Beams of electrons and ions are now fairly routinely focused to dimensions in the nanometer range. Since the beams can be used to locally alter material at the point where they are incident on a surface, they represent direct nanofabrication tools. The authors will focus here on direct fabrication rather than lithography, which is indirect in that it uses the intermediary of resist. In the case of both ions and electrons, material addition or removal can be achieved using precursor gases. In addition ions can also alter material by sputtering ͑milling͒, by damage, or by implantation. Many material removal and deposition processes employing precursor gases have been developed for numerous practical applications, such as mask repair, circuit restructuring and repair, and sample sectioning. The authors will also discuss structures that are made for research purposes or for demonstration of the processing capabilities. In many cases the minimum dimensions at which these processes can be realized are considerably larger than the beam diameters. The atomic level mechanisms responsible for the precursor gas activation have not been studied in detail in many cases. The authors will review the state of the art and level of understanding of direct ion and electron beam fabrication and point out some of the unsolved problems.

Dynamics of domain interfaces in a broad range of functional thin-film materials is an area of great current interest. In ferroelectric thin films, a significantly enhanced piezoelectric response should be observed if non-180 degrees domain walls were to switch under electric field excitation. However, in continuous thin films they are clamped by the substrate, and therefore their contribution to the piezoelectric response is limited. In this paper we show that when the ferroelectric layer is patterned into discrete islands using a focused ion beam, the clamping effect is significantly reduced, thereby facilitating the movement of ferroelastic walls. Piezo-response scanning force microscopy images of such islands in PbZr0.2Ti0.8O3 thin films clearly point out that the 90 degrees domain walls can move. Capacitors 1 microm2 show a doubling of the remanent polarization at voltages higher than approximately 15 V, associated with 90 degrees domain switching, coupled with a d33 piezoelectric coefficient of approximately 250 pm V-1 at remanence, which is approximately three times the predicted value of 87 pm V-1 for a single domain single crystal.

Ions of kiloelectron volt energies incident on a solid surface produce a number of effects: several atoms are sputtered off, several electrons are emitted, chemical reactions may be induced, atoms are displaced from their equilibrium positions, and ions implant themselves in the solid, altering its properties. Some of these effects, such as sputtering and implantation are widely used in semiconductor device fabrication and in other fields. Thus the capability to focus a beam of ions to submicrometer dimensions, i.e., dimensions compatible with the most demanding fabrication procedures, is an important development. The focused ion beam field has been spurred by the invention of the liquid metal ion source and by the utilization of focusing columns with mass separation capability. This has led to the use of alloy ion sources making available a large menu of ion species, in particular the dopants of Si and GaAs. The ability to sputter and to also induce deposition by causing breakdown of an adsorbed film has produced an immediate application of focused ion beams to photomask repair. The total number of focused ion beam fabrication systems in use worldwide is about 35, about 25 of them in Japan. In addition, there are many more simpler focused ion beam columns for specialized uses. The interest is growing rapidly. The following range of specifications of these systems has been reported: accelerating potential 3 to 200 kV, ion current density in focal spot up to 10 A/cm2, beam diameters from 0.05 to 1 μm, deflection accuracy of the beam over the surface ±0.1 μm, and ion species available Ga, Au, Si, Be, B, As, P, etc. Some of the applications which have been demonstrated or suggested include: mask repair, lithography (to replace electron beam lithography), direct, patterned, implantation doping of semiconductors, ion induced deposition for circuit repair or rewiring, scanning ion microscopy, and scanning ion mass spectroscopy.

We demonstrate the use of field-emission scanning electron microscopy for rapid imaging of small-diameter carbon nanotubes on insulating SiO 2 substrates. The image contrast stems from local potential differences between the nanotube and substrate and is insensitive to surface roughness and defects. This technique may also be used as a probe of the electrical connectivity of small structures without external leads.

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