Multiple beam interference lithography: A tool for rapid fabrication of plasmonic arrays of arbitrary shaped nanomotifs

Multi-functional dual-path self-aligned polarization interference lithography

Manufacturing sharp features is one of the most desired requirements for lithography. Here, we demonstrate a dual-path self-aligned polarization interference lithography (Dp-SAP IL) for fabricating periodic nanostructures, featuring high-steepness and high-uniformization. Meanwhile, it can manufacture quasicrystals with adjustable rotation symmetry. We reveal the change of the non-orthogonality degree under different polarization states and incident angles. We find that incident light's transverse electric (TE) wave results in high interference contrast at arbitrary incident angles, with a minimum contrast of 0.9328, that is, realizing the self-alignment of the polarization state of incident light and reflected light. We experimentally demonstrate this approach by fabricating a series of diffraction gratings with periods ranging from 238.3 nm to 851.6 nm. The steepness of each grating is greater than 85 degrees. Different from the traditional interference lithography system, Dp-SAP IL realizes a structure color using two mutually perpendicular and non-interference paths. One path is for the photolithography of patterns onto the sample, and the other path is for generating nanostructures on the patterns. Our technique showcases the feasibility of obtaining high contrast interference fringes by simply tuning the polarization, with the potential for cost-effective manufacturing of nanostructures such as quasicrystals and structure color.

Exploring SERS from complex patterns fabricated by multi-exposure laser interference lithography

Designing uniform plasmonic surfaces in a large area is highly recommended for surface-enhanced Raman scattering (SERS). As periodic morphologies exhibit uniform SERS and optical tunability, diverse fabrication methods of periodic nanostructures have been reported for SERS applications. Laser interference lithography (LIL) is one of the most versatile tools since it can rapidly fabricate periodic patterns without the usage of photomasks. Here, we explore complex interference patterns for spatially uniform SERS sensors and its cost-effective fabrication method termed multi-exposure laser interference lithography (MELIL). MELIL can produce nearly periodic profiles along every direction confirmed by mathematical background, and in virtue of periodicity, we show that highly uniform Raman scattering (relative standard deviation <6%) can also be achievable in complex geometries as the conventional hole patterns. We quantitatively characterize the Raman enhancement of the MELIL complex patterns after two different metal deposition processes, Au e-beam evaporation and Ag electroplating, which results in 0.387 × 10⁵and 1.451 × 10⁵in enhancement factor respectively. This alternative, vacuum-free electroplating method realizes an even more cost-effective process with enhanced performance. We further conduct the optical simulation for MELIL complex patterns which exhibits the broadened and shifted absorption peaks. This result supports the potential of the expanded optical tunability of the suggested process.

Multi-diffractive grating for surface plasmon biosensors with direct back-side excitation

A multi-diffractive nanostructure is reported for the resonant excitation of surface plasmons that are cross-coupled through a thin metallic film. It consists of two superimposed periodic corrugations that allow diffraction excitation of surface plasmons on the inner side of a thin metal film and their subsequent phase matching with counterpropagating surface plasmons travelling to the opposite direction on its other side. This interaction leads to establishing of a set of cross-coupled Bragg-scattered surface plasmon modes that exhibit an electromagnetic field localized on both metal film interfaces. The reported structure is attractive for surface plasmon resonance biosensor applications, where direct optical probing can be done through the substrate without the need of optical matching to a high refractive index prism. In addition, it can be prepared by mass production - compatible means with UV-nanoimprint lithography and its biosensing performance characteristics are demonstrated by refractometric and biomolecular affinity binding studies.

