Gas field ionization ion source, scanning charged particle microscope, optical axis adjustment method and specimen observation method

摘要

It is an object of the present invention to improve the stability of a gas field ionization ion source. A GFIS according to the present invention is characterized in that the aperture diameter of the extraction electrode can be set to any of at least two different values or the distance from the apex of the emitter to the extraction electrode can be set to any of at least two different values. In addition, solid nitrogen is used for cooling. According to the present invention, it is possible to not only let divergently emitted ions go through the aperture of the extraction electrode but also, in behalf of differential pumping, reduce the diameter of the aperture. In addition, it is possible to reduce the physical vibration of the cooling means. Consequently, it is possible to provide a highly stable GFIS and a scanning charged particle microscope equipped with such a GFIS.