We report complex plasma experiments, assisted by numerical simulations, providing an alternative qualitative link between the macroscopic response of polycrystalline solid matter to small shearing forces and the possible underlying microscopic processes. In the stationary creep regime we have determined the exponents of the shear rate dependence of the shear stress and defect density, being α = 1.15 ± 0.1 and β = 2.4 ± 0.4, respectively. We show that the formation and rapid glide motion of dislocation pairs in the lattice are dominant processes.The direct in situ observation of dynamical processes in bulk condensed matter is not yet available with atomic resolution in both space and time. Femtosecond pumpprobe techniques can resolve atomic motion, atomic force microscopy can detect atoms on surfaces, diffraction methods provide information about the bulk structure, but as long no method can combine all the benefits of these techniques, we are limited to rely of phenomenological models and numerical simulations. Alternative experimental methods have already proven to be helpful for the qualitative understanding of classical collective phenomena. Charged colloids suspended in a liquid environment, and dusty plasmas (solid micron sized particles charged and levitated in gas discharge plasmas) are both interacting many-particle systems that show very similar properties to conventional atomic matter, but at time and distance scales easily and directly accessible with simple video microscopy techniques. Both methods provide insight into the microscopic (particle level) details of different phenomena. Colloid systems are characterized by over-damped dynamics, due to the liquid environment, which makes them well suited for structural and phase transition studies [1], while the weak damping in low pressure gas discharges makes dusty plasmas perfect for studies of wave-dynamics, instabilities, and other collective excitations [2].In material science and metallurgy, creep is the time dependent plastic strain at constant stress and temperature; therefore, it is a special type of plastic deformation of solid matter. In general it is a slow process driven by the thermally activated movement of dislocations (dislocation creep), vacancies (vacancy creep) or diffusion (Nabarro-Herring and Coble creep). The applied stresses are below the rapid yield stress resulting in atomic movements that are crystallographically organized. The applied temperatures are usually above 1 2 T m , where T m is the melting temperature. The time (t) evolution of the deformation (strain ε) at constant stress is often described by one of the empirical formulae(1)where ε 0 is the immediate strain and δ, ϑ and φ are creep coefficients [3]. After a short transient phase ("primary creep"), approximated as logarithmic (∼ δ ln t) or using Andrade's law (∼ ϑt 1/3 ), this describes a steady-state "secondary" creep, dominated by the last term, where the rate φ is determined by the balance of work hardening and thermal softening. Under such circumstances the ste...

Experiments are performed in which dust particles are levitated at varying heights above the powered electrode in a RF plasma discharge by changing the discharge power. The trajectories of particles dropped from the top of the discharge chamber are used to reconstruct the vertical electric force acting on the particles. The resulting data, together with the results from a selfconsistent fluid model, are used to determine the lower levitation limit for dust particles in the discharge and the approximate height above the lower electrode where quasineutrality is attained, locating the sheath edge. These results are then compared with current sheath models. It is also shown that particles levitated within a few electron Debye lengths of the sheath edge are located outside the linearly increasing portion of the electric field.

We report a series of complex (dusty) plasma experiments, aimed at the study of the detailed time evolution of the re-crystallisation process following a rapid quench of a two dimensional dust liquid. The experiments were accompanied by large-scale (million particle) molecular dynamics simulations, assuming Yukawa type inter-particle interaction. Both experiment and simulation show a ∝ t α (power law) dependence of the linear crystallite domain size as measured by the bondorder correlation length, translational correlation length, dislocation (defect) density, and a direct size measurement algorithm. The results show two stages of order formation: on short time-scales individual particle motion dominates; this is a fast process characterized by α = 0.93 ± 0.1. At longer time-scales, small crystallites undergo collective rearrangement, merging into bigger ones, resulting in a smaller exponent α = 0.38 ± 0.06.From the very beginning of laboratory complex (dusty) plasma research, one of the main motivating and promising features of these strongly coupled many-particle systems has been the possibility for modeling classical collective phenomena occurring in atomic matter on a size and time scale that allows direct observation at the particle level [1]. Experiments addressing e.g. transport phenomena in two dimensions (heat conductivity [2], viscosity [3], and self-diffusion [4]), dislocation dynamics [5], various melting scenarios [6][7][8][9], and some aspects of freezing [10,11] have already been carried out.The fact that a two-dimensional, hexagonal crystalline structure could easily develop in a laboratory complex plasma experiment was clear from the early days of the field [12], even though the theoretical background explaining crystallization in low dimensions [13] is still incomplete and the subject of ongoing debate [14].Here we study the phenomena of pattern formation occurring when a liquid is rapidly quenched to a solid. Our qualitative expectation is that the initial amorphous liquid structure should evolve toward a ground state crystal through the process of domain coarsening, i.e., merging initially formed small crystallites into fewer and bigger ones. To characterize this process we measured the average linear size of the crystallites and recorded their time evolution. Size measurement is based on: (i) the bondangular correlation length, (ii) the translational correlation length, (iii) the inverse defect fraction, and (iv) a direct size measurement algorithm similar to the standard "flood fill" method used in simple graphical tools.Ref.[15] reported a time dependence of the orientational correlation length in the form t α with α ≈ 1/4 measured in a two dimensional temperature quenched experiment in a single layer of spherical block copolymer microdomains in a thin film. Recent experiments with superparamagnetic particles (∝ 1/r 3 interaction) have shed new light on the dynamics of crystallite formation in colloidal systems resulting in a currently accepted value of α ≈ 0.3 [16]. Recent equilibrium mel...

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The oscillation spectrum of a one-dimensional vertical dust string formed inside a glass box on top of the lower electrode in a gaseous electronics conference (GEC) reference cell was studied. A mechanism for creating a single vertical dust string is described. It is shown that the oscillation amplitudes, resonance frequencies, damping coefficients, and oscillation phases of the dust particles separate into two distinct groups. One group exhibits low damping coefficients, increasing amplitudes, and decreasing resonance frequencies for dust particles closer to the lower electrode. The other group shows high damping coefficients but anomalous resonance frequencies and amplitudes. At low oscillation frequencies, the two groups are also separated by a π phase difference. One possible cause for the difference in behavior between the two groups is discussed.