Diagnostics in a High-Flow-Rate (>6 L min−1) Helium Capacitively Coupled Microwave Plasma: Aqueous versus Organic Solution

Abstract

A helium capacitively coupled microwave plasma (CMP) with a high plasma gas flow rate (>6 L min−1) is described. Plasma gas flow rates above 6–8 L min−1 produce a cylindrical-shaped plasma. Diagnostic studies were performed. Electronic excitation ( Texc), rotational ( Trot), and ionization-recombination ( Tion) temperatures were determined, along with the electron number density ( ne). Texc was calculated from the slope of the Boltzmann plot with the use of Fe as the thermometric species. Values for Texc in aqueous and organic solution were 3430 and 3450 K, respectively. Trot determined with the use of both OH and N2+. With OH, Trot values were 1620 and 1660 K for aqueous and organic solutions, respectively. If no solution was introduced, a Trot value of 2350 K was determined with N2+. N2+ also gave Trot values of 1900 and 1930 K with aqueous and organic solutions, respectively. The Tion values were 6220 and 5610 K with the use Cd and Mg, respectively. The ne value was on the order of 4 × 1014 cm−3. Background spectra and limits of detection are also presented.