LIGO Document G1601703-v3

Preliminary Results of Cryogenic Losses for Titania, Silica, Silicon Nitride Films and Silicon Substrate

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We used our closed-loop cryogenic system to measure the mechanical losses of titania and silica films that were deposited by in-house ion beam sputter (IBS) system and silicon nitride films that were deposited by plasma-enhanced chemical vapor deposition (PECVD) system. Preliminary results are presented here. The IBS titania does not show cryogenic peak and the loss angle is in 10-4 range. The as-deposited IBS silica film has a cryogenic peak around 80K and the peak shifts to around 20K after 600oC annealing. Silicon nitride film with 0.87 nitrogen to silicon ratio has a cryogenic peak at around 40K. The silicon nitride film with 0.40 nitrogen to silicon ratio, however, does not show cryogenic peak, and the loss angle is 5.5x10-5 for 671 Hz and within lower 10-4 range for higher order modes at 10K. SiN0.40 is a promising film in terms of mechanical loss.
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