Sub-40nm Nanogratings Self-Organized in PVP-based Polymer Composite Film by Photoexcitation and Two Sequent Splitting under Femtosecond Laser Irradiation

TL;DR

This paper demonstrates the self-organization of sub-40nm nanogratings on Fe-doped PVP composite films using femtosecond laser irradiation, revealing a two-step formation mechanism and controllable nanostructure periods.

Contribution

It introduces a novel method to produce highly regular ultrafine nanogratings via femtosecond laser irradiation on composite films, supported by experimental, theoretical, and simulation analyses.

Findings

Nanogratings with a period as small as 35 nm were achieved.

The nanograting period can be controlled by laser scanning speed and film thickness.

A two-step formation mechanism involving excitation and splitting was proposed.

Abstract

Laser-induced periodic surface structures (LIPSSs) on various materials have been extensively investigated because of their wide applications. The combination of different materials allows for greater freedom in tailoring their functions and achieving responses not possible in a homogeneous material. By utilizing a femtosecond (fs) laser to irradiate the Fe-doped Polyvinyl Pyrrolidone (PVP) composite film, highly regular ultrafine nanogratings (U-nanogratings) with a period as small as 35.0 ($\pm$ 2.0) nm can be self-organized on the surface with extremely high efficiency. The period of the U-nanogratings can be controlled by varying the scanning speed of the laser beam (deposited energy) and the thickness of the composite film. Based on the experimental, theoretical, and simulation results, we propose a two-step formation mechanism: composite film excitation and two sequent grating-splitting. The high photosensitivity and low glass transition temperature of the composite film facilitate the fabrication of the ultrafine nanostructures. The proposed design method for the composite material and fabrication process could not only provide a strategy for obtaining highly regular U-nanogratings, but also offer a platform to explore the interaction physics between ultra-short pulses and matter under extreme conditions.