Capacitively coupled hydrogen plasmas sustained by tailored voltage waveforms: vibrational kinetics and negative ions control

Abstract

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Fokker–Planck equation for chemical reactions in plasmas

“…Another peculiarity of partially ionized gases subjected to electric fields is that energy levels of atoms and molecules are populated by specific mechanisms related to energy reservoirs not in equilibrium between them: for this reason, the excited state populations do not follow the distribution valid in the equilibrium case, that is, the Boltzmann distribution [2,3]. This leads to the state-to-state (STS) description.…”

“…This leads to the state-to-state (STS) description. This last is based on the idea that a molecule in any specific quantum state reacts with a specific reaction rate with other species to produce different excited states and other reaction products [2][3][4][5]. As a consequence, the only way to describe in a quantitatively correct way chemical reactions occurring in ionized gases is to calculate these populations as a function of time, by solving appropriate kinetic equations: the most widely used is the Master equation, a system of ordinary differential equations linking the distribution of populations of different levels.…”

“…As a consequence, the only way to describe in a quantitatively correct way chemical reactions occurring in ionized gases is to calculate these populations as a function of time, by solving appropriate kinetic equations: the most widely used is the Master equation, a system of ordinary differential equations linking the distribution of populations of different levels. The description of numerous kinds of plasma by this method produced excellent results in terms of comparison with experimental results, with the perspective to optimize the process for systems of applicative interest and it has also greatly contributed to the understanding of ionized gas kinetics by highlighting the complex and detailed pathways that produce variation in time of the chemical composition of the system, and cannot be replaced in any effective way by simpler approaches disregarding these distributions [2,3]. On the other hand, the Master equation is a very complex equation in that it has as many unknowns as the states considered in the model and a right-hand side that includes a large number of terms, each of which is connected to a single STS chemical process.…”

Monte Carlo calculation of the potential energy surface for octahedral confined H$$_2^+$$2+

“…KBr [18]) purposely. Confined H + 2 presents also an interest for materials science and microelectronics [13], being the probable outcome of H + 2 ions impact on solid substrates, which are charged at high negative voltage with respect to the plasma potential in a radio-frequency or microwave reactor with H 2 as main component of the feed: these devices have attracted much attention in the last few years also for their use in materials processing [19][20][21][22][23][24][25]. Although previous studies have shown that H + 3 is the main ion present in the plasma phase under typical pressure conditions for these devices, the triatomic ion dissociates above 4.37 eV and it is not found inside solid lattices after exposure to plasma [26].…”

Current status and nature of high-frequency electronegative plasmas: basis for material processing in device manufacturing

“…16. (Color online) Net dissociative attachment rate Λ DA (z, v) as a function of vibrational quantum number and position in a CCP in H 2 (X S + v ; g 1) 79). Λ DA is obtained by a 1D PIC/MCS for charged particles and a fluid model for neutrals.…”