Characterization and discrimination of periodic nanostructures with scanning-free GEXRF
Year of publicationPublished in:Nanotechnology
N. Wauschkuhn, Y. Kayser, J. Baumann, J. Degenhardt, T. Siefke, V. Truong, V. Soltwisch, B. Beckhoff, P. Hönicke
Instrumentation and uncertainty evaluation for absolute characterization of thin films and nanostructured surfaces in advanced optical metrology
Year of publicationPublished in:Metrologia
P. Hansen, L. Siaudinyte, S. Heidenreich, V. Soltwisch, H. Lokhorst, A. Tiwari, I. Makhotkin, A. Mattila, A. Lassila, S. Glabisch, S. Schröder, S. Brose, E. Nolot, T. Siefke, M. Asar, S. Memis, F. Yíldíz, M. Schiek, A. Rømer
Spectroscopic Ellipsometry of Plasmonic Gratings: Ideal Parameters for Sensing and Subpicometer Measurement Uncertainty
Year of publicationPublished in:ACS Omega
D. Mukherjee, S. Burger, T. Siefke, J. Gour, B. Bodermann, P. Petrik
Gold gratings were measured by spectroscopic ellipsometry in reflection mode and modeled by the finite element method to investigate the capabilities of optical dimensional metrology for plasmonic diffractive structures. The gratings were prepared by electron beam lithography using parameters determined by finite element simulations for significant variations of the amplitude ratio and phase shift of the polarized reflection coefficients to achieve high sensitivity for both the measurement of the grating dimensions and the sensing capabilities. The sensitivity largely depends on the values in the five-dimensional parameter space including the grating parameters such as the critical dimension, the period, and the thickness of the grating, as well as the measurement parameters comprising the wavelength and the angle of incidence. The best limit of detection values are in the picometer range for the critical dimension and the thickness of the overlayer, and ≈10⁻⁵ for the refractive index.
Ultra shallow silicon EUV gratings fabricated via ion irradiation
Year of publicationPublished in:EUV and X-Ray Optics: Synergy between Laboratory and Space IX: 7-8 April 2025, Prague, Czech Republic
J. Kaufmann, R. Ciesielski, K. Freiberg, M. Walther, A. Fernández Herrero, S. Lippmann, V. Soltwisch, T. Siefke, U. Zeitner
Fabrication of shallow EUV gratings on silicon by irradiation with helium ions
Year of publicationPublished in:Nanotechnology
J. Kaufmann, R. Ciesielski, K. Freiberg, M. Walther, A. Fernández Herrero, S. Lippmann, V. Soltwisch, T. Siefke, U. Zeitner
To accurately achieve structure height differences in the range of single digit nanometres is of great importance for the fabrication of diffraction gratings for the extreme ultraviolet range (EUV). Here, structuring of silicon irradiated through a mask by a broad beam of helium ions with an energy of 30 keV was investigated as an alternative to conventional etching, which offers only limited controllability for shallow structures due to the higher rate of material removal. Utilising a broad ion beam allows for quick and cost effective fabrication. Ion fluence of the irradiations was varied in the range of 10¹⁶ ... 10¹⁷ ions · cm⁻². This enabled a fine tuning of structure height in the range of 1.00 ± 0.05 to 20 ± 1 nm, which is suitable for shallow gratings used in EUV applications. According to transmission electron microscopy investigations the observed structure shape is attributed to the formation of point defects and bubbles/cavities within the silicon. Diffraction capabilities of fabricated elements are experimentally shown at the SX700 beamline of BESSY II. Rigorous Maxwell solver simulation based on the finite-element method and rigorous coupled wave analysis are utilised to describe the experimental obtained diffraction pattern.
