Leaf-like nanotips synthesized on femtosecond laser-irradiated dielectric material

摘要

Nanotips are the key nanostructures for the improvement of field emission, flat panel displays, force microscopy, and biosensor applications. We propose a single-step, rapid synthesis method to generate nanotips using femtosecond laser irradiation at megahertz frequency with a background flow of nitrogen gas at ambient conditions. Two different types of leaf-like nanotips can be grown on the target surface: randomly oriented multiple tips growing from a single large droplet and single tips growing from small droplets. In this report, we explain the mechanism accountable for the formation of such nanotips using known concepts of laser breakdown of dielectric materials, plasma plume generation, plasma interactions with incoming laser pulses and surrounding gas, as well as known thermal properties of target material. Nitrogen gas plays an interesting role for the resultant structural changes on the target surface and thus it is given special attention in our discussion. Our unique fabrication technique has enabled us to produce tips with nanoscale apexes with a stem and length ranging from few hundred nanometers to few micrometers.