High-Precision and Rapid Direct Laser Writing Using a Liquid Two-Photon Polymerization Initiator

Area of Science:

• Materials Science
• Nanotechnology
• Photochemistry

Background:

• Two-photon polymerization (TPP) based direct laser writing (DLW) is a key micronano 3D fabrication technology.
• Two-photon initiators (TPIs) are crucial for TPP-DLW, controlling polymerization and feature resolution.
• Poor solubility of conventional TPIs limits their application in DLW systems.

Purpose of the Study:

• To address the solubility limitations of TPIs in DLW.
• To develop liquid TPIs through molecular design for enhanced photoresist compatibility.
• To demonstrate the performance of liquid TPIs in achieving high-resolution 3D microstructures and 2D devices.

Main Methods:

• Molecular design strategy to synthesize liquid two-photon initiators (TPIs).
• Incorporation of liquid TPIs into photoresist systems at increased weight fractions.
• Evaluation of TPI solubility, absorption cross-section, and polymerization initiation efficiency.
• Fabrication of micro/nanostructures using TPP-DLW with the developed liquid TPIs.

Main Results:

• Liquid TPIs achieved a significantly higher maximum weight fraction (2.0 wt%) in photoresists compared to commercial TPIs.
• The liquid TPI demonstrated an excellent absorption cross-section (64 GM) for efficient femtosecond laser absorption.
• Achieved minimum feature sizes of 47 nm for line arrays and 20 nm for suspended lines, comparable to electron beam lithography.
• Successful fabrication of high-quality 3D microstructures and large-area 2D devices at a writing speed of 1.045 m s^-1.

Conclusions:

• The developed liquid TPIs overcome solubility challenges, enabling higher initiator concentrations in photoresists.
• Liquid TPIs facilitate high-resolution patterning and efficient fabrication of complex 3D microstructures and 2D devices.
• This advancement positions liquid TPIs as promising initiators for the future development of DLW technology.