Engineering the Dynamics of Active Colloids by Targeted Design of Metal–Semiconductor Heterojunctions

Self-propelled colloids are primed to become scaled up, nano- and microscale inorganic analogues of molecular motors and machines. In order to advance toward the ambitious goal of employing such active particles to form genuine man-made small scale machinery, a significantly diversified library of particle types, capable of a wide range of motive behaviors, must be available. Here, it is shown that the dynamics of photoactivated, self-phoretic particles can be engineered by targeted design of metal–semiconductor heterojunctions. This effect is demonstrated with three different microswimmers consisting of an elongated semiconducting tail made from anatase titanium dioxide; all three of which would otherwise be identical absent vapor-deposited coatings of gold at different locations on the tails. The specific location of the heterojunction determines the swimming behavior for each type. Although here only one shape and material combination is focused upon, engineering active particles with site-specific metal–semiconductor heterojunctions is a general technique for achieving desired kinematic behavior in active colloidal matter.