Materials with nanoscale dimensions can have optoelectronic, chemical, and structural properties so different from their bulk counterparts that potentially they can provide solutions for the greatest energy production, storage, and delivery challenges of the future. The size-dependent properties of nanoparticles (0D), nanowires (1D), and nanosheets (2D) arise from the unique combination of high surface areas, charge confinement, and strength resulting from the perfection, geometry, and configurational diversity of materials, which at the same time have properties like molecules and macroscopic materials.
A great variety of synthesis techniques are employed to synthesize nanomaterials at ORNL. “Bottom up” synthesis techniques utilize nature’s desire to self-assemble materials into energetically favorable configurations. At low temperatures, scientists use chemical reactions to drive nanocrystalline quantum dots to form in a beaker, to self-segregate diblock polymers into nanoscale domains, and to harness bacteria’s natural ability to ferment reactants into nanoparticles.
At much higher temperatures, lasers, plasmas, and reactive gases are used to provide highly non-equilibrium conditions to rapidly condense or precipitate nanomaterials with metastable shapes and crystal structures. Nanoparticles of one material are introduced as “catalysts” to guide the growth of long nanotubes, nanowires, and nanobelts by exploring how bulk crystal growth techniques operate at nanoscale dimensions. To understand these processes, scientists use real-time imaging and spectroscopy with lasers, X-rays, electrons, and neutrons to provide kinetic growth data for comparison with computational simulations and atomistic modeling.
Alternatively, state-of-the-art nanofabrication tools are used at ORNL for the “top down” synthesis of nanomaterials by design. Using a combination of ingenious processing steps that include thin film deposition and chemical etching, substrates and films are lithographically patterned, cut, and etched into nanoscale dimensions with spatial control provided by the focused beams of electrons, ions, and light.
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