"The hydrogen bond likes to have directionality in its orientation," Landman explained. "When you press on the superlattice, it wants to maintain the hydrogen bonds. In the process of trying to maintain the hydrogen bonds, all the organic ligands bend the silver cores in one layer one way, and those in the next layer bend and rotate the other way."
When the nanoclusters move, the structure pivots about the hydrogen bonds, which act as "molecular hinges" to allow the rotation. The compression is possible at all, Landman noted, because the crystalline structure has about half of its space open.
The movement of the silver nanocrystallites could allow the superlattice material to serve as an energy-absorbing structure, converting force to mechanical motion. By changing the conductive properties of the silver superlattice, compressing the material could also allow it be used as molecular-scale sensors and switches.
The combined experimental and computation study makes the silver superlattice one of the most thoroughly studied materials in the world.
"We now have complete control over a unique material that by its composition has a diversity of molecules," Landman said. "It has metal, it has organic materials and it has a stiff metallic core surrounded by a soft material."
For the future, the researchers plan additional experiments to learn more about the unique properties of the superlattice system. The unique system shows how unusual properties can arise when nanometer-scale systems are combined with many other small-scale units.
"We make the small particles, and they are different because small is different," said Landman. "When you put them together, having more of them is different because that allows them to behave collectively, and that collective activity makes the difference."
|Contact: John Toon|
Georgia Institute of Technology