@article{KlingspornKirnerVillringeretal.2016, author = {Klingsporn, M. and Kirner, S. and Villringer, Claus and Abou-Ras, D. and Costina, Ioan and Lehmann, M. and Stannowski, Bernd}, title = {Resolving the nanostructure of plasma-enhanced chemical vapor deposited nanocrystalline SiOx layers for application in solar cells}, series = {Journal of Applied Physics}, volume = {119}, journal = {Journal of Applied Physics}, number = {22}, issn = {1089-7550}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-9727}, year = {2016}, abstract = {Nanocrystalline silicon suboxides (nc-SiOx) have attracted attention during the past years for the use in thin-film silicon solar cells. We investigated the relationships between the nanostructure as well as the chemical, electrical, and optical properties of phosphorous, doped, nc-SiO0.8:H fabricated by plasma-enhanced chemical vapor deposition. The nanostructure was varied through the sample series by changing the deposition pressure from 533 to 1067 Pa. The samples were then characterized by X-ray photoelectron spectroscopy, spectroscopic ellipsometry, Raman spectroscopy, aberration-corrected high-resolution transmission electron microscopy, selected-area electron diffraction, and a specialized plasmon imaging method. We found that the material changed with increasing pressure from predominantly amorphous silicon monoxide to silicon dioxide containing nanocrystalline silicon. The nanostructure changed from amorphous silicon filaments to nanocrystalline silicon filaments, which were found to cause anisotropic electron transport.}, language = {en} } @article{KsianzouVillringerGrytsenkoetal.2025, author = {Ksianzou, Viachaslau and Villringer, Claus and Grytsenko, Kostyantyn and Pekur, Demyd and Lytvyn, Peter and Sopinskyy, Mykola and Lebedyeva, Iryna and Niemczyk, Agata and Baranowska, Jolanta}, title = {Structural and Optical Anomalies in Thin Films Grown in a Magnetic Field by Electron-Assisted Vacuum Deposition of PTFE}, series = {Macromolecular Materials and Engineering}, volume = {310}, journal = {Macromolecular Materials and Engineering}, number = {3}, publisher = {Wiley}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-19712}, year = {2025}, abstract = {Polytetrafluoroethylene (PTFE) films are deposited in parallel and perpendicular magnetic fields (MF) by electron-enhanced vacuum deposition (EVD) and EVD + low-temperature plasma (LTP) methods. The structure, morphology, and nanomechanical properties of the films are studied by infrared spectroscopy (IRS), atomic force microscopy (AFM), and spectroscopic ellipsometry. The structure of the thicker films is closer to that of bulk PTFE than that of thin films. The films' crystallinity and surface roughness are higher than those deposited without MF. The birefringence of the refractive index (n) of the films deposited in the MF is inverse to the anisotropy of the n of the films deposited without MF. The hardness of the films is close to that of bulk PTFE.}, language = {en} } @misc{SteglichVillringerPulweretal.2016, author = {Steglich, Patrick and Villringer, Claus and Pulwer, Silvio and Bauer, Joachim and Heinrich, Friedhelm and Casalboni, Mauro and Schrader, Sigurd}, title = {Advanced Nanophotonics: Silicon-Organic Hybrid Technology}, series = {Wissenschaftliche Beitr{\"a}ge 2016}, volume = {20}, journal = {Wissenschaftliche Beitr{\"a}ge 2016}, issn = {0949-8214}, doi = {10.15771/0949-8214_2016_1_6}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-5337}, pages = {45 -- 48}, year = {2016}, abstract = {Integrated photonic devices have gained increasing research interests. Especially silicon photonics have become very attractive for various optical applications. Using silicon-on-insulator as a material platform provides the ability to fabricate photonic devices with electronic devices on a single chip. Driven by substantial research investments, the integration of photonic devices on silicon-on-insulator substrates has reached a degree of maturity that already permits industrial adoption. However, silicon has the disadvantage of linear electro-optical effects, and, therefore, advanced modulation formats are difficult to realize when using silicon-based high-speed modulators. Hence, a new approach was proposed: the silicon-organic hybrid technology. This technology is a viable extension of the silicon-on-insulator material system for efficient high-speed modulation. We herewith present our theoretical and experimental investigations of the silicon-organic hybrid slot-waveguide ring resonator. The advanced device design is described in detail, which allows using both, the efficient silicon-on-insulator strip-waveguides and the silicon-organic hybrid slot-waveguides in single ring resonator. For the first time, we report the transmission spectra of such a resonator covered with an electro-optical polymer.