Normally, when a piece of metal - such as a paperclip - is bent, the change in shape becomes permanent. But, when heat is added to bent metal films having the right microstructure, the researchers found, the films return to their original shapes. The higher the temperature, the sooner the metal films revert.
"It's as though the metal has a memory of where it came from," said Taher A. Saif, a professor of mechanical science and engineering at Illinois, and senior author of a paper that describes the findings in the March 30 issue of the journal Science.
In the study, Saif and graduate students Jagannathan Rajagopalan and Jong H. Han explored aluminum films and gold films. The aluminum films were 200 nanometers thick, 50-60 microns wide and 300-360 microns long. The gold films were 200 nanometers thick, 12-20 microns wide and 185 microns long. The average grain size in the aluminum films was 65 nanometers; in the gold films, 50 nanometers.
"We found that the type of metal doesn't matter, said Saif, who also is a Willett Faculty Scholar and a researcher at the university's Micro and Nanotechnology Laboratory. "What matters is the size of the grains in the metal's crystalline microstructure, and a distribution in the size."
Grain sizes are typically one-third to one-half the thickness of a metal film. Raising the temperature by about 50 degrees Celsius causes the grains to grow larger.
If the grains are uniformly too small, the metal will be brittle and break while being bent. If the grains are uniformly too large, the metal will bend, but then stay in that position. To return to the initial shape, what's needed is a balance between brittleness and malleability.
That balance can be achieved through a combination of small and large grains, the researchers report.
Variations in the microstructure lead to plastic deformation in the larger grains and elastic accommodations in the smaller grains, Saif said. The bigger grains bend, but push and pull on the smaller grains, which become elastically deformed like a spring. If the metal is then left alone, the smaller grains will release this energy and force the bigger grains back to their original shapes over time. This local release of energy can be speeded up by applying heat.
Controlling the crystalline microstructure of thin films also could reduce energy loss in oscillators and resonators used in electronic circuits, Saif said. Oscillators and resonators are found in products ranging from air bag sensors and camcorders to digital projectors and global positioning systems.
"If the grains that constitute the metal films in these devices are between 50 and 100 nanometers, they can be very lossy," Saif said. "However, if we decrease the grain size, we can reduce much of the energy loss."
The work was funded by the National Science Foundation.
James E. Kloeppel | University of Illinois
SF State astronomer searches for signs of life on Wolf 1061 exoplanet
20.01.2017 | San Francisco State University
Molecule flash mob
19.01.2017 | Technische Universität Wien
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
20.01.2017 | Awards Funding
20.01.2017 | Materials Sciences
20.01.2017 | Life Sciences