On the difference between breakdown and quench voltages of argon plasma and its relation to $4p-4s$ atomic state transitions

TL;DR

This study measures and analyzes breakdown and quench voltages in argon microplasmas, revealing conditions where these voltages are equal and linking this to atomic state transitions, challenging classical Paschen's law in microgaps.

Contribution

It demonstrates that in argon microplasmas, breakdown and quench voltages can be equal under certain conditions, linked to atomic state transitions, which is a novel insight beyond classical models.

Findings

Breakdown and quench voltages can be equal in argon microplasmas.

Paschen's law does not apply in microgaps between needle probes.

Atomic state transitions influence plasma turn-off and turn-on voltages.

Abstract

Using a relaxation oscillator circuit, breakdown ($V_{\mathrm{BD}}$) and quench ($V_{\mathrm{Q}}$) voltages of a DC discharge microplasma between two needle probes are measured. High resolution modified Paschen curves are obtained for argon microplasmas including a quench voltage curve representing the voltage at which the plasma turns off. It is shown that, for a point to point microgap (e.g. the microgap between two needle probes) which describes many realistic microdevices, neither Paschen's law applies nor field emission is noticeable. Although normally $V_{\mathrm{BD}}>V_{\mathrm{Q}}$, it is observed that depending on environmental parameters of argon, such as pressure and the driving circuitry, plasma can exist in a different state with equal $V_{\mathrm{BD}}$ and $V_{\mathrm{Q}}$. Using emission line spectroscopy, it is shown that $V_{\mathrm{BD}}$ and $V_{\mathrm{Q}}$ are equal if the atomic excitation by the electric field dipole moment dominantly leads to one of the argon's metastable states ($4P_{5}$ in our study).