Multifunctional Nanostructures and Nanopocket Particles Fabricated by Nanoimprint Lithography

Abstract

Nanostructured surfaces and nanoparticles are already widely employed in many different fields of research, and there is an ever-growing demand for reliable, reproducible and scalable nanofabrication methods. This is especially valid for multifunctional nanomaterials with physical properties that are tailored for specific applications. Here, we report on the fabrication of two types of nanomaterials. Specifically, we present surfaces comprising a highly uniform array of elliptical pillars as well as nanoparticles with the shape of nanopockets, possessing nano-cavities. The structures are fabricated by nanoimprint lithography, physical and wet-chemical etching and sputter deposition of thin films of various materials to achieve a multifunctional nanomaterial with defined optical and magnetic properties. We show that the nanopockets can be transferred to solution, yielding a nanoparticle dispersion. All fabrication steps are carefully characterized by microscopic and optical methods. Additionally, we show optical simulation results that are in good agreement with the experimentally obtained data. Thus, this versatile method allows to fabricate nanomaterials with specific tailor-made physical properties that can be designed by modelling prior to the actual fabrication process. Finally, we discuss possible application areas of these nanomaterials, which range from biology and medicine to electronics, photovoltaics and photocatalysis.

Self-Assembled Au Nanoparticle Monolayers on Silicon in Two- and Three-Dimensions for Surface-Enhanced Raman Scattering Sensing

“…Top-down methods, such as electron-beam or nanoimprint lithography, have been successfully used for preparing well-defined Au or other metallic nanostructures on Si. ,− They require, however, expensive and elaborated lab equipment and clean-room conditions. ,,, Densely packed AuNP films can be formed via self-assembly at a liquid/liquid interface, which can be later transferred to a planar substrate. − However, the postfunctionalization of the AuNPs with a structure-directing molecule, such as mercapto-polyethylene glycol, 1-dodecanethiol, acrylamide molecules, or perfluorodecanethiol, complicates the approach, while the deposition of the resulting AuNP monolayers on substrates with complex topographies, such as VA-SiNW arrays, has not been successfully demonstrated. − The self-assembly of presynthesized AuNPs on functionalized Si, on the other hand, offers a low-cost and simple route that is amenable for mass-production and is compatible with the coating of nanostructured silicon. ,,,− The self-assembly process is self-limited, providing the opportunity to control AuNP coverage, and is potentially compatible with NPs of different sizes, compositions, and shapes. ,, However, the preparation of substrates with homogeneous AuNP assemblies providing uniform E-field enhancements over large areas remains a challenge. , To prepare such AuNPs@Si substrates, silanes containing amino- or mercapto-groups have been previously used to form siloxane bonds with the Si surface and to direct the assembly of AuNPs at the Si surface either via electrostatic interaction or covalent bonding. ,− Both the Si functionalization and the AuNP assembly step are sensitive to the experimental conditions. Among others, the quality of the silane layer is highly affected by the presence of water, temperature, heating speed, reaction time, and silane concentration, as well as the storage conditions after the functionalization itself has been completed. ,− The AuNP assembly on the Si surface is also sensitive to the pH and ionic strength of the solution, AuNP size and capping ligand, and immersion time in the AuNP solution. ,,, This self-assembly process is further complicated if topographically structured substrates, such as SiNWs, are to be uniformly coated because geometric restrictions may cause changes in accessibility and concentration profiles of the NPs to be deposited.…”

Novel multi-layer nanoimprint lithography material system enabling nano-patterning of functional optical layers

“…[6] Similar approaches has been used in the fabrication of metal particles. [7] figure 2 SEM images of the bilayer stack after metal deposition (left) and lift-off (right). [6] Alternatively, a dry etch process can be applied.…”

Plasmonic nanomaterials with responsive polymer hydrogels for sensing and actuation

“…9 Metallic nanostructures can be prepared by chemical synthesis in liquid media and subsequently assembled into more complex architectures, 10 or they can be directly fabricated by various lithography-based techniques on solid substrates. 11,12 However, these metallic structures are typically static, meaning their optical characteristics are determined by the chosen geometry and typically cannot be reconfigured after the preparation step.…”