Si3N4 membrane as entrance window for plasma-generated vacuum ultraviolet (VUV) radiation

Abstract

Vacuum ultraviolet (VUV) radiation produced by an atmospheric pressure plasma was successfully measured down to wavelengths of 58.4nm utilizing a 20nm thin Si3N4 membrane to transfer the VUV radiation into a vacuum monochromator. This method allows measurements without disturbing the plasma or the spectra. He2 absorption could be observed by filling the monochromator with He. Transmission of the Si3N4 membrane in the region of the He2 excimer continua (58nm to 100 nm) could indirectly be measured and confirms literature values.

Figures (4)

• Figure 1: Schematic sketch of the experimental setup. a) Overview of the plasma source and the vacuum monochromator. b) Magnification of the entrance area of the monochromator. c) Sketch of the Si3N4 membrane used as entrance window.
• Figure 2: a) Measured VUV spectra in dependence of the He pressure inside of the monochromator. b) Enlarged depiction of the first He2$^*$ excimer continuum. c) Enlarged depiction of the He resonance line.
• Figure 3: a) Potential energy curves for He2($X$) Prz2010 and He2($A$) Kom2006, as well as their difference in potential energy. b) Wavelength corresponding to the potential energy difference between the He2($X$) and He2($A$) state (left, blue) and fraction of Maxwell-Boltzmann distributed He atoms at 295.15K with the corresponding distance they can reach according to the potential energy of He2($X$) (right, red).
• Figure 4: a) Transmission through 10nm thick Si3N4 or SiO2 membranes with different densities as given by literature Hen1993CXRO2024 compared to experimental determined transmission of a 10nm Si3N4 membrane equivalent as explained in the text. b) VUV spectra normalized to the maximum of the first He2$^*$ excimer continuum and rescaled taking the transmission of the Si3N4 membrane according to Hen1993CXRO2024 into account.