}, language = {en} } @article{BaumannPohleZhangetal.2021, author = {Baumann, Elisabeth and Pohle, Ulrike and Zhang, Edward and Allen, Thomas and Villringer, Claus and Pulwer, Silvio and Gerhardt, Holger and Laufer, Jan}, title = {A backward-mode optical-resolution photoacoustic microscope for 3D imaging using a planar Fabry-P{\´e}rot sensor}, series = {Photoacoustics}, volume = {24}, journal = {Photoacoustics}, publisher = {Elsevier}, issn = {2213-5979}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-14701}, pages = {100293}, year = {2021}, abstract = {Optical-resolution photoacoustic microscopy (OR-PAM) combines high spatial resolution and strong absorption-based contrast in tissue, which has enabled structural and spectroscopic imaging of endogenous chromophores, primarily hemoglobin. Conventional piezoelectric ultrasound transducers are typically placed far away from the photoacoustic source due to their opacity, which reduces acoustic sensitivity. Optical ultrasound sensors are an alternative as their transparency allows them to be positioned close to the sample with minimal source-detector distances. In this work, a backward-mode OR-PAM system based on a planar Fabry-P{\´e}rot ultrasound sensor and coaxially aligned excitation and interrogation beams was developed. Two 3D imaging modes, using raster-scanning for enhanced image quality and continuous-scanning for fast imaging, were implemented and tested on a leaf skeleton phantom. In fast imaging mode, a scan-rate of 100,000 A-lines/s was achieved. 3D images of a zebrafish embryo were acquired in vivo in raster-scanning mode. The transparency of the FP sensor in the visible and near-infrared wavelength region makes it suitable for combined functional and molecular imaging applications using OR-PAM and multi-photon fluorescence microscopy.}, language = {en} } @inproceedings{PohleBaumannPulweretal.2019, author = {Pohle, Ulrike and Baumann, Elisabeth and Pulwer, Silvio and Villringer, Claus and Zhang, Edward and Gerhardt, Holger and Laufer, Jan}, title = {Development of a backward-mode photoacoustic microscope using a Fabry-P{\´e}rot sensor}, publisher = {SPIE}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-15349}, pages = {594 -- 598}, year = {2019}, abstract = {Optical-resolution photoacoustic microscopy (PAM) has been shown to enable the acquisition of high resolution (μm) functional and anatomical images. For backward-mode operation, conventional piezoelectric ultrasound transducers need to be placed far away from the signal source due to their opacity and size. This can result in reduced acoustic sensitivity. Planar Fabry-Perot polymer film interferometer (FPI) sensors have the potential to overcome this limitation since they are transparent to the excitation wavelength, can be placed immediately adjacent to the signal source for high acoustic sensitivity, and offer a broadband frequency response (0 -50 MHz). In this study, we present a high frame rate, backward-mode OR-PAM system based on a planar FPI ultrasound sensor. A ns-pulsed laser provides excitation pulses (<200 nJ, maximum pulse repetition frequency = 200 kHz, 532 nm) to generate photoacoustic waves that are detected using a planar FPI sensor interrogated at 765-781 nm. For backwardmode operation and highest acoustic sensitivity, the excitation and interrogation beams are coaxially aligned and rasterscanned. The optical transfer function of the sensor, the spatial resolution and the detection sensitivity were determined to characterise the set-up. Images of a leaf phantom and first in vivo images of zebrafish larvae were acquired. This approach will enable fast 3D OR-PAM with high resolution and high sensitivity for functional and molecular imaging applications. FPI-based ultrasound detection also has the potential to enable dual-mode optical- and acousticresolution PAM and the integration of photoacoustic imaging with purely optical modalities such as multi-photon microscopy.