Light-induced degradation transition energy barrier measured by photoluminescence spectra in Si:In. - In: Physica status solidi, ISSN 1862-6319, Bd. 0 (2024), 0, 2400570, S. 1-7
https://doi.org/10.1002/pssa.202400570
Supervised probabilistic dynamic-controlled latent-variable model for quality pattern prediction and optimisation. - In: ISA transactions, ISSN 1879-2022, Bd. 0 (2024), 0, S. 1-19
A supervised probabilistic dynamic-controlled latent-variable (SPDCLV) model is proposed for online prediction, as well as real-time optimisation of process quality indicators. Compared to existing probabilistic latent-variable models, the key advantage of the proposed method lies in explicitly modelling the dynamic causality from the manipulated inputs to the quality pattern. This is achieved using a well-designed, dynamic-controlled Bayesian network. Furthermore, the algorithms for expectation-maximisation, forward filtering, and backward smoothing are designed for learning the SPDCLV model. For engineering applications, a framework for pattern-based quality prediction and optimisation is proposed, under which the pattern-filtering and pattern-based soft sensor are explored for online quality prediction. Furthermore, quality optimisation can be realised by directly controlling the pattern to the desired condition. Finally, case studies on both an industrial primary milling circuit and a numerical example illustrate the benefits of the SPDCLV method in that it can fully model the process dynamics, effectively predict and optimise the quality indicators, and monitor the process.
https://doi.org/10.1016/j.isatra.2024.08.001
Surface structure of MOVPE-prepared As-modified Si(100) substrates. - In: Applied surface science, Bd. 675 (2024), 160879, S. 1-8
In the pursuit of high-efficiency tandem devices for solar energy conversion based on III-V-semiconductors, low-defect III-V nucleation on Si(100) substrates is essential. Here, hydrogen and arsenic are key ingredients in all growth processes with respect to industrially scalable metalorganic vapor phase epitaxy. Our study provides insight into Si(100) surface preparation for the initial stage of III-V nucleation. The samples investigated, prepared on substrates with different offcut angles, show single domain surfaces consisting of rows of preferentially buckled dimers. Low energy electron diffraction and reflection anisotropy spectroscopy confirm well-defined (1 × 2)/(2 × 1) majority domains. Fourier-transform infrared spectroscopy revealed hydrogen bonding to the surface dimers, while no impurities were found by XPS. Density functional theory calculations support the experimental results and reveal a novel surface motif of H-passivated Si-As mixed dimers.
https://doi.org/10.1016/j.apsusc.2024.160879
Model predictive control of a magnetic levitation system with prescribed output tracking performance. - In: Control engineering practice, ISSN 1873-6939, Bd. 151 (2024), 106018, S. 1-14
To guarantee the safe and dependable operation of a magnetic levitation train, the distance between the magnet and the reaction rail needs to be kept within a given range. In this work, we design model predictive controllers which, in addition to complying with these constraints, provide a favorable behavior with regard to performance criteria such as travel comfort and control effort. For this purpose, we present a model of the system and the disturbances affecting it. Several results regarding the mathematical properties of this model are proven to gain insight for controller design. Finally we compare three different controllers w.r.t. performance criteria such as robustness, travel comfort, control effort, and computation time in an extensive numerical simulation study: a linear feedback controller, a model predictive control (MPC) scheme with quadratic stage costs, and the recently-proposed funnel MPC scheme. We show that the MPC closed loop complies with the constraints while also exhibiting excellent performance. Furthermore, we implement the MPC algorithms within the GRAMPC framework. This allows us to reduce the computational effort to a point at which real-time application becomes feasible.
https://doi.org/10.1016/j.conengprac.2024.106018
Effect of inelastic ion collisions on low-gain avalanche detectors explained by an ASi-Sii-defect mode. - In: Nuclear instruments & methods in physics research, Bd. 555 (2024), 165472, S. 1-5
The acceptor removal phenomenon (ARP), which hampers the functionality of low-gain avalanche detectors (LGAD), is discussed in frame of the ASi-Sii-defect model. The assumption of fast diffusion of interstitial silicon is shown to be superfluous for the explanation of the BSi-Sii-defect formation under irradiation, particular at very low temperatures. The experimentally observed properties of the ARP are explained by the donor properties of the BSi-Sii-defect in its ground state. Additionally, low temperature photoluminescence spectra are reported for quenched boron doped silicon showing so far unidentified PL lines, which change due to well-known light-induced degradation (LID) treatments.
