Now, Cornell researchers have developed a method to self-assemble metals into complex nanostructures. Applications include making more efficient and cheaper catalysts for fuel cells and industrial processes and creating microstructured surfaces to make new types of conductors that would carry more information across microchips than conventional wires do.
The method involves coating metal nanoparticles -- about 2 nanometers (nm) in diameter -- with an organic material known as a ligand that allows the particles to be dissolved in a liquid, then mixed with a block co-polymer (a material made up of two different chemicals whose molecules link together to solidify in a predictable pattern). When the polymer and ligand are removed, the metal particles fuse into a solid metal structure.
"The polymer community has tried to do this for 20 years," said Ulrich Wiesner, Cornell professor of materials science and engineering, who, with colleagues, reports on the new method in the June 27 issue of the journal Science. "But metals have a tendency to cluster into uncontrolled structures. The new thing we have added is the ligand, which creates high solubility in an organic solvent and allows the particles to flow even at high density."
Another key factor, he added, is to make the layer of ligand surrounding each particle relatively thin, so that the volume of metal in the final structure is large enough to hold its shape when the organic materials are removed.
"This is exciting," Wiesner said. "It opens a completely novel playground because no one has been able to structure metals in bulk ways. In principle, if you can do it with one metal you can do it with mixtures of metals."
Wiesner and two Cornell colleagues, Francis DiSalvo, the J.A. Newman Professor of Chemistry and Chemical Biology, and Sol Gruner, the John L. Wetherill Professor of Physics, as well as other researchers, report in Science how they used the new method to create a platinum structure with uniform hexagonal pores on the order of 10 nm across (a nanometer is the width of three silicon atoms). Platinum is, so far, the best available catalyst for fuel cells, and a porous structure allows fuel to flow through and react over a larger surface area.
The researchers began by mixing a solution of ligand-coated platinum nanoparticles with a block co-polymer. The solution of nanoparticles combines with just one of the two polymers. The two polymers assemble into a structure that alternates between small regions of one and the other, in this case producing clusters of metal nanoparticles suspended in one polymer and arranged around the outside of hexagonal shapes of the other polymer. Many other patterns are possible, depending on the choice of polymers.
The material is then annealed in the absence of air, turning the polymers into a carbon scaffold that continues to support the shape into which the metal particles have been formed. Wiesner and colleagues have previously used the carbon scaffold approach to create porous nanostructures of metal oxides.
The final step is to heat the material to a higher temperature in air to oxidize the ligands and burn away the carbon. Metal nanoparticles have a very low melting point at their surface, so the particles sinter together into a solid metal structure. The researchers have made fairly large chunks of porous platinum this way, up to at least a half-centimeter across.
In addition to making porous materials, the researchers said, the technique could be used to create finely structured surfaces, the key to the new field of plasmonics, in which waves of electrons move across the surface of a conductor with the information-carrying capacity of fiber optics, but in spaces small enough to fit on a chip.
Blaine Friedlander | EurekAlert!
How nanoscience will improve our health and lives in the coming years
27.10.2016 | University of California - Los Angeles
3-D-printed structures shrink when heated
26.10.2016 | Massachusetts Institute of Technology
Physicists from the University of Würzburg have designed a light source that emits photon pairs. Two-photon sources are particularly well suited for tap-proof data encryption. The experiment's key ingredients: a semiconductor crystal and some sticky tape.
So-called monolayers are at the heart of the research activities. These "super materials" (as the prestigious science magazine "Nature" puts it) have been...
Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.
This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...
Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion
Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
28.10.2016 | Power and Electrical Engineering
28.10.2016 | Life Sciences
28.10.2016 | Life Sciences