Large-Scale Soft-Lithographic Patterning of Plasmonic Nanoparticles.

Micro- and nanoscale patterned monolayers of plasmonic nanoparticles were fabricated by combining concepts from colloidal chemistry, self-assembly, and subtractive soft lithography. Leveraging chemical interactions between the capping ligands of pre-synthesized gold colloids and a polydimethylsiloxane stamp, we demonstrated patterning gold nanoparticles over centimeter-scale areas with a variety of micro- and nanoscale geometries, including islands, lines, and chiral structures (e.g., square spirals). By successfully achieving nanoscale manipulation over a wide range of substrates and patterns, we establish a powerful and straightforward strategy, nanoparticle chemical lift-off lithography (NP-CLL), for the economical and scalable fabrication of functional plasmonic materials with colloidal nanoparticles as building blocks, offering a transformative solution for designing next-generation plasmonic technologies.

Hydroxypropyl Cellulose Adhesives for Transfer Printing of Carbon Nanotubes and Metallic Nanostructures.

Transfer printing is one of the key nanofabrication techniques for the large-scale manufacturing of complex device architectures. It provides a cost-effective and high-throughput route for the integration of independently processed materials into spatially tailored architectures. Furthermore, this method enables the fabrication of flexible and curvilinear devices, paving the way for the fabrication of a new generation of technologies for optics, electronics, and biomedicine. In this work, hydroxypropyl cellulose (HPC) membranes are used as water soluble adhesives for transfer printing processes with improved performance and versatility compared to conventional silicone alternatives. The high-water solubility and excellent mechanical properties of HPC facilitate transfer printing with high yield for both metal and carbon nanotubes (CNTs) inks. In the case of metal inks, crack-free stripping of silver films and the simple fabrication of Moiré Plasmonic architectures of different geometries are demonstrated. Furthermore, HPC membranes are used to transfer print carbon nanotube films with different thicknesses and up to 77% transparency in the visible and near infrared region with potential applications as transparent conductive substrates. Finally, the use of prepatterned HPC membranes enables nanoscale patterning of CNT with feature resolution down to 1 µm.

A water-processable cellulose-based resist for advanced nanofabrication.

The ideal nanofabrication technique is one that allows the mass production of high resolution submicrometric features in a cost efficient and environmentally friendly fashion. A great step towards achieving this goal has been the development of nanoimprinting lithography, a procedure with tenths of nanometres resolution while being compatible with roll-to-roll manufacturing. However, an ecofriendly resist that can be efficiently combined with this process is still missing. In this work, we demonstrate the use of hydroxypropyl cellulose (HPC) as a biocompatible, biodegradable, and water processable resist for temperature assisted nanoimprint lithography (tNIL) by fabricating different photonic architectures. The cellulose derivative is easily patterned with submicrometric features with aspect ratios greater than 1 using an elastomeric stamp and a hot plate. Silicon photonic crystals and metal nanoparticle arrays are fabricated combining cellulose with traditional nanofrabrication processes such as spincasting, reactive ion etching and metal lift off. Furthermore, advanced nanofabrication possibilities are within reach by combining the HPC with traditional resists. In particular, poly(methyl methacrylate) and HPC stacks are easily produced by liquid phase processing, where one of the two materials can be selectively removed by developing in orthogonal solvents. This capability becomes even more interesting by including nanoimprinted layers in the stack, leading to the encapsulation of arrays of air features in the resist.

Hydroxypropyl cellulose photonic architectures by soft nanoimprinting lithography.

As contamination and environmental degradation increase nowadays, there is a huge demand for new eco-friendly materials. Despite its use for thousands of years, cellulose and its derivatives have gained renewed interest as favourable alternatives to conventional plastics, due to their abundance and lower environmental impact. We report the fabrication of photonic and plasmonic structures by moulding hydroxypropyl cellulose into sub-micrometric periodic lattices, using soft lithography. This is an alternative way to achieve structural colour in this material which is usually obtained exploiting its chiral nematic phase. Cellulose based photonic crystals are biocompatible and can be dissolved in water or not depending on the derivative employed. Patterned cellulose membranes exhibit tuneable colours and may be used to boost the photoluminescence of a host organic dye. Furthermore, we show how metal coating these cellulose photonic architectures leads to plasmonic crystals with excellent optical properties acting as disposable surface enhanced Raman spectroscopy substrates.