Integration of multijunction absorbers and catalysts for efficient solar-driven artificial leaf structures: a physical and materials science perspective. - In: Solar RRL, ISSN 2367-198X, Bd. 0 (2024), 0, 2301047, S. 1-88
Artificial leaves could be the breakthrough technology to overcome the limitations of storage and mobility through the synthesis of chemical fuels from sunlight, which will be an essential component of a sustainable future energy system. However, the realization of efficient solar-driven artificial leaf structures requires integrated specialized materials such as semiconductor absorbers, catalysts, interfacial passivation, and contact layers. To date, no competitive system has emerged due to a lack of scientific understanding, knowledge-based design rules, and scalable engineering strategies. Here, we will discuss competitive artificial leaf devices for water splitting, focusing on multi-absorber structures to achieve solar-to-hydrogen conversion efficiencies exceeding 15%. A key challenge is integrating photovoltaic and electrochemical functionalities in a single device. Additionally, optimal electrocatalysts for intermittent operation at photocurrent densities of 10-20 mA cm^-2 must be immobilized on the absorbers with specifically designed interfacial passivation and contact layers, so-called buried junctions. This minimizes voltage and current losses and prevents corrosive side reactions. Key challenges include understanding elementary steps, identifying suitable materials, and developing synthesis and processing techniques for all integrated components. This is crucial for efficient, robust, and scalable devices. Here, we discuss and report on corresponding research efforts to produce green hydrogen with unassisted solar-driven (photo-)electrochemical devices. This article is protected by copyright. All rights reserved.
https://doi.org/10.1002/solr.202301047
Approaches for the RCWA-based non-destructive characterization of subwavelength-structured gratings. - In: EOS Annual Meeting (EOSAM 2022), (2022), 05012, S. 1-2
Nano-structuring enables us to add additional degrees of freedom to the design of optical elements. Especially the possibility of controlling the polarization is of great interest in the field of nano-structured optics. For being able to exploit the whole range of form-birefringent phase shifts, the aspect ratios of the resulting element are typically much higher than the aspect ratios of conventional diffractive optical elements (DOEs), which does not only pose a challenge on fabrication but also on characterization. We evaluate several well-established approaches for the nondestructive characterization, including Müller-Matrix-Ellipsometry, measurement of the diffraction efficiencies, scattering measurements and calibration with rigorous coupled-wave modelling. The goal is to understand the challenges with all these techniques and combine them to a reliable method for structural reconnaisance of high aspect ratio nanostructures.
https://doi.org/10.1051/epjconf/202226605012
Ellipsometry and polarimetry - classical measurement techniques with always new developments, concepts, and applications. - In: Advanced Optical Technologies, ISSN 2192-8584, Bd. 11 (2022), 3/4, S. 57-58
https://doi.org/10.1515/aot-2022-0025
Coherent acoustic phonon oscillations and transient critical point parameters of Ge from femtosecond pump-probe ellipsometry. - In: Physica status solidi, ISSN 1862-6270, Bd. 16 (2022), 7, 2200058, S. 1-7
Herein, the complex pseudodielectric function of Ge and Si from femtosecond pump-probe spectroscopic ellipsometry with 267, 400, and 800 nm pump-pulse wavelengths is analyzed by fitting analytical lineshapes to the second derivatives of the pseudodielectric function with respect to energy. This yields the critical point parameters (threshold energy, lifetime broadening, amplitude, and excitonic phase angle) of E 1 and E 1 + Δ 1 in Ge and E 1 in Si as functions of delay time. Coherent longitudinal acoustic phonon oscillations with a period of about 11 ps are observed in the transient critical point parameters of Ge. From the amplitude of these oscillations, the laser-induced strain is found to be on the order of 0.03% for Ge measured with the 800 nm pump pulse, which is in reasonable agreement with the strain calculated from theory.
https://doi.org/10.1002/pssr.202200058
Analysis of temperature-dependent and time-resolved ellipsometry spectra of Ge. - In: 2021 IEEE Photonics Society Summer Topicals Meeting Series (SUM), (2021), insges. 2 S.
https://doi.org/10.1109/SUM48717.2021.9505707
Broadband femtosecond spectroscopic ellipsometry. - In: Review of scientific instruments, ISSN 1089-7623, Bd. 92 (2021), 3, S. 033104-1-033104-14
We present a setup for time-resolved spectroscopic ellipsometry in a pump-probe scheme using femtosecond laser pulses. As a probe, the system deploys supercontinuum white light pulses that are delayed with respect to single-wavelength pump pulses. A polarizer-sample-compensator-analyzer configuration allows ellipsometric measurements by scanning the compensator azimuthal angle. The transient ellipsometric parameters are obtained from a series of reflectance-difference spectra that are measured for various pump-probe delays and polarization (compensator) settings. The setup is capable of performing time-resolved spectroscopic ellipsometry from the near-infrared through the visible to the near-ultraviolet spectral range at 1.3 eV-3.6 eV. The temporal resolution is on the order of 100 fs within a delay range of more than 5 ns. We analyze and discuss critical aspects such as fluctuations of the probe pulses and imperfections of the polarization optics and present strategies deployed for circumventing related issues.
