Evolution of plasma parameters in capacitively coupled He–O₂/Ar mixture plasma generated at low pressure using 13.56 MHz generator

Abstract

Low pressure capacitively coupled He–O2/Ar mixture plasma is investigated using optical emission spectroscopy and Langmuir probe (LP) techniques and the effects of discharge parameters i.e. radio frequency (RF) power, filling gas pressure and oxygen concentration on electron density (ne), electron temperature (Te), excitation temperature (Texc), plasma potential (Vp) and electron energy probability function (EEPF) are monitored. It is noted that increases with increase in RF power and filling gas pressure, while it decreases with increasing O2 concentration. The LP technique and Boltzmann plot method are employed to determine and and estimated by both methods shows similar decreasing trend with increasing RF power and filling gas pressure. A sudden increase in and decrease in is noted with RF power, indicating a mode transition i.e. from alpha to the gamma mode. The threshold RF power for the mode shifts from higher to lower value (150–120 W) with increasing gas pressure (0.3–0.5 mbar). This trend reverses and shifts from lower to higher RF value i.e. from 110 W (pure helium) to 150 W (8% O2) with increase in O2 concentration. Investigation of EEPF profile states evolution from Druyvesteyn-like to bi-Maxwellian distribution with increase in RF power and filling gas pressure; due to mode transition and decrease in the height of high energy tail of EEPF. Similarly, the effect of O2 mixing on the shape of EEPF is also investigated. It is noted that in pure helium discharge the EEPF is bi-Maxwellian in nature, while addition of O2 in the mixture results in the broadening of the EEPF. Moreover, the height of high energy tail of EEPF also increases. Finally, an increasing trend in atomic oxygen density is noted with increase in RF power, pressure and O2 concentration.

Concept of SUb-atmospheric Radio-frequency Engine (SURE) for near space environment

“…Results are for dual antennas with 5 turns, separation distance of 0.1 m and input power of 800 W. One can see that the plasma density largely decreases for enhanced pressure, while the plasma temperature increases on the whole. These opposite trends of plasma density and temperature are consistent with previous studies [30,31]. The underlying physics may be correlated with the mean free path of electrons, which is short for high density and thereby shortens the acceleration path, yielding low temperature under certain conditions.…”

Polymer surface modification using He/O2 RF remote low‐pressure plasma

“…These changes in EEPFS are reflected in the inset of the figure, which gives the variations of both electron density and effective electron temperature as a function of helium fraction in the He/O 2 discharge. It can be noticed that the maximum of ( n e ) and ( T eff ) at 30% helium fraction corresponds to the longest tail of high‐energy electron in the EEPF; this appearance of the maximum in ( n e ) can be explained by considering the Penning ionization of oxygen (O 2 ) by helium metastables (He m ) as follows 9,10 : …”

“…In the literature, there are limited works devoted to He/O 2 mixture plasma at a low pressure 7–10 ; in the low‐pressure plasma, the large mean‐free path of electrons enables the production of relatively high‐energy electrons (~10 eV) which provides excitation, ionization, and dissociation processes at relatively low gas temperature (~300 K).…”

Spectroscopic and electrical characterization of oxygen microwave discharge used for downstream plasma oxidation of Si

“…Figure 3 gives the typical I ‐ V characteristics of Langmuir probe in oxygen microwave plasma recorded at Z 1 for the three studied values of applied power. The EEPF in low temperature plasma has been intensively studied theoretically and experimentally 17,20–23 …”

“…The EEPF in low temperature plasma has been intensively studied theoretically and experimentally. 17,[20][21][22][23] The plasma potential (V p ) can be determined from the zero cross of the second derivative of the current and the floating potential (V f ) corresponds to the condition (I = 0).…”