Soft X-ray varied-line-spacing gratings fabricated by near-field holography using an electron beam lithography-written phase mask.

A fabrication method comprising near-field holography (NFH) with an electron beam lithography (EBL)-written phase mask was developed to fabricate soft X-ray varied-line-spacing gratings (VLSGs). An EBL-written phase mask with an area of 52 mm × 30 mm and a central line density greater than 3000 lines mm-1 was used. The introduction of the EBL-written phase mask substantially simplified the NFH optics for pattern transfer. The characterization of the groove density distribution and diffraction efficiency of the fabricated VLSGs indicates that the EBL-NFH method is feasible and promising for achieving high-accuracy groove density distributions with corresponding image properties. Vertical stray light is suppressed in the soft X-ray spectral range.

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.

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.

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.

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.

Optical modes excited by evanescent-wave-coupled PbS nanocrystals in semiconductor microtube bottle resonators.

We report on optical modes in rolled-up microtube resonators that are excited by PbS nanocrystals filled into the microtube core. Long ranging evanescent fields into the very thin walled microtubes cause strong emission of the nanocrystals into the resonator modes and a mode shift after a self-removal of the solvent. We present a method to precisely control the number, the energy and the localization of the modes along the microtube axis.