Face selection in one-step bending of Janus nanopillars.

We introduce a one-step procedure of bending nanopillars, which simply involves oblique metal deposition at a tilted angle of 45 degrees on the pillars by thermal evaporation. The face selection in the bending procedure was determined by the nature of residual stress generated in the metal film during evaporation. If the stress was tensile as with many metals (sigma(f) > 0), the Janus nanopillars were bent toward the metal face; if the residual stress was compressive as in the case of Al (sigma(f) < 0), they were bent toward the polymer face. It has also been demonstrated that groups of Janus nanopillars could be bent in different directions on the same substrate with the aid of a shadow-mask deposition. The degree of bending increased with the decrease in pillar diameter in the range of 360-800 nm for a fixed height of 1 microm.