Correlation between structures and vibration properties of germanene grown by Ge segregation

The vibrational properties of different Ge phases formed on Ag(111) thin films by the Ge segregation method were investigated using in situ Raman spectroscopy. As the segregation temperature is increased, the striped phase, the less-ordered phase and the long-range ordered phase appear in that order. While the less-ordered and long-range ordered phases showed Raman peaks assignable to germanene, featureless Raman spectra of the striped phase indicate that the striped phase is Ag–Ge surface alloy. The germanene Raman peaks shift to higher wavenumbers with the segregation temperature, which could be due to reduction of the tensile strain in germanene.