Direct laser writing system for high-resoluti

Peripheral photoinhibition (PPI) direct laser writing (DLW) is a lithography technique used to fabricate intricate 3D nanostructures widely used in photonics and electronics. PPI-DLW uses two beams, one to excite the substrate and induce polymerization and the other to inhibit and quench the excitation at the edges. The capacity is limited in some systems, which can be improved by multifocal arrays. However, the calculation of these rays is both time and memory intensive.

Recently, a group of researchers from Zhejiang University developed a parallel peripheral photoinhibition lithography (P³L) system that can achieve higher efficiency nanoscale manufacturing. Their work is published in Advanced Photonics. “The P³L-system uses two channels, which enables the execution of different printing tasks and allows the system to produce highly complex structures with different periodicities,” says Liu.

The P³L system consists of a physical arrangement of eight modules. The system starts with two pressure channels, consisting of an excitation solid spot and a doughnut-shaped inhibition beam. The two beams are first stabilized and then split into two sub-beams with the help of a polarization filter. This allows the individual on-off control of each sub-beam by an acousto-optic modulator. Next, the two sub-beams are recombined to recover the excitation and inhibition beams. The beams are then modulated using spatial light modulators. Finally, the two beams are combined and passed through a microscope, after which they focus as two spots on the substrate.

The individual control of each sub-beam allows the printing of non-periodic and complex patterns simultaneously, without compromising on scanning speed, thus doubling the efficiency of the system. It is easy to adjust the position and separation of the two spots. These features make the proposed system more flexible and functional than conventional systems with uniform focus control.

The researchers confirmed the feasibility and potential of the system by fabricating a variety of nanostructures. They first produced a 2D sub-40 nm nanowire. A sub-20 nm-thick suspended nanowire was also fabricated. Next, the researchers created two rows of alphabet patterns by printing dots—each 200 nm apart. Finally, they produced 3D structures, including nonperiodic cubic frames, hexagonal lattices, wire structures, and spherical architectures, all of which exhibit exceptional resolution.

The identical on-off control of each focus increases the flexibility of the system and allows the rapid fabrication of complex, non-periodic patterns and structures. The parallel scanning feature of the system also reduces the time cost required to produce large-scale, complex structures and patterns. In addition, the new P³L-system achieves a lithography efficiency that is twice that of conventional systems, regardless of whether the structure is uniform or complex.

Senior author Xu Liu, discussing the future potential of the work, says: “Multifocus parallel scanning and PPI have the ability to overcome the current challenges in DLW optical fabrication and the fabrication of flamed gratings, microlens arrays, microfluidic structures and metasurfaces The proposed system can further facilitate the realization of portable, high-resolution, high-throughput DLW.”

Based on these results, it is clear that the proposed P³L-system will serve as a useful tool for the development of a wide range of fields using nanotechnology.

Read the Gold Open Access article by Dazhao Zhu et al., “Direct laser writing breaking diffraction barrier based on two-focus parallel peripheral-photoinhibition lithography,” Adv. Photon. 4(6), 066002 (2022), doi 10.1117/1.AP.4.6.066002.

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