VUV irradiance measurement of a 2.45 GHz microwave-driven hydrogen discharge

Abstract

Absolute values of VUV-emission of a 2.45 GHz microwave-driven hydrogen discharge are reported. The measurements were performed with a robust and straightforward method based on a photodiode and optical filters. It was found that the volumetric photon emission rate in the VUV-range (80-250 nm) is 10 16 -10 17 1/cm 3 s, which corresponds to approximately 8% dissipation of injected microwave power by VUV photon emission. The volumetric emission of characteristic emission bands was utilized to diagnostics of molecular plasma processes including volumetric rates of ionization, dissociation and excitation to high vibrational levels and metastable states. The estimated reaction rates imply that each injected molecule experiences several inelastic electron impact collisions. The upper limit for the total density of metastable neutrals (2S atoms and c 3 Π u molecules) was estimated to be approximately 0.5% of the neutral gas density.

Plasma heating power dissipation in low temperature hydrogen plasmas

“…Total photon emission of at least 15-30% of the discharge power in VUV-range has been measured with a filament driven arc discharge 39 . For a 2.45 GHz microwave discharge the corresponding number is approximately 10% 40 . These values are consistent with this study.…”

Hydrogen plasma induced photoelectron emission from low work function cesium covered metal surfaces

“…Theoretical calculations based on fundamental conservation laws and reaction cross sections show that at least 10% of plasma heating power is dissipated via photon emission in low temperature hydrogen plasmas. 9 The theoretical result is supported by experimental evidence showing that low temperature hydrogen plasmas are strong sources of vacuum ultraviolet (VUV) radiation with up to 15%-30% of the discharge power radiated at wavelengths of 120-250 nm in filamentdriven arc discharge, 10 up to 8% of the injected microwave power at 80-250 nm in ECR discharge, 11 and up to 21% of RF power at 117-280 nm in RF discharge. 12 Electrons in the conduction band of a metal follow the Fermi-Dirac distribution which can be used to derive the following relation for the quantum efficiency Y of the PE emission: 13 Y / ðh À /Þ 2 ðU 0 À hÞ 1=2 ; when h !…”

Radiofrequency and 2.45 GHz electron cyclotron resonance H−volume production ion sources

“…In addition it can be expected that their hydrogen atom or proton fraction is more significant in comparison to arc discharge sources. The difference between the discharge types has been experimentally verified by comparing the volumetric rates of molecular ionization and excitation in an ECR discharge [28] and an arc discharge [29] indicating that the ionization and vibrational heating rates/kW of input power are higher in the arc discharge. Thus, from the -H volume production point-of-view RF or ECR discharges cannot be expected to be as power efficient as arc discharge sources.…”