Integrated “Hot Spots”: Tunable Sub‐10 nm Crescent Nanogap Arrays

Abstract

trapping, [5] single-molecule analysis, [6,7] surface plasmon (SP) enhanced spectroscopy. [6,8,9] To achieve the extremely concentrated and strong electric fields, lots of efforts are contributed to fabricate kinds of plasmonic structures, revealing that sub-10 nm nanogap and nanotip are the two key characteristics. [10,11] In theory, as predicted by Maxwell's equations, the electric fields would become stronger with the decreasing distance between metal nanostructures and can be confined in the gaps; [12][13][14][15][16][17][18][19][20][21] for nanotips, more electrons are distributed at the structural features with high curvature and thus lead to stronger electric fields. [22][23][24][25][26][27][28][29][30] Various plasmonic nanostructures with either nanogaps or nanotips have been fabricated, successfully enhancing the electric fields to several orders of magnitude and confining them in extremely small areas. To obtain better performances, a natural thought is to include both nanogaps and nanotips in one plasmonic nanostructure, i.e., integrated "hot spots." Impressive efforts have been made to develop the multifeature nanostructures. For example, spilt-wedge antenna structures with sub-5 nm gaps, [10] 3D sub-10 nm nanostar dimers gap, [6] and 3D sub-10 nm Ag/SiN x gap with an pair of uniform tips, [31] have been fabricated and highly boosted the local optical field intensity. The fabrication of most these structures has primarily relied on electron beam lithography (EBL) [6,[32][33][34] and focused-ion beam (FIB). [35] These techniques can facilely control the patterns and precisely tune the size and separation, but they suffer from the drawbacks of high-cost, time-consuming, and low-throughput. It is urgently needed to develop a simple and scalable process for their production.Nanoskiving, that combines the deposition of thin metal layers on substrates (flat or structured) and sectioning using a unity of ultramicrotome and diamond knife, would be an alternative fabrication technique for plasmonic nanostructures with both nanogaps and nanotips. [36][37][38][39] Compared with the conventional fabrication techniques (EBL and FIB), nanoskiving is uncomplicated, fast, and scalable, requiring no sophisticated equipment. Nanoskiving has been widely used in fabricating numerous nanostructures, showing the strong capability for nanostructures on-demand. In particular, our research group has reported 3D zig-zag nanowires that possess both nanogaps and nanotips via combining photolithography Plasmonic crescent nanogap arrays (CNGAs) integrated by nanoscale gaps and nanotips exhibit strong capability of light confinement and thus lead to extremely electric field enhancement. The CNGAs with tunable gap-width are fabricated via a low-cost and simple process combining colloidal lithography and nanoskiving techniques. Incident light is captured in the nanogaps and at the two tips of nanocrescent, where extremely strong electric fields are excited. The strong electric fields lead to greatly enhanced surface-enhanced Raman s...

Plasmonic Chiral Metamaterials with Sub-10 nm Nanogaps

“…Fabrication of Chiral Nanogaps. The preparation process of the chiral nanogaps is shown in Figure 1a: (I) Epoxy nanopillar arrays substrates were first fabricated via colloidal lithography, 46,51,52 and (II) 40 nm Au was deposited with the azimuthal angle α 1 = 0°and polar angle θ = 35°onto the nanopillar substrate (deposition 1). The azimuthal angle was indicated by the black dashed line (in-plane projection of the material vapor beam in the substrate plane), and the polar angle is relative to the substrate normal.…”

“…Here, we propose a low-cost and alternative method to fabricate a chiral metamaterial with sub-10 nm nanogaps (chiral nanogaps). Two Au nanocrescents separated by a sub-10 nm nanogap were fabricated based on subsequent depositions with different azimuthal angles − and the following nanoskiving , technique. The fabrication method is in common use and able to form large-area chiral metamaterials in parallel at low cost.…”

Metallic Plasmonic Array Structures: Principles, Fabrications, Properties, and Applications

“…[39] One effective way to obtain a narrow gap is to flexibly tune the metal deposition process during the preparation of a metallic plasmonic array. [177][178][179][180] In Figure 6b, Li et al extended the sputtering time to enlarge the diameter of the plasmonic nanopillars pre-fabricated by using immersion lithography. [178] Thus, the gap distance between neighboring particles can be narrowed, greatly improved the enhancement effect of the array substrate.…”

Recent Progress in the Nanoskiving Approach: A Review of Methodology, Devices, and Applications

“…As shown in Figure 10e, Zhang et al fabricated crescent nanogap arrays (CNGAs) that contained sub10 nm nanogaps and nanotips using colloidal lithography and nanoskiving tech niques. [83] The electric field is further enhanced effectively in the gaps and at the two crescents of the nanocrescents, which then greatly promotes the enhancement and reproduction of the SERS signal. The SERS signals of the CNGAs showed typical enhancement factors of 8 and 360 times when com pared with those of the tiponly crescent gold nanoparticles and the linear gold nanowires, respectively.…”

“…[13] The second pro cess (Figure 3b) yields 2D arrays of nanostructures. Patterning the film and combined with different sectioning directions Adaptation for semiconductor materials [32,34] Adaptation for polymeric materials [42] Embedding medium Thiol-containing polymeric embedding materials [48] Sectioning parameters Cutting direction [49,50] Cutting depth [34,52] Manipulation of slices Aligning-bonding approach [34] "Perfect transfer" approach [54] Applications development of nanoskiving Optical modulation Nanogaps for SERS [74,76,77,82,83] Photoluminescence [32,89] Electrochemical analysis Preparation of electrochemical nanoelectrodes [97][98][99][100] Electronic switches and sensors Light gating of molecular tunneling junctions [103] Mechanical strain sensors [107] Control of biomolecules and cells The detection of DNA-protein interactions [112] The control of cell organization [119] can prepare nanostructures with accurately defined length and spacing. [1] For example, perpendicular sectioning to the pat terned surface causes the production of rectangular wavy nano structure and parallel sectioning to the patterned surface causes the production of nanowire array.…”