Excited State Distributions of Hydrogen Atoms in the Microwave Discharge Hydrogen Plasma and the Effect of Electron Energy Probabilistic Function

Abstract

To understand the essentiality of the electron energy distribution function in a low-pressure discharge plasma, an experimental study is carried out on the diagnostics of microwave discharge hydrogen plasma with its discharge pressure ∼1 torr in a cylindrical quartz tube. The electron kinetic temperature and density are measured by a Langmuir double probe. Number densities of electronically excited states of hydrogen atoms are experimentally examined by an optical emission spectroscopic (OES) measurement of line intensities of the Balmer series. The rotational and vibrational temperatures are observed for the Fulcher-α band spectrum of hydrogen molecule to understand the approximate value to the neutral gas temperature. The number density of the ground state of hydrogen atom is also experimentally estimated from the actinometry measurement. The electron energy probabilistic function (EEPF) is numerically calculated as a solution to the Boltzmann equation. Number densities of excited hydrogen atoms are calculated with the collisional-radiative (CR) model with experimentally measured data as input parameters. It is found that the population densities of excited states of hydrogen atoms become about one order or much larger than those determined by OES measurement if we assume Maxwellian EEPF. The CR model with the EEPF as a solution to the Boltzmann equation theoretically reproduce the experimentally measured values very well.Index Terms-Collisional-radiative (CR) model, electron energy probabilistic function (EEPF), low-pressure hydrogen plasma, number density of excited H atoms, plasma spectroscopy, the Boltzmann equation for EEPF.

Spatially Resolved Optical Emission and Modeling Studies of Microwave-Activated Hydrogen Plasmas Operating under Conditions Relevant for Diamond Chemical Vapor Deposition

“…The radiative decay rates derived from these rate constants are, respectively, higher (for reaction (26)), comparable to (for reaction (25)) and lower (for reactions (22)(23)(24)…”

“…H 2 shows a wealth of rovibrational structures in the visible and near-infrared (IR) spectral regions associated with transitions between bound excited electronic states. − Most prior experimental studies of MW-activated hydrogen-containing plasmas have focused on the d 3 Π u –a 3 Σ g + (Fulcher) system, − ,− though lines within the G 1 Σ g + –B 1 Σ u + origin band − and a 3 Σ g + –b 3 Σ u + continuum emission , have been used for plasma diagnostics, and limited studies have been undertaken using the e 3 Σ u + –a 3 Σ g + system . As Figure shows, the structured emissions are from excited states that lie at energies > 13 eV above the ground (X 1 Σ g + ) state of H 2 .…”

Influence of hydrogen addition on methane coupling in a moderate pressure microwave plasma

“…In fact, in the diamond deposition process, where mixtures of methane highly diluted in hydrogen are used in low pressure MW plasma, reaction R3 is the dominant route leading to methane decomposition [38,59]. This phenomenon can be explained by a high concentration of H radicals (reaching up to 10% [60,61]) and high temperatures in the MW plasma region that affect the reaction R3 (with the reaction rate constant being T 3 dependent) and a subsequent R4 and R5, resulting in a higher conversion rate of methane and its radicals. Secondly, the dilution with hydrogen suppresses the production of benzene and soot by inhibiting the decomposition of acetylene [37,50,62].…”

Nonequilibrium characteristics in the rotational temperature of CO excited states in microwave discharge CO2 plasma

“…These observed values are considerably common to the microwave discharge plasmas of any gaseous species in the present device. 34,35,39,40,43) The characteristics of the nonequilibrium were considered to have been caused by the low ionization degree and the resultant electron collisions with atoms and molecules, which were more essential than the Coulomb collisions between the charged species.…”

“…It is identical to the one applied in the previous experiments. [34][35][36][37][38][39][40][41][42][43][44][45][46] The magnetron generates a microwave with a frequency of 2.45 GHz, as a general-purpose variable output microwave oscillator with its output of 0.2-4.9 kW equipped with a built-in isolator. It was connected to the discharge tube via a set of waveguides with a power monitor and a 3-stub tuner, which was finally terminated with a movable short-circuited plunger.…”