Magnetic microlens with an atomically sharp field emitter

The design and performance of a simple magnetic microlens for the focusing of electron beams are described. A chemically etched tungsten field emission tip was placed between the poles of two high strength permanent magnets, and the emitted electrons focused. By in situ sharpening of the tip, an emission angle of 2° was obtained and a 2σ spot size of 80 nm was achieved at a distance of 2 mm. By mechanically scanning a sample through the focused beam, images of a test sample were obtained.