The simultaneous formation of single domain (3×3) and multi domain (√7×√7)R(±19.1°) germanene phases on Al(111) surface in the sub-monolayer range was studied using scanning tunneling microscopy (STM) and density functional theory (DFT) based simulations. Experimental results revealed that both germanene phases nucleate and grow independently from each other and regardless of Al substrate temperature within significantly expanded range T_s = 27–200 ℃. Our results unambiguously showed that STM images with hexagonal contrast yield correct-resolved structure for both germanene phases, while honeycomb contrast is a result of an artificial tip-induced STM resolution. First-principles calculations suggested atomic models with strongly buckled germanene (2×2)/Al(111)(3×3) and (√3×√3)R30°/Al(111)(√7×√7)R(±19.1°) with one of eight and one of six Ge atoms protruding upward respectively, that consistently describe the experimentally observed STM images both for single and multi domain surface phases. According to the DFT based simulations both germanene (2×2) and (√3×√3)R30° superstructures have a stretched lattice strain with respect to the ideal free-standing germanene by 6.2% and 13.9%, respectively. Hence, numerous small domains separated by domain boundaries in the (√3×√3)R307Al(111)(√7×√7)R(±19.1°) germanene phase tend to reduce the surface energy and prevent the formation of extended single domains, in contrast to the (2×2)/Al(111)(3×3) phase. However, our experimental results showed that the nucleation and growth of germanene on Al(111) surface yield strong modifications of Al surface even at room temperature (RT), which may be contributed to the formation of Al-Ge alloy due to Ge surface solid-states reactivity that was ignored in recent studies. It is already evident from our present findings that the role of Al atoms in the formation of (3×3) and (√7×√7)R(±19.1°) germanene phases is worthy to be carefully studied in the future, which could be an important knowledge for large-quantity fabrication of germanene on aluminum.

In this study, the evolution of C₆₀F₁₈ molecules on a Cu(001) surface was studied by means of scanning tunneling microscopy and density functional theory calculations. The results showed that fluorinated fullerenes (tortoise-shaped polar C₆₀F₁₈) decay on Cu(001) surfaces by a step-by-step detachment of F atoms from the C₆₀ cage. The most favorable adsorption configuration was realized when the F atoms of C₆₀F₁₈ pointed towards the Cu surface and six F atoms were detached from it. The results also showed that a further decay of C₆₀F₁₂ molecules strongly depended on the initial C₆₀F₁₈ coverage. The detached F atoms initially formed a two-dimensional (2D) gas phase which then slowly transformed into F-induced surface structures. The degree of contact between the C₆₀F₁₂ molecules and the Cu(001) surface depended on the density of the 2D gas phase. Hence, the life-time of fluorinated fullerenes was determined by the density of the 2D gas phase, which was affected by the formation of new F-induced structures and the decay of C₆₀F₁₂ molecules.