}, language = {en} } @inproceedings{PulwerFiebelkornZeschetal.2019, author = {Pulwer, Silvio and Fiebelkorn, Richard and Zesch, Christoph and Steglich, Patrick and Villringer, Claus and Villasmunta, Francesco and Gedat, Egbert and Handrich, Jan and Schrader, Sigurd and Vandenhouten, Ralf}, title = {Endoscopic orientation by multimodal data fusion}, series = {Proc. SPIE 10931, MOEMS and Miniaturized Systems XVIII}, booktitle = {Proc. SPIE 10931, MOEMS and Miniaturized Systems XVIII}, issn = {1996-756X}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-11420}, year = {2019}, abstract = {To improve the feasibility of endoscopic inspection processes we developed a system that provides online information about position, orientation and viewing direction of endoscopes, to support the analysis of endoscopic images and to ease the operational handling of the equipment. The setup is based on an industrial endoscope consisting of a camera, various MEMS and multimodal data fusion. The software contains algorithms for feature and geometric structure recognition as well as Kalman filters. To track the distal end of the endoscope and to generate 3D point cloud data in real time the optical and photometrical characteristics of the system are registered and the movement of the endoscope is reconstructed by using image processing techniques.}, language = {en} } @article{SteglichMaiVillringeretal.2021, author = {Steglich, Patrick and Mai, Christian and Villringer, Claus and Dietzel, Birgit and Bondarenko, Siegfried and Ksianzou, Viachaslau and Villasmunta, Francesco and Zesch, Christoph and Pulwer, Silvio and Burger, Martin and Bauer, Joachim and Heinrich, Friedhelm and Schrader, Sigurd and Vitale, Francesco and De Matteis, Fabio and Prosposito, Paolo and Casalboni, Mauro and Mai, Andreas}, title = {Silicon-organic hybrid photonics: an overview of recent advances, electro-optical effects and CMOS integration concepts}, series = {Journal of Physics: Photonics}, volume = {3}, journal = {Journal of Physics: Photonics}, number = {2}, issn = {2515-7647}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-13882}, year = {2021}, abstract = {In recent decades, much research effort has been invested in the development of photonic integrated circuits, and silicon-on-insulator technology has been established as a reliable platform for highly scalable silicon-based electro-optical modulators. However, the performance of such devices is restricted by the inherent material properties of silicon. An approach to overcoming these deficiencies is to integrate organic materials with exceptionally high optical nonlinearities into a silicon-on-insulator photonic platform. Silicon-organic hybrid photonics has been shown to overcome the drawbacks of silicon-based modulators in terms of operating speed, bandwidth, and energy consumption. This work reviews recent advances in silicon-organic hybrid photonics and covers the latest improvements to single components and device concepts. Special emphasis is given to the in-device performance of novel electro-optical polymers and the use of different electro-optical effects, such as the linear and quadratic electro-optical effect, as well as the electric-field-induced linear electro-optical effect. Finally, the inherent challenges of implementing non-linear optical polymers on a silicon photonic platform are discussed and a perspective for future directions is given.}, language = {en} } @inproceedings{VillasmuntaSteglichVillringeretal.2024, author = {Villasmunta, Francesco and Steglich, Patrick and Villringer, Claus and Schrader, Sigurd and Schenk, Harald and Mai, Andreas and Regehly, Martin}, title = {Design, fabrication, and characterization of integrated optical through-silicon waveguides for 3D photonic interconnections}, series = {Optical Interconnects XXIV}, volume = {12892}, booktitle = {Optical Interconnects XXIV}, editor = {Chen, Ray T. and Schr{\"o}der, Henning}, publisher = {Society of Photo-Optical Instrumentation Engineers (SPIE)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-19759}, year = {2024}, abstract = {In the context of an ever-growing volume of data generated by established and emerging technologies, such as 5G, the Internet of Things, artificial intelligence, machine learning, blockchain, and virtual reality, faster communication speed is demanded by data centers and high-performance computing. Transceiver requirements surged from 100 to 400 Gb/s and beyond. In this scenario, photonics aims to enable Tb/s optical communication at energies below 1 pJ/bit. Targeting