"This is a new area of science," said associate professor Balaji Panchapakesan. "Few materials can convert photons directly into mechanical motion. It is a material distinguished by its strength and its enhanced optical absorption when placed under mechanical stress.
"Grippers and actuators made with this material could be used on Mars rovers to capture fine dust particles. They could travel through the bloodstream on robots to capture cancer cells or take minute tissue samples. The material could be used to make micro-actuators for rotating mirrors in optical telecommunications systems; they would operate strictly with light, and would require no other power source." Panchapakesan added.
In their experiments, the researchers observed that the atomic orbitals of the molybdenum and sulphur atoms in molybdenum disulphide are arranged in such a way that permits excitons within the conduction band to interact with the p-orbitals of the sulphur atoms.
This ‘exciton resonance’ contributes to the strong sigma bonds that give the 2D array of atoms in molybdenum sulphide its strength. The strength of the resonance is responsible for an effect that can generate heat within the material that gives rise to a chromatic mechanical response.
To take advantage of the phenomenon, the group created thin films made up of just one to three layers of molybdenum disulphide encased in layers of a rubber-like polymer. They exposed these nanocomposites to various wavelengths of light and found that the heat generated as a result of the exciton resonance caused the polymer to expand and contract, depending on the wavelength of the light used. The team harnessed this photo-mechanical response by fabricating grippers that open and close in response to light pulses.
