Patent ID: 8847173

Claim:
A gas field ion source comprising: an emitter tip configured to have a conductive needle-like tip and held in vacuum; an extraction electrode configured to have an opening at a position separated from the emitter tip in the tip direction of the emitter tip; a gas supply pipe configured to supply gas to the vicinity of the apex of the emitter tip; and an extraction voltage application means configured to apply an extraction voltage between the emitter tip and the extraction electrode, so as to form an electric field for ionizing the gas, wherein: at least the base body of the emitter tip is a single crystal metal, and the apex of the emitter tip has a pyramid shape or a cone shape having a single atom at the top, and the emitter tip with the single atom at the top has a shape configured to satisfy at least one of the following conditions: (A) a minimum threshold value voltage at which the single atom is field-evaporated is 11 kV; (B) the extraction voltage being the extraction voltage that is applied by the extraction voltage application means when an ion beam generated from the single atom in the case of ionizing helium gas satisfies conditions to form a best image is a minimum voltage of 10 kV; and (C) a maximum emission half-opening angle of the ion beam from the single atom in the case of ionizing helium gas is 0.7° .