Various configurations of free space and phase mask beam splitting have permitted flexible tuning of the crystal symmetry between Tetragonal (TTR) 17, woodpile 18, 19 and diamond-like 20, 21, 22 structures and from simple Bravais lattices 23, 24, 25 to compound 26, chiral 27 and quasi-crystalline structures 28. On the other hand, today’s highly powered lasers are highly favored in holographic interference lithography (HIL) for expanding the fabrication area and speeding the process time of 3D PC templates with resolution at one half optical wavelength 7. This patterning approach has underpinned many broadly based nanostructure applications 4, 7, 8, 9, 10, 11, 12, 13, while offering the flexibility to machine fully-3D-shaped microdevices 14, optical waveguides embedded in 3D PC templates 15 and optical cloaking metamaterials 16. Hence, high resolution 3D patterning has been best met with optical approaches 4, 7 to provide advanced nanostructures that underlie omnidirectional stopbands 7 and superprism effects 8 in photonic crystals (PCs), negative refraction 9 and broadband circular polarizers 10 in metamaterials, engineered tissue growth 11 and controlled drug release 12 in scaffolds and carbon nano-tube composites 13 in 3D templates.ĭirect writing with tightly focused laser beams has been attractive for flexible and high resolution structuring of 3D features to sizes as small as 9 nm, representing a small fraction of the laser wavelength (~λ/90) in photoresist 4. ![]() Assembled layering of 2D-structures is exceptionally tedious and slow 6 and direct 3D nano-structuring is highly challenging, as charged particles cannot propagate without scattering inside solid material. An emerging opportunity here centers on new approaches that can transform rapid nano-structuring into the third dimension. Smaller 4 nm dimensions are otherwise available at much slower processing speed by direct writing with electron or ion beams 2, 3. Highly resolving beams of electrons 2, ions 3 and photons 4, 5 are regularly applied in high resolution surface patterning, for example, providing the narrow 16-nm (and beyond) transistor gate widths as required in today’s commercial microchips with laser lithography 5. The top-down approach to nano-structuring 1 has greatly evolved over the decades to underpin today’s most important trends in science and technology. In this way, laser scanning is presented as a facile means to embed 3D PC structure within microfluidic channels for integration into an optofluidic lab-on-chip, demonstrating a new laser HIL writing approach for creating multi-scale integrated microsystems. Phase mask interference patterns accumulated over multiple overlapping scans are shown to stitch seamlessly and form uniform 3D nanostructure with beam size scaled to small 200 μm diameter. ![]() Here, we introduce a laser scanning holographic method for 3D exposure in thick photoresist that combines the unique advantages of large area 3D holographic interference lithography (HIL) with the flexible patterning of laser direct writing to form both micro- and nano-structures in a single exposure step. However, formation of uniform and defect-free 3D periodic structures over large areas that can further integrate into multifunctional devices has remained a major challenge. ![]() Three-dimensional (3D) periodic nanostructures underpin a promising research direction on the frontiers of nanoscience and technology to generate advanced materials for exploiting novel photonic crystal (PC) and nanofluidic functionalities.
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