Analysis of Zn i emission lines observed during a spark discharge in liquid nitrogen for zinc nanosheet synthesis

Abstract

High-voltage pulsed discharges of a few milliwatts in liquid nitrogen between two zinc electrodes are investigated by optical emission spectroscopy. The possibility to account by modeling for the time evolution of selected zinc lines that are sufficiently intense gives access to the dynamics of the discharge. The intense background emission at short times (from 50 to 100 ns) is satisfactorily described by Planck's continuum with a temperature of 0.9 eV and an electron density of 1017 cm-3. Later on, when zinc lines start appearing in the spectrum, i.e. beyond 300 ns typically when the background emission drops, the electron density and the electron temperature decrease exponentially (from 5.3 to 3.5 eV at 700 ns and from 4 × 1016 to 1015 cm-3). The modeling of the time evolution of three selected zinc lines at 468.01, 472.22 and 481.05 nm gives a coherent insight of the discharge behavior and structure, especially in terms of species gradient and optical thickness. It is also used to check the reliability of the extracted data.