In accordance with the invention, there are electron emitters, charging devices, and methods of forming them. An electron emitter array can include a plurality of nanostructures, each of the plurality of nanostructures can include a first end and a second end, wherein the first end can be connected to a first electrode and the second end can be positioned to emit electrons, and wherein each of the plurality of nanostructures can be formed of one or more of oxidation resistant metals, doped metals, metal alloys, metal oxides, doped metal oxides, and ceramics. The electron emitter array can also include a second electrode in close proximity to the first electrode, wherein one or more of the plurality of nanostructures can emit electrons in a gas upon application of an electric field between the first electrode and the second electrode.