International Business Machines Corporation

Werner Stocker

Heinz Schmid

Hans-Werner Fink

Roger Morin

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 electrons 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 &lt;2.degree.. 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 atmosphere, 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 frequency.

Low-voltage source for narrow electron/ion beams

A method for fabricating exactly aligned apertures for use in electron and ion microscopy involves the placing of a very sharply pointed tip (1) in front of a set of extremely thin, precisely spaced metal foils (3,5) in an atmosphere of heavy gas atoms. The application of an elevated voltage at the tip (1) will result in a sputtering operation to commence and erode the metal foils (3,5) at a location underneath the facing tip (1). The sputtering operation is continued until the first ions are detected to emerge on the far side of the lens structure (2).

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Wadenswil, Switzerland

Werner Stocker