https://doi.org/10.1016/j.nimb.2024.165472
Gigahertz and terahertz transistors for 5G, 6G, and beyond mobile communication systems. - In: Applied physics reviews, ISSN 1931-9401, Bd. 11 (2024), 3, 031318, S. 031318-1-031318-37
Mankind is currently living in the era of mobile communication. Mobile communication encompasses almost all areas of our daily life and is heavily used in most sectors of economy, including agriculture, healthcare, education, and so on. With mobile devices such as smart phones, people can connect to any other people somewhere on the earth, can access huge databases via the internet, stream videos and movies, to name just a few of the many mobile services that are routinely used in the early 2020s. Artificial intelligence, virtual reality, and other emerging new applications will further boost the importance of mobile communication. It is a general trend that with progressing evolution of mobile communication, the amount of data to be transmitted wirelessly increases rapidly and continuously. To enable this, a suitable well-performing hardware infrastructure is needed. The hardware used so far in the successively introduced generations of systems for mobile communication is essentially based on fast transistors. We designate these transistors as gigahertz (GHz)-terahertz (THz) transistors, as the high data rates to be transferred require an electronic hardware operating properly at frequencies in the GHz-THz range. The present paper provides a comprehensive in-depth discussion of these transistors. After a short survey of the evolution of mobile communication systems, the different categories and classes of GHz-THz transistors are introduced, relevant transistor performance measures called figures of merit are defined, issues of transistor design are dealt with, and general design rules for GHz-THz transistors are established. This is followed by a tour through the evolution of these transistors, starting in the 1950s, when the first transistors with GHz capabilities were demonstrated, up to the latest developments since the turn of the millennium and to the state-of-the-art in mid-2024. The discussion includes evolutionary advances as well as true breakthroughs, both contributing to the significant performance improvements achieved over the years. Furthermore, some research activities on GHz-THz transistors, which, unfortunately, led to a dead end as well as ongoing efforts with still unclear outcome are presented and the approaching limits of transistor performance are critically examined. Finally, we take a short view on alternative hardware options for mobile communication systems beyond the limits of transistors.
https://doi.org/10.1063/5.0213011
Compressible turbulent convection: the role of temperature-dependent thermal conductivity and dynamic viscosity. - In: Physics of fluids, ISSN 1089-7666, Bd. 36 (2024), 7, 076132, S. 076132-1-076132-11
The impact of variable material properties, such as temperature-dependent thermal conductivity and dynamical viscosity, on the dynamics of a fully compressible turbulent convection flow beyond the anelastic limit is studied in the present work by two series of three-dimensional direct numerical simulations in a layer of aspect ratio 4 with periodic boundary conditions in both horizontal directions. One simulation series is for a weakly stratified adiabatic background and the other one for a strongly stratified one. The Rayleigh number is 10^5 and the Prandtl number is 0.7 throughout this study. The temperature dependence of material parameters is imposed as a power law with an exponent β. It generates a superadiabaticity ε (z) that varies across the convection layer. Central statistical quantities of the flow, such as the mean superadiabatic temperature, temperature and density fluctuations, or turbulent Mach numbers are compared in the form of horizontal plane-time averaged profiles. It is found that the additional material parameter dependence causes systematic quantitative changes of all these quantities, but no qualitative ones. A growing temperature power law exponent β also enhances the turbulent momentum transfer in the weak stratification case by 40%, and it reduces the turbulent heat transfer by up to 50% in the strong stratification case.
