1. X-ray absorption spectroscopy (XAS)
When x-ray (light) pass a distance x in material, the intensity drops
I(x) = I0 e-µx
µ = linear attenuation coefficient (depends on material and photon energy). The lost part is due to absorption. In the same material, the absorption will have very strong peaks when the photon energy exactly able to excite certain energy level to the unoccupied states. This is called absorption edges.
Dipole transition from core-levels to unoccupied valence bands

2. Elemental sensitivit
As in XPS, XAS core-level edges gives same elemental sensitivity.

3. Chemical sensitivity
XAS is a Dipole transition from core-levels to unoccupied valence bands, which is sensitive to chemical surrounding like XPS
Spectra show one kind of Fe nano-particles are Fe oxide

4. Ways to measure XAS
Different surface sensitivity
Saturation effects
And more ways…..?

5. X-ray Absorption Near Edge Structure
More details
X-ray Absorption Near Edge Structure
and
Extended X-ray Absorption Fine Structure
Better for very deep core-levels

6. X-ray magnetic circular dichroism (XMCD)
Selection rules
For left-circular
Dml = -1
Dms = 0
For right-circular
Dml = +1
Dms = 0

8. How synchrotron works hn e
Sychrotron light source is essential part of XAS (XMCD, EXAFS, etc), and very useful for XPS etc. It generate in forward direction of relativistic electrons with circular movement. hn e

9. The beamline SINS beamline
Gratings
RFM
Bending magetnic
VFM
HFM
The beamline is the bridge form synchrotron to workstation. It consists of many optics to let the light source to be monochromatic(change photon energy) and well focused on the sample.

10. The high intensity

11. Secondary Ion Mass Spectrometry
SIMS is based on the mass/charge ratio measurement of both atomic and molecular ions ejected under energetic particle bombardment.
1-10 keV
Static with low energy for surface. Dynamic with high energy for depth study

12. Three regimes for sputtering

13. Energy Distribution of Sputtered Particles

14. Sputter Yields
Yields depends on atomic number, displacement energy, matrix of the solids.

15. Quantitative description
The detected secondary ion intensity is described by:
I=- a T dN/dt= N A Y n a T
a: Ionization probability to certain charge state;
T: Instrumental transmission function;
N: density of surface atoms;
A: surface area with incident beam;
Y: sputter yield, number of secondary ions per incident ion.
n: the primary ion current
SIMS process can be seen as two stages: a. sputter
b. ionization.

16. A for different elements and their oxides
(Matrix Effect)

17. The choosing of ions
Oxygen bombardment increases the yield of positive ions and cesium bombardment increases the yield of negative ions. The increases can range up to four orders of magnitude.

18. Instrumentation
Ion Sources: discharge type ion gun, ion source using thermionic emitter, duoplasmatron type ion source
Mass Analyzers:Magnetic sector analyzer, Quadrupole mass analyzer, Time-Of-Flight mass analyzer
Ion Detectors: Faraday cup, Daly detector, channeltron

19. Duoplasmatron Mixture of hydrogen and CO2 gas For C ions
The duoplasmatron is the source of the ion beam. It consists of a highly charged, evacuated ``source-head'' which contains several components. The ions are produced within the source-head by bombarding atoms of the chosen gas (carbon for here) with electrons.
The free electrons are produced by boiling them off of a heated cathode which is charged, along with an intermediate electrode (IE) to kV. Atoms of the gas are injected into a chamber containing the cathode and a positively charged (-50 kV) anode. There is a 150 V potential difference between the cathode, the heated filament, and the anode. As the electrons fly toward the anode, they collide with the atoms of the gas, producing ions. An electron can either be absorbed by the atom thereby creating a negative ion, or it can knock an electron off of the atom producing a positively charged ion. The ions are then focused electrostatically and magnetically by the shape of the electric and magnetic fields into a dense plasma in the region just before the anode aperture. The plasma bulges slightly through the anode aperture forming an "expansion ball". The negative ions are then selected out by an extractor which is at ground potential. The ions form a beam flowing into the beam-tube toward the accelerator.
Duoplasmatron
Mixture of hydrogen and CO2 gas
For C ions

21. Typical spectrum
Typical spectrum
Depth Profiling