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- ItemCollaborative Research Center 917 : Resistively Switching Chalcogenides for Future Electronics : Structure, Kinetics, and Device Scalability : Final report : 2019/2-2020-2021-2022-2023/1(Hannover : Technische Informationsbibliothek, 2025-03-25) Wuttig, Matthias; Waser, Rainer; Dronskowski, Richard; Dittmann, Regina; Simon, Ulrich; Mayer, JoachimThe goal of SFB 917 has been the development of novel nanoswitches that can be reproducibly and reversibly changed between two states on very short time and length scales. Such nanoswitches can enable new storage and memory devices as well as neuro-inspired architectures for information technology. In the third and final funding period of SFB 917 we have witnessed and contributed to three major trends. The exponential growth in the demand for data storage and processing has continued. Hardware improvements are therefore urgently needed to meet the increased demands for data storage and processing as well as the related increase in energy consumption. SFB 917 strives to realize novel storage devices by exploiting the full potential of chalcogenide-based nanoswitches. Yet, it has become increasingly clear in the last few years, that improvements in device performance alone are insufficient to deal with the exponential growth mentioned above. The advance of Large Language Models (LLMs) like ChatGPT and related software has produced a further increase in data processing related energy consumption. This is a major challenge considering the expected further increase of professional and private usage of such machine learning tools. To minimize the related energy consumption, particularly energy-efficient software and hardware developments are mandatory. Within SFB9917, we have this intensified our efforts to work on effects related to a reduction in energy consumption. While energy-efficient devices can help, an improvement in hardware architecture offers significantly more leverage. We have thus explored the potential of chalcogenide based nano-switches in neuro-inspired computer architectures. To this end, several new large-scale research projects have been initiated (NeuroSys and NeuroTec), which extend our research on these devices in increasingly more complex architectures, offering new opportunities to harvest the findings of SFB 917 in new applications. To tailor chalcogenide-based nano-switches, major advances in instrumentation as well as an in-depth understanding of the origin of underlying phenomena and unconventional properties in these materials have been mandatory. Challenges included the characterization of switching in these materials on nanosecond time and nanometer length scales. Sophisticated tools have been built and utilized. Understanding unconventional properties are required building a bridge between concepts of inorganic chemistry and material properties leading to novel treasure maps which help to identify and tailor chalcogenides for specific applications. These successes are described in detail in the present report. To demonstrate that these findings are also relevant for industry, close cooperation with industrial partners has been established to ensure that the findings made within SFB 917 can also be implemented on the shortest possible time scales.
- ItemSedimentation of binary mixtures: Phase stacking and Nonequilibrium dynamics(Hannover : Technische Informationsbibliothek, 2024-12-30) Schmidt, Matthias; de las Heras, DanielBased on equilibrium sedimentation path theory and the local density functional approximation, we investigated the effects of gravity on several relevant types of binary colloidal mixtures. Settled systems are represented by so-called sedimentation paths, which determine the variation of the species-resolved chemical potentials with altitude. Analysing the resulting line segments in the plane of chemical potentials of the bulk phase diagram allows one to rationalize the full equilibrium stacking phenomenology for a given system under gravity. The approach predicts theoretically the stacking sequences of colloidal rod-plate mixtures that were observed in iconic experiments by van der Kooij and Lekkerkerker. Thereby the occurrence of up to five simultaneous phase layers emerges naturally from the mere interplay of gravity and two-phase bulk coexistence, without invoking particle polydispersity. We studied the effects on equilibrium phase stacking upon varying the buoyant mass ratio of both components and our predictions are testable in experiments by systematic variation of the height of sedimentation columns. We have carried out similar sedimentation studies for: plate-spheres mixtures, mass-polydisperse systems, and hard spherocylinders. We suggest that microscopic particle properties, such as the buoyant mass, can be inferred from macroscopic measurements of layer thicknesses in phase stacking sequences. We addressed gravity-induced nonequilibrium flow and structure formation on the basis of power functional theory, adaptive Brownian dynamics computer simulations, and functional machine learning. Power functional theory allows one to rationalize and to model the nonequilibrium behaviour of many-body systems based on the one-body density and velocity field. We have used the approach to categorize systematically the different types of relevant nonequilibrium force contributions and have developed corresponding analytical gradient approximations. Neural functionals, as trained on the basis of both equilibrium and nonequilibrium computer simulation data, were shown to yield accurate predictions for structure formation and design of nonequilibrium flow. We have formulated force-based density functional theory and have demonstrated that neural density functionals outperform the best available hard sphere fundamental measure functionals. We have developed adaptive Brownian dynamics as a performant and highly stable numerical integration scheme for the temporal integration of overdamped many-body Langevin equations of motion, as demonstrated for a particle gel subject to convective sedimentation flow. We have put forward general frameworks for fluctuations of general hyperobservables, for their associated hyperforce correlation functions, and for the gauge invariance of statistical mechanics, where Noether's theorem yields exact sum rules that constrain correlations, as exemplified for ideal and for active sedimentation.
