Scanning tunneling microscopy of thick quasiperiodic Sn layer*

Quasicrystals (QCs) have an aperiodic long-range order with forbidden rotational symmetries but lack translational symmetry. These are very attractive due to their remarkable physical properties such as low surface energy, low thermal and electrical conductivity. Inorganic QCs exist mostly as ternary systems. However, elemental quasicrystal in bulk form has not been discovered so far, which would be important for understanding the physical properties of QCs independent of their chemical complexity. Although tremendous efforts in this direction have been made to grow elemental adlayers on quasicrystalline substrates but only 1-2 pseudomorphic monolayers of a few elemental metals have been reported to show quasiperiodicity since last three decades [1].  In the present work, we have established the thickest (4 nm) quasiperiodic Sn layer reported to date using scanning tunneling microscopy (STM) and other related techniques including density functional theory calculations [2]. The unique motifs made up of P-tiles and hexagonal tile such as a crown, wheel and triplet are different from the motifs observed on the substrate indicating different quasiperiodic arrangements of Sn. Also, the low-energy electron diffraction patterns are distinct from the substrate and support the STM results. Interestingly, the thicker Sn layer indicates 3-dimensional quasiperiodic growth. We propose Sn grows as a novel form of clathrate quasicrystal from our density functional theory calculations. The motifs observed by STM corroborate with the clathrate model. 

 

References:

[1] K. J. Franke et al., Phys. Rev. Lett. 89, 156104 (2002); A. K. Shukla et al., Phys. Rev. B 79, 134206 (2009); H. R. Sharma et al., Nat Commun 4, 2715 (2013).

[2] V. K. Singh et al., Phys. Rev. Research 2, 013023 (2020).