This source for charged particles comprises a sharply pointed tip (1) and an aperture (2) in a thin sheet of material. If the point of the tip (1) is made sharp enough, i.e., if it ends in a single atom or a trimer of atoms, the electric field existing between the tip (1) and the aperture (2) will cause a stream of electrons to be emitted from the tip (1), pass the aperture (2) and to continue as a beam (4) of free electroms beyond said aperture (2). The sheet (3) carrying the aperture (2) may, for example, be a carbon foil or a metallic foil, including gold.
The distance of the tip (1) from the aperture (2) is in the submicron range, and so is the diameter of said aperture (2). The distance is being held essentially constant by means of a feedback loop system. The divergence of the beam (4) is
If the source is operated in an ultra-high vacuum, the particle beam (4) will consist of free electrons, whereas, if the source is operated in a noble-gas atmospere, the beam (4) will consist of noble-gas ions. Both, the electron beam, as well as the ion beam, contains particles of a very low frequemcy.