Heat engines have been around since the 19th century but the new device, designed by Jong Hak Lee and Barbaros Oezyilmaz, is the first nanoscale version. The nanoengine is made of graphene and weakly chemisorbed ClF3 molecules, which act as the actuators in the system. A laser light beam is used as the “ignition plug”.

“When we expose the ClF3 molecules on the graphene engine to 532 nm wavelength laser light, these molecules sublimate – something that rapidly expands the volume at the interface between the graphene and the substrate it is grown on,” explains Lee. “This expansion, which generates high pressures (of around 23 MPa), creates a dome-like blister on the surface of the graphene (see figure). When the laser is switched off, the graphene returns to its original flat state. This elastic expansion and contraction of the graphene sheet is equivalent to the motion of a piston in an internal combustion engine.”

The size of the blister can easily be controlled by changing the ignition parameters, that is, the laser power, he explains. The estimated internal pressure per expansion cycle of the engine is about 106 Pa and the blister forms extremely quickly (in less than 0.001 s). The engine is also robust and does not degrade, even after 10,000 cycles.

“If we are able to use techniques already routinely employed in micro- and nano-electromechanical systems (MEMS and NEMS), and transfer the generated force to external moving parts, our new engine could be ideal in various applications, such as nanorobots and nanomachines,” Lee told nanotechweb.org. “We might even exploit the bulging motion of the engine as a pump or valve for nanofluidics.”

Graphene is the strongest material known to man, which makes it perfect as a nanoengine. “Whenever we talk about a nanomachine, we know that the engine is its most crucial part,” added Oezyilmaz. “Here, we have a simple and reliable nanodevice that produces no waste by-products, and which requires no complicated machinery to operate.”

This is also the first time that anyone has thought of using graphene as a nanoengine, so the research opens up (yet another) new field of research for the 2D carbon sheet, he says.

The engine is described in Nano Letters DOI: 10.1021/nl500568d.