An electron emission element (20) includes a first electrode (30a) and a second electrode (40) which are arranged facing each other, an intermediate layer (50) that is provided between the first electrode (30a) and the second electrode (40), and an insulating layer (60) that is formed with a thickness d1 on a substrate (30). A level difference between the insulating layer (60) and the first electrode (30a) is smaller than the thickness d1 of the insulating layer (60).

An electron emission device having a narrow electron energy range and excellent electron emitting efficiency, and an electron microscope using the electron emission device. An electron emission device having a laminated structure in which a first electrode, an electron accelerating layer made of an insulating film, and a second electrode are laminated in this order, in which the second electrode through which electrons transmit and from whose surface electrons emit, and the energy width of the emitted electrons is 100 meV or more and 600 meV or less. For example, graphene having one or more layers and 20 layers or less can be used as the second electrode, and hexagonal boron nitride can be used as the insulating film.

An electron emission device having a narrow electron energy range and excellent electron emitting efficiency, and an electron microscope using the electron emission device. An electron emission device having a laminated structure in which a first electrode, an electron accelerating layer made of an insulating film, and a second electrode are laminated in this order, in which the second electrode through which electrons transmit and from whose surface electrons emit, and the energy width of the emitted electrons is 100 meV or more and 600 meV or less. For example, graphene having one or more layers and 20 layers or less can be used as the second electrode, and hexagonal boron nitride can be used as the insulating film.

In an embodiment an ionization detector includes a gate-insulator-substrate electron-emission structure (GIS-EE) configured to emit low-energy electrons, a sample chamber configured for at least one gas to be detected, the sample chamber being adjacent to the GIS-EE and a measuring unit configured to detect and/or select charged particles, wherein the charged particles are due to the emitted electrons and/or comprise the emitted electrons.

In an embodiment an ionization detector includes a gate-insulator-substrate electron-emission structure (GIS-EE) configured to emit low-energy electrons, a sample chamber configured for at least one gas to be detected, the sample chamber being adjacent to the GIS-EE and a measuring unit configured to detect and/or select charged particles, wherein the charged particles are due to the emitted electrons and/or comprise the emitted electrons.

The present disclosure relates to a field emission device that generates X-rays by emitting an electron beam, and an X-ray generating apparatus using the same, including a semiconductor substrate; a bottom electrode disposed below the semiconductor substrate; an insulating layer disposed above the semiconductor substrate; a gate electrode disposed on the insulating layer; and, a top electrode disposed on the gate electrode; wherein the gate electrode is composed of a material satisfying at least one of a first condition for work function, a second condition for Gibbs free energy of a redox reaction with the insulating layer, a third condition for sublimation energy, and a fourth condition for electron mean free path.