higher communication rates while maintaining a low power budget can significantly benefit from 3D photonic chip architectures. This paper presents the simulation-based design, fabrication, and characterization of a monolithically integrated optical through-silicon waveguide that facilitates the connection between different surfaces of a silicon chip. Deep reactive ion etching was employed in both the Bosch and Cryogenic variants to evaluate the effect of sidewall roughness on propagation losses. The mechanical stability of the waveguide was ensured by interrupting the annular trench with a bridging structure. The high-refractive-index contrast to air provides tight light confinement for a core size of up to 50 μm and multimode operation at 1550 nm. The morphology was characterized using scanning electron microscopy (SEM), and optical transmission characterization was performed using relative power loss measurements. A tunable laser source was buttcoupled to a waveguide to analyze light transmission efficiency. Preliminary measurements using single-mode fiber show that the transmitted values exceeded 99\% for all structures.}, language = {en} } @article{BauerHeinrichVillasmuntaetal.2025, author = {Bauer, Joachim and Heinrich, Friedhelm and Villasmunta, Francesco and Villringer, Claus and Reck, Johanna and Peters, Sven and Treffer, Alexander and Kuhnt, Christian and Marschmeyer, Steffen and Fursenko, Oksana and Stolarek, David and Mai, Andreas and Regehly, Martin}, title = {Reflectometric method for measuring residual oxides in through-silicon vias for 3D chip integration}, series = {Optics Express}, volume = {33}, journal = {Optics Express}, number = {15}, publisher = {Optica}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-20633}, pages = {32175 -- 32189}, year = {2025}, abstract = {A significant aspect of fabricating 3D chip architectures is ensuring proper contact between the different layers of the chip, which often requires removing the underside of isolation layers before filling vias with conductive material. Currently, scanning electron microscopy is the established method for investigating such structures. In this paper, we propose a rapid, non-destructive optical analysis technique for the simultaneous measurement of through-silicon vias (TSV) depths, silicon wafer thickness, and residual oxide thickness. The proposed method utilizes Fourier peak shift analysis (FPSA) of reflectance measurements in the near-infrared (1200 nm—2200 nm) spectral regions. The application of FPSA to representative samples taken from a commercial TSV integration process for MEMS and CMOS fabrication demonstrated good agreement with reference scanning electron microscopy measurements, confirming the feasibility of the method for in-line and in-situ metrology. The results indicate that FPSA has great potential for real-time process monitoring and control during 3D chip manufacturing.}, language = {en} } @article{BauerFursenkoMarschmeyeretal.2019, author = {Bauer, Joachim and Fursenko, Oksana and Marschmeyer, Steffen and Heinrich, Friedhelm and Villasmunta, Francesco and Villringer, Claus and Zesch, Christoph and Schrader, Sigurd}, title = {Spectroscopic reflectometry for characterization of Through Silicon Via profile of Bosch etching process}, series = {Journal of Vacuum Science \& Technology B}, volume = {37}, journal = {Journal of Vacuum Science \& Technology B}, number = {6}, publisher = {American Vacuum Society (AVS)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-16093}, year = {2019}, abstract = {Through Silicon Via (TSV) technology is a key in 3D integration of circuits by the creation of interconnects using vias, which go through the full silicon wafer. Typically, a highly-selective Bosch Si etch process is used. It is characterized by a high etch rate at a high aspect ratio, whereby scallops on the sidewalls are generated. In this work, square via arrays with dimensions from 3 to 50 μm and up to 300 μm depth were fabricated and analyzed by spectroscopic reflectometry. The reflectometric data are compared to simulations by a novel theoretical approach. In order to simulate the reflectance spectra of TSV arrays, a combination of 2D and 3D rigorous coupled wave analysis was applied. Besides the via depth, the sidewall angle and the corner radius of the bottom profile were considered in the model. The general requirements on spectral resolution in TSV metrology are discussed.}, language = {en} }