Three-dimensional Chiral Plasmonic Oligomers

Abstract

First, the quartz glass substrate (Suprasil, Heraeus) is covered with a 70 nm thick spacer layer by spin-coating. A solidifiable photopolymer, PC403 (JCR, Japan), is used. A prebaking process is first carried out to remove the solvent from the polymer (increase of the baking temperature from 90 °C to 130 °C). A sufficiently long bake at a higher temperature (30 min at 180 °C) further hardens the layer. Next the three particle L-shape layer (dot diameter 200 nm, surface-to-surface distance 20 nm) and alignment markers are defined in resist (double layer PMMA, Allresist) using electron-beam lithography (Raith e_Line). The substrate is then covered with a 2 nm Cr adhesion layer and a 40 nm gold film using thermal evaporation followed by a lift-off procedure. Subsequently, a 70 nm thick spacer layer of PC403 is applied. Afterwards the substrate is coated once more with PMMA resist. Computercontrolled alignment at the sub-10 nm level using the gold alignment markers is applied to ensure the accurate positioning of the upper dot layer. Metal evaporation, lift off, and final planarization are repeated. All samples have a total area of 30 µm ×30 µm. All scanning electron microscope (SEM) images are taken with a Hitachi S-4800 scanning electron microscope. Optical characterisationThe spectra are measured using a Fourier-transform infrared spectrometer (Bruker Vertex 80, tungsten lamp), equipped with an infrared microscope (Bruker Hyperion). The incident light is focused with a Cassegrain objective with numerical aperture N = 0.4, and the transmitted intensities are detected with Si and InGaAs diodes. The incident polarization is set with an infrared polarizer and a broadband (700 nm -2500 nm) infrared quarterwaveplate (B. Halle Nachfl., Berlin). The measured spectra are normalized with respect to the substrate.

Large‐Area Low‐Cost Plasmonic Nanostructures in the NIR for Fano Resonant Sensing

“…Our method will allow for large-area low-cost fabrication of high-quality complex plasmonic structures, such as oligomers [ 38 , 39 ] and chiral structures. [ 40 ] This technique will pave the road for real-life plasmonic applications like optical gas sensors, [ 41 , 42 ] biosensors, [ 22 , 43 ] leak detectors, [ 44 ] artifi cial nanonoses, [ 45 ] as well as chiral plasmonic enantiomer sensors [ 46 ] that could for example detect specifi cally glucose, which is a handed molecule. Our method is very fl exible towards other structure geometries, scalable to even larger areas, very reproducible, and adaptable for other substrate materials and metals.…”

Enantioselective control of lattice and shape chirality in inorganic nanostructures using chiral biomolecules

“…These effects, which may be useful for biomolecular sensing 9,12 and are fundamentally interesting, are nevertheless limited in magnitude. Stronger effects could be obtained in systems of achiral nanoparticles arranged in a chiral superstructure with strong interparticle interaction [13][14][15][16] . Recently, Kotov and colleagues 17 demonstrated that the chiroptical activity of a chiral particle dimer is intense enough to monitor on a single nanoparticle level.…”

The surface plasmon modes of self-assembled gold nanocrystals

“…The novel DNA-based assembly method developed here paves the way for fabricating other interesting plasmonic structures, such as chiral nanostructures. 41,42 Methods Chemicals and gold nanosphere assembly. Gold(III) chloride trihydrate (99.9 þ %) and tris(2-carboxyethyl)phosphine hydrochloride (TCEP) were purchased from Sigma Aldrich.…”