Recent advances in vacuum-ultraviolet (VUV) light sources based on dielectric barrier discharges for emerging applications in photochemistry and surface treatment

Dielectric barrier discharge (DBD) excitation of the rare-gases provides a practical and efficient method for generating pulsed incoherent vacuum-ultraviolet (VUV) radiation from excited diatomic molecules (excimers) in the wavelength bands λ=60-100nm (He₂*), λ=80-90nm (Ne₂*), λ=120-130nm (Ar₂*), λ=140-150nm (Kr₂*), & λ=165-175nm (Xe₂*). Due to their high electrical to VUV conversion efficiencies (5%-60%) [1-3], simple construction, and size/output-power scalability, these deep ultraviolet light sources are now being used in a growing range of applications covering photo-chemistry [1], materials processing/deposition & nanofabrication [2]; surface modification, cleaning & etching [3].In the current study, the temporal characteristics of the VUV output pulses generated by a DBD excimer-based light source (e.g. pulse width, rise-time, instantaneous peak-power etc.) have been investigated in detail. The ability to tailor pulse shapes is known to be important for niche applications in surface cleaning based on VUV source irradiation, for example, in the removal of organic surface layers and in dehydroxylation of glass and polymer substrates [3]. DBD sources with optimised VUV pulse shapes may be important for a wider range of materials processing applications, representing a new research direction that has yet to be fully explored. In DBD light sources, the VUV pulse shapes are highly dependent on the method of electrical excitation used to generate the plasma. High-voltage sinusoidal, square-wave, or short-pulse waveforms are generally employed to drive DBD’s at kHz repetition frequencies. Previously, we reported detailed experimental and theoretical studies investigating the critical importance of the shape of the applied voltage waveform in determining the temporal evolution of the VUV pulse shapes observed in Xe DBDs [4]. However, analogous studies of the influence of the voltage waveform on DBD lamp performance using the lighter rare gases He, Ne, Ar and Kr are generally scarce. In this paper we investigate the electrical and optical characteristics of a DBD with He, Ne, Ar, and Kr gas fills. In addition, issues relating to the efficient production of Ne2* species are of interest in their own right to underpin the parallel development of high pressure Ne/H₂ plasma lamps generating relatively narrow line-width VUV emission at λ=121.6nm (H Lyman α) [5].