Comment on "Plasma fireball: A unique tool to fabricate patterned nanodots" [Rev. Sci. Instrum. 88, 063507 (2017)].

The article of Chauhan et al. ["Plasma fireball: A unique tool to fabricate patterned nanodots," Rev. Sci. Instrum. 88(6), 063507 (2017)] describes the very interesting idea of utilising the plasma phenomenon of fireballs for the creation of patterned nanodots on a GaSb substrate. For this purpose, the authors obtained a large plasma fireball in a magnetised background plasma and used it to accelerate ions in the sheath, which surrounds such a fireball. Chauhan et al. were able to demonstrate the production of large ion fluxes that can be extracted from the fireball and that the properties of these fluxes define the geometric structure of the nanodots on the substrate surface. Hence, the nanodot pattern can be easily controlled by the discharge parameters of the plasma fireball. This is clearly a novel method of fireball-induced surface modification. However, plasma fireballs themselves have been known for about hundred years, although as a very particular plasma phenomenon. Therefore, this letter aims at providing some additional background information and references on this topic for the interested reader.