arXiv subjects

Thomas Mussenbrock

Publications and source records attributed to Thomas Mussenbrock.

At least 19 recordsLinked to original sources

arXiv2026

On the physical origins of switching diversity in Cu-embedded SiO$_x$ memristive devices

Resistive switching devices with sub-stoichiometric SiO$_x$ and pancake-like Cu nanoparticles (Cu-PCs) exhibit distinct macroscopic current-voltage characteristics classified as capacitive or gradual (interface-type switching) and abrupt or resistive (filamentary-type switching), motivating an analysis of the microscopic processes underlying this diversity. It is proposed that the device defect landscape is largely shaped by two charged defect types, mobile oxygen vacancies and immobile Cu-related defects, whose distributions jointly govern interfacial and bulk transport. An effective one-dimensional cloud-in-a-cell simulation framework is employed to reproduce the phenomenological picture of both interface-type and filamentary-type switching by incorporating the dominant coupled ionic and electronic processes underlying these mechanisms. The model includes oxygen-vacancy drift-diffusion, Schottky-limited injection at the metal/oxide interfaces, and bulk trap-assisted transport via Poole-Frenkel conduction, with Cu-PCs near the top interface treated effectively. A simulation-based parametric study varying voltage stress, sweep rate, and oxide thickness is used to examine how these factors rebalance voltage partitioning and the spatiotemporal electric field distribution, thereby altering vacancy redistribution and the relative contributions of interface- and bulk-limited conduction. Using representative, physically motivated parameter sets informed by prior device-level studies, the simulations accurately reproduce the characteristic $I$-$V$ signatures of seven different experimentally observed switching responses. Overall, the findings help to link microscopic defect landscapes and transport processes to experimentally measured macroscopic responses within a single, self-consistent modeling framework.

cond-mat.mtrl-sci↗

arXiv2026

A Minimal Self-Consistent Model for the Nonlinear Dynamics of Asymmetric Capacitively Coupled Radio-Frequency Plasmas

We develop a minimal self-consistent lumped-element model for the nonlinear radio-frequency dynamics of geometrically asymmetric capacitively coupled plasmas. The fast electrical response is described by three dynamical variables: the powered-sheath charge, the blocking-capacitor voltage, and the discharge current. The periodic RF solution is coupled to stationary particle and energy balances, which determine the electron temperature and plasma density from the operating conditions and the absorbed power. For an argon discharge, the model produces nonlinear current oscillations and a broad higher-harmonic response associated with the plasma series resonance. Variation of the RF voltage leads to correlated changes in the harmonic spectrum, absorbed power, and plasma density. Linearization about the periodic state relates the high-frequency response to the time-dependent differential sheath elastance. A moment-based effective elastance provides a compact estimate of the corresponding characteristic PSR frequency. The model thereby connects nonlinear RF dynamics and plasma sustainment within a minimal self-consistent description.

physics.plasm-ph↗

arXiv2025

Characterization of a laser filament-induced plasma in air at 10 kHz using optical emission spectroscopy

The increasing availability of high-power Yb-based ultrafast laser-amplifier systems has opened the possibility of air filamentation at high repetition rates >1 kHz. In this new regime, accumulation effects cannot be ruled out, therefore, characterizing the plasma parameters and afterglow plasma-chemical kinetics becomes increasingly relevant. In this work, we use optical emission spectroscopy to measure nanosecond dynamics of gas temperature and electron temperature, species-specific decay times, and electron density of an atmospheric air laser filament produced by high average power femtosecond laser at a high repetition rate of 10 kHz. The molecular excitation mechanisms behind the nitrogen photoemissions are derived from vibrational distributions and temporal behavior of the studied emission bands. The presented diagnostic technique offers a complementary but more holistic measurement approach to optical probe schemes to characterize the laser-filament-induced plasma wake for high repetition rate filaments.

physics.plasm-ph↗

arXiv2025

Two-dimensional spatially resolved measurements of helium metastable densities by tunable diode laser absorption spectroscopy in atmospheric pressure RF plasma jets

