Nanolithography and electron holography with ultrasharp field emitters

This paper reviews recent applications of ultrasharp field emitters in the characterization and modification of materials on the nanometer scale. Atomically defined 'ultrasharp' tips with radii < 10 nm can be routinely prepared by field emission and field ion microscopy techniques. In proximal probe lithography such a tip irradiates a resist material with low energy electrons. With the tip similar to 100 nm away from the surface, electron beams of extremely small spot sizes are achievable and structures with lateral dimensions of similar to 20 nm can be created in self-assembled monolayers. Limitations of the technique due to secondary electrons that are mirrored by the electric field between tip and surface an discussed. In low energy electron holography (kendroscopy) an atomically sharp field emitter acts as a point source for coherent electrons. If such a source illuminates an isolated molecule, interference between the part of the electron wave scattered by the atoms in the molecule and the unscattered part leads to the formation of a hologram. Structural information on the molecule is then obtained by numerical reconstruction of the hologram. Holograms of rod-like phthalocyaninato polysiloxane molecules are shown, reconstructed, analyzed and compared to numerical simulations. The potential of the techniques is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.