Atomic hydrogen determination in medium-pressure microwave discharge hydrogen plasmas via emission actinometry

Abstract

Atomic hydrogen plays an important role in the chemical vapour deposition of functional materials, plasma etching and new approaches to the chemical synthesis of hydrogen-containing compounds. This work reports experimental determinations of atomic hydrogen in microwave discharge hydrogen plasmas formed from the TM 01 microwave mode in an ASTeX-type reactor, via optical emission spectroscopy using Ar as an actinometer. The relative intensities of the H atom Balmer lines and Ar-750.4 nm emissions as functions of input power and gas pressure have been investigated. At an input microwave power density of 13.5 W cm −3 , the approximate hydrogen dissociation fractions calculated from electron-impact excitation and quenching cross sections in the literature, decreased from ∼0.08 to ∼0.03 as the gas pressure was increased from 5 to 25 Torr. The influences of the above cross sections, and the electron and gas temperatures of the plasmas on the determination of the hydrogen dissociation fraction data have been discussed.

Hydrogen Chemical Configuration and Thermal Stability in Tungsten Disulfide Nanoparticles Exposed to Hydrogen Plasma

“…Such a substantial expansion can only be due to stuffing some material between the WS 2 layers. The plasma conditions provide the energy required for the H 2 molecules to intercalate in the following way: In the plasma formed sheath on the surface of the sample, the plasma ions are accelerated by the potential drop of ~3 T e , where T e is the electron temperature: ~2 eV in the conditions similar to those used by us 34. These accelerated ions collide with neutrals and form an energetic mixture of ions-neutrals flowing toward the sample surface.…”

Validating optical emission spectroscopy as a diagnostic of microwave activated CH4/Ar/H2 plasmas used for diamond chemical vapor deposition

“…The principles underpinning actinometry and its use as a plasma diagnostic have been thoroughly described elsewhere. 4,5,[22][23][24][25] Briefly, the method involves the addition of a small, known, amount of an inert tracer species ͑e.g., Ar, as here͒-the actinometer-to the gaseous medium of interest. Then, by comparing the intensities of specific emissions of the actinometer and of the species ͑X͒ of interest, the concentration of the latter can be deduced from the relation ͓X͔/͓act͔ = kI X /I act , ͑1͒…”

Combined Spatially Resolved Optical Emission Imaging and Modeling Studies of Microwave-Activated H2/Ar and H2/Kr Plasmas Operating at Powers and Pressures Relevant for Diamond Chemical Vapor Deposition

“…10,11 Small additions of Ar have been used as an actinometer for estimating relative H atom concentrations in CH4/H2 plasmas. [12][13][14][15] Larger additions of Ar (and other noble gases) substantially affect the relative intensities of the various features in the optical emission spectrum of the plasma, as a result of changes in gas temperature and the plasma chemistry. [16][17][18][19][20][21] Successful CVD of high-quality diamond depends on the availability of suitable concentrations of both H atoms and CHx (x = 0-3) radicals, particularly CH3 radicals, in the gas phase adjacent to the growing surface.…”