1. Field Emission Measurements From Cesiated Titanium and Stainless Steel Electrodes K.Surles-law, P.Adderley, J.Brittian, D.Charles, J.Clark, J.Grames, J.Hansknecht, M.Poelker, M.Stutzman

2. Field Emission from 25deg Electrodes POISSON model of 25deg electrode E-fields shown are for V = -100kV

3. Field Emission Electrons are confined in a metal by a potential well Energy of electron insufficient to escape from metal Electron must be given extra energy to escape (thermal, photoemission) QM demonstrates the electron wavefunction attenuates rapidly outside potential barrier

4. Field Emission Application of external fields lowers and thins the potential barrier Fowler- Nordheim used quantum mechanics to demonstrate that some electrons can tunnel through the potential barrier and escape into the vacuum

5. Field Emission: Fowler-Nordheim Equation This is the Fowler-Nordheim expression for field emission E is the electric field (MV/m)  is the work function of the material (eV)  is the field enhancement factor A is the effective emitting area

6. Field Emission: Fowler-Nordheim Equation Plot of Fowler-Nordheim equation with b = 200. The electric field gradients were generated from POISSON model of the 25 degree electrode. The potential varied from 10 to 125kV

7. Field Emission: Fowler-Nordheim Equation One can use exponential form of FN to compare field emission from Ti and SS

8. Field Emission: Fowler-Nordheim Plot 210min of Cs for Ti and SS

9. Field Emission: Fowler-Nordheim Plot More interesting to plot ln(I/V^2) vs. 1/V The slope of the fitted data is proportional to the work function to the 3/2 power If work function changes, the slope of FN plot changes

10. Field Emission: Fowler-Nordheim Plot

11. Now let’s observe FN plots for Ti and SS with no Cs and 210min of Cs

12. Field Emission: Fowler-Nordheim Plot

15. Field Emission: Fowler-Nordheim Equation Next, decrease cathode-anode spacing Take FE data for Ti and SS with no Cs Compare FE vs. spacing: Is Ti or SS better, or same?