Growth mechanism of germanene Segregated on Ag(111) thin films
Terasawa, Tomoo
; Katsube, Daiki*; Yano, Masahiro
; Ozawa, Takahiro*; Tsuda, Yasutaka
; Yoshigoe, Akitaka
; Asaoka, Hidehito
; Suzuki, Seiya

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.