Abstract
Nanoscale surface texturing, drilling, cutting, and spatial sculpturing, which are essential for applications, including thin-film solar cells, photonic chips, antireflection, wettability, and friction drag reduction, require not only high accuracy in material processing, but also the capability of manufacturing in an atmospheric environment. Widely used focused ion beam (FIB) technology offers nanoscale precision, but is limited by the vacuum-working conditions; therefore, it is not applicable to industrial-scale samples such as ship hulls or biomaterials, e.g., cells and tissues. Here, we report an optical far-field-induced near-field breakdown (O-FIB) approach as an optical version of the conventional FIB technique, which allows direct nanowriting in air. The writing is initiated from nanoholes created by femtosecond-laser-induced multiphoton absorption, and its cutting “knife edge” is sharpened by the far-field-regulated enhancement of the optical near field. A spatial resolution of less than 20 nm (λ/40, with λ being the light wavelength) is readily achieved. O-FIB is empowered by the utilization of simple polarization control of the incident light to steer the nanogroove writing along the designed pattern. The universality of near-field enhancement and localization makes O-FIB applicable to various materials, and enables a large-area printing mode that is superior to conventional FIB processing.
Highlights
Lasers are becoming one of the dominant tools in the current manufacturing industry[1,2,3,4]
Much effort has been devoted to improving the processing accuracy, and spatial resolutions as low as micrometers have been achieved in laser cutting, welding, marking, and stereolithography in an atmospheric environment[3,4,5,6]
Optical far-field-induced near-field breakdown, which we abbreviate as O-focused ion beam (FIB), combines the concepts of FIB with the advantages of fs-laser-induced multiphoton excitation and optical near-field superresolution, and enables far-field nanofabrication in the atmosphere that is
Summary
Nanoholes as seeds for near-field enhancement Fs-laser direct nanowriting is initiated with a nanohole as a seed (Fig. 1), which is ablated by few fs-laser pulses on the surface of a solid-state sample via multiphoton absorption[31,32]. The nanohole-enhanced optical near field provides the spatial resolution and reduces the light intensity required for laser ablation at the nanoscale. The ideal nanowriting parameter window defined by the exposure dose (influenced by the scan speed, repetition rate, and pulse energy) is generally quite wide, spanning up to one order of magnitude Within this condition, nanogrooves with uniform widths from 113 ± 5 nm down to 18 ± 3 nm have been realized (Fig. 2f), comparable to those achieved with standard FIB processing. Polarization control for free direct nanowriting O-FIB allows the free writing of arbitrary planar patterns, for which polarization control is critical (Fig. S2) This is a natural requirement, considering that the near-field enhancement always occurs at the two sides of the nanogroove/hole in the polarization plane (Fig. 1a, b and Fig. S4).
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