The near-Earth asteroid (162173) Ryugu is thought to be a primitive carbonaceous object that contains hydrated minerals and organic molecules. We report sample collection from Ryugu’s surface by the Hayabusa2 spacecraft on 21 February 2019. Touchdown images and global observations of surface colors are used to investigate the stratigraphy of the surface around the sample location and across Ryugu. Latitudinal color variations suggest the reddening of exposed surface material by solar heating and/or space weathering. Immediately after touchdown, Hayabusa2’s thrusters disturbed dark, fine grains that originate from the redder materials. The stratigraphic relationship between identified craters and the redder material indicates that surface reddening occurred over a short period of time. We suggest that Ryugu previously experienced an orbital excursion near the Sun.

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A new method has been proposed for depositing silicon dioxide films on semiconductors at low temperatures by using ultraviolet (UV) lights. In this method, UV light emitted from a low-pressure Hg lamp is irradiated onto spin-on material which contains tetraethoxysilane Si(OC2H5)4. The light decomposes this compound, leading to the formation of silicon dioxide films. It is found that the physical properties of silicon dioxide films deposited on silicon are similar to those of oxide films obtained by conventional deposition methods, Evidence is presented indicating that UV light irradiation plays an important role in the formation of silicon oxides.

Articles you may be interested inAn ultrahigh vacuum compatible sample holder for studying complex metal surfaces Rev. Sci. Instrum. 81, 043907 (2010); 10.1063/1.3367302Ultrahighvacuum compatible mirrorpolished aluminumalloy surface: Observation of surfaceroughness correlated outgassing rates From its extremely low outgassing rate, the aluminum-alloy UHV system possesses substantial advantages in the fabrication processes of next-generation semiconductor devices. In order to realize the advantages, however, its vacuum properties must be tested under actual fabrication circumstances where the inner surface of the chamber is continuously irradiated with chemically reactive species or energetic ions and photons. In this study, the effects of reactive gas (dichlorosilane: SiH 2 Cl 2 ) on the outgassing rates of aluminum-alloy surfaces were examined for three different surface treatments: the ethanol lathing (EL), the special extrusion (EX), and the ceramic coating (CC). Without exposures to the reactive gas, all three surfaces, after having been baked, resulted in extremely low outgassing rates below the experimental limit of 10 -12 Torr lis cm 2 to prove their usefulness as UHV materials. After an exposure to the reactive gas, however, the outgassing rates of EL and EX increased by about a factor of 50, while that of CC remained basically of the same order. Changes in the surface morphology and the surface layer compositions were also examined by scanning electron microscopy and energy dispersive x-ray analyzer, respectively, which revealed the extent of their corrosions to be in the order EX> EL ~ Cc. Ceramic coating technique will provide us with a promising surface treatment for aluminum alloy used in reactive semiconductor processes.