Helium metastable species play a critical role in sustaining radio-frequency (RF) driven micro atmospheric pressure plasma jets through Penning ionization and for the generation of reactive oxygen and nitrogen species (RONS). Their densities are typically measured using tunable diode laser absorption spectroscopy (TDLAS). Most spatially resolved TDLAS approaches rely on mechanical scanning of a narrow laser beam across the plasma, which is time-consuming and limits spatial resolution. In this work, we present an advanced two-dimensional (2D) TDLAS method that enables direct spatial mapping of helium metastable densities without the need for mechanical scanning. A rotating optical diffuser is employed to suppress speckle interference and generate uniform illumination across the plasma region. The absorption profile is captured using a short-wavelength infrared camera equipped with a telecentric lens, achieving high spatial resolution (approximately 10 μm) across the entire field of view. This approach significantly enhances both data quality and acquisition speed. The improved 2D TDLAS system is applied to measure helium metastable densities in plasma jets with structured electrodes driven by different tailored voltage waveforms. The results show very good qualitative agreement with fluid simulations and previously reported experimental data.

physics.plasm-ph↗

arXiv2025

Synergistic control of radical generation in a radio frequency atmospheric pressure plasma jet via voltage waveform tailoring and structured electrodes

The synergy between voltage waveform tailoring and structured electrodes is investigated in a radio-frequency (RF) atmospheric-pressure microplasma jet operated in helium with a 0.1% oxygen admixture. The device incorporates rectangular trenches in both electrodes and is driven by "Peaks" and "Valleys" waveforms synthesized from four harmonics (base frequency $f_{\rm b} = 13.56$~MHz, $V_{\rm pp} = 500$~V, $P=$1.2~W). Two-dimensional plasma fluid simulations, together with spatially and temporally resolved optical diagnostics (Phase-Resolved Optical Emission Spectroscopy and Tunable Diode Laser Absorption Spectroscopy), are used to demonstrate that the combination of asymmetric voltage waveforms with electrode structuring leads to strong spatial localization of electron power absorption and radical generation. This synergy results in a single pronounced maximum inside a trench at either the powered or grounded electrode, depending on the applied waveform, unlike a symmetric excitation, which produces a spatially symmetric enhancement at both electrodes. The effect is attributed to the interplay between waveform-induced sheath dynamics and geometric focusing provided by the trenches, enabling electrically reversible and selective enhancement of electron power absorption at a chosen location.

physics.plasm-ph↗

arXiv2025

Electronegativity effects on plasma dynamics in He/O$_2$ RF microplasma jets at atmospheric pressure

This work investigates the transitions between ohmic mode and Penning-Gamma mode in a capacitively coupled radio frequency micro atmospheric pressure plasma jets (CCRF $μ$APPJ) operated in He/O$_2$ mixtures by comparing phase-resolved optical emission spectroscopy (PROES) measurements of helium excitation with numerical simulations. The simulations employ a hybrid model that treats electrons kinetically via PIC/MCC, while ions and neutrals are modeled fluid dynamically. These results reveal that increasing electronegativity causes inhomogeneities in the bulk electric field, consequently modulating electron impact excitation dynamics. A good agreement was found between experiments and simulations.

physics.plasm-ph↗

arXiv2025

Dynamics of reactive oxygen species produced by the COST microplasma jet

This study is focused on measuring the densities of the excited molecular oxygen species, O$_{2}(\text{a}^{1}Δ_{\text{g}})$ and O$_{2}(\text{b}^{1}Σ_{\text{g}}^{+})$, produced in a COST atmospheric pressure plasma jet using a helium-oxygen mixture. Knowledge of the ozone density is critical for measurements because of its high quenching rate of these species. Additionally O$_{2}(\text{a}^{1}Δ_{\text{g}})$ is difficult to measure, due to its low emission intensity and sensitivity to background interference in the plasma region. Therefore a flow cell was used to enhance signal detection in the effluent region. To validate the measurements and improve understanding of reaction mechanisms, results were compared with two simulation models: a pseudo-1D plug flow simulation and a 2D fluid simulation. The plug flow simulation provided an effective means for estimating species densities, with a fast computation time. The 2D simulation offered a more realistic description of the flow dynamics, which proved critical to correctly describe the experimental trends. However, it requires long computation times to reach an equilibrium state in the flow cell. Otherwise, it leads to discrepancies to the experimental data. Further discrepancies arose, from an overestimation of the ozone density from the models, as validated from the O$_{2}(\text{b}^{1}Σ_{\text{g}}^{+})$ density measurements. Optimizing the reaction rate coefficients for the effluent region might improve the agreement with the experimental results. Despite these limitations both simulations aligned reasonably well with experimental data, showcasing the well validated plasma chemistry of the models, even for complicated effluent geometries.

