The Science
Structures built on the scale of nanometers (a human hair is around 80,000 nanometers wide) could build new and improved light sources, sensors and computers. Scientists created a novel way to 3-D print on virtually any material or shape without costly and time-consuming masking steps. In a patterned sequence, researchers used a focused electron beam to dissociate surface-bound carbon- and metal-containing molecules and deposit them with precision. The result is a 3-D gold-carbon shape (shown here in a style reminiscent of Gandalf’s staff). They purified these structures in situ (inside the growth reactor) to remove carbon. They tested the resulting freestanding pure-gold architectures for plasmonic behavior—tiny, rapid waves of electron density created when light hits metal.
The Impact
The 3-D printing approach produces customized, from the bottom up, nanostructures on demand. The technology paves the way to maskless fabrication of custom 1-, 2-, and 3-D architectures on virtually any material and surface shape. The materials can have specific plasmonic behaviors. Plasmonic oscillations encode more data than possible with conventional technologies. Thus, this advance may speed the advent of novel light sources, sensor devices and ultra-dense information storage technologies.
Summary
Structures on the scale of nanometers—much smaller than wavelengths of light—may improve transmission of plasmons, or small waves of electron density created when light hits an electron conductor, such as a metal. To 3-D print nanoscale shapes with controlled properties, researchers integrated design, simulation and experiment. They used pattern sequencing to guide focused electron beams in inducing deposition of organometallic precursor molecules on a surface. Then, they removed residual carbon via in situ purification with water vapor to produce purely metallic freestanding 3-D nanostructures—an advance over previous 2-D nanoprinting with materials that contained significant carbon in addition to the desired metal. The structure that was produced—akin to the outline of up- and down-facing pyramids connected at their bases—demonstrated high plasmonic resonance at branches and tips. On-demand 3-D printing can take place on virtually any material and surface shape, pushing nanoscale optical, mechanical, magnetic and even multifunctional materials beyond current limits and paving the way to functional plasmonic architectures for next-generation photonic, photovoltaic and data-storage technologies.
Funding
The Oak Ridge National Laboratory portion of this research was supported by the Center for Nanophase Materials Sciences (CNMS), a U.S. Department of Energy Office of Science user facility at Oak Ridge National Laboratory. The University of Graz (CNMS users) research received funding from the European Union 7th Framework programme [FP7/2007-2013] (Enabling Science and Technology through European Electron Microscopy (ESTEEM2)). Individual researchers received support from Chemistry for ELectron-Induced NAnofabrication (CELINA) European Cooperation in Science and Technology (COST) Action, the Eurostars project triple-scanning microscope (TRIPLE-S), and the Chancellor’s Fellowship program at the University of Tennessee.
Publications
R. Winkler, F.P. Schmidt, U. Haselmann, J.D. Fowlkes, B.B. Lewis, G. Kothleitner, P.D. Rack, and H. Plank, “Direct-write 3D nanoprinting of plasmonic structures.” ACS Applied Materials & Interfaces 9(9), 8233-8240 (2017). [DOI: 10.1021/acsami.6b13062]
