Up Close: Nanoscale Science Research Centers
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Up Close: Nanoscale Science Research Centers Julia M. Phillips The following article is an edited transcript based on the Symposium X presentation given by Julia M. Phillips of Sandia National Laboratories and director of the Center for Integrated Nanotechnologies. The presentation was delivered on March 30 at the 2005 Materials Research Society Spring Meeting in San Francisco.
Introduction Nanoscience has, in many ways, grown up in parallel with the Materials Research Society. Although “nanoscience” and “nanotechnology” are buzzwords that were “discovered” in Washington, D.C., and in the capitals of countries around the world a number of years ago, nanoscience has actually been developing for several decades. The emergence of nanoscience as a fascinating and fruitful area of research has occurred primarily for two reasons: (1) materials have new and unpredictable properties at the nanoscale; and (2) it is now possible to make things controllably on the nanoscale and to see them.
New and Unpredictable Properties When one works at very small length scales, in the range of a few atoms or a few molecules, one finds properties that cannot be predicted from what is seen at larger length scales. This happens for a number of reasons. For example, many of the atoms and molecules in these tiny structures are at surfaces and interfaces. They are not in the same environment that they would typically see at larger length scales. Therefore, they behave differently; for example, the chemical reactivity of nanoparticles is very different from their bulk counterparts. In addition, when we are working at these very small length scales, quantum effects come into play—effects that would be completely hidden at longer length scales. This gives rise to new properties. For example, the electronic and optoelectronic properties can be dramatically different; semiconducting quantum dots have different optical emission properties from those found in bulk semiconductors for the same general reasons that the energy levels for the “particle in the box” problem in ele44
mentary quantum mechanics depend on the dimensions of the box.
Ability to Work Efficiently at the Nanoscale The second reason for the increased emphasis on nanoscience over the past decade has been our evolving ability to make things on a very small scale and to do it in a controllable way. Along with that, we are able to visualize nanostructures with atomic resolution. Better yet, we are improving our ability to control structures at the nanoscale. Our ability to construct one-, two-, and three-dimensional nanomaterials reproducibly is improving at an impressive rate. A relatively early example is strained-layer superlattices, which came into being in the 1980s, fundamentally changing the way we use and control semiconductor structures. We can now construct molecular nanocomposites where, at the nanoscale, we controllably combine materials that historically have been viewed as very different, or even incompatible. For example, we can take a regular, nanostructured inorganic
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