Self-organized tungsten nanospikes grown on subwavelength ripples induced by femtosecond laser pulses.

We report on the formation of nanoscale tungsten spikes generated on subwavelength periodic ripples which built up by single beam 800 nm femtosecond laser pulses. The nanospikes have a diameter ranging from 10 to 100 nm and are up to 250 nm in length. The nanospikes orientate from the ridges toward the valleys of the ripple structures independent of the polarization of the light. The heterogeneous nucleation of the liquid phase at the irradiated surface and the inhomogeneous surface roughness are considered as the mechanism of this nanospike formation.