The etching process of single polymer particles is investigated using a noninvasive in situ light scattering technique, based on two different wavelengths. A systematic variation of admixed oxygen to an argon discharge allows us to investigate and model the basic etching processes and connect the experimentally available size evolution with surface properties and processes. The comparison of particles with different materials allows us to differentiate between the influence of the discharge itself and the material-specific aspects of the particles. The same reaction mechanism of ion-assisted surface reactions fits both investigated particle species, melamine formaldehyde (MF) and polymethyl-methacrylate (PMMA). The etching rates of PMMA were four times larger than in the case of MF under the same discharge conditions and match the stronger surface modification of PMMA particles, highlighting the possibility of the presented setup to systematically study plasma-particle and thus plasma-surface interactions.

Measuring diffusion in strongly coupled systems is challenging due to collective interactions and dynamic heterogeneity, which limit the effectiveness of traditional methods. We propose a novel differential dynamic microscopy approach based on short-time dynamics, which directly extracts diffusion coefficients by focusing on short-time behavior, avoiding the effects of dynamic heterogeneity in strongly coupled systems without requiring particle tracking. Using Langevin simulations of dusty plasmas, we validate the method by comparing it with theoretical results. This approach provides a new pathway for precise diffusion measurements in strongly interacting systems and offers a reliable framework for studying transport in complex, correlated environments.

An enhanced, dual wavelength light scattering technique to investigate the surface properties of single MF particles is presented. By using a core-shell approach, it is possible to map the optical properties of the particle to the surface morphology, and thus the surface structure becomes accessible in situ. Using 1% and 5% of admixed oxygen in the argon discharge, the particle surface can be modified by a controlled etching process. The measurements show a saturated surface modification of the upper approximate to 80 nm that dominates the interaction between particle and illumination laser, while an analysis of the levitation height of differently modified particles shows a clear effect of the surface morphology on the particle charge. The findings emphasize the significance of the particle morphology for the overall plasma-particle interaction.

The applicability of the Stokes-Einstein (SE) relation in two-dimensional finite binary mixtures is tested using the Langevin simulation method. Calculations of viscosity and self-diffusion coefficients are compared between monodisperse and binary systems. It is shown that adapted definitions of coupling strength Γ and screening parameter κ allow to describe the transport properties for both monodisperse and binary systems consistently. Further, it is discussed how the mixing ratio and charge ratio of the binary mixture affects transport properties.

The melting process of two-dimensional binary mixtures is studied using the Langevin simulation method. The melting point of each component in a binary mixture is determined by the local relative interparticle distance fluctuation method. The results show that, compared with the monodisperse system, the components of the binary mixture exhibit a multi-step melting characteristic. Further, the melting process of binary mixtures is found to depend on the mixing ratio and charge ratio. It is shown that particle hopping motion plays a key role in understanding melting in binary mixtures.

The shear viscosity of a finite two-dimensional (2D) Yukawa liquid is calculated using non-equilibrium Langevin simulations. Two counter-propagating shear forces are used to push the particles and cause shear-induced melting of the cluster. The melting temperature of the 2D cluster system is used to derive the effective coupling parameter Γ * of this finite system and allows us to investigate the relationship between shear viscosity and system properties Γ * and κ. The simulation data shows that the value of the shear viscosity rises for coupling parameters Γ * > 20 and follows a simple universal scaling for appropriate normalization. It is further found that the Green–Kubo relation is applicable to determine viscosity in finite non-equilibrium systems with Γ * < 80.

This contribution summarizes recent experiments in dusty plasmas and puts their results into context. The aim is to discuss the fundamental question whether a dusty plasma can be regarded as a model system for strong coupling and whether the treatment as a one-component plasma is a good and valid approximation.

Dusty plasmas are electrically quasi-neutral media that, along with electrons, ions, neutral gas, radiation, and electric and/or magnetic fields, also contain solid or liquid particles with sizes ranging from a few nanometers to a few micrometers. These media can be found in many natural environments as well as in various laboratory setups and industrial applications. As a separate branch of plasma physics, the field of dusty plasma physics was born in the beginning of 1990s at the intersection of the interests of the communities investigating astrophysical and technological plasmas. An additional boost to the development of the field was given by the discovery of plasma crystals leading to a series of microgravity experiments of which the purpose was to investigate generic phenomena in condensed matter physics using strongly coupled complex (dusty) plasmas as model systems. Finally, the field has gained an increasing amount of attention due to its inevitable connection to the development of novel applications ranging from the synthesis of functional nanoparticles to nuclear fusion and from particle sensing and diagnostics to nano-contamination control. The purpose of the present perspectives paper is to identify promising new developments and research directions for the field. As such, dusty plasmas are considered in their entire variety: from classical low-pressure noble-gas dusty discharges to atmospheric pressure plasmas with aerosols and from rarefied astrophysical plasmas to dense plasmas in nuclear fusion devices. Both fundamental and application aspects are covered.

Commonly used melamine formaldehyde micro-particles exposed to an rf discharge are known to be etched by a plasma as soon as an admixture of oxygen is present. By means of in situ high precision size measurements, the plasma–surface interaction is investigated. A comparison of experimental data, advanced Mie-scattering techniques, and a reaction rate model allows, for the first time, to quantitatively describe the etch process.

