Influence of the temporal variations of plasma composition on the cyclic formation of dust in hexamethyldisiloxane-argon radiofrequency discharges: Analysis by time-resolved mass spectrometry

Abstract

Cyclic formation of dust nanoparticles in hexamethyldisiloxane (HMDSO, Si2O(CH3)6)-argon RF discharge with pulsed injection of HMDSO was studied using time-resolved mass spectrometry (MS) and optical emission spectroscopy (OES). A large amount of C2H2, considered as promoter of dust nucleation in hydrocarbon plasmas, was found as a by-product of HMDSO fragmentation. Although no negative ions were detected the presence of C2H2 in the HMDSO-Ar discharge supports the hypothesis of a dust growth mechanism based on negative ions being trapped in the plasma. It was found that at the beginning of each cycle of dust formation during α–γ′ transition, the discharge sustaining process is accompanied by a strong consumption of the HMDSO main by-products: HMDSO-15, CH4 and C2H2. At the end of the cycle, corresponding to the progressive disappearance of dust, the discharge switches back to its initial conditions. The beginning of the inverse transition, i.e. γ′–α, is most likely correlated to the growing void in the dust cloud and dust disappearance. In presence of dust nanoparticles, Ar+ and ArH+ dominate the ion population and consequently the discharge maintenance. When the dust particles gradually disappear, the discharge is rather controlled by Si2O(CH3)5+ ions. Moreover, the increased amount of such heavy ions reveals clearly their important income in the dust repelling process due to the drag force on the large sized dust even at short time scale during the injection time of HMDSO. Atomic-H production increases during the transition from dusty plasma to HMDSO-rich plasma with no dust and its role is associated to a delay in the dust nucleation stage.

Multi-scale investigation in the frequency domain of Ar/HMDSO dusty plasma with pulsed injection of HMDSO

“…The maximum and following decrease of ν quenching occurs when dust starts to grow in the plasma. HMDSO and its plasma-generated compounds see their density decrease with dust formation and growth, as previously reported through plasma sampling mass spectrometry measurements [23]. Smaller fragments, resulting from the C 2 H 2 dissociation, are not efficient for quenching argon metastable atoms [60].…”

“…The cyclic phenomena presented above have already been observed for the same Ar/HMDSO dusty plasma [22,23,48], and its response was analysed in the mHz frequency domain using TRG-OES coupled with a collisionalradiative model [48,51]. It was shown that both the electron temperature and density have cyclic behaviour, with a frequency corresponding to the dust formation/disappearance cycle.…”

“…In argon plasmas in the presence of precursors such as HMDSO, many species are expected to play important roles in the quenching of argon 1s states, and thus on the population-depopulation dynamics of argon 2p states. For example, over the range of experimental conditions investigated, the dissociation degree of HMDSO reaches 95% [23]. In such plasmas, a large number of compounds generated in the gas phase or at the chamber walls, including acetylene (C 2 H 2 ) and methane (CH 4 ) [23,57], participate in the quenching of metastable and resonant argon atoms [58][59][60].…”

Time‐resolved analysis of the precursor fragmentation kinetics in an hybrid PVD/PECVD dusty plasma with pulsed injection of HMDSO

“…Though judicious control of the operating conditions, it was however found that pulsing the injection of HMDSO can lead to the formation of successive generations of nanoparticles, or dust, in the gas phase . A recent PSMS study in such conditions showed that acetylene (C 2 H 2 ) is formed as a result of HMDSO fragmentation in Ar/HMDSO plasmas and may be considered as the main origin of dust formation in analogy with hydrocarbon dusty plasmas. Acetylene‐based dusty plasmas have been extensively studied, proving that C 2 H 2 is a strong dust promoter via the confinement of the C 2 H − ion.…”

Binder‐Free Nanoparticulate Coating of a Polyethylene Separator via a Reactive Atmospheric Pressure Plasma for Lithium‐Ion Batteries with Improved Performances

“…Recently, nonthermally reactive atmospheric pressure plasma has attracted much attention as a dry method of film deposition for its simplicity and versatility . The plasma is composed of charged particles and excited neutral precursors with high reactive energies . It can provide a unique environment for chemical reactions and film growth, which is distinct from typical condensed chemical reactions driven by a single heat source.…”