Vacuum UV broad-band absorption spectroscopy: a powerful diagnostic tool for reactive plasma monitoring

Abstract

Broad band UV-visible absorption spectroscopy is widely used to measure the concentration of radicals in reactive plasmas. We extended the applicability of this technique to the VUV (115 nm to 200 nm), the spectral range in which the electronic transitions from the ground state to the Rydberg or pre-dissociated states of many closed shell molecules are located. This gives access to the absolute densities of species which do not, or weakly absorb in the UV/visible range. The technique is demonstrated by measuring the densities of HBr and Br 2 molecules in HBr high-density ICP plasmas.

Density of atoms in Ar*(3p54s) states and gas temperatures in an argon surfatron plasma measured by tunable laser spectroscopy

“…7,8 The other route is that of active spectroscopy in which an external radiation source is used to study how the beam generated by that source is absorbed by the plasma. For that, three different types of sources can be used: a spectral broad band source providing a quasi continuum, 9,10 an atomic transition source, delivered by another Ar plasma 11,12 or narrow band sources given by tunable lasers.…”

Reptation Aggregation of Liquid Silicon Oils Modified by Ar Plasmas

“…Since the high energy of photons (∼ 6 eV up to greater than 10 eV) in the VUV spectral range exceeds covalent chemical bond energies found in most polymers (≤ 5 eV), the absorption of the VUV radiation results in bond scission and the formation of free radicals. The subsequent reactions can lead to the crosslinking of polymer and the polymerization of monomers . Typical examples include the formation of a crosslinked surface layer on polyethylene and polytetrafluoroethylene exposed to inert gase discharges, the crosslinking of ethylene‐tetrafluoroethylene copolymer exposed to an argon plasma, as well as plasma‐initiated polymerization of phosphazene crystal and methyl methacylate .…”

Broadband Time-Resolved Absorption and Dispersion Spectroscopy of Methane and Ethane in a Plasma Using a Mid-Infrared Dual-Comb Spectrometer

“…To characterize the plasma process and maximize the conversion efficiency, various molecular species and reaction processes have to be measured and monitored during plasma operation. For this, methods are employed based on mass spectrometry [10] and optical detection, for the latter, specifically emission/absorption spectroscopy [11][12][13][14][15]. The main advantage of optical-based detection is their fast response time, in-situ measurement, and species specificity.…”