Identifying the alloy structures of germanene grown on Al(111)

Abstract

While the growth of germanene has been claimed on many substrates, the exact crystal structures remain controversial. Here, we systematically explore the possible structures formed by Ge deposition onto Al(111) surface by combining density-functional theory (DFT) and global optimization algorithm. We show that, by high level randomphase approximation (RPA) calculations, the formation of germanene on Al(111) is energetically unfavorable with positive formation energy. The two experimental phases are identified as honeycomb alloys Al 3 Ge 3 /Al(111)( √7×√7) and Al 3 Ge 4 /Al(111)(3×3), by combining ab initio evolutionary simulations, RPA calculations, and available experimental data from scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). Al 3 Ge 4 /Al(111)(3×3) is an interesting structure with a vacancy in the substrate, which accounts for the dark clover pattern in the experimental STM image. Our results clarify the structural controversy of the Ge/Al(111) system and indicate the fabrication of germanene may remain challenging.

The Renaissance and Golden Age of Epitaxial Dry Germanene

“…Firstly, let us stress that in our opinion, that despite the use of sophisticated van der Waals functionals, the calculations restricted to a four Al layer slab as used by Yan et al [29] may not lead to more convincing conclusions than any other standard calculations. In this respect, we note that in the work of Yuhara et al [26], the simulated surface was modeled with a symmetric slab with 18 layers in which the central eight layers were fixed, while in the band calculation of Kubo et al [20], the number of Al layers was set at 20.…”

“…Here, it is worth citing a recent theoretical paper, where the authors explore systematically explored the structures of the surface of Ge deposition onto the Al(111) surface by sophisticated theoretical calculations combined with available STM and LEED data [29]. Using ab initio evolutionary simulations and high-level random-phase approximation (RPA) calculations, they showed that the formation of germanene on Al(111) There are many conflicting conclusions, often in regard to strong contradictory assertions, are extremely confusing and raise fundamental questions.…”