Materials and Nanotechnology
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MATERIAL MATTERS
Materials and Nanotechnology Alexandra Navrotsky The following is an edited transcript of a talk presented during the Franklin Institute Awards program in the symposium on “Materials Science and the Future of Nanotechnology,” co-hosted by Drexel University on April 25, 2002. I would like to address three issues in order of increasing generality. I first want to comment on structural chemistry, energetics, and materials in a world that now includes a much greater awareness of phenomena at the nanoscale. This also includes a more general definition, or a more general applicability, of nanomaterials, not just to conventional nanotechnology, but to other areas where the same sort of understanding is essential. The second is to talk about the impact of this work and this sort of thinking on education, particularly at the graduate and postdoctoral level. How do we best take advantage of changing needs to really get people thinking properly? The third is a more general potpourri of societal issues that are with us whether or not we have nanomaterials. These issues are, perhaps, brought to the fore by this latest industrial revolution.
Nanoscale Science Let us begin with the science. I am a solid-state chemist and thermodynamicist by training and practice. We are interested in the structure of the solid state and the energies that hold molecules or atoms together in solids. I sometimes say I count calories for a living, for the energetics of materials offers tremendous insight, particularly in a systematic way, into the bonding of atoms and molecules. The energies of phase transitions and chemical reactions whisper of the interatomic forces and bond energies that put atoms and molecules together. The entropies of materials sing of lattice vibrations, of magnetics, of electronic transitions, of order-disorder. These items, put together, determine the sorts of materials that we can have and do have, both in classical and nonclassical ways. An example in the classical equilibrium way is represented by “heat it and beat it” metallurgy and ceramic science, in which the 92
end product is essentially an equilibriumphase assemblage; then, in the nonclassical way, the preparative pathway still has to be energetically possible, but the product we obtain is a kinetic result of the pathway and not an equilibrium material. This liberation from the tyranny of equilibrium has led, in part, to the nanotechnology revolution. The fact that we can now make inorganic materials, as well as inorganic–organic composite materials, by processes such as layer-by-layer deposition, chemical vapor deposition, and laser ablation, means that the material we make is tailored by the process, just as a biochemical reaction is tailored by the available enzymes and reagents. One does not generally have to worry that we as organisms are metastable with respect to carbon dioxide and water. So, the richness of materials we can make depends on having control at the molecular level of the process that makes those materials. A number of acciden
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