Abstract The artificial postgraphene two-dimensional (2D) materials termed 2D-Xenes, which consist of atoms arranged in atomically thin sheets with a honeycomb lattice, have received extensive attention because of their unique electronic properties. Insights into the growth mechanism at the atomic scale constitute a major challenge for realizing high-quality 2D materials, as often the substrate and deposited atoms tend to form alloys. Here, we present evidence for intrinsic growth of germanene on Al (111), i.e. a postgraphene elemental 2D atomically thin sheet. The atomic-scale extra-high resolution scanning tunneling microscopy (STM) characterization supported by density functional theory–based calculations provides deeper insight into the true atomic arrangement for the (2 × 2)/Al (111) (3 × 3) and (√3 × √3)R (30°)/Al (111) (√7 × √7)R (±19.1°) germanene phases and unambiguously confirms their real 2D honeycomb nature, which till now lacks convincing experimental proof. First-principles calculations suggest atomic models with strongly buckled (2 × 2) and (√3 × √3)R (30°) germanene, with one of eight and one of six Ge atoms protruding upward, respectively, providing perfect atom-by-atom agreement with the true atomically resolved STM images for both germanene phases. Moreover, the experimentally observed phenomena of local removal of the buckling is consistent with the formation of a flat germanene structure. Furthermore, the formation of bilayer germanene with AB-stacking is demonstrated by means of re-deposition of germanene flakes from the STM tip on top of single layer germanene, indicating that germanene flakes can be easily torn off from the aluminum substrate and attached to the STM tip, retaining their 2D configuration. On the other hand, the formation of bilayer germanene suggests an increased electronic decoupling of the bottom germanene layer from the substrate, in contrast to single layer germanene.

中文翻译：

---

对 Al(111) 表面单层和双层锗烯的原子洞察

摘要 人造后石墨烯二维 (2D) 材料称为 2D-Xenes，由排列在具有蜂窝晶格的原子薄片中的原子组成，因其独特的电子特性而受到广泛关注。深入了解原子尺度的生长机制是实现高质量 2D 材料的主要挑战，因为基板和沉积的原子往往会形成合金。在这里，我们展示了锗烯在 Al (111) 上固有生长的证据，即后石墨烯元素 2D 原子薄片。由基于密度泛函理论的计算支持的原子级超高分辨率扫描隧道显微镜 (STM) 表征提供了对 (2 × 2)/Al (111) (3 × 3) 和 ( √3 × √3)R (30°)/Al (111) (√7 × √7)R (±19. 1°) 锗烯相，并明确证实了它们真正的 2D 蜂窝性质，但到目前为止还缺乏令人信服的实验证据。第一性原理计算表明具有强烈屈曲 (2 × 2) 和 (√3 × √3)R (30°) 锗烯的原子模型，其中八个 Ge 原子中的一个和六个 Ge 原子中的一个分别向上突出，提供完美的原子比- 原子与两个锗烯相的真实原子分辨 STM 图像一致。此外，实验观察到的局部屈曲消除现象与平坦锗烯结构的形成一致。此外，通过将来自 STM 尖端的锗烯薄片重新沉积在单层锗烯顶部，证明了具有 AB 堆叠的双层锗烯的形成，表明锗烯薄片可以很容易地从铝基板上撕下并连接到 STM 尖端，保持其 2D 配置。另一方面，与单层锗烯相比，双层锗烯的形成表明底部锗烯层与衬底的电子去耦增加。