Rapid large-scale fabrication of multipart unit cell metasurfaces

Periodic diffractive elements known as metasurfaces constitute platform technology whereby exceptional optical properties, not attainable by conventional means, are attained. Generally, with increasing unit-cell complexity, there emerges a wider design space and bolstered functional capability. Advanced devices deploying elaborate unit cells are typically generated by electron-beam patterning which is a tedious, slow process not suitable for large surfaces and quick turnaround. Ameliorating this condition, we present a novel route towards facile fabrication of complex periodic metasurfaces based on sequential exposures by laser interference lithography. Our method is fast, cost-effective, and can be applied to large surface areas. It is enabled by precise control over periodicity and exposure energy. With it we have successfully patterned and fabricated one-dimensional (1D) and two-dimensional (2D) multipart unit cell devices as demonstrated here. Thus, zero-order transmission spectra of an etched four-part 1D grating device are simulated and measured for both transverse-electric (TE) and transverse-magnetic (TM) polarization states of normally incident light. We confirm non-resonant wideband antireflection (∼800 nm) for TM-polarized light and resonance response for TE-polarized light in the near-IR band spanning 1400-2200 nm in a ∼100 mm² device. Furthermore, it is shown that this method of fabrication can be implemented not only to pattern periodic symmetric/asymmetric designs but also to realize non-periodic metasurfaces. The method will be useful in production of large-area photonic devices in the realm of nanophotonics and microphotonics.

"Double" displacement Talbot lithography: fast, wafer-scale, direct-writing of complex periodic nanopatterns

We describe a new low-cost nanolithographic tool for creating periodic arrays of complex, nano-motifs, across large areas within minutes. Displacement Talbot lithography is combined with lateral nanopositioning to enable large-area patterning with the flexibility of a direct-write system. In this way, we can create different periodic patterns in short timescales using a single mask with no mask degradation. We demonstrate multiple exposures, combined with discrete lateral displacements, and single exposures, with continuous displacements, to achieve image inversion, pitch reduction, and nanogaps between metal nanoparticles. Our approach provides a flexible route to create large-area nanopatterned materials and devices in high volumes.

Parallel direct writing achromatic talbot lithography: a method for large-area arbitrary sub-micron periodic nano-arrays fabrication

Metasurfaces with complex periodic nanoarrays have attracted a large amount of attention over the past decades due to their pronounced plasmonic and photonic properties. Though various metasurface properties have been theoretically and experimentally investigated, the realization of practical metasurface applications remains a big challenge due to very limited large-area complex nanostructure fabrication. In this paper, we demonstrate a parallel direct writing achromatic Talbot lithography (DW-ATL) technique for large-area arbitrary sub-micron periodic nano-arrays fabrication. By using a laser interferometer, the sparse hole/dot arrays obtained by ATL could be stitched precisely between discrete multiple exposures. Complex sub-micron periodic nanoarrays, such as elliptical discs, rods, L-shaped and Y-shaped periodic nanoarrays, with a sub-hundred nm resolution were fabricated over an area of ∼mm².

Fast Acoustic Light Sculpting for On-Demand Maskless Lithography

Light interference is the primary enabler of a number of optical maskless techniques for the large-scale processing of materials at the nanoscale. However, methods controlling interference phenomena can be limited in speed, ease of implementation, or the selection of pattern designs. Here, an optofluidic system that employs acoustic standing waves in a liquid to produce complex interference patterns at sub-microsecond temporal resolution, faster than the pulse-to-pulse period of many commercial laser systems, is presented. By controlling the frequency of the acoustic waves and the motion of a translation stage, additive and subtractive direct-writing of tailored patterns over cm2 areas with sub-wavelength uniformity in periodicity and scalable spatial resolution, down to the nanometric range, are demonstrated. Such on-the-fly dynamic control of light enhances throughput and design flexibility of optical maskless lithography, helping to expand its application portfolio to areas as important as plasmonics, electronics, or metamaterials.

Fast and large-area fabrication of plasmonic reflection color filters by achromatic Talbot lithography

To overcome the limits of traditional technologies, which cannot achieve high resolution and high throughput simultaneously, here we propose, to the best of our knowledge, a novel method, i.e., achromatic Talbot lithography, to fabricate large-area nanopatterns fast and precisely. We successfully demonstrate reflection color filters with a maximum size of about 0.72×0.72  mm² with a time of only 20 s that have colors similar to simulations and small-area devices fabricated by electron beam lithography. These results indicate the possibility of large-scale fabrication of plasmonic color filters with high resolution efficiently by the achromatic Talbot lithography method.