Characterization of the flowing afterglows of an N₂–O₂reduced-pressure discharge: setting the operating conditions to achieve a dominant late afterglow and correlating the NO_βUV intensity variation with the N and O atom densities

Abstract

The flowing afterglow of an N2–O2 discharge in the 0.6–10 Torr range is examined in the perspective of achieving sterilization of medical devices (MDs) under conditions ensuring maximum UV intensity with minimum damage to polymer-based MDs. The early afterglow is shown to be responsible for creating strong erosion damage, requiring that the sterilizer be operated in a dominant late-afterglow mode. These two types of afterglow can be characterized by optical emission spectroscopy: the early afterglow is distinguished by an intense emission from the 1st negative system (band head at 391.4 nm) while the late afterglow yields an overpopulation of the v′ = 11 ro–vibrational level of the N2(B) state, indicating a reduced contribution from the early afterglow N2 metastable species. We have studied the influence of operating conditions (pressure, O2 content in the N2–O2 mixture, distance of the discharge from the entrance to the afterglow (sterilizer) chamber) in order to achieve a dominant late afterglow that also ensures maximum and almost uniform UV intensity in the sterilization chamber. As far as operating conditions are concerned, moving the plasma source sufficiently far from the chamber entrance is shown to be a practical means for significantly reducing the density of the characteristic species of the early afterglow.Using the NO titration method, we obtain the (absolute) densities of N and O atoms in the afterglow at the NO injection inlet, a few cm before the chamber entrance: the N atom density goes through a maximum at approximately 0.3–0.5% O2 and then decreases, while the O atom density increases regularly with the O2 percentage. The spatial variation of the N atom (relative) density in the chamber is obtained by recording the emission intensity from the 1st positive system at 580 nm: in the 2–5 Torr range, this density is quite uniform everywhere in the chamber. The (relative) densities of N and O atoms in the discharge are determined by using the actinometry method: the density of N atoms decreases from its maximum value at 0% O2 as the percentage of O2 is increased while the density of O atoms increases, almost linearly, as a function of the percentage of O2, as in the afterglow. The intensity variation of the NOβ UV emission as a function of the percentage of O2 is characterized by a maximum around 0.6% O2 (2 Torr) followed by an approximately exponential decay. We observe that, in the 0–1% O2 range, the UV emission is limited by the availability of O atoms. Beyond this point, the decrease of the UV intensity follows the decrease in the N atom density, while on the average, the O atom density keeps on increasing with O2%. Erosion of polymer microspheres is found to be strongest at the chamber axis when no O2 is present, implying a dominant early afterglow. Adding even only 1% O2 causes a strong quenching of the N2 metastable species, leading to a dominant late afterglow and therefore considerably reducing the etching rate at the axis. In contrast, at 5 cm from the axis under the same operating conditi...

NanoSIMS50 analyses of Ar/18O2plasma-treatedEscherichia colibacteria

“…The plasma is created on the left of the 5 mm inner diameter cylindrical quartz tube exposed to 2.45 GHz microwaves by means of a surfaguide wave launcher. The delivered microwave power is 200 W. The species of the discharge are then flowing through the 5 mm inner diameter cylindrical quartz tube, in a zone called the early afterglow, still containing charged species [26]. Then, the early afterglow enters a larger quartz tube (28 mm inner diameter) that is 45 cm from the discharge and is becoming a late afterglow, because no more charged species are present [26].…”

Low-pressure water vapour plasma treatment of surfaces for biomolecules decontamination

“…Depending on the reactor design, Ar/O 2 gas mixtures showed best biomaterial removal efficiency in RF discharges [9][10][11][12], when treated samples were placed in to active plasma. In addition, interesting results in terms of sterilization capability of plasmas were also reached using H 2 /O 2 gas mixtures [13,14], N 2 /O 2 gas mixtures [15][16][17] or pure O 2 discharge plasma [18,19].…”

O2 dissociation in Ar–O2 surface-wave microwave discharges

“…Afterglow systems based on oxygen containing surface-wave microwave discharges meet several applications in the fields of biomedicine [1][2][3][4] and surface treatment [5,6], with further potential in areas such as nanotechnology [7][8][9]. In numerous applications the major role is played by the O-atoms, although most of the time a synergetic effect between the O-atoms and ions or UV photons is observed.…”

“…In numerous applications the major role is played by the O-atoms, although most of the time a synergetic effect between the O-atoms and ions or UV photons is observed. For example in the removal of biological contaminants/etching of hydrocarbons the crucial process is the chemical sputtering induced by the Ar + ions and O-atoms [10], while in the bacterial inactivation [3,11,12] and etching of polyolefins (hexatriacontane -HTC) [5] the synergetic effect between the O-atoms and the VUV/UV radiation, which can originate e.g. from the NO(A) and NO(B) molecules or the resonant state Ar atoms, has been found.…”