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nanoclusters appear on the surface of Sn-II as the coverage is much higher than 1 ML [Figure 4A], which
indicates that Sn-II phase is acting as a “buffer” layer that decreases the interaction between the surplus tin
atoms and the substrate and enables the formation of Sn nanocluster. The dI/dV spectra on Sn-II phase
[Figure 4D] show apparent depression of local density of states in the close vicinity of the Fermi level
compared to Sn-I phase, which agrees with the decoupling effect.

CONCLUSIONS
In summary, two 2D tin allotropes with quasi-periodic lattice and square-like lattice are fabricated on
Al(111) by epitaxial growth method at different tin coverages. Beyond sub-monolayer coverage, the
enhanced decoupling effect occurs and induces a square-like lattice, which is rarely found among epitaxial
elemental monolayers on metal substrates with hexagonal lattice. The presence of these two well-defined
structures adds another degree of freedom to stanene and other 2D elemental monolayers beyond the
honeycomb and buckled honeycomb lattices regarding the lattice symmetry design and tunning the
interaction between epitaxial films and substrates.

DECLARATIONS
Authors’ contributions
Made substantial contributions to conception and design of the study and performed data analysis and
interpretation: Feng H, Du Y
Performed data acquisition and provided administrative, technical, and material support: Feng H, Xu X, Liu
Y, Zhuang J, Hao W, Dou SX

Availability of data and materials
Not applicable.

Financial support and sponsorship
This work is supported by the National Natural Science Foundation of China (12074021, 12104033,
12004321, 12274016, 52073006), the Fundamental Research Funds for the Central Universities and
Australian Research Council (LP180100722).

Conflicts of interest
All authors declared that there are no conflicts of interest.

Ethical approval and consent to participate
Not applicable.

Consent for publication
Not applicable.

Copyright
© The Author(s) 2023.

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