SrTiO 3 thin films were deposited on vitreous silica substrates at various substrate temperatures (300–700°C) by rf magnetron sputtering technique. The transition from amorphous phase to polycrystalline phase for the films occurred at the substrate temperatures of 300–400°C. Their optical properties were investigated by transmittance measurements. The fitting method was used to calculate the refractive index and the film thickness from the transparent region of the transmittance spectra. The refractive index increased and the film thickness decreased with the substrate temperatures increasing. The dispersion of the refractive index was studied by considering a single electronic oscillator model. The band gaps of the films were estimated from Tauc’s law and showed a decreasing tendency to that of the bulk SrTiO3 with the substrate temperatures increasing. These results provide some useful references for the potential application of SrTiO3 films in integrated optics devices.
The China Spallation Neutron Source started delivering neutron beams to users in March 2018. To upgrade the beam power to 500 kW and improve the performance of the ion source, an RF-driven negative hydrogen (H−) ion source is under development. The source has a silicon nitride ceramic plasma chamber surrounded by a 4.5-turn antenna. The plasma is ignited by a pulsed DC spark gap and then driven by a 2 MHz solid-state amplifier with a repetition rate of 25 Hz. The commissioning of the source started in January 2019. When uncesiated, it produced about 20 mA beam at an RF power of 32 kW and pulse width of 450 μs. This paper describes the configuration of the ion source, several peculiar technologies used in it, and the first negative hydrogen (H−) ion beam extraction.
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