[en] Emissive probe diagnostics in saturated floating potential mode was carried out in RF plasmas of argon (Ar)–methane (CH₄) and Ar–CH₄–hexa methyl disiloxane (HMDSO). These plasmas are used for the deposition of diamond-like carbon (DLC) and SiO_x-containing DLC films, respectively. While performing the experiments it was found that the probe characteristics had two saturation regions instead of one. The same measurements when repeated in Ar and Ar–N₂ plasmas showed a single saturation as expected. The first experiments when repeated again showed the same anomaly. The experimental findings question the validity of emissive probe diagnostics in reactive plasmas. A possible model of dust formation inside the reactive plasma is predicted and the first saturation is linked to dust. The second saturation is credited as the actual plasma potential. The concept of dust was invoked after being sure that no effects of RF and reference electrode contamination are responsible for this behavior. The results indicate that we should remain cautious when using emissive probes in reactive plasmas as they may occasionally lead to erroneous results. (paper)

[en] MAT Lab of Chemistry Division, BARC (A Class 10000 Clean room laboratory) has been in operation since 2004 for process development of ultra-purification of several strategically important materials (Ga, As, Sb, In, CsI and Ge) and synthesis of their organometallic compounds. Of these, work related to purification of As, Sb, and In, has been discontinued. Due to high toxicity and pyrophoric nature of some of the compounds, stringent safety regulations were formulated and subsequently implemented by the division