Mechanistic study of self-assembled tungsten nanogratings on solids induced by femtosecond laser beam.

摘要

This dissertation describes a mechanistic study on the spontaneous formation of tungsten nanograting induced by a 400 nm femtosecond laser beam on solids observed in laser induced chemical vapor deposition configuration. The formed tungsten nanograting has a periodicity less than half the laser wavelength, and the orientation of the nanograting is parallel to the laser polarization direction, given that the laser is linearly polarized. By translating the substrate with respecting to the fixed laser beam, long-range ordered transverse or longitudinal nanograting is produced depending on the angle between the translating and laser polarization directions. Systematic experimental studies on the effect of laser power, scanning speed of substrate, laser polarization, wavelength and substrate were carried out in detail. The formation of tungsten nanograting is nearly a universal phenomenon observed on a wide range of substrates. Appearance of tungsten nanograting requires a threshold laser power which varies for different substrates. The grating period can be tuned simply by managing writing parameters. Scaling to large area grating pattern and feasibility of growing nanograting on curved surfaces were also demonstrated. Evidence shows that laser heating and local field enhancement are involved in the formation of tungsten nanograting. A crude conjectured theoretical model was proposed to explain the mechanism of tungsten nanograting formation. Due to the novel nature of self-assembled tungsten nanograting, this study is expected to advance the knowledge on laser-material interaction field.