LEIS

Question 1

sleection of scattering angle

Answer 1

> 90 degrees only one Ef available

Question 2

matrix effects?

Answer 2

oscillatory - quantum mechanical phase oscillations

Low work function - element lower energy of film and thus more ions are neutralised - can be overcome by using beams of different energies

Question 3

spectral resolution of leis

Answer 3

100 eV

Question 4

Altering energy resolution

Answer 4

Changing primary ion beam type - increase mass of ion beam (He - least, Ne - better but not all, Ar - better for those not present before but lost one of the peaks visible in Ne)

Question 5

Cleaning samples before LEIS

Answer 5

1. hydrogen plasma cleaning - good for removing oxides, v useful for metals
2. oxygen plasma cleaning - good for removing hydrocarbons and salts
3. Heating under vacuum - particularly useful for moisture in powder
4. Ligh tsputtering - v low Ar ion beam removes contamination from surface (5-10 sec)

Question 6

Applications

Answer 6

catalysis studies - atomic layer deposition films - measuring completion of layer
Quantification of layer coverage (plot areas under peaks in different samples, then compare and you can extrapolate coverage)
coatings in nanoparticles - measure thickness