Nanotechnology: an Emerging Science

Nanotechnology/science studies materials on a nanoscale, ~1-100 nanometers (nm) in size. To put this scale in perspective, "Trying to find a nanoparticle on the surface of a soccer ball is just as hard as finding a soccer ball on the surface of the Earth" (Michael Hochella).

The reason that nanotechnology is so interesting is that materials at the nanoscale have entirely different properties than materials on the macroscale. All of the physical, chemical and biological properties and processes we are familiar with on scales of observation within day-to-day human perception may be fundamentally different on the nanoscale: conductivity of heat and electricity, magnetic properties, optical properties, physical strength of materials, reactivity and reaction rates....This has opened up entirely new lines of research to understand the occurrences, composition and structure, of nanoparticles and the fundamental principles that control chemical, physical and biological processes on the nanoscale.

A New Kind of Science

In a visionary talk to the American Physical Society at Caltech in 1959, Richard Feynman outlined an entirely new type of science in a talk There's Plenty of Room at the Bottom (pdf): "What I want to talk about is the problem of manipulating and controlling things on a small scale....I don't know how to do this on a small scale in a practical way, but I do know that computing machines are very large; they fill rooms. Why can't we make them very small, make them of little wires, little elements, and by little, I mean little?" (See the YouTube video Tiny Machines given by Dr. Feynman in 1984 at the Esalen Institute). A revolution was started. We now have the analytical tools needed to observe and characterize, theory and computational models to explain, and the ability to engineer and manufacture new types of materials on the nanoscale that have begun to realize Richard Feynman's vision. These are the foundations of nanoscience and nanotechnology.

Classical models of the properties of materials applied at the macroscale break down for very small nanoscale particles. The "rules" are different at the nanoscale:

• Materials (of the same composition and structure) may exhibit completely different properties for macro- v. nanoscale particles. The figure on the right shows how color varies for CdSe particles in suspension as a function of their particle size.
• At the nanoscale, surface areas (and therefore, surface energies) tend to be relatively large with respect to particle volume. Surface energies are usually ignored in classical thermodynamics (relative to Gibbs Free Energy), but may have a significant influence on reactivities and reaction rates at the nanoscale.
• At the nanoscale, inter-atomic forces often dominate materials, and therefore, applications of quantum mechanics (don't panic!) becomes the most important approach for interpreting and explaining material properties.
• The chemical environment on the nanoscale may be very different than the bulk chemical environment on the macroscale; the interfaces across boundaries between a nanoparticle (or even a living cell) and an ambient environment may very locally establish chemical potential gradients that influence nucleation, growth, and reaction rates that do not represent the physico-chemical conditions of the bulk system.

Nanoscience also addresses one of NSF's "10 Big Ideas: "Growing Convergent Research". Convergence research is a means of solving vexing research problems, in particular, complex problems focusing on societal needs. It entails integrating knowledge, methods, and expertise from different disciplines and forming novel frameworks to catalyze scientific discovery and innovation. NSF identifies Convergence Research as having two primary characteristics:

• Research driven by a specific and compelling problem. Convergence Research is generally inspired by the need to address a specific challenge or opportunity, whether it arises from deep scientific questions or pressing societal needs.
• Deep integration across disciplines. As experts from different disciplines pursue common research challenges, their knowledge, theories, methods, data, research communities and languages become increasingly intermingled or integrated. New frameworks, paradigms or even disciplines can form sustained interactions across multiple communities.

Dimensions of Nanotechnology/Science Research

Nanoscience explores the fundamental properties of matter in 1, 2, and 3 dimensions. It is primarily focused on changes with variation of size and dimension of particles on the nanoscale.

Nanotechnology is focused on manipulating matter on the nanoscale (nano-particles, rods, sheets, thin film coatings) to exploit changes in physical properties to create materials that will be beneficial to society.

Advances in nanoscience and nanotechnology require observations and measurements of chemical, electrical and mechanical properties on the nanoscale.

• Characterization of nanoparticles. The composition, atomic structure, size and shape, and surface properties all contribute to the physical, chemical and biological properties expressed by particles on the nanoscale. We now have an arsenal of analytical methods that allow us to observe materials down to the atomic scale: TEM, FE-SEM, AFM, XRD, and many more. Computational and theoretical approaches also contribute to the characterization of nanoparticles and predicting their behaviors.
• Nanomanufacturing. Whole new classes of materials are being designed and developed using the remarkable properties being discovered in nanoparticles. "Nanotechnology is helping to considerably improve, even revolutionize, many technology and industry sectors: information technology, homeland security, medicine, transportation, energy, food safety, and environmental science, and among many others" (see Benefits and Applications from the National Nanotechnology Initiative.
• Discovery of nanoparticles in natural systems. What are their composition and structure? What are their occurrences? How do these affect reactivities, reaction rates, energy and mass balance in natural systems? How are nanoparticles related to biological systems, as products of biogenic processes, or in their ability to influence biological (e.g., metabolic) functions? How do these impact global biogeochemical cycling. The role of nanoparticles, whether natural or introduced as anthropogenic materials, in the Earth system are largely unknown. "You can see a lot just by looking" (attributed to that great 20th Century philosopher, Yogi Berra). There is a great need to systematically survey and inventory the types of nanoparticles that abound in the solid Earth, soils, natural waters, and atmosphere.

Hochella et al. (2008) have defined a "cycle of nanogeoscience research (see Figure 1). This includes: a) experimental methods that synthesize nanoparticles of specific sizes and shapes for further study; b) experiments that simulate exposure to variable natural conditions; c) collection and analysis of nanoparticles using varied analytical methods; from the natural environment; d) discovery of nanoparticles in natural environments; which in turn, inform future experimental and analytical approaches. The study of nanoparticles must employ all the tools typically used by Earth scientists: field studies, analytical methods, experiment, theoretical and computational methods--but all finely focused on the nanoscale. (Hochella, M. F., Lower, S. K., Maurice, P. A., Penn, R. L., Sahai, N., Sparks, D. L., and Twining, B. S., 2008, Nanominerals, mineral nanoparticles, and earth systems: Science, v. 319, no. 5870, p. 1631-1635).