New Tools For Nanoscience

Theory and modeling help explain nanoscale interactions.

Researchers at Oak Ridge National Laboratory, along with colleagues at other institutions, are synthesizing, characterizing, and manipulating nanoscale structures. While opening a broad range of opportunities in both fundamental and applied science, their work also poses formidable experimental challenges.

Stable position of a tetrafluorotetracyano-p-quinodimethane encapsulated in a single-wall carbon nanotube, as predicted by first-principles calculations.

Because the experimental observations are being made at the nanoscale, many such measurements cannot be interpreted without a theoretical model of the interaction between the measuring "device" and the measured structure.

For example, in a neutron scattering experiment on complex nanostructures, a model is required to describe interactions between neutrons and the atoms in the nanostructure in order to extract information about the location of the atoms. In another example, to understand the information obtained from an atomic force microscope moving across a surface, a model is needed to describe how the AFM tip interacts with the molecules on the surface.

Additionally, achieving high reproducibility and product quality in the large-scale manufacture of nanostructured materials, most likely by self-assembly, requires deep understanding of the connection between nanofabrication and the manipulation of macroscale processing variables, such as temperature, pressure, exposure time, and concentration. As a result of these and other considerations, from the beginning of the National Nanotechnology Initiative, theory, modeling, and simulation have been expected to play a very significant role in nanoscience and nanotechnology. The result has been strong interplay between theory and simulation on the one hand, and experiment on the other, leading to rapid advances in various areas of nanoscience, as well as improvements in both theory and experiment.

Binding of buckyballs, made of 60 carbon atoms, with DNA in aqueous solution, as predicted by an atomistic simulation. Such studies address fundamental aspects of the potential health impacts of nanoparticles released to the environment.

ORNL's Vision

ORNL's successful proposal to build the Center for Nanophase Materials Sciences articulated a vision in which a theory, modeling, and simulation group plays a major role in support of the experimental programs. The proposal also anticipated the development of new theoretical insights into complex nanoscale phenomena and new theoretical and simulation capabilities. The Nanomaterials Theory Institute is the realization of this vision.

The institute, which occupies the top two floors of the office block of the nanocenter, currently has space for 20 researchers and visitors, with the flexibility to expand to 36. The institute already has 10 user projects supported by NTI staff. The projects include the electronic structure of inorganic nanostructured materials, electron transport between inorganic surfaces and organic molecules (related to molecular electronics devices), self-assembly of polymer nanostructures, and the nanostructural properties and mechanism of an enzymatic catalyst that might be used to optimize the energy obtained from biomass. Additionally, several projects are methodological, aimed at developing new theories or algorithms.

The institute draws on ORNL's traditional strengths in materials modeling and theoretical and computational chemistry and physics. Expertise exists at the Laboratory in a number of areas relevant to theoretical and computational nanoscience. Supported by these capabilities, NTI researchers can model the most fundamental electronic structure level in which the quantum mechanical Schrödinger's equation is solved for electronic or spin degrees of freedom. Theorists can do atomistic simulation by describing systems at the level of atoms and molecules and the forces between them using force fields derived from more fundamental methods. Likewise, scientists can provide more coarse-grained descriptions, known as mesoscale simulation methods, which are used to describe systems with larger spatial structures and longer relaxation times, such as polymer nanostructures and biomolecular nanosystems.

NTI's User Projects

The 10 user projects that the NTI currently supports span the range of these methods. The institute is currently hiring staff to support existing and future user needs by ensuring representation of expertise in all of these theory areas.

Crystal structure of polyhedral silicon-oxygen nanocubes with organic tethers, as predicted by atomistic simulation.

Because state-of-the-art instrument development is a primary focus of the CNMS, the center also is securing the expertise needed to support new instrument design. Through collaboration with ORNL's Condensed Matter Sciences Division, the institute's researchers are focusing on developing the theoretical description of, and simulation methods for, neutron scattering from nanostructures, whether they are magnetic, metallic, organic, biological, or some combination of these. The theory support now being offered to the nanocenter's experimental users suggests that over the next few years, NTI researchers will have increasing opportunities to become intimately involved in user-driven experimental programs.

Nanoscience offers the possibility of bringing together into complex nanoscale structures materials that were once regarded as incompatible. For example, by working at the nanoscale level, inorganic surfaces might be chemically bonded to biological molecules to make new biomimetic devices in a controlled and reproducible fashion. The reason: at the nanoscale level the exploitation of the principles of physics, chemistry, and biology becomes feasible, as the similarities of physical, chemical, and biological systems come into play at the atomic and molecular level. Hence, in creating functional nanostructures, the nanoscientist has a palette to work with that is far broader than that of a traditional materials scientist, physicist, or chemist. The wide variety of nanoscale systems that researchers are developing provides both daunting challenges and exciting opportunities for the NTI theory community at CNMS—Peter Cummings, director, Nanomaterials Theory Institute, Center for Nanophase Materials Sciences

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