- ItemEffect of a high-voltage mesh electrode on the volume and surface characteristics of pulsed dielectric barrier discharges(Melville, NY : American Inst. of Physics, 2020) Kettlitz, M.; van Rooij, O.; Höft, H.; Brandenburg, R.; Sobota, A.Electrical breakdown in a pulsed asymmetric dielectric barrier discharge between a glass-covered mesh electrode and a grounded metal electrode in the air at atmospheric pressure is investigated. Volume discharge forms between the metal tip and the dielectric surface and spreads over the dielectric surface. Breakdown and discharge behaviors depend on the polarity of the charged electrode covered with glass compared to the metal rod electrode. In the case of the dielectric cathode (covered mesh), volume discharge features a stronger and longer-lasting emission. Volume discharge is weaker with outstretched surface discharge developing on the opposite glass electrode sustained by the embedded mesh when the metal rod functions as a cathode. The development and spatial distribution of the surface discharge depend on the relative polarity of the dielectrics caused by the charge deposition of the preceding discharge and is independent of the polarity of the applied high voltage. The discharge emission is brighter for the metal cathode and dielectric anode than for the metal anode, with a branching discharge developing and spreading in a star-like structure along the embedded grid, while a ring-like structure was observed for the metal anode and dielectric cathode. The duty cycle influences the discharge development and properties through the effects of the gas phase and surface pre-ionization.
- ItemMicroplasmas: A Review(Oak Park, Ill. : Bentham Science Publ., 2011) Papadakis, A. P.In this paper, a review on microplasma discharges is conducted. The different types and configurations used in microplasmas such as the Cathode Boundary Layer (CBL), Dielectric Barrier Discharge (DBD), Capillary Plasma Electrode Discharge (CPED), Inverted Square Pyramid (ISP), Square Cross Sectional Cavities (SCSC), Radio Frequency Inductively Coupled Discharge (RFIC), Radio Frequency Capacitive Coupled Discharge (RFCC), Micro-Hollow Cathode Discharge (MHCD), and microstrip technology (MS) discharges at different operating conditions are discussed. Numerical and experimental methods used for the analysis of the physics involved in these microplasmas, as well as the different construction methods used, are also described.
- ItemA unified view of acoustic-electrostatic solitons in complex plasmas([London] : IOP, 2003) McKenzie, J. F.; Doyle, T. B.A fluid dynamic approach is used in a unified fully nonlinear treatment of the properties of the dust-acoustic, ion-acoustic and Langmuiracoustic solitons. The analysis, which is carried out in the wave frame of the soliton, is based on total momentum conservation and Bernoulli-like energy equations for each of the particle species in each wave type, and yields the structure equation for the 'heavy' species flow speed in each case. The heavy (cold or supersonic) species is always compressed in the soliton, requiring concomitant contraints on the potential and on the flow speed of the electrons and protons in the wave. The treatment clearly elucidates the crucial role played by the heavy species sonic point in limiting the collective species Mach number, which determines the upper limit for the existence of the soliton and its amplitude, and also shows the essentially similar nature of each soliton type. An exact solution, which highlights these characteristic properties, shows that the three acoustic solitons are in fact the same mathematical entity in different physical disguises.