The etching of natural alpha-recoil tracks in mica with an argon RF-plasma discharge and their imaging via atomic force microscopy

The conventional technique used to reveal the natural alpha-recoil tracks, as well as other nuclear tracks, in muscovite mica is to etch the mica sheets in a concentrated hydrofluoric (HF) acid solution. However, because of the fast etching along the basal plane of the mica when using HF acid, the recoil-disturbed regions are commonly enlarged laterally so that it is difficult to determine the real size of these regions. In the present study, etching with an argon radio-frequency (RF) plasma discharge is used for the first time to locate and size the alpha-recoil tracks in the mica. The investigation of the etched tracks which followed was carried out using atomic force microscopy (AFM). From a consideration of the topography observed and of the characteristics of the interactions between the argon RF-plasma and the mica substrate, it is suggested that the etch pit dimensions as revealed by the low power argon RF-plasma discharge used and imaged by AFM correspond to the actual scales of the etchable damaged regions induced by the alpha-recoils in the mica, in contrast to those revealed by etching in HF acid. The mechanism of the preferential sputter etching observed at low power levels in an argon RF-plasma discharge at the etchable regions is discussed.