Semiconductor nanowires are drawing more and more interest due to their numerous potential applications in
nanoelectronics devices [1,2], including interconnects, transistor channels, nanoelectrodes, or in the emerging application
areas of photonics , chemistry  and photovoltaics . In this context, optical tweezers appear like a pertinent tool
for the manipulation and assembly of nanowires into complex structures.
It was previously shown that the near-field existing at the surface of a waveguide allows the micromanipulation of
nanoparticles and biological objects [6,7]. In this article, we investigate for the first time to our knowledge the motion of
silicon nanowires above silicon nitride waveguides. The nanowires in aqueous solution are attracted toward the
waveguide by optical gradient forces. The nanowires align themselves according to the axis of the waveguide and get
propelled along the waveguide due to radiation pressure. Velocities are up to 40 μm/s.
For a better understanding of the experimental results, the distribution of the electromagnetic field in the nanowire is
calculated using the finite element method. Then, the resulting optical forces exerted on the nanowires are calculated,
thanks to the Maxwell stress tensor formalism.