Experimental investigation of test particle induced micro-structural changes in a finite two-dimensional complex plasma crystal

The microstructural changes induced in a two dimensional complex plasma crystal by the movement of a single extra particle existing below it are investigated experimentally using a DC glow discharge device. The finite monolayer crystal consisting of monodispersive melamine formaldehyde particles is created in the background of an Argon plasma. The crystal formation is frequently found to be accompanied by the presence of one or more slightly heavier particles suspended a little below the monolayer. The interplay of one such test particle with the crystal is investigated for two distinct cases-(i) when the particle remains confined (trapped) in the space below the crystal and (ii) when it interacts for a short while with the crystal and then moves out of the vicinity. The trapped particle orbit induces permanent structural changes in the crystal in the form of microcracks, and these changes are identified using a variety of diagnostic analyses. The cracks can be enhanced by energizing the test particle with an incident laser. The passing particle, on the other hand, induces only transient changes in the crystal from which it is able to recover and return to its initial state in a clear demonstration of the viscoelastic property of a strongly coupled system. Published under license by AIP Publishing.