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鈴木 誠也; 勝部 大樹*; 矢野 雅大; 津田 泰孝; 寺澤 知潮; 小澤 孝拓*; 福谷 克之; Kim, Y.*; 朝岡 秀人; 柚原 淳司*; et al.
Small Methods, 9(3), p.2400863_1 - 2400863_9, 2025/03
被引用回数：3 パーセンタイル：34.72(Chemistry, Physical)For group 14 monoelemental two-dimensional materials, such as silicene, germanene, and stanene, oxidation is a severe problem that alters or degrades their physical properties. This study shows that the oxidized germanene on Ag(111)/Ge(111) can be reformed to germanene by simple heating around 500 
C in a vacuum. The key reaction in reforming germanene is the desorption of GeO and GeO
during heating around 350 C. After removing surface oxygen, Ge further segregates to the surface, resulting in germanene. The reformed germanene has the same crystal structure, a (7
7) R19.1 supercell with respect to Ag(111), and has equivalent high quality to that of as-grown germanene on Ag(111)/Ge(111). Even after air oxidation, germanene can be reformed by annealing in a vacuum. On the other hand, the desorption of GeO and GeO at high temperatures was not suppressed even in the O backfilling atmosphere. This instability of oxidized germanene/Ag(111)/Ge(111) at high temperatures contributes to the ease of germanene reformation without oxygen. In other words, the present germanene reformation, as well as the segregation of germanene on Ag(111)/Ge(111), is a highly robust process as a synthesis method of germanene.
鈴木 誠也; 根本 善弘*; 椎木 菜摘*; 中山 佳子*; 竹口 雅樹*
Annalen der Physik, 535(9), p.2300122_1 - 2300122_12, 2023/09
被引用回数：1 パーセンタイル：0.00(Physics, Multidisciplinary)Germanene is a two-dimensional (2D) germanium (Ge) analogous of graphene, and its unique topological properties are expected to be a material for next-generation electronics. However, no germanene electronic devices have yet been reported. One of the reasons for this is that germanene is easily oxidized in air due to its lack of chemical stability. Therefore, growing germanene at solid interfaces where it is not oxidized is one of the key ideas for realizing electronic devices based on germanene. In this study, the behavior of Ge at the solid interface at high temperatures was observed by transmission electron microscopy (TEM). To achieve such in situ heating TEM observation, we fabricated a graphene/Ge/graphene encapsulated structure. In situ heating TEM experiments revealed that Ge like droplets moved and coalesced with other Ge droplets, indicating that Ge remained as a liquid phase between graphene layers at temperatures higher than the Ge melting point.
寺澤 知潮; 勝部 大樹*; 矢野 雅大; 小澤 孝拓*; 津田 泰孝; 吉越 章隆; 朝岡 秀人; 鈴木 誠也
no journal, ,
Germanene, an atomically thin single layer of Ge, has widely attracted attention because of its theoretically predicted ultrahigh carrier mobility and non-zero bandgap. Among the growth methods of germanene, germanene segregation from Ag thin films deposited on Ge (111) substrate showed the high quality revealed by scanning tunneling microscopy and low energy electron diffraction. However, the mechanism of the segregation of Ge atoms and the subsequent formation of the germanene lattice has not been clarified yet. Here, we discuss the growth mechanism of germanene on Ag (111) thin films, using in-situ Raman spectroscopy and in-situ X-ray photoemission spectroscopy (XPS). The sample preparation involved the deposition of Ag (111) on Ge (111) using electron beam evaporation, followed by Ar
sputtering and annealing. During the annealing and cooling processes, we conducted in-situ Raman and XPS in Japan Atomic Energy Agency using a 473 nm excitation laser and in SPring-8 BL23SU using a synchrotron radiation light of 700 eV, respectively, in ultrahigh vacuum chambers. The Raman spectra of the sample during the annealing show that at 320 and 390 C, a strong peak appeared around 300 cm
, indicating the segregated Ge atoms formed a sp3-Ge lattice. The sp3-Ge peak disappeared at 520 C, indicating that the sp3-Ge is no longer stable at 520 C. Finally, after the rapid cooling down from 520 C to room temperature, the peaks around 160 and 260 cm appeared, indicating that the Ge atoms formed a germanene lattice.
鈴木 誠也
no journal, ,
Germanene, a graphene-like two-dimensional sheet of germanium (Ge), has attracted immense attention owing to its theoretically predicted outstanding 2D topological properties. However, unlike graphene, germanene is easily oxidized in air, making it difficult to realize electrical devices using germanene. To overcome the drawback of the chemical stability of germanene, it is necessary to understand how germanene is oxidized. Also, chemical functionalization is expected to be an effective strategy for providing antioxidant functionality to germanene, although no experimental studies have been reported. Among the possible approaches, hydrogenation is a promising candidate due to its potential to enhance the chemical stability of germanene. Here we report our investigation of the oxidation and hydrogenation reactions of germanene, including an evaluation of their thermal stability. In this study, germanene was synthesized via the segregation method from an Ag(111) thin film deposited on a Ge(111) substrate. Our oxidation study revealed that germanene can be reformed from its oxidized phase through vacuum heating. Careful investigation revealed that the desorption of Ge oxides is the key reaction in the reformation. Hydrogenation studies revealed a continuous change from GeH (monohydride) to GeH
(trihydride) evidenced by Fourier transform infrared spectroscopy. We are the first to demonstrate the reversible hydrogenation and dehydrogenation of monolayer germanene. The details of this study will be reported and discussed in the presentation.
鈴木 誠也; 小澤 孝拓*; 植田 寛和; 福谷 克之
no journal, ,
Germanene, a graphene-like atomic sheet of Ge, has attracted immense attention owing to its theoretically predicted outstanding 2D topological properties. However, because of its chemical instability, electronic devices of germanene have not yet been reported. As one approach, hydrogenation is expected to increase the chemical stability of germanene, leading to the realization of germanene electronic devices. Here, we report on the direct hydrogenation of germanene by atomic hydrogen exposure. The germanene sample was prepared by the segregation method on a Ag(111)/Ge(111) substrate. The atomic hydrogen was generated by cracking of H molecules with a hot tungsten filament. We have studied the hydrogenation of germanene by fourier transform infrared (FT-IR) spectroscopy, themal desorption spectroscopy, and low energy electron diffraction.
鈴木 誠也; 小澤 孝拓*; 植田 寛和; 福谷 克之
no journal, ,
ゲルマネンは、グラフェンに類似したGeの2次元単原子層物質であり、理論予測されているトポロジカル物性により注目を集めている。しかし、その化学的不安定性がこれまでデバイス応用を妨げてきた。この課題に対する一つのアプローチとして、水素化による安定性向上がある。水素化ゲルマネン(GeH)はCaGeからのトポケミカル反応により得られることが知られているが、得られるGeHは多層であり、厚さ制御とスケーラビリティの両立に課題がある。本研究では、厚さ制御とスケーラビリティを両立させる水素化手法として、Ag(111)/Ge(111)基板上に偏析(表面析出)合成した単層ゲルマネンへの直接水素化を報告する。水素化には原子状水素曝露を用いた。原子状水素曝露後のフーリエ変換赤外分光スペクトルから、GeH、GeH、GeHに対応するピークが確認された。また、ゲルマネンの水素化反応飽和時の表面水素濃度を核反応解析により定量評価した。一方、水素化したゲルマネンを加熱すると、水素の脱離とゲルマネンの結晶性の回復が確認された。これはゲルマネンの水素化が可逆的反応であることを示す。
