Visible-light driven Si-Au micromotors in water and organic solvents.

We report the fabrication of tadpole-shaped Si-Au micromotors using glancing angle deposition. These micromotors are activated by visible light and can move in either deionized water or organic solvents without the addition of chemical fuels. By controlling the light intensity, the velocity of the micromotors can be modulated and the motion can be switched on and off reversibly. Gas chromatographic measurements and buffered oxide etch (BOE) experiments show that the mechanism of propulsion is self-electrophoresis modulated by the photoconductivity of the amorphous silicon segment. The direction of motion of the microswimmers can also be controlled by applying an external magnetic field if a ferromagnetic Ni layer is added in the fabrication process.