Assessment of the relative role of Penning ionization in low-pressure glow discharges

Abstract

Optical Investigations Into the relative role of Penning Ionization as a mechanism for the Ionization of sputtered species In low-pressure argon glow discharges were carried out. These studies employed methane as a quenching agent to effectively reduce the argon metastable population. This reduction of metastable atoms significantly limits the extent of Penning Ionization present In the discharge, which will decrease ion emission signals from the sputtered species. The magnitude of the decrease In these Ion emission signals may then be related to the relative importance of the Penning Ionization process In overall discharge Ionization of the sputtered species. These studies show Penning ionization to account for approximately 40-80% of the ionization of sputtered species, depending upon discharge conditions of current and pressure.

Millisecond pulsed radio frequency glow discharge time of flight mass spectrometry: Temporal and spatial variations in molecular energetics

“…The result is that charge transfer can be very efficient for the ionization of molecular species in the plasma. Penning ionization, on the other hand, is negligible at pressures lower than 0.3 torr [21]. This explains the low population of the distribution in the 8 -12 eV energy range.…”

“…Penning ionization is a major ionization mechanism for species with ionization potentials lower than the energy level of metastable argon atoms. Smith et al observed that in the steady state plasma, Penning ionization accounts for 40 -80% of the ionization of sputtered species [21]; it is thus expected to play an important role in W(CO) 6 ionization and excitation as well. Charge transfer processes of Ar ϩ with W(CO) 6 result in an energy distribution between 13 to 20 eV with the maximum around argon's ionization potential at ϳ15 eV [20].…”

“…The P() plots acquired at 0.4 and 0.6 torr exhibit populations in the lower energy range down to ϳ11 eV, which can be ascribed to the contribution from Penning ionization. It has been shown that Penning ionization increases with increasing discharge pressure and may account for about 40 -80% of total ionization in a continuous glow discharge [21]. Again, the convolution of various ionization and excitation mechanisms results in the broadened energy distributions that can produce mass spectra rich in structural information.…”

18O/16O isotopic separation in anodic tantala films by glow discharge time‐of‐flight mass spectrometry

“…[24] It has been shown that Penning ionisation accounts for 40-80% of the total sputtered atom ionisation occurring in a GD source. [25] The maximum of the argon metastable population is therefore determined by the time required for the electrons to thermalise. The enhanced 181 Ta + signal in the afterglow follows the second Ar peak of the afterglow, indicating ion formation through Penning ionisation processes.…”

Characterization and applications of pulsed millisecond glow discharge sources

“…80% of all sputtered atom ionization in analytical glow discharges plasmas. 10 In argon, the metastable states of 3 P 2 and 3 P 0 occur with energies at 11.52 eV and 11.72 eV. This energy is great enough to ionize a majority of the elements within the Periodic Table without ionizing may of the atmospheric impurities present in the discharge.…”