抄録
The quantum properties of ultrathin metal films and surface superstructures have generated significant interest due to the sensitivity of confined two-dimensional (2D) electronic states to subtle differences in film thickness. In/Si(111) shows metal-insulator transition [1, 2] and two-dimensional superconductivity [3] at different thickness. In/Si(111)-(√7 × √3)-rect structure is an indium double-layer structure with atomically sharp In/Si interface [4]. The atomic arrangement of this structure closely resembles that of bulk In with a body-centered tetragonal (bct) structure. This similarity raises the possibility of further growth of (001) oriented In films upon additional deposition. However, previous studies have reported the preferential growth of three-dimensional (3D) islands at and above room temperature [5]. As a result, the layer-by-layer growth on the double-layer structure has been considered challenging. A few preceding studies reported that a triple-layer structure with (6 × 6) periodicity fully cover the (√7 × √3)-rect structure by deposition at temperatures below 200 K [5, 6], while the detailed atomic and electronic structure have not yet been clarified. In the present study, we investigated the triple-layer structure using low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and angle-resolved photoelectron spectroscopy (ARPES).
Occupied state STM images showed that a hexagonal array of spots covered the (√7 × √3)-rect substrate at 80 K. On the other hand, empty state STM images did not reveal a (6 × 6) but a (11 × 11) periodicity of the triple-layer structure. We also confirmed the (11 × 11) superlattice by LEED. The large superlattice is explained by commensurate lattice matching between the Si and In hexagonal lattices, namely, 11aSi = 13aIn (aSi = 3.84 Å, aIn = 3.25 Å). The model shows a moiré modulation with a pseudo-(5.5 × 5.5)-periodicity.
ARPES measurements demonstrated that the Fermi surface consist of two circles (kF ~1.32, 1.46 Å-1) and warped hexagons. The warped hexagons are related to the circular Fermi surfaces by folding back at the first SBZ boundaries of Si(111) and hexagonal In lattices. The pair of two Fermi circles with different radii is considered as a characteristic feature of triple-layer structure [7].
References
[1] H. W. Yeom et al., Phys. Rev. Lett. 82, 4898 (1999).
[2] S. Terakawa et al., Phys. Rev. B 100, 115428 (2019).
[3] T. Uchihashi et al., Phys. Rev. Lett. 107, 207001 (2011).
[4] J. W. Park and M. H. Kang, Phys. Rev. Lett. 109, 166102 (2012).
[5] A. Pavlovska et al., J. Vac. Sci. Thechnol. B 20, 2478 (2002).
[6] T. Suzuki and K. Yagyu, Surf. Sci. 726, 122174 (2022).
[7] S. Terakawa et al., Phys. Rev. B 105, 125402 (2022).
