Smartphone need recharging? Someday you may be able to plug it into your shirt, say scientists who've develop a thin, 2D material that generates electricity during movement.

The new flexible, transparent material just one atom thick can produce electricity when it is stretched or bent, suggesting it could be sewn into clothing or incorporated in medical implants as a power source, they say.

"This material -- just a single layer of atoms -- could be made as a wearable device, perhaps integrated into clothing, to convert energy from your body movement to electricity and power wearable sensors or medical devices, or perhaps supply enough energy to charge your cell phone in your pocket," says James Hone of Columbia University, one of the leaders of a research team from Columbia and the Georgia Institute of Technology.

Walking, running or just everyday motions could be sufficient to generate electricity, the researchers say.

The material, molybdenum disulfide, is fussy about the way it wants to produce electricity, they report in the journal Nature.

When stacked in even numbers of layers, nothing happens, but when there are an odd number and the resultant assemblage is stretched in the correct direction, electricity flows, the researchers say.

That's because the material is highly polar, so even numbers of layers cancel each other out, they explain.

The energy is created by a phenomenon known as piezoelectricity, in which compressing or stretching an appropriate material results in its generating an electrical charge.

The finding of the effect in atom-thick materials like molybdenum disulfide creates the possibility of new kinds of mechanically controlled electronics, the researchers say.

"Proof of the piezoelectric effect and piezotronic effect adds new functionalities to these two-dimensional materials," says Georgia Tech researcher Zhong Lin Wang. "The materials community is excited about molybdenum disulfide, and demonstrating the piezoelectric effect in it adds a new facet to the material."

The researchers had theorized last year that molybdenum disulfide could generate electricity when compressed or stretched, but the latest work is the first instance of a demonstration in a lab.

The researchers say many 2D materials should have similar abilities and they have widened their studies to look for additional alternatives.

"This is the first experimental work in this area and is an elegant example of how the world becomes different when the size of material shrinks to the scale of a single atom," Hone says. "With what we're learning, we're eager to build useful devices for all kinds of applications."

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