physics.plasm-ph↗

arXiv2025

Nonlinear Power Absorption in CCRF Discharges: Transition from Symmetric to Asymmetric Configurations

This work builds upon previous studies of nonlinear dynamics in low-pressure capacitively coupled radio-frequency discharges, focusing on the electron power absorption mechanism in discharges with various geometric asymmetries. We present a comprehensive investigation using a fully kinetic electrostatic 1d3v Particle-in-Cell/Monte Carlo collision simulation in spherical geometry. By systematically varying the inner electrode radius and the electrode gap distance, we analyze the influence of geometric asymmetry on key plasma properties, including electron density, power absorption, electron dynamics, and current characteristics. A central focus is placed on the cumulative power density as a diagnostic for energy deposition. In strongly asymmetric configurations, the cumulative electron power density exhibits distinct stepwise increases during sheath expansion, corresponding to the acceleration of successive electron beams. These nonlinear signatures are directly linked to the excitation of plasma series resonance and enhanced beam-driven power absorption. In contrast, more symmetric configurations display smoother, more symmetric cumulative power evolution, indicating balanced energy transfer at both sheaths and reduced nonlinearities. Time- and space-resolved diagnostics of cumulative power, current waveforms, and densities of energetic electrons reveal the critical role of asymmetry in shaping electron confinement and beam-driven power absorption. These findings demonstrate that the discharge geometry is actually an important design parameter which needs to taken into account during the design and construction phase of a reactor as it directly influences the plasma behavior with respect to energy deposition.

physics.plasm-ph↗

arXiv2025

Electron dynamics of three distinct discharge modes of a cross-field atmospheric pressure plasma jet

This paper investigates the electron dynamics in three distinct discharge modes of a cross-field atmospheric pressure plasma jet, the COST-Jet. Thereby, the discharge modes are the non-neutral, the quasi-neutral, and the constricted mode. Using a hybrid Particle-In-Cell/Monte-Carlo Collisions (PIC/MCC) simulation, the study systematically varies the applied voltage and driving frequency to explore the operation modes and their relations. The results reveal that at low input power, the COST-Jet operates in a non-neutral mode, characterized by a discharge close to extinction, analogous to the chaotic mode observed in other plasma devices. As power increases, the jet transitions to a quasi-neutral mode, which aligns with the well-known Ω- and Penning modes, comparable to the bullet mode in parallel-field jets. At the highest power levels, the COST-Jet enters a constricted mode, where the plasma significantly densifies and constricts towards the electrodes along the entire discharge channel. Experimental validation using phase-resolved optical emission spectroscopy (PROES) supports the simulation findings, particularly identifying the constricted mode as a distinct operational regime. These insights into the mode transitions of the COST-Jet under varying operational conditions help optimize plasma applications in various fields.

physics.plasm-ph↗

arXiv2024

Physics-based Modeling and Simulation of Nanoparticle Networks

This study presents the computational modeling and simulation of silver nanoparticle networks (NPNs), which, in the realm of neuromorphic computation, suggest to be a promising candidate for nontraditional computation methods. The modeling of the networks construction, its electrical properties and model parameters are derived from well-established physical principles.

cond-mat.mtrl-sci↗

arXiv2024

The role of flow field dynamics in enhancing volatile organic compound conversion in a surface dielectric barrier discharge system

