Nano-Sized Light Mill Drives Microdisk

Researchers have created the first nano-sized light mill motor whose rotational speed and direction can be controlled by tuning the frequency of the incident light waves.

STM image shows a gammadion gold light mill nanomotor embedded in a 300 nanometers thick square-shaped silica microdisk. The inset shows a magnified top view of the light mill. (Image: Zhang group)

According to the group with the US Department of Energy’s (DoE) Lawrence Berkeley National Laboratory (LBNL) and the University of California (UC) Berkeley, this new light mill will open the door to a broad range of valuable applications, including a new generation of nanoelectromechanical systems (NEMS), nanoscale solar light harvesters, and robots that can perform in vivo manipulations of DNA and other biological molecules.

"We have demonstrated a plasmonic motor only 100 nanometers in size that when illuminated with linearly polarized light can generate a torque sufficient to drive a micrometer-sized silica disk 4000 times larger in volume," said Xiang Zhang, a principal investigator with Berkeley Lab's Materials Sciences Division and director of UC Berkeley's Nano-scale Science and Engineering Center (SINAM), who led this research. "In addition to easily being able to control the rotational speed and direction of this motor, we can create coherent arrays of such motors, which results in greater torque and faster rotation of the microdisk."

The success of this new light mill stems from the fact that the force exerted on matter by light can be enhanced in a metallic nanostructure when the frequencies of the incident light waves are resonant with the metal's plasmons - surface waves that roll through a metal's conduction electrons. Zhang and his colleagues fashioned a gammadion-shaped light mill type of nanomotor out of gold that was structurally designed to maximize the interactions between light and matter. The metamaterial-style structure also induced orbital angular momentum on the light that in turn imposed a torque on the nanomotor.

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