Now an entire new class of phase-change materials has been discovered by researchers with the Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley that could be applied to phase change random access memory (PCM) technologies and possibly optical data storage as well. The new phase-change materials – nanocrystal alloys of a metal and semiconductor – are called “BEANs,” for binary eutectic-alloy nanostructures.
“Phase changes in BEANs, switching them from crystalline to amorphous and back to crystalline states, can be induced in a matter of nanoseconds by electrical current, laser light or a combination of both,” says Daryl Chrzan, a physicist who holds joint appointments with Berkeley Lab’s Materials Sciences Division and UC Berkeley’s Department of Materials Science and Engineering. “Working with germanium tin nanoparticles embedded in silica as our initial BEANs, we were able to stabilize both the solid and amorphous phases and could tune the kinetics of switching between the two simply by altering the composition.”
Chrzan is the corresponding author on a paper reporting the results of this research which has been published in the journal NanoLetters titled “Embedded Binary Eutectic Alloy Nanostructures: A New Class of Phase Change Materials.”
Co-authoring the paper with Chrzan were Swanee Shin, Julian Guzman, Chun-Wei Yuan, Christopher Liao, Cosima Boswell-Koller, Peter Stone, Oscar Dubon, Andrew Minor, Masashi Watanabe, Jeffrey Beeman, Kin Yu, Joel Ager and Eugene Haller.
“What we have shown is that binary eutectic alloy nanostructures, such as quantum dots and nanowires, can serve as phase change materials,” Chrzan says. “The key to the behavior we observed is the embedding of nanostructures within a matrix of nanoscale volumes. The presence of this nanostructure/matrix interface makes possible a rapid cooling that stabilizes the amorphous phase, and also enables us to tune the phase-change material’s transformation kinetics.”
A eutectic alloy is a metallic material that melts at the lowest possible temperature for its mix of constituents. The germanium tin compound is a eutectic alloy that has been considered by the investigators as a prototypical phase-change material because it can exist at room temperature in either a stable crystalline state or a metastable amorphous state. Chrzan and his colleagues found that when germanium tin nanocrystals were embedded within amorphous silica the nanocrystals formed a bilobed nanostructure that was half crystalline metallic and half crystalline semiconductor.
"Rapid cooling following pulsed laser melting stabilizes a metastable, amorphous, compositionally mixed phase state at room temperature, while moderate heating followed by slower cooling returns the nanocrystals to their initial bilobed crystalline state,” Chrzan says. “The silica acts as a small and very clean test tube that confines the nanostructures so that the properties of the BEAN/silica interface are able to dictate the unique phase-change properties.”
While they have not yet directly characterized the electronic transport properties of the bilobed and amorphous BEAN structures, from studies on related systems Chrzan and his colleagues expect that the transport as well as the optical properties of these two structures will be substantially different and that these difference will be tunable through composition alterations.
“In the amorphous alloyed state, we expect the BEAN to display normal, metallic conductivity,” Chrzan says. “In the bilobed state, the BEAN will include one or more Schottky barriers that can be made to function as a diode. For purposes of data storage, the metallic conduction could signify a zero and a Schottky barrier could signify a one.”
Chrzan and his colleagues are now investigating whether BEANs can sustain repeated phase-changes and whether the switching back and forth between the bilobed and amorphous structures can be incorporated into a wire geometry. They also want to model the flow of energy in the system and then use this modeling to tailor the light/current pulses for optimum phase-change properties.
The in-situ Transmission electron microscopy characterizations of the BEAN structures were carried out at Berkeley Lab’s National Center for Electron Microscopy, one of the world’s premier centers for electron microscopy and microcharacterization.
Berkeley Lab is a U.S. Department of Energy (DOE) national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California for the DOE Office of Science. Visit our Website at http://www.lbl.gov.
For more information on the research of Daryl Chrzan, visit the Website at http://cms.mse.berkeley.edu/
For more information on the National Center for Electron Microscopy visit the Website at http://ncem.lbl.gov/
Lynn Yarris | EurekAlert!
Prediction: More gas-giants will be found orbiting Sun-like stars
22.02.2017 | Carnegie Institution for Science
NASA's fermi finds possible dark matter ties in andromeda galaxy
22.02.2017 | NASA/Goddard Space Flight Center
In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport
Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...
The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.
The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...
Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...
Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".
Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...
13.02.2017 | Event News
10.02.2017 | Event News
09.02.2017 | Event News
22.02.2017 | Power and Electrical Engineering
22.02.2017 | Life Sciences
22.02.2017 | Physics and Astronomy