This study investigates the correlation between flow fields induced by a surface dielectric barrier discharge (SDBD) system and its application for the volatile organic compound (VOC) gas conversion process. As a benchmark molecule, the conversion of n-butane is monitored using flame ionization detectors, while the flow field is analysed using planar particle image velocimetry. Two individual setups are developed to facilitate both conversion measurement and investigation of induced fluid dynamics. Varying the gap distance between two SDBD electrode plates for three different n-butane mole fractions reveals local peaks in relative conversion around gap distances of 16 mm to 22 mm, indicating additional spatially dependent effects. The lowest n-butane mole fractions exhibit the highest relative conversion, while the highest n-butane mole fraction conversion yields the greatest number of converted molecules per unit time. Despite maintaining constant energy density, the relative conversion exhibits a gradual decrease with increasing distances. The results of the induced flow fields reveal distinct vortex structures at the top and bottom electrodes, which evolve in size and shape as the gap distances increase. These vortices exhibit gas velocity magnitudes approximately seven times higher than the applied external gas flow velocity. Vorticity and turbulent kinetic energy analyses provide insights into these structures' characteristics and their impact on gas mixing. A comparison of line profiles through the centre of the vortices shows peaks in the middle gap region for the same gap distances, correlating with the observed peaks in conversion. These findings demonstrate a correlation between induced flow dynamics and the gas conversion process, bridging plasma actuator studies with the domain of chemical plasma gas conversion.

physics.plasm-ph↗

arXiv2024

Nonlinear behavior of memristive devices for hardware security primitives and neuromorphic computing systems

Nonlinearity is a crucial characteristic for implementing hardware security primitives or neuromorphic computing systems. The main feature of all memristive devices is this nonlinear behavior observed in their current-voltage characteristics. To comprehend the nonlinear behavior, we have to understand the coexistence of resistive, capacitive, and inertia (virtual inductive) effects in these devices. These effects originate from corresponding physical and chemical processes in memristive devices. A physics-inspired compact model is employed to model and simulate interface-type RRAMs such as Au/BiFeO$_{3}$/Pt/Ti, Au/Nb$_{\rm x}$O$_{\rm y}$/Al$_{2}$O$_{3}$/Nb, while accounting for the modeling of capacitive and inertia effects. The simulated current-voltage characteristics align well with experimental data and accurately capture the non-zero crossing hysteresis generated by capacitive and inductive effects. This study examines the response of two devices to increasing frequencies, revealing a shift in their nonlinear behavior characterized by a reduced hysteresis range and increased chaotic behavior, as observed through internal state attractors. Fourier series analysis utilizing a sinusoidal input voltage of varying amplitudes and frequencies indicates harmonics or frequency components that considerably influence the functioning of RRAMs. Moreover, we propose and demonstrate the use of the frequency spectra as one of the fingerprints for memristive devices.

cs.ET↗

arXiv2024

Coexistence of resistive capacitive and virtual inductive effects in memristive devices

This paper examines the coexistence of resistive, capacitive, and inertia (virtual inductive) effects in memristive devices, focusing on ReRAM devices, specifically the interface-type or non-filamentary analog switching devices. A physics-inspired compact model is used to effectively capture the underlying mechanisms governing resistive switching in NbO$_{\rm x}$ and BiFeO$_{3}$ based on memristive devices. The model includes different capacitive components in metal-insulator-metal structures to simulate capacitive effects. Drift and diffusion of particles are modeled and correlated with particles' inertia within the system. Using the model, we obtain the I-V characteristics of both devices that show good agreement with experimental findings and the corresponding C-V characteristics. This model also replicates observed non-zero crossing hysteresis in perovskite-based devices. Additionally, the study examines how the reactance of the device changes in response to variations in the device area and length.

cond-mat.mes-hall↗

arXiv2024

Non-zero crossing current-voltage characteristics of interface-type resistive switching devices

A number of memristive devices, mainly ReRAMs, have been reported to exhibit a unique non-zero crossing hysteresis attributed to the interplay of resistive and not yet fully understood `capacitive', and `inductive' effects. This work exploits a kinetic simulation model based on the stochastic cloud-in-a-cell method to capture these effects. The model, applied to Au/BiFeO$_{3}$/Pt/Ti interface-type devices, incorporates vacancy transport and capacitive contributions. The resulting nonlinear response, characterized by hysteresis, is analyzed in detail, providing an in-depth physical understanding of the virtual effects. Capacitive effects are modeled across different layers, revealing their significant role in shaping the non-zero crossing hysteresis behavior. Results from kinetic simulations demonstrate the impact of frequency-dependent impedance on the non-zero crossing phenomenon. This model provides insights into the effects of various device material properties, such as Schottky barrier height, device area and oxide layer on the non-zero crossing point.

cond-mat.mes-hall↗

arXiv2023

Interactions between flow fields induced by surface dielectric barrier discharge arrays

