JIJITANG2014-08-30 8:27 AM


A crystal that can form a paper-like sheet just three atoms thick could potentially create electronics that would be as light and flexible as fibers.

This could lead to flexible electronic materials and perhaps make it possible to weave cellphones or GPS, for example, into a shirt.

Computer simulations show that this crystalline lattice has the remarkable ability to behave like a switch: it can be mechanically pulled and pushed, back and forth, between two different atomic structures—one that conducts electricity well, the other that does not.

“Think of it like flicking a light switch on and off,” says Karel-Alexander Duerloo, a Stanford University engineering graduate student and first author of an article in Nature Communications.

So far this discovery only exists as a computer simulation. But coauthor and team leader Evan Reed, an assistant professor of materials science and engineering, hopes the work will inspire experimental scientists to fabricate this super-thin crystal for electronic devices.

Theoretically, such electronic materials have the potential to reduce battery-draining power consumption in existing devices such as smart phones. This new, power-efficient material could also make it possible to create “smart” clothing.

Duerloo says this switchable material is formed when one atomic layer of molybdenum atoms gets sandwiched between two atomic layers of tellurium atoms.

Molybdenum and tellurium are elements that are currently used as additives for making alloys, such as steel. Tellurium is also an important component of many modern solar cells.

In his simulation, Duerloo relied on the fact that molybdenum and tellurium form a sheet-like crystal lattice that is just three atoms thick. Notably, this atomic sandwich can form different crystalline structures that have useful properties: in one structure this lattice easily conducts electricity; in the other configuration it does not.

Duerloo’s simulations show that it takes just a tiny effort to toggle the atomic structure of this three-layer amalgam from a non-conductive state into a conductive state. A gentle push switches the material back to the off state.

These simulations, as yet unsupported by experimental confirmation, are at the leading edge of a new branch of materials science that delves into the behavior of monolayer substances.

The first and most famous monolayer is graphene, which was first observed in 2004. Graphene is a layer of carbon atoms that form a lattice that resembles chicken wire. Although it is just one atom thick, graphene is incredibly strong. A sheet of graphene could bear the weight of a cat without breaking.

Graphene is also electrically conductive. That makes it potentially useful as a light, low-power electronic component.

To help find the most promising materials from a vast universe of molecular structures, a new discipline is rising: computational materials science.

“We’re like the advance scouts that survey the terrain and look for the best materials,” Reed says.

Now that they have simulated the potential of this molybdenum-tellurium crystal, the Stanford researchers (the third team member is graduate student Yao Li) hope experimental scientists will explore possible uses of this three-atom-thick switch.

“No one would have known this was possible before because they didn’t know where to look,” Duerloo says.

Original Article: 
《Structural phase transitions in two-dimensional Mo- and W-dichalcogenide monolayers》, Published on Journal 《Nature》in July 2014. 






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