Exploring Spectroscopic Techniques for Studying Materials: MAX-lab Visit on October 2

1. Spectroscopic techniquesfor studying (atoms, molecules, and) solids

2. MAX-lab visit Suggested date: 2nd October, 17.00 Meeting place: Department of Physics, Reception

3. 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 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?

4. Photoemission spectroscopy

5. Photoemission spectroscopy (Photoelectron spectroscopy) PES = Photoemission Spectroscopy = Photoelectron Spectroscopy XPS = X-ray Photoelectron Spectrocopy UPS = Ultraviolet Photoelectron Spectroscopy

6. Reminder: characteristic x-rays in PIXE

7. Electron binding energies

8. Photoemission spectroscopy: an example

9. 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.

10. X-ray absorption spectroscopy

11. X-ray absorption spectroscopy XANES = X-ray Absorption Near Edge Structure = = NEXAFS = Near Edge X-ray Absorption Fine Structure (= XAS = X-ray Absorption Spectroscopy)

12. How to measure x-ray absorption spectra (a) True absorption measurement (b) Electron yield or fluorescence yield measurement 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, Dissertation SLU, 2008

13. Reminder: characteristic x-rays in PIXE

14. 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

15. X-ray emission spectroscopy

16. Reminder: characteristic x-rays in PIXE

17. X-ray emission spectroscopy XRF = X-ray fluorescence spectroscopy = = XES = X-ray emission spectroscopy M. Hollas, Modern Spectroscopy, John Wiley & Sons, New York 2004.

18. X-ray emission spectra:Comparison 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

19. 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