This study investigates the flow field induced by a surface dielectric barrier discharge (SDBD) system, known for its efficient pollution remediation of volatile organic compounds (VOCs). We aim to understand the flow dynamics that contribute to the high conversion observed in similar systems. Experimental techniques, including schlieren imaging and particle image velocimetry (PIV), applied with high temporal resolution, were used to analyse the flow field. Complementary, fluid simulations are employed to investigate the coupling between streamer and gas dynamics. Results show distinct fluid field behaviours for different electrode configurations, which differ in geometric complexity. The fluid field analysis of the most basic electrode design revealed behaviours commonly observed in actuator studies. The simulation results indicate the local information about the electron density as well as different temporal phases of the fluid flow. The electrode design with mostly parallel grid line structures exhibits confined vortices near the surface. In contrast, an electrode design also used in previous studies, is shown to promote strong gas transport through extended vortex structures, enhancing gas mixing and potentially explaining the high conversion observed.

physics.plasm-ph↗

arXiv2023

PECVD and PEALD on polymer substrates (Part II): Understanding and tuning of barrier and membrane properties of thin films

This feature article presents insights concerning the correlation of PECVD and PEALD thin film structures with their barrier or membrane properties. While in principle similar precursor gases and processes can be applied, the adjustment of deposition parameters for different polymer substrates can lead to either an effective diffusion barrier or selective permeabilities. In both cases the understanding of the film growth and the analysis of the pore size distribution and the pore surface chemistry is of utmost importance for the understanding of the related transport properties of small molecules. In this regard the article presents both concepts of thin film engineering and analytical as well as theoretical approaches leading to a comprehensive description of the state of the art in this field. Moreover, based on the presented correlation of film structure and molecular transport properties perspectives of future relevant research in this area is presented.

cond-mat.soft↗

arXiv2023

PECVD and PEALD on polymer substrates (part I): Fundamentals and analysis of plasma activation and thin film growth

This feature article considers the analysis of the initial states of film growth on polymer substrates. The assembled results are based on the cooperation between research groups in the field of plasma physics, chemistry, electric as well as mechanical engineering over the last years, mostly within the frame of the transregional project SFB-TR 87 ("Pulsed high power plasmas for the synthesis of nanostructured functional layers"). This feature article aims at bridging the gap between the understanding of plasma processes in the gas phase and the resulting surface and interface processes of the polymer. The results show that interfacial adhesion and initial film growth can be well controlled and even predicted based on the combination of analytical approaches.

cond-mat.soft↗

arXiv2023

Nonlocal dynamics of secondary electrons in capacitively coupled radio frequency discharges

In capacitively coupled radio frequency (CCRF) discharges, the interaction of the plasma and the surface boundaries is linked to a variety of highly relevant phenomena for technological processes. One possible plasma-surface interaction is the generation of secondary electrons (SEs), which significantly influence the discharge when accelerated in the sheath electric field. However, SEs, in particular electron-induced SEs ($\updelta$-electrons), are frequently neglected in theory and simulations. Due to the relatively high threshold energy for the effective generation of $\updelta$-electrons at surfaces, their dynamics are closely connected and entangled with the dynamics of the ion-induced SEs ($\upgamma$-electrons). Thus, a fundamental understanding of the electron dynamics has to be achieved on a nanosecond timescale, and the effects of the different electron groups have to be segregated. This work utilizes $1d3v$ Particle-in-Cell/Monte Carlo Collisions (PIC/MCC) simulations of a symmetric discharge in the low-pressure regime ($p\,=\, 1\,\rm{Pa}$) with the inclusion of realistic electron-surface interactions for silicon dioxide. A diagnostic framework is introduced that segregates the electrons into three groups ("bulk-electrons", "$\upgamma$-electrons", and "$\updelta$-electrons") in order to analyze and discuss their dynamics. A variation of the electrode gap size $L_\mathrm{gap}$ is then presented as a control tool to alter the dynamics of the discharge significantly. It is demonstrated that this control results in two different regimes of low and high plasma density, respectively. The fundamental electron dynamics of both regimes are explained, which requires a complete analysis starting at global parameters (e.g., densities) down to single electron trajectories.

physics.plasm-ph↗