https://doi.org/10.1063/5.0216623
Plasmon-enhanced light absorption below the bandgap of semiconducting SnS2 microcubes for highly efficient solar water evaporation. - In: Small, ISSN 1613-6829, Bd. 0 (2024), 0, 2400588, S. 1-9
Semiconducting materials show high potential for solar energy harvesting due to their suitable bandgaps, which allow the efficient utilization of light energy larger than their bandgaps. However, the photon energy smaller than their bandgap is almost unused, which significantly limits their efficient applications. Herein, plasmonic Pd/SnS2 microcubes with abundant Pd nanoparticles attached to the SnS2 nanosheets are fabricated by an in situ photoreduction method. The as-prepared Pd/SnS2 microcubes extend the light-harvesting ability of SnS2 beyond its cutoff wavelength, which is attributed to the localized surface plasmon resonance (LSPR) effect of the Pd nanoparticles and the 3D structure of the SnS2 microcubes. Pd nanoparticles can also enhance the light absorption of TiO2 nanoparticles and NiPS3 nanosheets beyond their cutoff wavelengths, revealing the universality for promoting absorption above the cutoff wavelength of the semiconductors. When the plasmonic Pd/SnS2 microcubes are integrated into a hydrophilic sponge acting as the solar evaporator, a solar-to-vapor efficiency of up to 89.2% can be achieved under one sun. The high solar-to-vapor conversion efficiency and the broad applicability of extending the light absorption far beyond the cutoff wavelength of the semiconductor comprise the potential of innovative plasmonic nanoparticle/semiconductor composites for solar desalination.
https://doi.org/10.1002/smll.202400588
Two quantum algorithms for solving the one-dimensional advection-diffusion equation. - In: Computers & fluids, ISSN 1879-0747, Bd. 281 (2024), 106369, S. 1-20
Two quantum algorithms are presented for the numerical solution of a linear one-dimensional advection-diffusion equation with periodic boundary conditions. Their accuracy and performance with increasing qubit number are compared point-by-point with each other. Specifically, we solve the linear partial differential equation with a Quantum Linear Systems Algorithm (QLSA) based on the Harrow-Hassidim-Lloyd method and a Variational Quantum Algorithm (VQA), for resolutions that can be encoded using up to 6 qubits, which corresponds to N=64 grid points on the unit interval. Both algorithms are hybrid in nature, i.e., they involve a combination of classical and quantum computing building blocks. The QLSA and VQA are solved as ideal statevector simulations using the in-house solver QFlowS and open-access Qiskit software, respectively. We discuss several aspects of both algorithms which are crucial for a successful performance in both cases. These are the accurate eigenvalue estimation with the quantum phase estimation for the QLSA and the choice of the algorithm of the minimization of the cost function for the VQA. The latter algorithm is also implemented in the noisy Qiskit framework including measurement noise. We reflect on the current limitations and suggest some possible routes of future research for the numerical simulation of classical fluid flows on a quantum computer.
https://doi.org/10.1016/j.compfluid.2024.106369
Determination of the true density and the filler content of pinus sylvestris wood particles in polymer-wood-composites. - In: Polymer composites, ISSN 1548-0569, Bd. 0 (2024), 0, S. 1-9
Measuring the natural fiber content in fiber-filled polymers remains challenging. Conventional methods, such as density calculations based on the specific bulk densities of the mixed components or determining the remaining fiber weights after calcination, often yield inaccurate results. Even helium pycnometer measurements tend to overestimate the true density of natural fibers. This study introduces a novel and potentially more cost-effective method to accurately determine the true density of natural filler materials. The approach involves mixing these fillers into plastic melts and injection molding them under pressures up to 1000 bar. Using this method, the true density of Pinus sylvestris heartwood chips combined with a lactic acid polymer was precisely calculated as 1.40092 g/cm3 ± 0.0102 g/cm3. Knowing the true density of material like Pinus sylvestris heartwood offers an accurate calculation of filler content in unknown recycled mixtures. This method can calculate the amount of wood fillers in polymer compounds, such as those from former decking, fences, privacy screens or soundproof wall claddings. Highlights: - Precise method to determine specific actual densities of biofillers, - High-resolution CT measurements of polymers filled with wood fibers, - Localization of density fluctuations in wood fiber filled polylactide, - Methodology for measuring the biofiber content of recyclates.
https://doi.org/10.1002/pc.28845