lunds universitet / Fysiska institutionen Fysikexperiment i forskning och samhälle HT 2008 Photoemission spectroscopy

5 Lunds universitet / Fysiska institutionen Fysikexperiment i forskning och samhälle HT 2008 PES = Photoemission Spectroscopy = Photoelectron Spectroscopy XPS = X-ray Photoelectron Spectrocopy UPS = Ultraviolet Photoelectron Spectroscopy Photoemission spectroscopy (Photoelectron spectroscopy)

6 Lunds universitet / Fysiska institutionen Fysikexperiment i forskning och samhälle HT 2008 Reminder: characteristic x-rays in PIXE

7 Lunds universitet / Fysiska institutionen Fysikexperiment i forskning och samhälle HT 2008 Electron binding energies

8 Lunds universitet / Fysiska institutionen Fysikexperiment i forskning och samhälle HT 2008 Photoemission spectroscopy: an example

9 Lunds universitet / Fysiska institutionen Fysikexperiment i forskning och samhälle HT 2008 XPS: Elemental and chemical analysis, primarily of surfaces, but at high primary energies also of the bulk. Sandström et al., Nature 415 (2002) 893. Vasa: XPS results

10 Lunds universitet / Fysiska institutionen Fysikexperiment i forskning och samhälle HT 2008 X-ray absorption spectroscopy

11 Lunds universitet / Fysiska institutionen Fysikexperiment i forskning och samhälle HT 2008 XANES = X-ray Absorption Near Edge Structure = = NEXAFS = Near Edge X-ray Absorption Fine Structure (= XAS = X-ray Absorption Spectroscopy) X-ray absorption spectroscopy

12 Lunds universitet / Fysiska institutionen Fysikexperiment i forskning och samhälle HT 2008 Measure I 1 (h )-I 0 (h ). The number of decays (as a function of photon energy) is (exactly) proportional to the number of excitations (as a function of photon energy)! True absorption measurementElectron yield or fluorescence yield measurement How to measure x-ray absorption spectra (b)(a) Wood from the Vasa warship, G. Almkvist, Dissertation SLU, 2008

13 Lunds universitet / Fysiska institutionen Fysikexperiment i forskning och samhälle HT 2008 Reminder: characteristic x-rays in PIXE

14 Lunds universitet / Fysiska institutionen Fysikexperiment i forskning och samhälle HT 2008 X-ray Data Booklet, Thompson and Vaughan (Eds.), Lawrence Berkely National Laboratory, available from Fluorescence decay: probability  f  f +  a = 1 Sum rule for Auger and fluorescence decay  f and  f : Probability of fluorescence and Auger decays Auger decay: probability  a

15 Lunds universitet / Fysiska institutionen Fysikexperiment i forskning och samhälle HT 2008 X-ray emission spectroscopy

16 Lunds universitet / Fysiska institutionen Fysikexperiment i forskning och samhälle HT 2008 Reminder: characteristic x-rays in PIXE

17 Lunds universitet / Fysiska institutionen Fysikexperiment i forskning och samhälle HT 2008 M. Hollas, Modern Spectroscopy, John Wiley & Sons, New York XRF = X-ray fluorescence spectroscopy = = XES = X-ray emission spectroscopy X-ray emission spectroscopy

18 Lunds universitet / Fysiska institutionen Fysikexperiment i forskning och samhälle HT 2008 PIXE – excitation by protons or particles in the MeV range XRF/XES – excitation by electrons in the keV range XRF/XES – excitation by photons (typically from soft x-rays to  -rays) 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 advantages:electron easy to focus, even down to small beam sizes lab source disadvantages:very low sensitivity to low-Z elements high bremsstrahlung background advantages:lab source possible low background disadvantages:very low sensitivity to low-Z elements photons hard to focus down to small beam sizes most surface sensitive X-ray emission spectra: Comparison of different ways of exciting

19 Lunds universitet / Fysiska institutionen Fysikexperiment i forskning och samhälle HT 2008 Regalskeppet Vasa – The Vasa warship Recent 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


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