Possibilities

The global excitement over nanotechnology has resulted from several discoveries late in the twentieth century. Primary among them is the ability to manipulate individual atoms in a controlled fashion, a sort of atomic brick-laying made possible by techniques such as scanning probe microscopy (SPM). The ability to produce significant amounts of nanoparticles, such as silver and gold nanoparticles, has also fed the excitement. And the underlying fact that materials and devices on the scale of atoms and molecules have new and useful propertiesdue in part to quantum and surface effectscan also be cited. Nanoscale quantum dots with remarkable optical properties are a prime example.

Another major contributor to the interest in nanotechnology was the discovery of carbon nanotubes (CNTs), which are extremely narrow, hollow cylinders made up of carbon atoms. With the possibility of single- and multiple-walled varieties, each with a myriad of potential applications, carbon nanotubes offer many exciting prospects. The single-walled versions can have various geometries, as shown in Figure 14-1. Depending upon the exact orientation of the carbon atoms, the nanotubes can exhibit either conducting (metallic) or semiconducting properties. This fact, plus the ability to grow CNTs at specific locations and to manipulate them after growth, leads to optimism that CNTs will be important for electronics and sensors, either alone or integrated with each other.

Figure 14-1. Carbon nanotubes can exist in a variety of forms, which can be either metallic or semiconducting in nature. (Courtesy of NASA Ames Research Center, Moffett Field, CA.)

Figure 14-1. Carbon nanotubes can exist in a variety of forms, which can be either metallic or semiconducting in nature. (Courtesy of NASA Ames Research Center, Moffett Field, CA.)

For these and other reasons, the funding for nanotechnology has increased more than a factor of 5 in the period 1997 to 2003, and it is still increasing.!?] With the major increase in funding and the resulting scientific breakthroughs, there is great potential for improvements in existing sensors and for the development of really new sensors. One market study of nanoenabled sensors predicts sales near $0.6 billion by 2009.!4! Another is much more aggressive, saying that the nanotechnology sensor market will generate global revenues of $2.7 billion by 2008.!!! Whatever the actual outcome, it seems clear that the sales of nano-enabled sensors will grow significantly, and the growth is largely a result of the research investment in nanoscience and nanotechnology.

Relentless Integration

Historically, there has been a relatively clean separation between the materials, device, and systems levels. However, in recent decades, integration has been a major theme of technology. First, transistors were made into integrated circuits. Then such microelectronics were integrated with microoptics and micromechanics. The microtechnology devices were packaged individually and mounted on printed circuit boards. The recent use of flip chipswhere the chip is the packageand the placement of passive components within printed r-iiviiit- hr┬╗arHc aro hliirrinn fho rlaccir-al Hic+in/H-irm hohAioan rlo\/iroc anH c\/cfomc Tho

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