In situ study of growth mechanism of germanene segregated through Ag(111) thin films by Raman and X-ray photoelectron spectroscopy

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

Chemistry of Materials, 38(6), p.2933 - 2945, 2026/03

AA2025-0822.pdf:1.33MB

https://doi.org/10.1021/acs.chemmater.5c03462

Germanene, a honeycomb lattice of Ge atoms, has attracted attention for next-generation electronics and as a topological material. Among reported synthesis routes, the segregation method enables reproducible monolayer germanene formation on Ag(111) through simply annealing an Ag(111) thin film on a Ge(111) substrate. Despite this success, the physical origins of its monolayer selectivity and the mechanism for suppressing competing Ge phases remain unclear. Here, we investigate germanene formation via Ge segregation using in situ Raman spectroscopy and X-ray photoelectron spectroscopy to directly track Ge behavior during annealing and cooling. In situ observations revealed that annealing at 500C yielded no Ge-related byproducts, and the system reached a high-temperature surface equilibrium state, independent of the initial Ge amount. Cooling from this state produced a Ge-enriched surface that stabilizes the formation of monolayer germanene. In contrast, heating only to 300C produced three-dimensional Ge islands without Ge-enrichment, followed by Ge-Ag alloy formation upon subsequent cooling. By integrating the temperature-dependent diffusion length and the process-dependent diffusion direction, we established a unified description of Ge behavior on Ag/Ge(111) substrates, in which cooling-induced Ge-enrichment at the surface reproducibly stabilizes the selective formation of monolayer germanene.

Growth mechanism of germanene Segregated on Ag(111) thin films

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.