1. INELASTIC SCATTERING AND BEAM DAMAGE
In. D.B Williams, C. B. Carter Transmission Electron Microscopy. Springer.
CHEM E5225 Electron microscopy

2. WHAT IS INELASTIC SCATTERING?
Inelastic scattering process means energy-loss process
Transfers energy to specimen
Conventionally TEM uses only elastic signals (direct beam and diffracted beams)
Vast amount of information from inelastic scatter is often thrown away
Can be used in TEM
Allows more complete characterization of the specimen

3. WHAT CAUSES INELASTIC SCATTERING/ENERGY-LOSS?
When electrons from the beam are focused on a specimen, they penetrate and interact with atoms
The deeper the penetration, the grater the energy that may be lost
Produces range of scattering angles:
X-ray
Other secondary electrons
Collective interactions with many atoms or electrons
These three processes are discussed further in the following slides

4. 1. X-ray emission signal
The most important of the three inelastic processes
Gives information what elements of the specimen interacts with beam and their quantification
Principle:
The electrons in the electron cloud have a set of energy levels = electron shells
From closest to the nucleus outwards: K, L, M, N, O, P, Q
K shell has the highest ionization energy (more energy needed to remove an electron from this shell)
Characteristic X-rays are produced by electron transitions between the electron shells

5. Production of X-rays
Electron is removed from one of the inner shells of the atom by an electron from the beam
The atom regains stability when electron from an outer shell fills the inner shell ”hole”
X-ray photon is emitted 3 2 1

6. 2. Secondary-electron emission4
Electrons within the specimen that are ejected by the beam electron
Far less likely process than all other inelastic processes
”Free electrons” – not associated with specific atoms – no specific elemental information
Can only escape if they are near the specimen surface
(standard signal in SEM)
Can provide high resolution topographig images of the surface (STEM) 3 2 1
1: electron removed by beam
2: L1 electron fills the hole in K shell
3: Energy released is transferred in the L2,3 shell
4: Ejection as Auger electron (no x-ray emerges from the atom)

7. 3. Collective interactions with many atoms or electrons
Transferred energy is usually small
Collisions
Cathodoluminenscence: electrons and holes will recombine and give off light
Plasmons and phonons: collective oscillations of free electrons in gas or atoms in crystal lattice

8. BEAM DAMAGE
Inelastic collisions cause electron-beam damage – it’s the drawback!
Once your thin specimen is damaged, its structure is changed and is not representative
But beam damage can be used purposely for in-situ transformations
Three forms of damage:
Radiolysis: inelastic scattering breaks chemical bonds
Knock-on damage or sputtering: displacement of atoms from crystal lattice
Heating: phonons heat specimen and damages polymers and biological tissue
Be avare of the dangers