Nonlinear harmonic generation in sub-5 nm plasmonic nanogap metasurfaces
Year of publicationPublished in:2025 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)
S. Beer, J. Gour, P. Paul, A. Alberucci, A. Szeghalmi, T. Siefke, U. Peschel, U. Zeitner, S. Nolte
Fabrication of low-loss lithium niobate on insulator waveguides on the wafer scale [Invited]
Year of publicationPublished in:Optical Materials Express
M. Younesi, T. Kasebier, I. Elmanov, Y. Li, P. Kumar, R. Geiss, T. Siefke, F. Eilenberger, F. Setzpfandt, U. Zeitner, T. Pertsch
We report on the wafer scale fabrication of single-mode low-loss lithium niobate on insulator waveguides utilizing a chemically amplified resist and an optimized dry etching method. The fabricated single-mode waveguides are free of residuals and re-deposition, with measured losses for straight waveguides around 2 dB/m (0.02 dB/cm). We present a method offering advantages for large-scale production mainly due to its cost-effectiveness and faster writing time. This work holds promise for advancing integrated photonics and optical communication technologies.
Resolution enhancement methods in optical microscopy for dimensional optical metrology
Year of publicationStatusReview pendingPublished in:Journal of the European Optical Society-Rapid Publications
M. Nouri, P. Olivero, S. Kroker, T. Käseberg, I. Ruo-Berchera, B. Bodermann, H. Tyagi, D. Roy, D. Mukherjee, T. Siefke, P. Hansen, A. Rømer, M. Valtr, P. Aprà, P. Petrik
In this paper, we discuss several enhancement approaches to increase the resolution and sensitivity of optical microscopy as a tool for dimensional nanometrology. Firstly, we discuss a newly developed through-focus microscopy technique providing additional phase information from the afocal images to increase the nanoscale sensitivity of classical microscopy. We also explore different routes to label-free or semiconductor compatible labelling super-resolution microscopy suitable for a broad range of technical applications. We present initial results from, a new wide-field super-resolution imaging technique enabled by Raman scattering. In addition, we discuss super-resolution imaging using NV centres in nano-diamonds as labels and their application in future reference standards.
Fabrication of ultra-shallow EUV gratings in silicon via ion irradiation
Year of publicationStatusReview pendingPublished in:Proceedings of SPIE - The International Society for Optical Engineering
J. Kaufmann, R. Ciesielski, K. Freiberg, M. Walther, A. Herrero, S. Lippmann, V. Soltwisch, T. Siefke, U. Zeitner
Laser-driven high-flux source of coherent quasi-monochromatic extreme ultraviolet radiation for coincidence spectroscopy
Year of publicationStatusReview pendingPublished in:The Review of scientific instruments
J. Späthe, S. Hell, M. Wünsche, R. Klas, J. Rothhardt, J. Limpert, T. Siefke, G. Paulus, M. Kübel
Scalable plasmonic metasurfaces with features down to 2 nm: advancing nanofabrication for enhancing nonlinear optical effects
Year of publication
J. Gour
This thesis focuses on the development of a scalable nanofabrication approach for plasmonic metasurfaces and on their linear and nonlinear optical characterization, supporting both localized and collective resonances. First, by combining high-throughput electron-beam writing techniques such as variable shaped beam and character projection strategies with standard metal lift-off processes, large-area plasmonic nanobar metasurfaces were realized on a 100 mm fused silica wafer. These nanobar arrays exhibit resonant lattice plasmon conditions at the excitation and emission wavelengths, leading to enhanced second- and third-harmonic generation. To push the limits of field confinement, a wafer-scale fabrication approach was developed to achieve plasmonic metasurfaces with sub-5 nm gap features. Through a wafer-scale nanofabrication process, independently shaped bow-tie antennas with gap widths down to 2 nm were achieved. Measurements and simulations confirm gap-plasmon modes and collective resonances, while deviations between experiment and theory indicate nonlocal effects. The 2 nm-gap metasurfaces achieve 2–3 orders of magnitude higher second-harmonic efficiency compared to larger-gap structures, and their angular nonlinear response correlates strongly with linear lattice resonance features. Overall, this work demonstrates reliable and scalable fabrication of plasmonic metasurfaces with controllable gap sizes approaching the sub-nanometer regime. The results highlight the need for advanced theoretical models that account for nonlocal response in sub-5 nm nanostructures and open pathways for metasurface-based applications in molecular sensing, nanoscale trapping, and petahertz optoelectronic devices.