https://doi.org/10.1063/5.0027219
Transient birefringence and dichroism in ZnO studied with fs-time-resolved spectroscopic ellipsometry. - In: Physical review research, ISSN 2643-1564, Bd. 3 (2021), 1, S. 013246-1-013246-12
The full transient dielectric-function (DF) tensor of ZnO after UV-laser excitation in the spectral range 1.4-3.6 eV is obtained by measuring an m-plane-oriented ZnO thin film with femtosecond (fs)-time-resolved spectroscopic ellipsometry. From the merits of the method, we can distinguish between changes in the real and the imaginary part of the DF as well as changes in birefringence and dichroism, respectively. We find pump-induced switching from positive to negative birefringence in almost the entire measured spectral range for about 1 ps. Simultaneously, weak dichroism in the spectral range below 3.0 eV hints at contributions of inter-valence-band transitions. Line-shape analysis of the DF above the band gap based on discrete exciton, exciton-continuum, and exciton-phonon-complex contributions shows a maximal dynamic increase in the transient exciton energy by 80 meV. The absorption coefficient below the band gap reveals an exponential line shape attributed to Urbach-rule absorption mediated by exciton-longitudinal-optic-phonon interaction. The transient DF is supported by first-principles calculations for 1020cm^-3 excited electron-hole pairs in ideal bulk ZnO.
https://doi.org/10.1103/PhysRevResearch.3.013246
Impact of defects on magnetic properties of spinel zinc ferrite thin films. - In: Physica status solidi, ISSN 1521-3951, Bd. 257 (2020), 7, 1900630, insges. 11 S.
The recent developments in the study of magnetic properties in the spinel zinc ferrite system are explored. Engineering of ionic valence and site distribution allows tailoring of magnetic interactions. Recent literature is reviewed, and own investigations are presented for a conclusive understanding of the mechanisms responsible for the magnetic behavior in this material system. By varying the Zn-to-Fe ratio, the deposition, as well as thermal annealing conditions, ZnFe2O4 thin films with a wide range of crystalline quality are produced. In particular, the focus is on the magnetic structure in relation to spectroscopic properties of disordered ZnFe2O4 thin films. Comparing the cation distribution in film bulk (optical transitions in the dielectric function) and near-surface region (X-ray absorption), it is found that an inhomogeneous cation distribution leads to a weaker magnetic response in films of inverse configuration, whereas defects in the normal spinel are likely to be found at the film surface. The results show that it is possible to engineer the defect distribution in the magnetic spinel ferrite film structure and tailor their magnetic properties on demand. It is demonstrated that these properties can be read out optically, which allows controlled growth of the material and applications in future magneto-optical devices.
https://doi.org/10.1002/pssb.201900630
Control of magnetic properties in spinel ZnFe2O4 thin films through intrinsic defect manipulation. - In: Journal of applied physics, ISSN 1089-7550, Bd. 128 (2020), 16, 165702, insges. 7 S.
Im Titel sind "2" und "4" tiefgestellt
We present a systematic study of the magnetic properties of ZnFe2O4 thin films fabricated by pulsed laser deposition at low and high oxygen partial pressure and annealed in oxygen and argon atmosphere, respectively. The as-grown films show strong magnetization, closely related to a non-equilibrium distribution of defects, namely, Fe cations among tetrahedral and octahedral lattice sites. While the concentration of tetrahedral Fe cations declines after argon treatment at 250 ˚C, the magnetic response is enhanced by the formation of oxygen vacancies, evident by the increase in near-infrared absorption due to the Fe2+-Fe3+ exchange. After annealing at temperatures above 300 ˚C, the weakened magnetic response is related to a decline in disorder with a partial recrystallization toward a less defective spinel configuration.
https://doi.org/10.1063/5.0019712
Ultrafast dynamics of hot charge carriers in an oxide semiconductor probed by femtosecond spectroscopic ellipsometry. - In: New journal of physics, ISSN 1367-2630, Bd. 22 (2020), 083066, insges. 14 S.
