Long-term spatio-temporal evolution of the dust distribution in dusty argon rf plasmas

Abstract

The 3D dust distribution in dense dust clouds confined in argon rf plasmas is measured by a computed tomography (CT) technique based on the extinction of visible light. On the one hand, clouds of micron-sized particles were created by injecting standardized plastic particles into the plasma. On the other hand, sub-micron sized dust with well-defined properties is grown in situ in an argon acetylene mixture. Once created, both kinds of dust clouds decay in the course of minutes to hours. This decay is monitored by CT measurements. It is revealed that micro-dust clouds feature a drastic change of the dust distribution due to a size reduction of the dust. Dust clouds of sub-micron particles, in contrast, show a strong variation of the overall dust density while the relative dust distribution remains nearly unchanged. The evolution of the overall dust density is subject to two effects: the loss of particles due to an imperfect confinement and the reduction of the dust size via etching.

Characterization of injected aluminum oxide nanoparticle clouds in an rf discharge

“…In contrast to the experiments of Killer et al [35,37], we now have a wider particle size distribution. We therefore had to account here for a size-dependent scattering cross section σ in evaluating the density from Eq.…”

In-situ analysis of optically thick nanoparticle clouds

“…In low temperature plasmas exist two scenarios exist where this approximation fails: (a) if the particle cloud is optically thick for the light going through it and (b) in the experimental analysis of dusty plasmas where the light source for illumination is not simply a laser beam but a laser fan or a volume source. Light sources different from laser beams are needed for imaging ellipsometry [11] or computed tomography of the particle cloud [12]. Regarding atmospheric pressure microplasmas, which are used to create nanoparticles [13], it is supposed that the high particle number density immediately leads to high optical * kirchschlager@astrophysik.uni-kiel.de depths.…”

Nanoparticle forming reactive plasmas: a multidiagnostic approach

“…For, example if it is a-priori known that n p (x) is rotationally symmetric one could record several transmission spectra at different distances from the rotational symmetry axis of the specimen and use the Radon transform to reconstruct n p (x) from the transmission spectra. This approach can even be extended to 3d distributions [76].…”

“…This approach has been successfully used by other groups to trap nanoparticle ensembles in discharges and investigate the trapped particles (cf. for example [76,152]). The growth of the nanoparticles was limited by injecting only a fixed amount of C 2 H 2 into the 'Pequod'-reactor after the Ar discharge had been ignited.…”