Zusammenfassung Der digitale Wandel stellt Lehrkräfte im Unterricht vor neue Anforderungen. Insbesondere Physiklehrkräfte müssen für das schulische Experimentieren nicht nur spezifische Messtechnik und Software nutzen können, sondern auch Grundkenntnisse des Programmierens beherrschen. Hinzu kommt, dass die (Physik-)Lehrkräfte sich in kurzen Zeitspannen immer wieder selbstständig neue digitale Technologien erschließen müssen. In diesem Buchkapitel wird das neu konzipierte lehramtsspezifische Elektronikpraktikum der Christian-Albrechts-Universität zu Kiel vorgestellt, in dem Physiklehramtsstudierende am Beispiel des Mikrocontrollers Arduino neben den Grundlagen der Elektronik auch diese digitalen Kompetenzen für ihre spätere Lehrtätigkeit entwickeln sollen. Durch die Begleitforschung im Design-based-Research-Ansatz konnte eine Reihe an konsistenten Indizien gesammelt werden, welche die Konzeption des lehramtsspezifischen Elektronikpraktikums stützen. Eine explorativ angelegte Interviewstudie zeigt, dass die Studierenden die wahrgenommene Relevanz aus einer schulpraktischen Perspektive beurteilen, Lerninhalte zur Förderung digitaler Kompetenzen erfolgreich integriert werden konnten und das Einüben selbstständigen Arbeitens das Selbstvertrauen der Studierenden fördert, sich in neue digitale Technologien einzuarbeiten.

An enhanced, high-precision, in situ method to determine the radii and refractive indices of single microparticles embedded in a plasma is presented. The particles are confined in the plasma sheath and illuminated with laser light that has a well-defined and adjustable state of polarization. Using an out-of-focus imaging setup, the angle- and polarization-resolved scattering intensities are measured and compared to Lorentz–Mie theory. A two-stage data evaluation process is used to obtain the particle size and the complex refractive index of different particle materials as a function of interaction time with the plasma.

The temperature of a dust ensemble in a dusty plasma is one of its most fundamental properties. Here, we present experiments using the configurational temperature as a for the temperature analysis in dusty plasmas. Using a model of the particle interactions, the configurational temperature allows us to determine the temperature of the dust ensemble from measurements of the particle positions, rather than particle velocities. The basic concept will be presented and the technique is applied to two-dimensional finite clusters as well as three-dimensional data from an extended dust cloud. Additionally, the configurational temperature can be used to derive the particle charge and the screening length from a comparison with the standard kinetic temperature.

Single micron-sized melamine-formaldehyde particles are levitated in the sheath of an rf-plasma and exposed to an intense laser beam, while being trapped in optical tweezers. A reversible change in the particles' properties is observed and quantitatively analyzed using reference particles. The investigations indicate a gain in particle charge where the initial charge restores within minutes. Possible reasons for these findings are discussed.

This tutorial covers recent developments in the field of dusty (complex) plasmas. After a brief summary of fundamental concepts, this tutorial will focus on novel diagnostics in dusty plasmas which have proven to be important tools on the route towards studying magnetized and polydisperse dust systems. These two hot topics of dusty (complex) plasma research are introduced, the current understanding is presented and open questions are identified. This tutorial is from an experimentalists' perspective. Hence, the recent experimental progress in diagnostics, as well as in magnetized and polydisperse systems is described and discussed.

An in-situ method to measure the radii of single microparticles in plasmas with high precision is presented. The particles are trapped in the plasma sheath and illuminated with laser light. Using out-of-focus imaging and polarizing optics, the angle- and polarization-resolved scattering intensities are measured and compared to Lorenz-Mie theory. A two-stage fit procedure is introduced to obtain the complex refractive index in addition to the particle radius. Complementary long-distance microscopy measurements are performed to compare with fit results. The method is applied to particles of different materials used in complex plasma research to measure etch rates due to plasma inherent processes.

The change in entropy of a system that is transferred between two states at different temperatures is measured in a two-dimensional plasma crystal experiment. One- and especially two-component dust clusters are confined in the plasma sheath and heated to different temperatures using laser manipulation. We find that entropies obtained from the phase space yield consistent results for, i.e., the heat capacity which shows excellent agreement with the Dulong-Petit law. The implications for the validity of basic thermodynamical principles in finite size complex (dusty) plasmas are discussed.

The dynamic evolution of the microscopic structure of solid and liquid phases of complex plasmas is studied experimentally and by means of molecular dynamics (MD) simulations. In small finite systems, the cooperative motion can be described in terms of discrete modes. These modes are studied with different experimental approaches. Using diffuse scattered laser light, applying laser tweezer forces to individual particles, and periodic laser pulses, the excitation of modes is investigated. The instantaneous normal mode analysis of experimental data from two-dimensional liquid clusters gives access to the local dynamics of the liquid phase. Our investigations shed light on the role of compressional and shear modes as well as the determination of diffusion constants and melting temperatures in finite systems. Special attention is paid to hydrodynamic situations with a stationary inhomogeneous dust flow. MD simulations allow to study the collective motion in the shell of nearest neighbors, which can be linked to smooth and sudden changes of the macroscopic flow. Finally, the observed micro-motion in all situations above allows to shed light on the preference of shear-like over compressional motion in terms of a minimized potential energy and a dynamic incompressibility.