Plasma diagnostics by optical emission spectroscopy on argon and comparison with Thomson scattering

Abstract

A novel optical emission spectroscopy (OES) technique for the determination of electron temperatures and densities in low-pressure argon discharges is compared with Thomson scattering (TS). The emission spectroscopy technique is based on the measurement of certain line ratios in argon and a collisional–radiative model (CRM) including metastable transport. The investigations are carried out in a planar inductively coupled neutral loop discharge (NLD) over a wide range of pressures, p = 0.05 Pa–5 Pa. This discharge is a weakly magnetized novel radio-frequency (rf) plasma source, proposed for plasma etching. The NLD is operated in pure argon at a frequency of f = 13.56 MHz and powers varied between P = 1 kW and 2 kW. Both diagnostics, OES and TS, are applied in parallel. The electron energy distribution functions obtained by TS are clearly Maxwellian at low pressures but exhibit a certain enhancement of the energetic tail at higher pressures. Electron densities and temperatures obtained by both diagnostic techniques are compared. Further, absolute numbers of the metastable densities derived from the measurement by the CRM are compared with earlier measurements under similar conditions. Excellent agreement is found throughout if depletion of the neutral gas density by increasing gas temperature and electron pressure is included in the CRM. Electron pressure is the dominant depletion mechanism at gas pressures p ⩽ 0.1 Pa and rf powers P > 1 kW. There, the electron pressure exceeds more than 3 times the neutral pressure and the ionization degree approaches 7% while at pressures p > 1 Pa the degree of ionization is relatively low (<10−3) and neutral gas depletion is dominated by gas heating.

Synthesis of Ni nanoparticles with controllable magnetic properties by atmospheric pressure microplasma assisted process

“…Based on preceding reports [18][19][20][21][22] and NIST Atomic Spectra Database, 23 detailed radiative transition information of species resulted by Ni(cp) 2 dissociation process is summarized in Supporting Information Table S1. The crystal size and phase composition is derived from the XRD results using Scherrer formula; fcc (face-centered-cubic Ni), hcp (hexagonal-close-packed Ni), C (crystalline carbon).…”

Wave propagation and noncollisional heating in neutral loop and helicon discharges

“…Details of the NLD static magnetic field configuration are described in previous papers. [28][29][30] Finally, by using only the bottom coil, the helicon discharge is generated. 33,34 A similar helicon configuration is reported by Stevens et al 35 Time-varying magnetic fields are measured via a bare single induction loop ͑B-dot probe͒.…”

“…In our discharge, it turned out that Landau damping is the dominant heating mechanism leading to efficient plasma ionization. Additionally, we present results in a so-called neutral loop discharge [24][25][26][27][28][29][30][31][32] ͑NLD͒ operated in the same setup with a null point configuration of the magnetic field. Theoretical investigations on the heating mechanisms in the NLD are limited to single particle pictures with simple geometry.…”

CVD Chemistry of Organoborons for Boron-Carbon Thin Film Depositions

“…Optical Emission spectroscopy (OES) analysis has been a widely implemented, fast, nonintrusive, technique to characterize plasma, which requires only moderate and inexpensive spectroscopic equipment and a high transparency optical window in the plasma reactor [75], [76]. Due to its versatility, OES has been used for different purposes and applications such as investigating electron temperatures, electron densities, electron energy distribution functions in low temperature plasmas and gas phase chemistry in plasma CVD [77]- [79].…”