Nanowires

Zhong Lin Wang

Semiconductor nanowires (NWs) are wires only a few nanometers in size that do not occur naturally. They represent an important broad class of nanometer-scale wire structures, which can be rationally and predictably synthesized in single-crystal form with all their key parameters controlled during growth: chemical composition, diameter, length, doping, and so on. Semiconductor NWs thus represent one of best-defined and best-controlled classes of nanoscale building blocks, which correspondingly have enabled a wide range of devices and integration strategies (Figure 13-5). For example, semiconductor NWs have been assembled into nanometer-scale field effect transistors (FETs), p-n diodes, light-emitting diodes (LEDs), bipolar junction transistors, complementary inverters, complex logic gates, and even computational circuits that have been used to carry out basic digital calculations. It is possible to combine distinct NW building blocks in ways not possible in conventional electronics. Leveraging the knowledge base of chemical modifications of inorganic surfaces can produce semiconductor NW devices that achieve new functions and produce novel device concepts.

Figure 13-5. Aligned semiconducting ZnO nanowire arrays. These wires are grown uniformly from a solid substrate, and their location and density can be defined by the deposited catalyst of gold.

Figure 13-5. Aligned semiconducting ZnO nanowire arrays. These wires are grown uniformly from a solid substrate, and their location and density can be defined by the deposited catalyst of gold.

Semiconducting oxide nanobelts (NBs) are another unique group of quasi-one-dimensional nanomaterials with well-defined side surfaces, which have been systematically studied for a wide range of materials having distinct chemical compositions and crystallographic structures. Beltlike, nanobelts (also called nanoribbons) have been synthesized for semiconducting oxides of zinc (Figure 13-6), tin, indium, cadmium, and gallium by simply evaporating the desired commercial metal oxide powders at high temperatures. These oxide nanobelts are pure, structurally uniform, single-crystalline, and largely free of imperfections; they have a rectangularlike cross section with controllable dimension. Field effect transistors and ultrasensitive nanosize gas sensors, nanoresonators, and nanocantilevers have also been fabricated based on individual nanobelts. Thermal transport along the nanobelt has also been measured. Nanobelts, nanosprings, and nanorings that exhibit piezoelectric properties have been synthesized that could eventually be used to make nanoscale traducers, actuators, and sensors.

Figure 13-6. Nanobelt of ZnO synthesized by a vapor-solid process. The nanobelt has a well-defined side surface, and it usually has a rectangular cross section.

Figure 13-6. Nanobelt of ZnO synthesized by a vapor-solid process. The nanobelt has a well-defined side surface, and it usually has a rectangular cross section.

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