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PEALD AlF3 films were deposited using trimethylaluminum and SF6 plasma precursors in a modified Veeco Fiji G2 reactor. ALD growth windows (the range of process parameters resulting in ideal growth) were established using an in situ ellipsometer to monitor the fluoride growth rate directly on Al substrates and supplemented with post-deposition x-ray photoelectron spectroscopy to elucidate process-structure property relationships. Optimal AlF3 films had a growth rate of 0.75-0.8Å/cycle, F/Al ratio of ≈3, < 2 at% O, indicating that PEALD is a beneficial process technique towards achieving optical coatings on a variety of potential mirror materials. The influence of PEALD parameters on the FUV optical performance of Al mirrors overcoated with PEALD-AlF3 will be also discussed.
We measured the 270-600 GHz dielectric losses of hydrogenated amorphous silicon carbide in superconducting microstrip lines. Furthermore, we measured the complex dielectric constant of the hydrogenated amorphous silicon carbide in the 3-100 THz range using Fourier transform spectroscopy. We modeled the loss data from 0.27-100 THz using a Maxwell-Helmholtz-Drude dispersion model. Our results demonstrate that phonon modes above 10 THz dominate the mm-submm losses in deposited dielectrics.
Efficient mirrors with high reflectivity over the ultra-violet, optical, and infra-red (UVOIR) spectral range are essential components in future space-based observatories. Aluminum mirrors with fluoride-based protective layers are commonly the baseline UV coating technology; these mirrors have been proven to be stable, reliable, and with long flight heritage. However, despite their optical performance to date, their reflectivity is still insufficient for future large telescope instrumentation in which several reflections are required.
Recently, a novel passivation procedure based on the exposure of bare Al to a fluorine containing electron beam generated plasma has been presented [1,2]. This research is framed in a collaboration between Goddard Space Flight Center (GSFC) and the U.S. Naval Research Laboratory (NRL), with plasma treatment carried out in NRL’s large area plasma processing system (LAPPS) using aluminum coated glass samples produced at GSFC coating facilities. The passivation of the bare Al is accomplished by using an electron-beam generated plasma produced in a fluorine-containing background to simultaneously remove the native oxide layer while promoting the formation of an AlF3 passivation layer with tunable thickness. Importantly, this new treatment uses benign precursors (SF6) and is performed at room temperature. In this work, details of the plasma process and in situ surface monitoring with spectroscopic ellipsometry are discussed. This novel procedure has demonstrated improved Al mirrors with state of the art far-ultraviolet (FUV) (λ = 90-200 nm) reflectivity (e.g. R=91% at 121.6 nm) paired with an excellent thickness control of the Al protective layer.
Comparing complex impedance and bias step measurements of Simons Observatory transition edge sensors
We explore observing strategies for both small (0.42 m) aperture telescopes (SAT) and a large (6 m) aperture telescope (LAT). We study strategies focused on small sky areas to search for inflationary gravitational waves as well as strategies spanning roughly half the low-foreground sky to constrain the effective number of relativistic species and measure the sum of neutrino masses via the gravitational lensing signal due to large scale structure. We present these strategies specifically considering the telescope hardware and science goals of the SO, located at 23° South latitude, 67.8° West longitude.
Observations close to the Sun and the Moon can introduce additional systematics by applying additional power to the instrument through telescope sidelobes. Significant side lobe contamination in the data can occur even at tens of degrees or more from bright sources. Therefore, we present several strategies that implement Sun and Moon avoidance constraints into the telescope scheduling.
Scan strategies can also be a powerful tool to diagnose and mitigate instrumental systematics either by using multiple scans to average down systematics or by providing null tests to diagnose problems. We discuss methods for quantifying the ability of an observation strategy to achieve this.
Strategies for resolving conflicts between simultaneously visible fields are discussed. We focus on maximizing telescope time spent on science observations. It will also be necessary to schedule calibration measurements, however that is beyond the scope of this work. The outputs of this study are algorithms that can generate specific schedule commands for the Simons Observatory instruments.
Design and characterization of the Cosmology Large Angular Scale Surveyor (CLASS) 93 GHz focal plane