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タイトル	en Transmission Electron Microscopy Study of the Morphology of Ices Composed of H2O, CO2, and CO on Refractory Grains
作成者	en Kouchi, Akira NRID 1000060161866 en Tsuge, Masashi en Hama, Tetsuya en Oba, Yasuhiro en Okuzumi, Satoshi en Sirono, Sin-iti en Momose, Munetake en Nakatani, Naoki en Furuya, Kenji en Shimonishi, Takashi en Yamazaki, Tomoya en Hidaka, Hiroshi NRID 1000000400010 en Kimura, Yuki NRID 1000050449542 en Murata, Ken-ichiro NRID 1000060646272 en Fujita, Kazuyuki en Nakatsubo, Shunichi en Tachibana, Shogo en Watanabe, Naoki NRID 1000050271531
アクセス権	metadata only access
主題	NDC 420
内容注記	Abstract en It has been implicitly assumed that ices on grains in molecular clouds and protoplanetary disks are formed by homogeneous layers regardless of their composition or crystallinity. To verify this assumption, we observed the H2O deposition onto refractory substrates and the crystallization of amorphous ices (H2O, CO2, and CO) using an ultra-high-vacuum transmission electron microscope. In the H2O-deposition experiments, we found that three-dimensional islands of crystalline ice (I-c) were formed at temperatures above 130 K. The crystallization experiments showed that uniform thin films of amorphous CO and H2O became three-dimensional islands of polyhedral crystals; amorphous CO2, on the other hand, became a thin film of nano-crystalline CO2 covering the amorphous H2O. Our observations show that crystal morphologies strongly depend not only on the ice composition but also on the substrate. Using experimental data concerning the crystallinity of deposited ices and the crystallization timescale of amorphous ices, we illustrated the criteria for ice crystallinity in space and outlined the macroscopic morphology of icy grains in molecular clouds as follows: amorphous H2O covered the refractory grain uniformly, CO2 nano-crystals were embedded in the amorphous H2O, and a polyhedral CO crystal was attached to the amorphous H2O. Furthermore, a change in the grain morphology in a protoplanetary disk is shown. These results have important implications for the chemical evolution of molecules, nonthermal desorption, collision of icy grains, and sintering.
出版者	en IOP Publishing
日付	Issued2021-09
言語	eng
資源タイプ	journal article
出版タイプ	NA
資源識別子	HDL http://hdl.handle.net/2115/82804
関連	isIdenticalTo DOI https://doi.org/10.3847/1538-4357/ac0ae6
収録誌情報	PISSN 0004-637X en Astrophysical journal 巻918 号2 開始ページ45
コンテンツ更新日時	2023-07-26