Ion source having secondary electron enhancing electrode

An ion source, comprising:

• a shell defining an ionization chamber, a gas inlet, and an ion output hole;
• an ion electrode located adjacent to the ion output hole;
• and
• a field emission device located in the ionization chamber, and comprising:
• an insulative substrate;
• an electron pulling electrode located on a surface of the insulative substrate;
• a secondary electron emission layer located on a surface of the electron pulling electrode;
• a first dielectric layer, wherein the first dielectric layer has a second opening;
• a cathode electrode located apart from the electron pulling electrode by the first dielectric layer, wherein the electron pulling electrode is located between the insulative substrate and the cathode electrode, the cathode electrode has a surface oriented to the electron pulling electrode, and the cathode electrode has a first opening, the first opening and the second opening have at least one part overlapping;
• a gate electrode located apart from and insulated from the cathode electrode by a second dielectric layer, the second dielectric layer having a third opening in alignment with the first and second openings;
• a secondary electron enhancing electrode located between the second dielectric layer and the gate electrode and insulated from the gate electrode by a third dielectric layer;
• the secondary electron enhancing electrode has a fourth opening in alignment with the third opening;
• an inner surface of the fourth opening is coated with a secondary electron emission material;
• and
• an electron emission layer located on the surface of the cathode electrode oriented to the electron pulling electrode.