2020 年 63 巻 1 号 p. 7-12
Recent progress of the microfabricated field emitter array (FEA) and the planar type electron source is overviewed. The volcano-structured double-gate FEA is promising for obtaining matrix driven and focused electron beams. The beam half angle less than one degree was achieved by using this structure. High current density of more than 25 A/cm2 is also achieved by using nickel-based alloy as an emitter material. A major breakthrough in the field of planar type electron sources is a using graphene as a top electrode in Metal/Oxide/Semiconductor type emitter, which is owing to the development of the direct deposition technique of graphene on insulating material. The emission efficiency of more than 30% is achieved. The graphene/oxide/semiconductor type electron source can emit electrons not only in poor vacuum but also in liquid. This unique feature enables new application, such as hydrogen production using non-electrolyte aqueous solution by injecting low energy electrons.