Kay Dietrich

Circular Dichroism from Chiral Nanomaterial Fabricated by On‐Edge Lithography

A novel-shaped plasmonic chiral nanomaterial exhibiting circular dichroism in the near-infrared spectral range is presented. Applying on-edge lithography, a large area with these nanostructures is efficiently covered. This fabrication method offers tunability of the operation bandwidth by tailoring the chiral shape.

Enhancing Second Harmonic Generation in Gold Nanoring Resonators Filled with Lithium Niobate

Plasmonic nanorings provide the unique advantage of a pronounced plasmonic field enhancement inside their core. If filled with a polarizable medium, it may significantly enhance its optical effects. Here, we demonstrate this proposition by filling gold nanorings with lithium niobate. The generated second harmonic signal is compared to the signal originating from an unpatterned lithium niobate surface. Measurements and simulation confirm an enhancement of about 20. Applications requiring nanoscopic localized light sources like fluorescence spectroscopy or quantum communication will benefit from our findings.

Plasmonic properties of aluminum nanorings generated by double patterning

In this Letter we evaluate a technique for the efficient and flexible generation of aluminum nanorings based on double patterning and variable shaped electron beam lithography. The process is demonstrated by realizing nanorings with diameters down to 90 nm and feature sizes of 30 nm utilizing a writing speed of one ring per microsecond. Because of redepositions caused by involved etching processes, the material of the rings and, therefore, the impact on the plasmonic properties, are unknown. This issue, which is commonly encountered when metals are nanostructured, is solved by adapting a realistic simulation model that accounts for geometry details and effective material properties. Based on this model, the redepositions are quantified, the plasmonic properties are investigated, and a design tool for the very general class of nanofabrication techniques involving the etching of metals is provided.

Elevating optical activity: Efficient on-edge lithography of three-dimensional starfish metamaterial

We present an approach for extremely fast, wafer-scale fabrication of chiral starfish metamaterials based on electron beam- and on-edge lithography. A millimeter sized array of both the planar chiral and the true 3D chiral starfish is realized, and their chiroptical performances are compared by circular dichroism measurements. We find optical activity in the visible and near-infrared spectral range, where the 3D starfish clearly outperforms the planar design by almost 2 orders of magnitude, though fabrication efforts are only moderately increased. The presented approach is capable of bridging the gap between high performance optical chiral metamaterials and industrial production by nanoimprint technology.

Plasmonic nanoring fabrication tuned to pitch: Efficient, deterministic, and large scale realization of ultra-small gaps for next generation plasmonic devices

A double-patterning process for scalable, efficient, and deterministic nanoring array fabrication is presented. It enables gaps and features below a size of 20 nm. A writing time of 3 min/cm2 makes this process extremely appealing for scientific and industrial applications. Numerical simulations are in agreement with experimentally measured optical spectra. Therefore, a platform and a design tool for upcoming next generation plasmonic devices like hybrid plasmonic quantum systems are delivered.

Multi-stencil character projection e-beam lithography: a fast and flexible way for high quality optical metamaterials

In this work we report on the strong improvement of pattern quality and significant write-time reduction using Character Projection with a multi-stencil character stage with more than 2000 apertures for the fabrication of nanomaterials and, in particular, on an optical metamaterial, which is called “Metamaterial Perfect Absorber”. The Character Projection ebeam lithography allows the transition from the time-consuming serial to a fast quasi-parallel writing method and opens the way for the fabrication of device areas which are impossible to realize with often in the R&D used SEM based Gaussian electron beam-writers. More than 150.000 times faster than the comparable Gaussian E-beam exposure, 100 times faster and with a factor of 10 improved pattern size homogeneity than the corresponding Variable Shaped E-beam exposure – these are our main results for the fabrication of optical metamaterials using a Variable Shaped E-beam with Character Projection.

Reducing Rowland ghosts in diffraction gratings by dynamic exposure near-field holography

Near-field holography (NFH) combined with electron beam lithography (EBL)-written phase masks is a promising method for the rapid realization of diffraction gratings with high resolution and high accuracy in line density distribution. We demonstrate a dynamic exposure method in which the grating substrate is shifted during pattern transfer. This reduces the effects of stitching errors, resulting in the decreased intensity of the optical stray light (i.e., Rowland ghosts). We demonstrate the intensity suppression of ghosts by 60%. This illustrates the potential for dynamic NFH to suppress undesirable periodic patterns from phase masks and alleviate the stitching errors induced by EBL.

Controlling the excitation of radially polarized conical plasmons in plasmonic tips in liquids

Having virtues from plasmons and scanning probe microscopy (SPM), plasmonic tips employ radially polarized conical plasmons and create hot-spots at their apexes. Plasmonic tips are tapered and fully metal-coated vortex fibers that have M-shaped refractive index profiles. Vortex fibers allow the radially polarized mode to propagate over a long distance with high modal purity. When the fiber mode reaches the tapered region, it resonantly excites the plasmon mode at a metal-dielectric outer interface. In this paper, we study the plasmonic tips behavior in liquids both theoretically and experimentally. By adiabatically tapering the vortex fiber, the radially polarized mode gets confined from the fiber with a diameter of 115 μm down to the tapered part with a diameter of 1.42 μm as a waveguide mode. In this region, the plasmon mode gets excited thus reaches the apex with a diameter of 200 nm. Our calculations show that the plasmon coupling efficiency increases in liquids due to two competing processes: a significant increase of the interaction region and slight decrease of the penetration depth of fields in metal. By choosing a liquid that either allows or forbids the phase-matching, we demonstrate that the plasmon coupling efficiency can increase or vanish. Due to the wetting effect, a tapered liquid-layer forms over the tip like an additional waveguide and allows resonant coupling of fiber modes to the liquid layer.

Chiral nanomaterial fabrication by means of on-edge lithography

We present an approach named on-edge lithography, where chiral shaped pattern are yield through the combination of electron beam lithography in variable shape or cell projection mode and shadow evaporation. On one hand, we describe the process and reveal advantages when opposed to other common nano fabrication techniques. On the other hand, we also figure out challenges for successful technological application. Finally we demonstrate the useability of the process by revealing SEM pictures of a couple of realized chiral nanostructures. In order to evaluate the process we further present optical measurements. We find peak values of circular dichroism of 44% at 420 THz (715 nm). The process is applicable on large scale and to the fullest compatible with other nano-lithographic tools e.g. nanoimprint replication techniques, thus pushing chiral nanomaterial fabrication towards highest efficiency.