Abstract
Surface-enhanced Raman spectroscopy (SERS) pushes past the boundaries and inherent weaknesses of Raman spectroscopy, with a great potential for a broad range of applications particularly, for sensing. Yet, current real world applications are limited due to poor reproducibility, low-throughput, and stability issues. Here, we present the design and fabrication of self-assembly guided structures based on adjustable block co-polymer (BCP) nanomorphologies and demonstrate reproducible SERS enhancement across large areas. Golden three-dimensional (3D) nanostructured morphologies with controllable dimensions and morphologies exhibit high chemical stability, enhanced plasmonic properties and are highly suitable for SERS substrates due to the strong enhancement of the electromagnetic field. Adjustable, free standing porous nanostructures, continuous in 3D space are achieved by removal of selected BCP constituents. Four BCP morphologies and the corresponding achievable enhancement factors are investigated at 633 and 785 nm excitation wavelengths. The choice of excitation laser is shown to greatly affect the observed signal enhancement, highlighting the sensitivity of the technique to the underlying surface architecture and length scales. By using BCP assemblies, it is possible to reliably tune these parameters to match specific applications, thus bridging the gap toward the realization of applied metamaterials. The fabricated SERS platforms via three-dimensional block co-polymer-based nanoarchitectures provide a recipe for intelligent engineering and design of optimized SERS-active substrates for utilization in the Raman spectroscopy-based devices toward enabling the next-generation technologies fulfilling a multitude of criteria.
Highlights
Block co-polymer (BCP) nanoarchitectures have been emerging as straightforward and high-throughput platforms for designing and fabricating a range of large-area nanostructures with controllable dimensions, composition, and spatial arrangement
Various morphologies that depend on the relative volume fraction of one block relative to the other produce complex nanostructures due to the microphase separation of the BCPs on the molecular scale resulting in a spontaneous formation of a broad spectrum of ordered nanostructures
The evolving nanomorphologies from the BCP melt are determined by the competition of entropy and the enthalpy between the two blocks and eventually result in the minimization of the system’s energy, yielding the most favorable configurations
Summary
Block co-polymer (BCP) nanoarchitectures have been emerging as straightforward and high-throughput platforms for designing and fabricating a range of large-area nanostructures with controllable dimensions, composition, and spatial arrangement. Many studies exploit nanoparticle-based systems for SERS enhancement and their reproducibility, stability, and practical applications remain debatable.[22−25] The vast majority of top-down synthetic routes to generate nanostructures are based on conventional patterning techniques and are typically expensive, complex and often require precise integration of multistep processes while exhibiting a limited scalability, highlighting the need for more reliable and straightforward lithographic methods to develop efficient access to adjustable three-dimensionally (3D) isotropic nanostructures This has driven extensive efforts to explore novel processes for the fabrication of highly ordered 3D structures with sub-micrometer periodicities, signposting BCP self-assembly as an alternative bottom-up lithographic method, enabling specific orientations from chosen materials on supporting substrates, as a platform for a generation of miniaturized devices. The obtainable optical properties can be further tuned immensely by variation of the unit cell size, the fill fraction, choice of the BCP morphology, and the plasmonic metal used for filling into the template, building upon the various approaches developed to tune the size, shape, and spacing of BCP domains and the nanostructures derived from them.[31−35] The architectures fabricated here can provide low-cost, simple, large-active-area substrates, with broad plasmon resonances which open a window for a range of SERS active, switchable structures to accommodate various applications toward developing novel, adjustable photonic metamaterials and miniaturized devices
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