Two- and four-probe electrical measurements on individual tin oxide (SnO(2)) nanowires were performed to evaluate their conductivity and contact resistance. Electrical contacts between the nanowires and the microelectrodes were achieved with the help of an electron- and ion-beam-assisted direct-write nanolithography process. High contact resistance values and the nonlinear current-bias (I-V) characteristics of some of these devices observed in two-probe measurements can be explained by the existence of back-to-back Schottky barriers arising from the platinum-nanowire contacts. The nanoscale devices described herein were characterized using impedance spectroscopy, enabling the development of an equivalent circuit. The proposed methodology of nanocontacting and measurements can be easily applied to other nanowires and nanometre-sized materials.

This article is divided into four sections. The first section discusses FIB micro-and nanomilling and covers aspects such as pattern densities and milling threedimensional (3D) shapes. The second section covers FIB lithography, that is, Ga implantation or milling followed by a pattern transfer or growth step. The third section discusses FIB implantation for patterning and device fabrication. The fourth section highlights other fabrication techniques such as in situ micromanipulation. The article concludes with a discussion of possible future developments for enhancing the nanofabrication capabilities of FIB systems. FIB Micro-and NanomillingFIB milling, whether for sample preparation for electron microscopy or direct maskless patterning, is the most commonly used application of the systems and has been used to prepare a range of devices including lenses on the ends of fibers, 6 pseudo spin valves, 7 pillar microcavities, 8 and stacked Josephson junctions. 9 The smallest ion beam spot size is approximately 5-10 nm, which enables correspondingly small features to be patterned. The shape of an FIB cut is dependent on many factors, such as its geometry, milled depth, ion beam profile, and the redeposition of sputtered material. (Other factors, such as self-focusing, are discussed in the section "Micromachining 3D Structures with Complicated Shapes"). The combination of ion beam profile effects and sputter yield changes with the FIB angle of incidence causes rounding of the top edges of an FIB cut and the sidewalls to be inclined a few degrees from the perpendicular (the exact angles depend on the ion beam profile and milled depth). Redeposition may also cause the sidewalls to incline.As the milling depth increases, the probability of the sputtered material redepositing onto the sidewalls increases. If a line or hole is milled 10 to 15 times deeper than its width, redeposition results in V-shaped cross sections. The aspect ratio (depth to width) can be improved by using gas-enhanced etching (see the article by MoberlyChan et al. in this issue). Because the shape of a cut is dependent on the milled depth, the milling is referred to as 2D patterning if the sputtered depth is <100 nm, and 3D micromachining if the sputtered depth is >100 nm. FIB 2D PatterningFIB 2D patterning is used to pattern a diverse range of materials into dots, lines, and arrays. The 2D pattern densities MRS BULLETIN • VOLUME 32 • MAY 2007 • www/mrs.org/bulletin 417 AbstractThis article discusses applications of focused ion beam micro-and nanofabrication. Emphasis is placed on illustrating the versatility of focused ion beam and dual-platform systems and how they complement conventional processing techniques. The article is divided into four parts: maskless milling, ion beam lithography, ion implantation, and techniques such as in situ micromanipulation.

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