Max Schoengen

Enhancement of the zero phonon line emission from a single nitrogen vacancy center in a nanodiamond via coupling to a photonic crystal cavity

Using a nanomanipulation technique a nanodiamond with a single nitrogen vacancy center is placed directly on the surface of a gallium phosphide photonic crystal cavity. A Purcell-enhancement of the fluorescence emission at the zero phonon line (ZPL) by a factor of 12.1 is observed. The ZPL coupling is a first crucial step toward future diamond-based integrated quantum optical devices.

A realistic fabrication and design concept for quantum gates based on single emitters integrated in plasmonic-dielectric waveguide structures.

Tremendous enhancement of light-matter interaction in plasmonic-dielectric hybrid devices allows for non-linearities at the level of single emitters and few photons, such as single photon transistors. However, constructing integrated components for such devices is technologically extremely challenging. We tackle this task by lithographically fabricating an on-chip plasmonic waveguide-structure connected to far-field in- and out-coupling ports via low-loss dielectric waveguides. We precisely describe our lithographic approach and characterize the fabricated integrated chip. We find excellent agreement with rigorous numerical simulations. Based on these findings we perform a numerical optimization and calculate concrete numbers for a plasmonic single-photon transistor.

Integration of moth-eye structures into a poly(dimethylsiloxane) stamp for the replication of functionalized microlenses using UV-nanoimprint lithography

The increasing demand for low cost camera modules for mobile devices requires technological solutions for the manufacturing process. One of the most promising fabrication processes for microlenses for camera modules is UV-nanoimprint lithography. In a typical fabrication process, an elastomer stamp is used to replicate microlenses. In this work, a method is presented to integrate moth-eye structures as an antireflective layer into a poly(dimethylsiloxane) (PDMS) stamp containing a microlens array. The integration of these structures is done by a thermoforming process. Due to the integration of the moth-eye structures into the PDMS stamp, the optical performance of the replicated microlenses can be improved and no additional processing steps are necessary after the replication process.

Correlated Diffuse X-ray Scattering from Periodically Nano-Structured Surfaces

Laterally periodic nanostructures were investigated with grazing incidence small angle X-ray scattering. To support an improved reconstruction of nanostructured surface geometries, we investigated the origin of the contributions to the diffuse scattering pattern which is correlated to the surface roughness. Resonant diffuse scattering leads to a palm-like structure of intensity sheets. Dynamic scattering generates the so-called Yoneda band caused by a resonant scatter enhancement at the critical angle of total reflection and higher-order Yoneda bands originating from a subsequent diffraction of the Yoneda enhanced scattering at the grating. Our explanations are supported by modelling using a solver for the time-harmonic Maxwells equations based on the finite-element method.

Grazing incidence X-ray fluorescence of periodic structures – a comparison between X-ray standing waves and geometrical optics calculations

Grazing incidence X-ray fluorescence spectra of nano-scaled periodic line structures were recorded at the four crystal monochromator beamline in the laboratory of the Physikalisch-Technische Bundesanstalt at the synchrotron radiation facility BESSY II. For different tilt angles between the lines and the plane of incidence of the monochromatic synchrotron radiation, spectral features are observed which can be understood and explained with calculations of the emerging X-ray standing wave (XSW) field. On the other hand, there are structures, i.e., pronounced modulations above the substrates critical angle of external total reflection, which are not included in the XSW concept. Novel geometrical optics calculations can reproduce these structures taking the samples specific geometric conditions into account.

Metrology of nanoscale grating structures by UV scatterometry

In this contribution we demonstrate goniometric scatterometry measurements of gratings with linewidths down to 25 nm on silicon wafers with an inspection wavelength of 266 nm. For each sample, measurements have been performed in four different configurations and the obtained data have been evaluated in parallel. As results we present the reconstruction of the complete cross-section profile. We introduce a novel geometry parameterization which overcomes some limitations of the default parameterization. A co-variance analysis of the parameters is offered to indicate the soundness of the results. A qualitative comparison with cross-section scanning electron microscope (SEM) images shows excellent agreement.

Nanometrology on gratings with GISAXS: FEM reconstruction and fourier analysis

The aim of the semiconductor industry to decrease the feature size of integrated circuits poses a huge technological endeavor. Consequently, new challenges are arising for metrology on structures in the nanometer regime. Scatterometry is a fast method which provides non-contact non-destructive characterization of structures on photomasks or exposed wafers. However, the determination of important line structure parameters with subnanometer accuracy still needs further investigation. Grazing incidence small-angle X-ray scattering (GISAXS) is a scatterometry technique to measure both vertical and lateral structural features in the nanometer range with high sensitivity. We apply GISAXS to the investigation of structural parameters such as period length, sidewall angle, linewidth and height on silicon gratings. Our test structures with nominal widths of 35 nm to 100 nm and a pitch from 100 nm to 250 nm were fabricated by electron beam lithography. The diffraction patterns have been analyzed by power spectral density analysis which directly yields periodical modulations of the structured surface such as line width or groove width. We also apply a finite element method (FEM) to the diffraction peak intensity of the grating structure obtained with GISAXS for the geometric reconstruction of the line shape.

Development of a scatterometry reference standard

Scatterometry is a common technique for dimensional characterisation of nanostructures in the semiconductor industry. Currently this technique is limited to relative measurements for process development and process control. Although the high sensitivity of scatterometry is well known, it is not yet applied for absolute measurements of critical dimensions (CD) and quality control due to the lack of traceability. Thus we aim to establish scatterometry as traceable and absolute metrological method for dimensional measurements. Suitable high quality calibrated scatterometry reference standard samples are currently developed as one important step to enable traceable absolute measurements in industrial applications. The reference standard materials will base either on Si or on Si3N4. A traceable calibration of these standards will be provided by applying and combining different scatterometric as well as imaging calibration methods. First Silicon test samples have been manufactured and characterised for this purpose. The etched Si gratings have periods down to 50 nm and contain areas of reduced density to enable AFM measurements for comparison. We present the current design and first characterisations of structure details and the grating quality based on AFM measurements, optical, EUV and X-Ray scatterometry as well as spectroscopic ellipsometry. Finally we discuss possible final designs and the aimed specifications of the standard samples to face the tough requirements for future technology nodes in lithography.

Miniaturized Bragg-grating couplers for SiN-photonic crystal slabs.

We report on an experimental and theoretical investigation of an integrated Bragg-like grating coupler for near-vertical scattering of light from photonic crystal waveguides with an ultra-small footprint of a few lattice constants only. Using frequency-resolved measurements, we find the directional properties of the scattered radiation and prove that the coupler shows a good performance over the complete photonic bandgap. The results compare well to analytical considerations regarding 1d-scattering phenomena as well as to FDTD simulations.

Nanodiamonds for Integrated Quantum Technology: Charm and Challenge

Nitrogen-vacancy (NV) centers in nanodiamonds are attractive for solid state quantum technology. We report on integrating NV-centers into photonic hybrid-devices, point out future applications and address possible obstacles, like spectral diffusion.