https://doi.org/10.1088/1367-2630/aba7f3
Hybrid GA-gradient method for thin films ellipsometric data evaluation. - In: Journal of computational science, ISSN 1877-7503, Bd. 47 (2020), 101201
A global-search method which applies the concept of genetic algorithm (GA) with gradient-based optimizer is proposed for the problem of experimental data analysis from spectroscopic ellipsometry on thin films. The method is applied to evaluate the data obtained for samples with different structure complexity, starting with transparent monolayers (SiO2, HfO2) on a substrate, through absorbing film (diamond-like carbon) and multilayer structures. We demonstrate that by using this method we are able to find material parameters even for limited a priori knowledge about the sample properties, where classical methods fail.
https://doi.org/10.1016/j.jocs.2020.101201
Structure and dielectric function tensor of (Al,Sc)N thin films. - In: DPG-Frühjahrstagung (DPG Spring Meeting) of the Condensed Matter Section (SKM) together with the DPG Division Environmental Physics and the Working Groups Accelerator Physics; Equal Opportunities; Energy; Industry and Business; Physics, Modern IT and Artificial Intelligence, Young DPG, (2020), HL 30.29
Ellipsometric study of defect induced magnetism in spinel ferrite thin films. - In: DPG-Frühjahrstagung (DPG Spring Meeting) of the Condensed Matter Section (SKM) together with the DPG Division Environmental Physics and the Working Groups Accelerator Physics; Equal Opportunities; Energy; Industry and Business; Physics, Modern IT and Artificial Intelligence, Young DPG, (2020), DS 39.3
Carbon nanodots: luminescence properties tuned by microcavity devices. - In: DPG-Frühjahrstagung (DPG Spring Meeting) of the Condensed Matter Section (SKM) together with the DPG Division Environmental Physics and the Working Groups Accelerator Physics; Equal Opportunities; Energy; Industry and Business; Physics, Modern IT and Artificial Intelligence, Young DPG, (2020), HL 64.45
Exceptional Points in optical anisotropic semiconductors. - In: DPG-Frühjahrstagung (DPG Spring Meeting) of the Condensed Matter Section (SKM) together with the DPG Division Environmental Physics and the Working Groups Accelerator Physics; Equal Opportunities; Energy; Industry and Business; Physics, Modern IT and Artificial Intelligence, Young DPG, (2020), HL 75.20
Dielectric function tensor of ZnO microwires determined by spatially resolved spectroscopic ellipsometry. - In: DPG-Frühjahrstagung (DPG Spring Meeting) of the Condensed Matter Section (SKM) together with the DPG Division Environmental Physics and the Working Groups Accelerator Physics; Equal Opportunities; Energy; Industry and Business; Physics, Modern IT and Artificial Intelligence, Young DPG, (2020), HL 75.26
Richtiger Name des 1. Verfassers: Noah Hill
Surface modification and charge carrier dynamics of materials and structures for semiconductor-based solar water splitting applications under operation conditions. - In: DPG-Frühjahrstagung (DPG Spring Meeting) of the Condensed Matter Section (SKM) together with the DPG Division Environmental Physics and the Working Groups Accelerator Physics; Equal Opportunities; Energy; Industry and Business; Physics, Modern IT and Artificial Intelligence, Young DPG, (2020), HL 75.25
Coherent polariton modes and lasing in ZnO microcavities. - Leipzig. - Seite ii-vi, 40 Seiten, Seite a-f
Universität Leipzig, Habilitationsschrift 2020
Molybdenum silicide in infrared emitting devices. - In: MOEMS and Miniaturized Systems XIX, (2020), S. 112930Y-1-112930Y-9
https://doi.org/10.1117/12.2556681
Exceptional points in optical anisotropic thin films. - In: Quantum science and information technologies, (2019), FM 83.7
Femtosecond-time-resolved imaging of the dielectric function of ZnO in the visible to near-IR spectral range. - In: Applied physics letters, ISSN 1077-3118, Bd. 115 (2019), 21, S. 212103-1-212103-5
https://doi.org/10.1063/1.5128069
Voigt exceptional points in an anisotropic ZnO-based planar microcavity: square-root topology, polarization vortices, and circularity. - In: Physical review letters, ISSN 1079-7114, Bd. 123 (2019), 22, 227401, insges. 7 S.
https://doi.org/10.1103/PhysRevLett.123.227401
On the optical properties of thin-film vanadium dioxide from the visible to the far infrared. - In: Annalen der Physik, ISSN 1521-3889, Bd. 531 (2019), 10, 1900188, S. 1-7
https://doi.org/10.1002/andp.201900188
Dielectric function of ZnO and MgZnO and application to bragg reflectors and micro-resonators, 2007. - XVI, 190 Bl. : Leipzig, Univ., Diss., 2007
Zsfassung in dt. Sprache