Manipulating metal-oxide nanowires using counter-propagating optical line tweezers.

Semiconducting nanowires, such as ZnO and Si, are used in the fields of nanophotonics and nanoelectronics. Optical tweezers offer the promise of flexible positional control of such particles in a liquid, but so far this has been limited to either manipulation close to the surface, or to axial trapping of nanowires. We show the three-dimensional trapping of ZnO and silica-coated Si nanowires in counter-propagating line tweezers, and demonstrate translational and rotational in-plane manipulation, away from the surfaces. The high-refractive index particles investigated - ZnO wires (n~1.9) with varying lengths up to 20mum and 6-mum-long silica-coated Si wires (n =3.6) - could not be trapped in single-beam line traps. Opposite surface charges are used to fix the nanowires to a surface. Full translational and in-plane rotational control of semiconducting nanowires expands the possibilities to position individual wires in complex geometries significantly.