x-ray emission and absorption Flashcards
How does x-ray emission spectroscopy work?
Matter is bombarded with high energy electrons and the electrons in the atoms are excited to higher energy states before relaxing and emitting the excess energy
What can you use XRF for?
Determining stoichiometry and composition of a material
What is a major advantage to using XRF?
It can show non-stoichiometry as it gives a ratio between elements
What are the limitations of using XRF?
It cannot distinguish between lighter atoms
How does Energy Dispersive X-Ray Spectroscopy work?
Attaching XRF technology to an electron microscope
How does x-ray absorption spectroscopy work?
Matter absorbs x-rays which can cause ionisation of electrons, edges show the relative difference in energy between atomic energy levels
What are the disadvantages of using XAS technology?
Need a synchrotron energy source
What are the two types of XAS technology?
X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS)
What information does XANES data tell you?
Oxidation state of a given atom, nature of surrounding ligands, nature of bonding
What information does XANES not tell you?
Gives NO structural information
What does XANES measure?
Probes the local structure around metal centers and shows inter-shell electron transitions
How does EXAFS work?
Studies oscillations in absorption x-rays that are caused by interference from neighboring atoms
What modifications need to be made to the data before it can be analysed in EXAFS?
Fourier transform
What information does EXAFS tell you about a sample?
Atomic number of neighboring atoms (within 2) , how many neighboring atoms (within 1) and bond lengths (between 0.01)
What are some limitations of EXAFS data?
Can’t discriminate between atoms next to each other on the periodic table and gives no bond angles
