Self-assembly of tunable and highly uniform tungsten nanogratings induced by a femtosecond laser with nanojoule energy

Tunable and highly uniform tungsten nanogratings on sapphires are demonstrated by scanning a 400 nm femtosecond-pulsed laser with pulse energy less than half of a nanojoule during laser-induced chemical vapor deposition. These gratings possess very good uniformity in both the grating period (standard deviation less than 1.5%) and the tooth length (less than 4%), and can be tuned by controlling the laser power and scanning speed. We show that nanogratings can be easily fabricated on non-planar substrates such as glass optical fibers, and can be turned into larger-area one-dimensional gratings by an appropriate offset during multiple scans. A model based on local field enhancement and interference between the incident light and plasmon radiation is proposed to explain the anisotropic shape and the periodic appearance of the observed tungsten nanogratings